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Terrestrial impact of the galactic historical SNe
Journal of Atmospheric and Solar-Terrestrial Physics 64 (2002) 669 – 676
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Terrestrial impact of the galactic historical SNe A.F. Iyudin ∗ Max-Planck-Institut fur extraterrestrische Physik, Postfach 1312, D-85741 Garching, Germany
Abstract Galactic supernovae (SNe) of the last millennium have left their signatures in many energy domains, with the optical being the best known due to the absence of astronomical instruments before the 17th century being more sophisticated than the human eye. Alongside with these records found in the scriptes of the ancient eastern and western astronomers, quite recently other signatures were recognised as valuable tracers of historical SNe, for example, di1erent ionic and=or molecular depositions in the polar ice, radioactive isotopes depositions, and the -ray emission from the radioactive 44 Ti produced in the SN explosion. While the ice depositions are expected to be the result of the supernova 3ash in the UV and soft X-rays, the 60 Fe radioactive isotope deposition into the deep-ocean ferromanganese crust is the result of direct isotope transfer by cosmic rays dust grains originating in the SN blast wave. These and other impacts of the galactic SNe are important from the point of view of their possible in3uence on the terrestrial environment. In this paper we consider known tracers of historical SNe and compare them to the proposed new tracer based on the atmospheric response to the galactic supernova emission in the UV and X-rays. In addition to using the 44 Ti radioactive decay line photons for uncovering hidden galactic supernova remnants by imaging c 2002 Elsevier Science Ltd. -ray telescopes, all such tracers form an important complement to the historical SNe record. All rights reserved. Keywords: Historical SNe tracers; Ionic, molecular and isotope depositions; Yearly temperature; Climate forcing; Aurorae
1. Introduction Early publications addressing the possible impact of nearby supernovae (SNe) on the Earth’s environment were based on recognising the link between the abundant production of nitric oxides (mainly NO and NO2 ) and the ozone layer destruction resulting from intensive nuclear testing (Foley and Ruderman, 1973; Hampson, 1974; Whitten et al., 1975; Whitten et al., 1976; Holdsworth, 1986). The enhanced ionisation in the upper atmosphere (Ruderman, 1974) and the supersonic transport emission (Warneck, 1972) were also recognised as agents responsible for ozone destruction. This research was supported by the German Bundesministerium fEur Bildung, Wissenschaft, Forschung and Technologie under contract No. FKZ 50 OR 9201 4. It is a pleasure to acknowledge Rudolf Treumann for his comments on this work. ∗ Tel.: +49-89-30000-3606; fax: +49-89-30000-3535. E-mail address: [email protected] (A.F. Iyudin).
A mechanism that might a1ect the terrestrial life via catalytic destruction by NOx of a small amount of O3 that shields the Earth’s surface from intense solar ultraviolet radiation was proposed by Ruderman (1974). Measurements at two ozone stations (Tromso and Arosa) analysed by Ruderman and Chamberlain (1975), established a 11-yr periodicity in the integrated ozone-column densities, indicating a dependence on solar activity with a predictable phase-lag relative to the sunspot cycle. Worldwide data available after the mid-1950s, show a dependence of this correlation on latitude. Single solar 3ares, like that of August 1972, have also been shown to contribute to global ozone depletion (Heath et al., 1977; Stephenson and ScourLeld, 1991). It is plausible that an event which is energetically similar to the August 1972 3are may produce a strong environmental e1ect by causing a reduction in the solar radiation reaching the surface of the Earth in the visible part of the spectrum due to the absorption by stratospheric NO2 that is formed by the ozone-destroying reaction NO + O3 → NO2 + O2 .
c 2002 Elsevier Science Ltd. All rights reserved. 1364-6826/02/$ - see front matter PII: S 1 3 6 4 - 6 8 2 6 ( 0 2 ) 0 0 0 2 8 - 7
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Temperature anomaly
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Fig. 1. Winter temperature anomaly in Eastern Europe, covering the region from Ireland to Moscow and Kiev, as compiled from manuscript records and smoothed with a 50-yr running average (black line, adapted from Lamb (1969)) and 50-yr mean values of the yearly temperature of London area (red histogram, Lamb (1965)). Error bars show the 1 error estimate from Lamb (1965).
A decrease in the total solar radiation available for heating of lower atmosphere and the Earth’s surface can eventually lead to decrease of the surface temperature (Hunt, 1978; Reid et al., 1978). A possibility of such a sequence follows from the sharp peak in nitrate deposition dated 1972–1973, found in samples taken from di1erent Antarctic ice cores (Zeller et al., 1986; Drescho1 and Zeller, 1990), and from the fact that nitrate (NO− 3 ) generation is strongly dependent on the NO2 concentration (Drescho1 et al., 1999). Obviously, a nearby SN may produce a strong depression in the Earth ozone layer by depositing an enormous amount of energy in the upper atmosphere and eventually ionising the atmospheric constituents. The 1972–1973 nitrate peak, produced by the most energetic solar 3are of the satellite era (August 1972), is a good calibrator of the SN-related atmospheric and ionospheric e1ects. It is important that the relatively short residence times of the NOx which is formed by an ionising event in the atmosphere (¡3 yr) ensure a good timing of the galactic SN explosion. Rather inspiring conLrmation of such a possibility came from the analysis of the South Pole ice core (Rood et al., 1979). An analysis led to the discovery of the four outstanding [Fig. 1 in the paper by Rood et al. (1979)] and narrow NO− 3 deposition spikes. Three of those spikes were identiLed in the original paper as coinciding with three historical SNe SN1181, SN1572 and SN1604. The fourth spike was identiLed much later by Burgess and Zuber (2000) with a new galactic supernova remnant (SNR) RXJ0852-4622 which was discovered in 1997 by X- and -ray astronomers (Aschenbach, 1998; Iyudin et al., 1998). A reason for the proposed identiLcation of RXJ0852-4622 with a fourth spike was a suggested young age of the SNR (∼700 yr) and its proximity to Earth (∼200 pc). If this identiLcation is correct, we have a rather accurate dating of the SN event, namely 1340 ± 20 AD, as could be derived from the plot of Rood et al. (1979).
Analysis of the nitrate deposition in the polar (Antarctic) ice was repeated by Zeller and Parker (1981) with samples taken from two di1erent cores (South Pole and Vostok). It is important to note that NO− 3 deposition spikes found in these two additional samples [Fig. 1 in the paper by Zeller and Parker (1981)] are more rich in number than those published by Rood et al. (1979), but appears to support spikes corresponding to SN 1181, SN1604, SN1340 (RXJ0852-4622). Additionally, there is a spike which possibly is related to SN1054 (Crab Nebula). Two weaker spikes might be related to SN1680 (Cas A) and to SN1006. There are also additional spikes that may be explained by undetected SNe, or, alternatively, they could be related to very strong solar 7ares similar to the August 1972 7are. It is important that at least in the three cases of SN1181, SN1340 (RXJ0852-4622?), and SN1604, all three samples (Rood et al., 1979; Zeller and Parker, 1981) show a convincing coincidence in the positions (dates) of the spikes. Dates of NO− 3 depositions suspected to be related to the galactic SNe explosions could also be compared to the dates of H+ deposition (acidity) record taken by Hammer et al. (1980) in Crete, Greenland. Some spikes in the H+ record are marked as unknown (1260 and 1601–1602 AD), e.g. unidentiLed with known volcanic events, or not marked at all, like those at 625, 900, 960, 1006, 1230 and 1340 AD. The majority of unidentiLed peaks (spikes) in the H+ deposition record of Hammer et al. (1980) are not of the same signiLcance like the one corresponding to the big vulcano eruption, but they clearly stand out above the values of H+ depositions of adjacent years. Even though the emerging picture looks rather consistent, it is complicated by the di1erences in the eRciency of the NO− 3 deposition which depends on the solar modulation, geographical position, and the season of the deposition (Zeller and Parker, 1981; Zeller et al., 1986; Drescho1 and Zeller, 1990; Legrand and Kirchner, 1990; Wol1, 1995).
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Additionally, the ice core datings su1er from the (in)accuracy of the chronology of depositions. For the upper part of the ice sheets, the accuracy can be very high (1–2 yr). Annual layers can be counted from the seasonal variations of various parameters such as the visual stratigraphy, physical properties, isotopic compositions, electrical conductivity, chemicals, etc., but at great depth they become indiscernible. Even though there are promising possibilities to obtain absolute ages for ice-core records from radioactive and other dating techniques, long-term timescales remain unreliable. The accuracy of dating depends on a number of factors, but change of the accumulation rate is the most important parameter to consider (Lorius, 1990). Nevertheless, taking the NO− 3 depositions in the Antarctic ice cores described above as traces left by galactic SNe, let us consider other possible e1ects that result from the enhanced ionisation produced by the SN radiation in the Earth environment. In what follows, we will discuss short time (6100 yr) e1ects related to a nearby galactic SN explosion and the possibility to recognise traces of such an event in the Earth environment and=or their in3uence on the Earth climate.
from 1400 AD onward, as well, as with a 1400-yr record of summer temperatures in Fennoscandia (Bri1a et al., 1990). The Northern Russian record of summer (June–July) temperature anomaly, reconstructed by Graybill and Shiyatov (1995) for the time interval 963 till 1970 AD from the tree rings of samples taken in the North Ural area at latitude ∼67◦ and longitude ∼65◦ 30 , just south of the Kara Sea, also broadly consistent with the record of Lamb (1965, 1969). Surprisingly, many of the spikes found in the NO− 3 deposition, namely those with datings of 900, 1006, 1054, 1280, 1572 and 1604 AD, as well, as with the dating of the recently detected SNR RXJ0852-4622, derived from the NO− 3 deposition curves of Rood et al. (1979) and Zeller and Parker (1981), also appear in the yearly mean temperature anomaly record of Lamb (1965) as the times of brake points. A brake point is deLned as the time when a temperature anomaly record changes from a warming trend to a cooling trend, e.g. a point in the temperature anomaly dependence with the property d(ST ) d(ST ) (1) ¿ 0 for t ¡ ti ; dt = 0; dt ti
2. Climate forcing by a nearby SN
d(ST ) ¡0 dt
The Earth’s climate depends on how the radiation from the Sun is absorbed, redistributed by the atmosphere and the oceans, and eventually re-radiated into space. If the atmospheric ionisation plays an important role in the regulation of the radiation balance between stratosphere and Earth surface (Reid et al., 1978; Hunt, 1978), then the Earth’s surface temperature may contain information supporting the suggested connection of the NO− 3 deposition to the galactic SNe explosions. It was proposed that cloud formation is related to the ionisation level in the atmosphere (Pudovkin and Raspopov, 1992). Pudovkin and Veretenenko (1995) detected local decreases in local cloud coverage related to Forbush decreases. Svensmark (1998) showed that during the last solar cycle Earth’s cloud coverage was changing in phase with the galactic cosmic ray 3ux. Assuming this as a real causal connection, one may expect a drop in the Earth surface temperature following the ionisation of the atmosphere by a nearby SN. As the climate record of the past 1000 yr, we will use an estimate of yearly or winter temperatures in Eastern Europe, as compiled from Lamb (1965, 1969). The Lamb (1969) record was modiLed by a 50-yr smoothing with overlapping average. Additionally, we have marked the known historical SNe and those suspected from the NO− 3 record (Zeller and Parker, 1981), as shown in Fig. 1. The temperature record reconstructed by Lamb (1965, 1969) is broadly consistent with the reconstruction of the summer temperature anomaly in the Northern Hemisphere as was presented by Bradley and Jones (1995) and Mann et al. (1999) for the period
for t ¿ ti ;
(2)
where (ST ) is the value of temperature anomaly, and ti is the braking point. The temperature anomaly record derived by Lamb (1969) for Northern Europe, covering longitudes from Ireland to Russia, could be compared with the temperature anomaly proxy in the form of the yearly duration of the ice coverage of the Iceland coast averaged over 20 yr time intervals. This record, given in Fig. 2, seems to support the notion that the time intervals following a known (or a suspected) galactic SNe are markedly colder than the preceding years. We note here that a volcanic-activity-related cooling periods are easily discernible from the SNe-related e1ects as the latter are usually marked by the H+ depositions (see Hammer et al., 1980; Cowley et al., 1993), have a duration of ∼3 yr, and could be adjusted for in the global temperature trend by a procedure similar to that introduced by Angell (1990) for eruptions of Agung and El Chichon (see for details Iyudin et al., 2002). The conspicuous correlation between SNe events and the change in the temperature trend makes sense if the cloud cover increases following the SN-related enhancement of the ionisation in the upper atmosphere. It also points to a rather short time delay between the optical maximum brightness of the SN and its e1ect on the climate. The smallness of this time delay could be explained only by the ionisation increase in the atmosphere via energy deposition by an agent moving with the speed of light. Especially spectacular changes appear in the trend of the temperature anomaly at two brake points caused by two known SNe, SN1572 and SN1604, as
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Fig. 2. 20 yr average number of weeks per year of the ice covered coast of Iceland. Values are adopted from Lamb (1970). Times of the known and suspected galactic SNe are marked by arrows with dates.
well as by two other SNe, both with dating from the NO− 3 records (Zeller and Parker, 1981), speciLcally, SN1280 and SN1340 (RXJ0852-4622?). Possibly, the short time separation of SNe in these two pairs of SN events (30 –60 yr) is comparable to the value of the relaxation time of the ocean– atmosphere system. We will address in more detail this exciting correspondence of SNe dates and climate turning points in a future publication on this topic (Iyudin et al., 2002). Here, it is suRcient to mention that any ionisation e1ects produced in the atmosphere by supernovae, most likely in combination with the solar forcing, appear to be important in the climate evolution. It is likely that something similar to the “stochastic resonance”, e.g. nonlinear ampliLcation of the e1ect, has happened in the Earth climatic system whenever two forcing agents (solar forcing and SN forcing) start to work in accord for the limited time of ∼1 yr. Obviously, the coadding e1ect is large enough to overcome the minimum (threshold) value of the atmospheric ionisation necessary to produce a suRciently large cloud coverage that shifts the energy balance of the ocean–atmospheric system in favour of the cooling trend. It is conceivable to think of galactic SNe as an entity causing cooling periods in the Earth climatic records, inclusive of “The Little Ice Age”, and in this fashion breaking the general warming trend of the last millennium. This idea complements the existing models of climate forcing (see Lean et al., 1995; Svensmark and Frijs-Christensen, 1997; Svensmark, 1998; Cliver et al., 1998; Reid, 1999; Lean and Rind, 1999). 3. Aurorae If we accept that the NO− 3 deposition and climate forcing discussed above are: (1) driven by the enhancement of ionisation at stratospheric heights, and (2) appear coincident in time with the known or suspected galactic SNe (see
above), we may ask what additional e1ects could else be produced in the Earth environment by SNe via the ionisation of the atmosphere. The possible e1ects that immediately come to mind are: (1) an increase in the frequency of appearance of aurorae due to the energy deposit in the high-altitude atmosphere caused by the X- and -ray illumination of the nearby galactic SN; and (2) the ionospheric e1ect (radiowave phase delay) similar to those detected in coincidence with a giant outburst of the soft -ray repeater (SGR 1900+14) (Inan et al., 1999) or in relation to the classical -ray burst GB830801 (Fishman and Inan, 1988). The latter will likely follow the short-time (61 day) energy deposition (ionisation) correlated with the SN UV-3ash (see below) and because of its short timescale will be diRcult to detect without prior knowledge of the time of event. But the former, which follows an energy deposition on the timescale of ∼1 yr, might lead to a detectable increase in auroral frequency during 1–2 yr following the SN explosion. The light of the night sky was extensively discussed in a number of review articles (e.g., Rees and Roble, 1975; Strickland et al., 1989; Kozyra et al., 1997). But until present, we are not aware of a paper discussing the relation between an aurorae of any kind and a SN event. It is well known that a necessary condition for polar aurorae is electron precipitation which results in ionisation and excitation of atmospheric oxygen and nitrogen. Quite di1erently, mid-latitude SARs are caused by the heating (excitation) of the atomic oxygen with the necessary conditions being the presence of the high-temperature electrons at an altitude of ∼400 km in the Earth atmosphere (Rees and Roble, 1975). The heating mechanism of SARs is not clear at present (Kozyra et al., 1997). Ring current protons are suspected to be responsible for most of the energy transfer (Rees and Roble, 1975). For example, the known strongest solar 3are of August 1972, was accompanied by a classical SAR X arc of about 18 kRayleighs, by thermally excited 6300-A ◦ emission below 51 invariant latitude from an unidentiLed
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X feaheating mechanism, and by a sharply deLned 6300-A ture observed at 27◦ invariant latitude (Brace et al., 1974; Shepherd et al., 1976). Ring current protons have energies of the order of 40 – 400 keV. The most probable mechanism in exciting SARs is charge exchange in the upper atmosphere as a consequence of ring current proton precipitation. The resulting hot neutral gas atoms emit some of their energy in the form of radiation. For SNe illumination, this mechanism does not work, but one may envisage that the atmospheric gas is not only ionised but also heated by photon impact. In particular, during ionisation, hot photoelectrons are generated in multitude forming a broad electron spectrum. Collisions with these electrons will cause the atmospheric gas to emit normal auroral radiation in the typical auroral wavebands at low altitudes. This may be not visible at the sunlit hemisphere during 3ares but will be seen as SNe-caused aurorae in the entire night hemisphere. From the combined X- and -ray luminosities of SNe, including the UV-3ash and the radioactive decay component (see below), one can evaluate the energy deposited in the Earth atmosphere following a galactic SN explosion with the 3uence being on the level of that of the strongest solar 3are or even larger. As suggested above, an energy deposit in the high-altitude atmosphere caused by the X- and -ray illumination from a nearby galactic SN will necessarily lead to an increased frequency of aurorae for the period of 1–2 yr after the galactic SNe explosion not only in the polar region(s). It is noteworthy that during the XIII and XIV centuries there was an increase in auroral detections by Korean astronomers especially in the direction south of the observation site (Zhang, 1985). This points to the possible increase of the SARs frequency due to a number of SNe, which is a reasonable assumption considering the geometry of the Earth atmosphere illumination, and the necessary minimum energy deposition. For the SAR to become visX light it is necessary to deposit about ible in the 6300 A 0:07 erg=cm2 s in the atmospheric upper layers in order to exceed the visual threshold brightness (20; 000 Rayleighs) of the oxygen red line. An interpretation of auroral records and their use for the deduction of the secular solar variability is a well known and accepted approach to analyse solar activity in the past millennium, before the optical telescope and satellite era (Siscoe, 1980; Silverman, 1992; Mendoza, 1997). The alternative interpretation seems to also have a reasonable backing from the consideration of the time-correlated excesses in auroral frequency with the known galactic SNe explosion time and from lags of the solar spot numbers (see Figs. 3 and 4). There are clearly visible excesses that might correspond to the galactic SNe with the known date of explosion, namely, SN1006, SN1181, SN1572, SN1604 and SN1680. At least for three SNe it is known that at the time of their explosion no strong solar activity was observed, that is for SN1006, SN1604 and SN1680 (Clark and Stephenson, 1978; Eddy, 1976; Silverman, 1992; Mendoza,
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1997). In fact, 1680 AD corresponds to the year of solar minimum. It is tempting to sort out frequency excesses in the aurorae records according to the known galactic SNe type and distances. But, in this exercise at least two diRculties are foreseeable at the moment: Lrst, it is the uncertainty of the known SNe parameters, like their distances and the luminosities in the X- and -rays; and, second, it is not easy to clearly separate e1ects arising due to the periodicities in the solar activity, from those related to the SNe explosion. It is likely that at least some of the auroral frequency excesses present in the auroral record are a result of the superposition of two e1ects, due to the solar activity and due to the SNe energy input into the Earth atmosphere. The better timing of the solar-activity-related aurorae excesses and of the SNe-related depositions might help to solve ambiguity of the aurorae excesses casualness. 4. E ects of the nearby SN Potential radiation hazards of nearby SN explosion were broadly discussed by Terry and Tucker (1968), Ruderman (1974), Hunt (1978), Reid et al. (1978). Clark et al. (1977) suggested that a SN is likely to occur within 10 pc of the solar system approximately once in every 108 yr during passage through one of the spiral arms of the galaxy. At a distance of 10 pc, the solar system would probably lie within the SNR for a period of several hundred years. Possible consequences of such an event were discussed in relation with the enhancement of 10 Be detected in ice cores (Raisbeck et al., 1987; McHargue et al., 1995) and marine sediments (Cini Castagnoli et al., 1995). According to Sonett et al. (1987), an event that eventually left a 10 Be deposition has happened ∼35 kyr before the present and could have been responsible for the birth of Geminga (Gehrels and Chen, 1993; Ellis et al., 1996). Similar but much older events have produced evidence for the depositions of 60 Fe (t1=2 = 1:5 Myr) and of 53 Mn (t1=2 = 3:7 Myr) in the deep-ocean ferromanganese crust measurements (Knie et al., 1999; Fields and Ellis, 1999). Cosmic-ray-related traces, though important, are much less precise in the timing of the SN, than timing based on the NO− 3 deposition or the aurorae frequency. The delay between the SN and its impact on the Earth environment is quite large for cosmic rays and proportional to d2 =D, where d is the distance to the SN, and D is a di1usion coeRcient. The total 3uence from SN-related CRs could be as high as 750 erg=cm2 for a SN at a distance of ∼1 kpc. An important consequence of cosmic ray di1usion is that an impact of cosmic rays produced by the nearby SN will be delayed and extended in time (Fields and Ellis, 1999). Contrary to cosmic rays, an impact of X- and -rays produced by the SN explosion is relatively instantaneous and may be divided into two components. The Lrst one corresponds to the so-called UV-3ash, which overlaps in
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Events per decade
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Fig. 3. The number of days on which aurorae were reported by naked eye observations per decade in the period of 450 –1450 AD (Siscoe, 1980) shown in black lines histogram compiled from (Link, 1962; Newton, 1972; Keimatsu, 1976; Dall’Olmo, 1979), and of solar spot observations (Clark and Stephenson, 1978) marked by red lines.
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Fig. 4. Distribution of aurorae reported by naked eye observations in the period of 1500 –1710 AD. Data [black line histogram] are compiled from Link (1964), Keimatsu (1976), Krivsky and Pejml (1988), Silverman (1992). Data of solar spot distribution from observations by naked eye before 1610 AD and by telescopes afterwards are shown as red line histogram.
time with the blast wave break-out. The second component corresponds to the emergent X- and -ray spectrum of the SN that is powered by the decaying radioisotopes of 56 Ni, 56 Co, and 57 Co. The secondary component is usually delayed by ∼100 days, relatively to the SN explosion, and lasts a few hundred days. UV-7ash: The dynamical and radiative relaxation of the SN star responding to the propagation of a strong shock wave from a SN explosion leads to the appearance of the so-called precursor (UV-3ash), which is a short burst in the UV and soft X-ray radiation that emerges from the SN photosphere. Calculations performed by Klein and Chevalier (1978), Falk (1978) and Chevalier and Klein (1979) have shown that luminosities of Type II SN precursor in the soft X-ray energy domain (0.2–0:5 keV) could reach peak values of (4 –8)×1045 ergs=s and have a duration of about (3–7)×104 s (Chevalier and Klein, 1979). The above lumi-
nosities are consistent with the predictions of Lasher and Chan (1979) for Type II and Type I SNe, even though spectra of the emergent X-rays are somewhat di1erent. The mean 3ux of a precursor ranges from 7 to 135 erg=cm2 s for the assumed distance to the SN of ∼1 kpc (Lasher and Chan, 1979; Chevalier and Klein, 1979) with an integrated 3uence up to ∼2 × 107 erg=cm2 . The peak 3ux from the UV-3ash may reach a value of (4 –8)×103 erg=cm2 s. Secondary component: The secondary component of the X- and -ray emission of galactic SNe consists of Compton-scattered nuclear -ray lines escaping the expanding ejecta of the SN. As these -rays propagate through the SN envelope, they are degraded by Compton scattering into hard X-rays. Assuming a simple spherical (free) expansion model of the SN envelope for the time after explosion 61 month similar to that developed by Chan and Lingenfelter (1987), one can draw a simple picture of the emergent
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X- and -ray 3ux for a radioactive source that decays with mean life-time ti . Let Pesc be the probability that a -ray will escape without scattering. Assuming spherically symmetric expansion of the supernova envelope, Pesc = e−i , where i is the optical depth of the overlaying material for the ith -ray line. The -ray luminosity of the SN (in erg=s) is largely deLned by the abundantly produced isotope 56 Ni, and can be written as L = 1:26 × 1042
d M56 (e−t=113:7 )Pesc : 0:1M
(3)
The X- and -ray 3ux at the Earth’s orbit is smaller than that from the UV-3ash and is of the order of 0:8 erg=cm2 s. But the duration of the second component is ∼1 yr. Therefore, the second component 3uence is of the order of 8 × 106 erg=cm2 for M56 = 0:6M . From the -ray spectrum infalling on the Earth atmosphere, one can calculate the fraction of the deposited energy that goes into heating, ionisation and excitation. Generally, these fractions depend on the composition of the gas (atmosphere), the state of ionisation and the electron fraction.
5. Discussion At least three synchronous and di1erent e1ects: (1) NO− 3 polar ice deposition, (2) SNe synchronised changes in the Earth climate trend, and (3) excesses in the frequency of appearance of aurorae, could at present be used as indications of the galactic SNe in3uence on the terrestrial environment. Unfortunately, it is almost not possible to clearly separate e1ects of a strong solar 3are from that of a SN-related illumination of the Earth atmosphere. In fact, it is very likely that both agents, solar 3are activity and SN explosions, if overlapping in time, produce a total e1ect which exceeds the simple sum of the two. The question is: could the two e1ects ever be clearly separated? At the moment one may state that e1ects related to SN explosion, like depositions, aurorae, etc., can be used as time markers of SNe. Potentially, the possibility to supplement these datings with the dating from SNR detection in X-rays and in the 44 Ti -ray line emission is a way to distinguish between solar 3ares and SNe-related e1ects in the records that are used for reconstruction of solar activity for the past two millenia. An interesting example of quite a di1erent tracer is the detection of the 14 C excess in wood samples probably related to the SN1006 explosion (see Damon et al., 1995). An increase in 14 C was dated ∼3 yr after the explosion of SN1006 (Damon et al., 1995). The best Lt to the 14 C deposition in the sequoia wood samples was made with a model where the 14 C production rate was increased by a factor of 1.75 relatively to the normal value, taken as the mean rate for 1003–1009 AD. The increase itself has a signiLcance of 99.6% (Damon et al., 1995). The lag of the 14 C concentration excess relative to the SN1006 explosion was explained by the residence time of 14 C in the atmosphere.
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The increase found in the 14 C concentration in the samples of sequoia wood could result from the (; n) reaction sequence on any of the abundant C, N, O atmospheric nuclei, followed by the n +14 N → 14 C + p reaction (Damon et al., 1995). This sequence can be started by photons with energy 10 MeV, that were produced either during the blast-wave break out, or by the promptly accelerated protons interacting with the circumstellar matter. The amplitude of the 14 C excess requires an energy input into the Earth atmosphere per unit area of 1:71×105 erg=cm2 via -photons (Damon et al., 1995). This corresponds to a SN energy output in -rays with E ¿ 10 MeV of 4 × 1049 ergs (for d = 0:8 kpc). Of course, the origin of such a high -ray 3ux in SN1006 has still to be explained. 6. Conclusions (1) The possibility of some of the auroral frequency excesses being conceived by galactic supernova events may eventually lead to the re-evaluation of the solar activity indexes of the past. (2) Comparison of the di1erent depositions, winter temperatures in Eastern Europe and of frequency of aurorae plots indicates possibly missed SNe in the past. (3) A climate forcing related to, or enhanced by the neutral emission of the galactic SNe is an important conclusion which goes far beyond the scope of this paper and may need more proof and consideration. References Angell, J.K., 1990. Geophysical Research Letters 17, 1093. Aschenbach, B., 1998. Nature 396, 141. Brace, L.H., Maier, E.J., Ho1man, J.H., Whitteker, J., Sheperd, G.G., 1974. Journal of Geophysical Research 79, 5211. Bradley, R.S., Jones, P.D., 1995. In: Bradley, R.S., Jones, P.D. (Eds.), Climate Since A.D. 1500. Routledge, London, New York, p. 666. Bri1a, K.R., Bartholin, T.S., Eckstein, D., et al., 1990. Nature 346, 434. Burgess, C.P., Zuber, K., 2000. Astroparticle Physics 14, 1. Chan, K.W., Lingenfelter, R.E., 1987. Astrophysical Journal 318, L51. Chevalier, R.A., Klein, R.I., 1979. Astrophysical Journal 234, 597. Cini Castagnoli, G., Albrecht, A., Beer, J., et al., 1995. Geophysical Research Letters 22, 707. Clark, D.H., McCrea, W.H., Stephenson, F.R., 1977. Nature 265, 318. Clark, D.H., Stephenson, F.R., 1978. Quaternary Journal of Royal Astronomical Society 19, 387. Cliver, E.W., Boriako1, V., Feynman, J., 1998. Geophysical Research Letters 25, 1035. Cowley, T.J., Criste, T.A., Smith, N.R., 1993. Geophysical Research Letters 20, 209. Dall’Olmo, U., 1979. Journal of Geophysical Research 84, 1525. Damon, P.E., et al., 1995. Proceedings of the 25th ICRC, Vol. 4, Rome, p. 311.
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Drescho1, G.A.M., Boyarchuk, K.A., Jungner, H., et al., 1999. Proceedings of the 26th ICCR, Vol. 4, Salt Lake City, p. 318. Drescho1, G.A.M., Zeller, E.J., 1990. Solar Physics 127, 333. Eddy, J.A., 1976. Science 192, 1189. Ellis, J., Fields, B.D., Schramm, D.N., 1996. Astrophysical Journal 470, 1227. Falk, S.W., 1978. Astrophysical Journal 226, L133. Fields, B.D., Ellis, J., 1999. New Astronomy 4, 419. Fishman, G.J., Inan, U.S., 1988. Nature 331, 418. Foley, H., Ruderman, M.A., 1973. Journal of Geophysical Research 78, 4441. Gehrels, N., Chen, W., 1993. Nature 361, 706. Graybill, D.A., Shiyatov, S.G., 1995 In: Bradley, R.S., Jones, P.D. (Eds.), Climate Since A.D. 1500. Routledge, London, New York, p. 393. Hammer, C.U., Clausen, H.B., Dansgaard, W., 1980. Nature 288, 230. Hampson, J., 1974. Nature 250, 189. Heath, D.F., Krueger, A.J., Crutzen, P.J., 1977. Science 197, 886. Holdsworth, G., 1986. Nature 324, 551. Hunt, G.E., 1978. Nature 271, 430. Inan, U.S., et al., 1999. Journal of Geophysical Research 26, 3357. Iyudin, A.F., et al., 1998. Nature 396, 142. Iyudin, A.F., et al., 2002, Astronomy and Astrophysics, in preparation. Keimatsu, M., 1976. Annals of Science Kan. University 13, 1. Klein, R.I., Chevalier, R.A., 1978. Astrophysical Journal 223, L109. Knie, K., Korschinek, G., Faestermann, T., et al., 1999. Physics Review Letters 83, 18. Kozyra, J.U., Nagy, A.F., Slater, D.W., 1997. Review of Geophysics 35, 155. Krivsky, L., Pejml, K., 1988. Astronomical Institute of Czechoslovakian Academy of Science 75, 32. Lamb, H.H., 1965. Palaeogeography Palaeoclimatology Palaeoecology 1, 13. Lamb, H.H., 1969. Climatic 3uctuations. In: Flohn, H. (Ed.), World Survey of Climatology, General Climatology, Vol. 2. Elsevier, New York, p. 173. Lamb, H.H., 1970. Philosophical Transactions of Royal Society A 266, 52. Lasher, G.J., Chan, K.L., 1979. Astrophysical Journal 230, 742. Lean, J., Beer, J., Bradley, R., 1995. Geophysical Research Letters 22, 3195. Lean, J., Rind, D., 1999. Journal of Atmospheric and Solar-Terrestrial Physics 61, 25. Legrand, M.R., Kirchner, S., 1990. Journal of Geophysical Research 95, 3493. Link, F., 1962. Geophysicalni Sbornik 173, 297. Link, F., 1964. Geophysicalni Sbornik 212, 501. Lorius, C., 1990. Philosophical Transactions of Royal Society of London A 330, 459.
Mann, M.E., Bradley, R.S., Hughes, M.K., 1999. Geophysical Research Letters 26, 759. McHargue, L.R., Damon, P.E., Donahue, D.J., 1995. Geophysical Research Letters 22, 659. Mendoza, B., 1997. Annals of Geophysics 15, 397. Newton, R.R., 1972. Medieval Chronicles and the Rotation of the Earth. John Hopkins University Press, Baltimore. Pudovkin, M.I., Raspopov, O.M., 1992. Geomagnetic Aeronomy 32, 593. Pudovkin, M.I., Veretenenko, S.V., 1995. Journal of Atmospheric and Solar-Terrestrial Physics 57, 1349. Raisbeck, G.M., Yiou, F., Bourles, D., et al., 1987. Nature 326, 273. Rees, M.H., Roble, R.G., 1975. Review of Geophysics & Space Physics 13, 201. Reid, G.C., 1999. Journal of Atmospheric and Solar-Terrestrial Physics 61, 3. Reid, G.C., McAfee, J.R., Crutzen, P.J., 1978. Nature 275, 489. Rood, R.T., Sarazin, C.L., Zeller, E.J., Parker, B.C., 1979. Nature 282, 701. Ruderman, M., 1974. Science 184, 1079. Ruderman, M., Chamberlain, J.W., 1975. Planetary Space Science 23, 247. Shepherd, G.G., Cogger, L.L., Burrows, J.R., 1976. Journal of Geophysical Research 81, 4597. Silverman, S.M., 1992. Review of Geophysics 30, 333. Siscoe, G.L., 1980. Review of Geophysics & Space Physics 18, 647. Sonett, C.P., MorLll, G.E., Jokipii, J.R., 1987. Nature 330, 458. Stephenson, J.A.E., ScourLeld, M.W.J., 1991. Nature 352, 137. Strickland, D.J., Meier, R.R., Hecht, J.H., Christensen, A.B., 1989. Journal of Geophysical Research 94, 13,527. Svensmark, H., Frijs-Christensen, E., 1997. Journal of Atmospheric and Solar-Terrestrial Physics 59, 1225. Svensmark, H., 1998. Physics Review Letters 81, 5027. Terry, K.D., Tucker, W.H., 1968. Science 159, 421. Warneck, P., 1972. Journal of Geophysical Research 77, 6589. Whitten, R.C., Borucci, W.J., Turco, R.P., 1975. Nature 257, 38. Whitten, R.C., Cuzzi, J., Borucci, W.J., Wolfe, J.H., 1976. Nature 263, 398. Wol1, E.W., 1995 In: Delmas, R.J. (Ed.), Ice Core Studies of Global Geochemical Cycles, NATO ASI Series, Vol. 130. Springer, Berlin=Heidelberg, p. 195. Zeller, E.J., Parker, B.C., 1981. Geophysical Research Letters 8, 895. Zeller, E.J., Dreschho1, G.A.M., Laird, C.M., 1986. Geophysical Research Letters 13, 1264. Zhang, Zh., 1985. Journal of British Astronomical Association 95, 205.
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Terrestrial impact of the galactic historical SNe A.F. Iyudin ∗ Max-Planck-Institut fur extraterrestrische Physik, Postfach 1312, D-85741 Garching, Germany
Abstract Galactic supernovae (SNe) of the last millennium have left their signatures in many energy domains, with the optical being the best known due to the absence of astronomical instruments before the 17th century being more sophisticated than the human eye. Alongside with these records found in the scriptes of the ancient eastern and western astronomers, quite recently other signatures were recognised as valuable tracers of historical SNe, for example, di1erent ionic and=or molecular depositions in the polar ice, radioactive isotopes depositions, and the -ray emission from the radioactive 44 Ti produced in the SN explosion. While the ice depositions are expected to be the result of the supernova 3ash in the UV and soft X-rays, the 60 Fe radioactive isotope deposition into the deep-ocean ferromanganese crust is the result of direct isotope transfer by cosmic rays dust grains originating in the SN blast wave. These and other impacts of the galactic SNe are important from the point of view of their possible in3uence on the terrestrial environment. In this paper we consider known tracers of historical SNe and compare them to the proposed new tracer based on the atmospheric response to the galactic supernova emission in the UV and X-rays. In addition to using the 44 Ti radioactive decay line photons for uncovering hidden galactic supernova remnants by imaging c 2002 Elsevier Science Ltd. -ray telescopes, all such tracers form an important complement to the historical SNe record. All rights reserved. Keywords: Historical SNe tracers; Ionic, molecular and isotope depositions; Yearly temperature; Climate forcing; Aurorae
1. Introduction Early publications addressing the possible impact of nearby supernovae (SNe) on the Earth’s environment were based on recognising the link between the abundant production of nitric oxides (mainly NO and NO2 ) and the ozone layer destruction resulting from intensive nuclear testing (Foley and Ruderman, 1973; Hampson, 1974; Whitten et al., 1975; Whitten et al., 1976; Holdsworth, 1986). The enhanced ionisation in the upper atmosphere (Ruderman, 1974) and the supersonic transport emission (Warneck, 1972) were also recognised as agents responsible for ozone destruction. This research was supported by the German Bundesministerium fEur Bildung, Wissenschaft, Forschung and Technologie under contract No. FKZ 50 OR 9201 4. It is a pleasure to acknowledge Rudolf Treumann for his comments on this work. ∗ Tel.: +49-89-30000-3606; fax: +49-89-30000-3535. E-mail address: [email protected] (A.F. Iyudin).
A mechanism that might a1ect the terrestrial life via catalytic destruction by NOx of a small amount of O3 that shields the Earth’s surface from intense solar ultraviolet radiation was proposed by Ruderman (1974). Measurements at two ozone stations (Tromso and Arosa) analysed by Ruderman and Chamberlain (1975), established a 11-yr periodicity in the integrated ozone-column densities, indicating a dependence on solar activity with a predictable phase-lag relative to the sunspot cycle. Worldwide data available after the mid-1950s, show a dependence of this correlation on latitude. Single solar 3ares, like that of August 1972, have also been shown to contribute to global ozone depletion (Heath et al., 1977; Stephenson and ScourLeld, 1991). It is plausible that an event which is energetically similar to the August 1972 3are may produce a strong environmental e1ect by causing a reduction in the solar radiation reaching the surface of the Earth in the visible part of the spectrum due to the absorption by stratospheric NO2 that is formed by the ozone-destroying reaction NO + O3 → NO2 + O2 .
c 2002 Elsevier Science Ltd. All rights reserved. 1364-6826/02/$ - see front matter PII: S 1 3 6 4 - 6 8 2 6 ( 0 2 ) 0 0 0 2 8 - 7
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Temperature anomaly
0
9 0 0 ⇓
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Fig. 1. Winter temperature anomaly in Eastern Europe, covering the region from Ireland to Moscow and Kiev, as compiled from manuscript records and smoothed with a 50-yr running average (black line, adapted from Lamb (1969)) and 50-yr mean values of the yearly temperature of London area (red histogram, Lamb (1965)). Error bars show the 1 error estimate from Lamb (1965).
A decrease in the total solar radiation available for heating of lower atmosphere and the Earth’s surface can eventually lead to decrease of the surface temperature (Hunt, 1978; Reid et al., 1978). A possibility of such a sequence follows from the sharp peak in nitrate deposition dated 1972–1973, found in samples taken from di1erent Antarctic ice cores (Zeller et al., 1986; Drescho1 and Zeller, 1990), and from the fact that nitrate (NO− 3 ) generation is strongly dependent on the NO2 concentration (Drescho1 et al., 1999). Obviously, a nearby SN may produce a strong depression in the Earth ozone layer by depositing an enormous amount of energy in the upper atmosphere and eventually ionising the atmospheric constituents. The 1972–1973 nitrate peak, produced by the most energetic solar 3are of the satellite era (August 1972), is a good calibrator of the SN-related atmospheric and ionospheric e1ects. It is important that the relatively short residence times of the NOx which is formed by an ionising event in the atmosphere (¡3 yr) ensure a good timing of the galactic SN explosion. Rather inspiring conLrmation of such a possibility came from the analysis of the South Pole ice core (Rood et al., 1979). An analysis led to the discovery of the four outstanding [Fig. 1 in the paper by Rood et al. (1979)] and narrow NO− 3 deposition spikes. Three of those spikes were identiLed in the original paper as coinciding with three historical SNe SN1181, SN1572 and SN1604. The fourth spike was identiLed much later by Burgess and Zuber (2000) with a new galactic supernova remnant (SNR) RXJ0852-4622 which was discovered in 1997 by X- and -ray astronomers (Aschenbach, 1998; Iyudin et al., 1998). A reason for the proposed identiLcation of RXJ0852-4622 with a fourth spike was a suggested young age of the SNR (∼700 yr) and its proximity to Earth (∼200 pc). If this identiLcation is correct, we have a rather accurate dating of the SN event, namely 1340 ± 20 AD, as could be derived from the plot of Rood et al. (1979).
Analysis of the nitrate deposition in the polar (Antarctic) ice was repeated by Zeller and Parker (1981) with samples taken from two di1erent cores (South Pole and Vostok). It is important to note that NO− 3 deposition spikes found in these two additional samples [Fig. 1 in the paper by Zeller and Parker (1981)] are more rich in number than those published by Rood et al. (1979), but appears to support spikes corresponding to SN 1181, SN1604, SN1340 (RXJ0852-4622). Additionally, there is a spike which possibly is related to SN1054 (Crab Nebula). Two weaker spikes might be related to SN1680 (Cas A) and to SN1006. There are also additional spikes that may be explained by undetected SNe, or, alternatively, they could be related to very strong solar 7ares similar to the August 1972 7are. It is important that at least in the three cases of SN1181, SN1340 (RXJ0852-4622?), and SN1604, all three samples (Rood et al., 1979; Zeller and Parker, 1981) show a convincing coincidence in the positions (dates) of the spikes. Dates of NO− 3 depositions suspected to be related to the galactic SNe explosions could also be compared to the dates of H+ deposition (acidity) record taken by Hammer et al. (1980) in Crete, Greenland. Some spikes in the H+ record are marked as unknown (1260 and 1601–1602 AD), e.g. unidentiLed with known volcanic events, or not marked at all, like those at 625, 900, 960, 1006, 1230 and 1340 AD. The majority of unidentiLed peaks (spikes) in the H+ deposition record of Hammer et al. (1980) are not of the same signiLcance like the one corresponding to the big vulcano eruption, but they clearly stand out above the values of H+ depositions of adjacent years. Even though the emerging picture looks rather consistent, it is complicated by the di1erences in the eRciency of the NO− 3 deposition which depends on the solar modulation, geographical position, and the season of the deposition (Zeller and Parker, 1981; Zeller et al., 1986; Drescho1 and Zeller, 1990; Legrand and Kirchner, 1990; Wol1, 1995).
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Additionally, the ice core datings su1er from the (in)accuracy of the chronology of depositions. For the upper part of the ice sheets, the accuracy can be very high (1–2 yr). Annual layers can be counted from the seasonal variations of various parameters such as the visual stratigraphy, physical properties, isotopic compositions, electrical conductivity, chemicals, etc., but at great depth they become indiscernible. Even though there are promising possibilities to obtain absolute ages for ice-core records from radioactive and other dating techniques, long-term timescales remain unreliable. The accuracy of dating depends on a number of factors, but change of the accumulation rate is the most important parameter to consider (Lorius, 1990). Nevertheless, taking the NO− 3 depositions in the Antarctic ice cores described above as traces left by galactic SNe, let us consider other possible e1ects that result from the enhanced ionisation produced by the SN radiation in the Earth environment. In what follows, we will discuss short time (6100 yr) e1ects related to a nearby galactic SN explosion and the possibility to recognise traces of such an event in the Earth environment and=or their in3uence on the Earth climate.
from 1400 AD onward, as well, as with a 1400-yr record of summer temperatures in Fennoscandia (Bri1a et al., 1990). The Northern Russian record of summer (June–July) temperature anomaly, reconstructed by Graybill and Shiyatov (1995) for the time interval 963 till 1970 AD from the tree rings of samples taken in the North Ural area at latitude ∼67◦ and longitude ∼65◦ 30 , just south of the Kara Sea, also broadly consistent with the record of Lamb (1965, 1969). Surprisingly, many of the spikes found in the NO− 3 deposition, namely those with datings of 900, 1006, 1054, 1280, 1572 and 1604 AD, as well, as with the dating of the recently detected SNR RXJ0852-4622, derived from the NO− 3 deposition curves of Rood et al. (1979) and Zeller and Parker (1981), also appear in the yearly mean temperature anomaly record of Lamb (1965) as the times of brake points. A brake point is deLned as the time when a temperature anomaly record changes from a warming trend to a cooling trend, e.g. a point in the temperature anomaly dependence with the property d(ST ) d(ST ) (1) ¿ 0 for t ¡ ti ; dt = 0; dt ti
2. Climate forcing by a nearby SN
d(ST ) ¡0 dt
The Earth’s climate depends on how the radiation from the Sun is absorbed, redistributed by the atmosphere and the oceans, and eventually re-radiated into space. If the atmospheric ionisation plays an important role in the regulation of the radiation balance between stratosphere and Earth surface (Reid et al., 1978; Hunt, 1978), then the Earth’s surface temperature may contain information supporting the suggested connection of the NO− 3 deposition to the galactic SNe explosions. It was proposed that cloud formation is related to the ionisation level in the atmosphere (Pudovkin and Raspopov, 1992). Pudovkin and Veretenenko (1995) detected local decreases in local cloud coverage related to Forbush decreases. Svensmark (1998) showed that during the last solar cycle Earth’s cloud coverage was changing in phase with the galactic cosmic ray 3ux. Assuming this as a real causal connection, one may expect a drop in the Earth surface temperature following the ionisation of the atmosphere by a nearby SN. As the climate record of the past 1000 yr, we will use an estimate of yearly or winter temperatures in Eastern Europe, as compiled from Lamb (1965, 1969). The Lamb (1969) record was modiLed by a 50-yr smoothing with overlapping average. Additionally, we have marked the known historical SNe and those suspected from the NO− 3 record (Zeller and Parker, 1981), as shown in Fig. 1. The temperature record reconstructed by Lamb (1965, 1969) is broadly consistent with the reconstruction of the summer temperature anomaly in the Northern Hemisphere as was presented by Bradley and Jones (1995) and Mann et al. (1999) for the period
for t ¿ ti ;
(2)
where (ST ) is the value of temperature anomaly, and ti is the braking point. The temperature anomaly record derived by Lamb (1969) for Northern Europe, covering longitudes from Ireland to Russia, could be compared with the temperature anomaly proxy in the form of the yearly duration of the ice coverage of the Iceland coast averaged over 20 yr time intervals. This record, given in Fig. 2, seems to support the notion that the time intervals following a known (or a suspected) galactic SNe are markedly colder than the preceding years. We note here that a volcanic-activity-related cooling periods are easily discernible from the SNe-related e1ects as the latter are usually marked by the H+ depositions (see Hammer et al., 1980; Cowley et al., 1993), have a duration of ∼3 yr, and could be adjusted for in the global temperature trend by a procedure similar to that introduced by Angell (1990) for eruptions of Agung and El Chichon (see for details Iyudin et al., 2002). The conspicuous correlation between SNe events and the change in the temperature trend makes sense if the cloud cover increases following the SN-related enhancement of the ionisation in the upper atmosphere. It also points to a rather short time delay between the optical maximum brightness of the SN and its e1ect on the climate. The smallness of this time delay could be explained only by the ionisation increase in the atmosphere via energy deposition by an agent moving with the speed of light. Especially spectacular changes appear in the trend of the temperature anomaly at two brake points caused by two known SNe, SN1572 and SN1604, as
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1 6 0 4
Weeks per year of ice
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Fig. 2. 20 yr average number of weeks per year of the ice covered coast of Iceland. Values are adopted from Lamb (1970). Times of the known and suspected galactic SNe are marked by arrows with dates.
well as by two other SNe, both with dating from the NO− 3 records (Zeller and Parker, 1981), speciLcally, SN1280 and SN1340 (RXJ0852-4622?). Possibly, the short time separation of SNe in these two pairs of SN events (30 –60 yr) is comparable to the value of the relaxation time of the ocean– atmosphere system. We will address in more detail this exciting correspondence of SNe dates and climate turning points in a future publication on this topic (Iyudin et al., 2002). Here, it is suRcient to mention that any ionisation e1ects produced in the atmosphere by supernovae, most likely in combination with the solar forcing, appear to be important in the climate evolution. It is likely that something similar to the “stochastic resonance”, e.g. nonlinear ampliLcation of the e1ect, has happened in the Earth climatic system whenever two forcing agents (solar forcing and SN forcing) start to work in accord for the limited time of ∼1 yr. Obviously, the coadding e1ect is large enough to overcome the minimum (threshold) value of the atmospheric ionisation necessary to produce a suRciently large cloud coverage that shifts the energy balance of the ocean–atmospheric system in favour of the cooling trend. It is conceivable to think of galactic SNe as an entity causing cooling periods in the Earth climatic records, inclusive of “The Little Ice Age”, and in this fashion breaking the general warming trend of the last millennium. This idea complements the existing models of climate forcing (see Lean et al., 1995; Svensmark and Frijs-Christensen, 1997; Svensmark, 1998; Cliver et al., 1998; Reid, 1999; Lean and Rind, 1999). 3. Aurorae If we accept that the NO− 3 deposition and climate forcing discussed above are: (1) driven by the enhancement of ionisation at stratospheric heights, and (2) appear coincident in time with the known or suspected galactic SNe (see
above), we may ask what additional e1ects could else be produced in the Earth environment by SNe via the ionisation of the atmosphere. The possible e1ects that immediately come to mind are: (1) an increase in the frequency of appearance of aurorae due to the energy deposit in the high-altitude atmosphere caused by the X- and -ray illumination of the nearby galactic SN; and (2) the ionospheric e1ect (radiowave phase delay) similar to those detected in coincidence with a giant outburst of the soft -ray repeater (SGR 1900+14) (Inan et al., 1999) or in relation to the classical -ray burst GB830801 (Fishman and Inan, 1988). The latter will likely follow the short-time (61 day) energy deposition (ionisation) correlated with the SN UV-3ash (see below) and because of its short timescale will be diRcult to detect without prior knowledge of the time of event. But the former, which follows an energy deposition on the timescale of ∼1 yr, might lead to a detectable increase in auroral frequency during 1–2 yr following the SN explosion. The light of the night sky was extensively discussed in a number of review articles (e.g., Rees and Roble, 1975; Strickland et al., 1989; Kozyra et al., 1997). But until present, we are not aware of a paper discussing the relation between an aurorae of any kind and a SN event. It is well known that a necessary condition for polar aurorae is electron precipitation which results in ionisation and excitation of atmospheric oxygen and nitrogen. Quite di1erently, mid-latitude SARs are caused by the heating (excitation) of the atomic oxygen with the necessary conditions being the presence of the high-temperature electrons at an altitude of ∼400 km in the Earth atmosphere (Rees and Roble, 1975). The heating mechanism of SARs is not clear at present (Kozyra et al., 1997). Ring current protons are suspected to be responsible for most of the energy transfer (Rees and Roble, 1975). For example, the known strongest solar 3are of August 1972, was accompanied by a classical SAR X arc of about 18 kRayleighs, by thermally excited 6300-A ◦ emission below 51 invariant latitude from an unidentiLed
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X feaheating mechanism, and by a sharply deLned 6300-A ture observed at 27◦ invariant latitude (Brace et al., 1974; Shepherd et al., 1976). Ring current protons have energies of the order of 40 – 400 keV. The most probable mechanism in exciting SARs is charge exchange in the upper atmosphere as a consequence of ring current proton precipitation. The resulting hot neutral gas atoms emit some of their energy in the form of radiation. For SNe illumination, this mechanism does not work, but one may envisage that the atmospheric gas is not only ionised but also heated by photon impact. In particular, during ionisation, hot photoelectrons are generated in multitude forming a broad electron spectrum. Collisions with these electrons will cause the atmospheric gas to emit normal auroral radiation in the typical auroral wavebands at low altitudes. This may be not visible at the sunlit hemisphere during 3ares but will be seen as SNe-caused aurorae in the entire night hemisphere. From the combined X- and -ray luminosities of SNe, including the UV-3ash and the radioactive decay component (see below), one can evaluate the energy deposited in the Earth atmosphere following a galactic SN explosion with the 3uence being on the level of that of the strongest solar 3are or even larger. As suggested above, an energy deposit in the high-altitude atmosphere caused by the X- and -ray illumination from a nearby galactic SN will necessarily lead to an increased frequency of aurorae for the period of 1–2 yr after the galactic SNe explosion not only in the polar region(s). It is noteworthy that during the XIII and XIV centuries there was an increase in auroral detections by Korean astronomers especially in the direction south of the observation site (Zhang, 1985). This points to the possible increase of the SARs frequency due to a number of SNe, which is a reasonable assumption considering the geometry of the Earth atmosphere illumination, and the necessary minimum energy deposition. For the SAR to become visX light it is necessary to deposit about ible in the 6300 A 0:07 erg=cm2 s in the atmospheric upper layers in order to exceed the visual threshold brightness (20; 000 Rayleighs) of the oxygen red line. An interpretation of auroral records and their use for the deduction of the secular solar variability is a well known and accepted approach to analyse solar activity in the past millennium, before the optical telescope and satellite era (Siscoe, 1980; Silverman, 1992; Mendoza, 1997). The alternative interpretation seems to also have a reasonable backing from the consideration of the time-correlated excesses in auroral frequency with the known galactic SNe explosion time and from lags of the solar spot numbers (see Figs. 3 and 4). There are clearly visible excesses that might correspond to the galactic SNe with the known date of explosion, namely, SN1006, SN1181, SN1572, SN1604 and SN1680. At least for three SNe it is known that at the time of their explosion no strong solar activity was observed, that is for SN1006, SN1604 and SN1680 (Clark and Stephenson, 1978; Eddy, 1976; Silverman, 1992; Mendoza,
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1997). In fact, 1680 AD corresponds to the year of solar minimum. It is tempting to sort out frequency excesses in the aurorae records according to the known galactic SNe type and distances. But, in this exercise at least two diRculties are foreseeable at the moment: Lrst, it is the uncertainty of the known SNe parameters, like their distances and the luminosities in the X- and -rays; and, second, it is not easy to clearly separate e1ects arising due to the periodicities in the solar activity, from those related to the SNe explosion. It is likely that at least some of the auroral frequency excesses present in the auroral record are a result of the superposition of two e1ects, due to the solar activity and due to the SNe energy input into the Earth atmosphere. The better timing of the solar-activity-related aurorae excesses and of the SNe-related depositions might help to solve ambiguity of the aurorae excesses casualness. 4. E ects of the nearby SN Potential radiation hazards of nearby SN explosion were broadly discussed by Terry and Tucker (1968), Ruderman (1974), Hunt (1978), Reid et al. (1978). Clark et al. (1977) suggested that a SN is likely to occur within 10 pc of the solar system approximately once in every 108 yr during passage through one of the spiral arms of the galaxy. At a distance of 10 pc, the solar system would probably lie within the SNR for a period of several hundred years. Possible consequences of such an event were discussed in relation with the enhancement of 10 Be detected in ice cores (Raisbeck et al., 1987; McHargue et al., 1995) and marine sediments (Cini Castagnoli et al., 1995). According to Sonett et al. (1987), an event that eventually left a 10 Be deposition has happened ∼35 kyr before the present and could have been responsible for the birth of Geminga (Gehrels and Chen, 1993; Ellis et al., 1996). Similar but much older events have produced evidence for the depositions of 60 Fe (t1=2 = 1:5 Myr) and of 53 Mn (t1=2 = 3:7 Myr) in the deep-ocean ferromanganese crust measurements (Knie et al., 1999; Fields and Ellis, 1999). Cosmic-ray-related traces, though important, are much less precise in the timing of the SN, than timing based on the NO− 3 deposition or the aurorae frequency. The delay between the SN and its impact on the Earth environment is quite large for cosmic rays and proportional to d2 =D, where d is the distance to the SN, and D is a di1usion coeRcient. The total 3uence from SN-related CRs could be as high as 750 erg=cm2 for a SN at a distance of ∼1 kpc. An important consequence of cosmic ray di1usion is that an impact of cosmic rays produced by the nearby SN will be delayed and extended in time (Fields and Ellis, 1999). Contrary to cosmic rays, an impact of X- and -rays produced by the SN explosion is relatively instantaneous and may be divided into two components. The Lrst one corresponds to the so-called UV-3ash, which overlaps in
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A.F. Iyudin / Journal of Atmospheric and Solar-Terrestrial Physics 64 (2002) 669 – 676
Events per decade
1 0 0 6
9 0 0
20
⇓
15
1 0 5 4
⇓⇓
1 1 8 1
1 2 8 0
1 3 4 0
⇓
⇓ ⇓
1200
1300
10
5
0 500
600
700
800
900
1000
1100
1400
Date (year A.D.)
Fig. 3. The number of days on which aurorae were reported by naked eye observations per decade in the period of 450 –1450 AD (Siscoe, 1980) shown in black lines histogram compiled from (Link, 1962; Newton, 1972; Keimatsu, 1976; Dall’Olmo, 1979), and of solar spot observations (Clark and Stephenson, 1978) marked by red lines.
15
Events per decade
1 6 0 4
1 5 7 2
1 6 8 0
⇓
⇓
⇓
10
5
0 1500
1520
1540
1560
1580
1600
1620
1640
1660
1680
1700
Date (year A.D.)
Fig. 4. Distribution of aurorae reported by naked eye observations in the period of 1500 –1710 AD. Data [black line histogram] are compiled from Link (1964), Keimatsu (1976), Krivsky and Pejml (1988), Silverman (1992). Data of solar spot distribution from observations by naked eye before 1610 AD and by telescopes afterwards are shown as red line histogram.
time with the blast wave break-out. The second component corresponds to the emergent X- and -ray spectrum of the SN that is powered by the decaying radioisotopes of 56 Ni, 56 Co, and 57 Co. The secondary component is usually delayed by ∼100 days, relatively to the SN explosion, and lasts a few hundred days. UV-7ash: The dynamical and radiative relaxation of the SN star responding to the propagation of a strong shock wave from a SN explosion leads to the appearance of the so-called precursor (UV-3ash), which is a short burst in the UV and soft X-ray radiation that emerges from the SN photosphere. Calculations performed by Klein and Chevalier (1978), Falk (1978) and Chevalier and Klein (1979) have shown that luminosities of Type II SN precursor in the soft X-ray energy domain (0.2–0:5 keV) could reach peak values of (4 –8)×1045 ergs=s and have a duration of about (3–7)×104 s (Chevalier and Klein, 1979). The above lumi-
nosities are consistent with the predictions of Lasher and Chan (1979) for Type II and Type I SNe, even though spectra of the emergent X-rays are somewhat di1erent. The mean 3ux of a precursor ranges from 7 to 135 erg=cm2 s for the assumed distance to the SN of ∼1 kpc (Lasher and Chan, 1979; Chevalier and Klein, 1979) with an integrated 3uence up to ∼2 × 107 erg=cm2 . The peak 3ux from the UV-3ash may reach a value of (4 –8)×103 erg=cm2 s. Secondary component: The secondary component of the X- and -ray emission of galactic SNe consists of Compton-scattered nuclear -ray lines escaping the expanding ejecta of the SN. As these -rays propagate through the SN envelope, they are degraded by Compton scattering into hard X-rays. Assuming a simple spherical (free) expansion model of the SN envelope for the time after explosion 61 month similar to that developed by Chan and Lingenfelter (1987), one can draw a simple picture of the emergent
A.F. Iyudin / Journal of Atmospheric and Solar-Terrestrial Physics 64 (2002) 669 – 676
X- and -ray 3ux for a radioactive source that decays with mean life-time ti . Let Pesc be the probability that a -ray will escape without scattering. Assuming spherically symmetric expansion of the supernova envelope, Pesc = e−i , where i is the optical depth of the overlaying material for the ith -ray line. The -ray luminosity of the SN (in erg=s) is largely deLned by the abundantly produced isotope 56 Ni, and can be written as L = 1:26 × 1042
d M56 (e−t=113:7 )Pesc : 0:1M
(3)
The X- and -ray 3ux at the Earth’s orbit is smaller than that from the UV-3ash and is of the order of 0:8 erg=cm2 s. But the duration of the second component is ∼1 yr. Therefore, the second component 3uence is of the order of 8 × 106 erg=cm2 for M56 = 0:6M . From the -ray spectrum infalling on the Earth atmosphere, one can calculate the fraction of the deposited energy that goes into heating, ionisation and excitation. Generally, these fractions depend on the composition of the gas (atmosphere), the state of ionisation and the electron fraction.
5. Discussion At least three synchronous and di1erent e1ects: (1) NO− 3 polar ice deposition, (2) SNe synchronised changes in the Earth climate trend, and (3) excesses in the frequency of appearance of aurorae, could at present be used as indications of the galactic SNe in3uence on the terrestrial environment. Unfortunately, it is almost not possible to clearly separate e1ects of a strong solar 3are from that of a SN-related illumination of the Earth atmosphere. In fact, it is very likely that both agents, solar 3are activity and SN explosions, if overlapping in time, produce a total e1ect which exceeds the simple sum of the two. The question is: could the two e1ects ever be clearly separated? At the moment one may state that e1ects related to SN explosion, like depositions, aurorae, etc., can be used as time markers of SNe. Potentially, the possibility to supplement these datings with the dating from SNR detection in X-rays and in the 44 Ti -ray line emission is a way to distinguish between solar 3ares and SNe-related e1ects in the records that are used for reconstruction of solar activity for the past two millenia. An interesting example of quite a di1erent tracer is the detection of the 14 C excess in wood samples probably related to the SN1006 explosion (see Damon et al., 1995). An increase in 14 C was dated ∼3 yr after the explosion of SN1006 (Damon et al., 1995). The best Lt to the 14 C deposition in the sequoia wood samples was made with a model where the 14 C production rate was increased by a factor of 1.75 relatively to the normal value, taken as the mean rate for 1003–1009 AD. The increase itself has a signiLcance of 99.6% (Damon et al., 1995). The lag of the 14 C concentration excess relative to the SN1006 explosion was explained by the residence time of 14 C in the atmosphere.
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The increase found in the 14 C concentration in the samples of sequoia wood could result from the (; n) reaction sequence on any of the abundant C, N, O atmospheric nuclei, followed by the n +14 N → 14 C + p reaction (Damon et al., 1995). This sequence can be started by photons with energy 10 MeV, that were produced either during the blast-wave break out, or by the promptly accelerated protons interacting with the circumstellar matter. The amplitude of the 14 C excess requires an energy input into the Earth atmosphere per unit area of 1:71×105 erg=cm2 via -photons (Damon et al., 1995). This corresponds to a SN energy output in -rays with E ¿ 10 MeV of 4 × 1049 ergs (for d = 0:8 kpc). Of course, the origin of such a high -ray 3ux in SN1006 has still to be explained. 6. Conclusions (1) The possibility of some of the auroral frequency excesses being conceived by galactic supernova events may eventually lead to the re-evaluation of the solar activity indexes of the past. (2) Comparison of the di1erent depositions, winter temperatures in Eastern Europe and of frequency of aurorae plots indicates possibly missed SNe in the past. (3) A climate forcing related to, or enhanced by the neutral emission of the galactic SNe is an important conclusion which goes far beyond the scope of this paper and may need more proof and consideration. References Angell, J.K., 1990. Geophysical Research Letters 17, 1093. Aschenbach, B., 1998. Nature 396, 141. Brace, L.H., Maier, E.J., Ho1man, J.H., Whitteker, J., Sheperd, G.G., 1974. Journal of Geophysical Research 79, 5211. Bradley, R.S., Jones, P.D., 1995. In: Bradley, R.S., Jones, P.D. (Eds.), Climate Since A.D. 1500. Routledge, London, New York, p. 666. Bri1a, K.R., Bartholin, T.S., Eckstein, D., et al., 1990. Nature 346, 434. Burgess, C.P., Zuber, K., 2000. Astroparticle Physics 14, 1. Chan, K.W., Lingenfelter, R.E., 1987. Astrophysical Journal 318, L51. Chevalier, R.A., Klein, R.I., 1979. Astrophysical Journal 234, 597. Cini Castagnoli, G., Albrecht, A., Beer, J., et al., 1995. Geophysical Research Letters 22, 707. Clark, D.H., McCrea, W.H., Stephenson, F.R., 1977. Nature 265, 318. Clark, D.H., Stephenson, F.R., 1978. Quaternary Journal of Royal Astronomical Society 19, 387. Cliver, E.W., Boriako1, V., Feynman, J., 1998. Geophysical Research Letters 25, 1035. Cowley, T.J., Criste, T.A., Smith, N.R., 1993. Geophysical Research Letters 20, 209. Dall’Olmo, U., 1979. Journal of Geophysical Research 84, 1525. Damon, P.E., et al., 1995. Proceedings of the 25th ICRC, Vol. 4, Rome, p. 311.
676
A.F. Iyudin / Journal of Atmospheric and Solar-Terrestrial Physics 64 (2002) 669 – 676
Drescho1, G.A.M., Boyarchuk, K.A., Jungner, H., et al., 1999. Proceedings of the 26th ICCR, Vol. 4, Salt Lake City, p. 318. Drescho1, G.A.M., Zeller, E.J., 1990. Solar Physics 127, 333. Eddy, J.A., 1976. Science 192, 1189. Ellis, J., Fields, B.D., Schramm, D.N., 1996. Astrophysical Journal 470, 1227. Falk, S.W., 1978. Astrophysical Journal 226, L133. Fields, B.D., Ellis, J., 1999. New Astronomy 4, 419. Fishman, G.J., Inan, U.S., 1988. Nature 331, 418. Foley, H., Ruderman, M.A., 1973. Journal of Geophysical Research 78, 4441. Gehrels, N., Chen, W., 1993. Nature 361, 706. Graybill, D.A., Shiyatov, S.G., 1995 In: Bradley, R.S., Jones, P.D. (Eds.), Climate Since A.D. 1500. Routledge, London, New York, p. 393. Hammer, C.U., Clausen, H.B., Dansgaard, W., 1980. Nature 288, 230. Hampson, J., 1974. Nature 250, 189. Heath, D.F., Krueger, A.J., Crutzen, P.J., 1977. Science 197, 886. Holdsworth, G., 1986. Nature 324, 551. Hunt, G.E., 1978. Nature 271, 430. Inan, U.S., et al., 1999. Journal of Geophysical Research 26, 3357. Iyudin, A.F., et al., 1998. Nature 396, 142. Iyudin, A.F., et al., 2002, Astronomy and Astrophysics, in preparation. Keimatsu, M., 1976. Annals of Science Kan. University 13, 1. Klein, R.I., Chevalier, R.A., 1978. Astrophysical Journal 223, L109. Knie, K., Korschinek, G., Faestermann, T., et al., 1999. Physics Review Letters 83, 18. Kozyra, J.U., Nagy, A.F., Slater, D.W., 1997. Review of Geophysics 35, 155. Krivsky, L., Pejml, K., 1988. Astronomical Institute of Czechoslovakian Academy of Science 75, 32. Lamb, H.H., 1965. Palaeogeography Palaeoclimatology Palaeoecology 1, 13. Lamb, H.H., 1969. Climatic 3uctuations. In: Flohn, H. (Ed.), World Survey of Climatology, General Climatology, Vol. 2. Elsevier, New York, p. 173. Lamb, H.H., 1970. Philosophical Transactions of Royal Society A 266, 52. Lasher, G.J., Chan, K.L., 1979. Astrophysical Journal 230, 742. Lean, J., Beer, J., Bradley, R., 1995. Geophysical Research Letters 22, 3195. Lean, J., Rind, D., 1999. Journal of Atmospheric and Solar-Terrestrial Physics 61, 25. Legrand, M.R., Kirchner, S., 1990. Journal of Geophysical Research 95, 3493. Link, F., 1962. Geophysicalni Sbornik 173, 297. Link, F., 1964. Geophysicalni Sbornik 212, 501. Lorius, C., 1990. Philosophical Transactions of Royal Society of London A 330, 459.
Mann, M.E., Bradley, R.S., Hughes, M.K., 1999. Geophysical Research Letters 26, 759. McHargue, L.R., Damon, P.E., Donahue, D.J., 1995. Geophysical Research Letters 22, 659. Mendoza, B., 1997. Annals of Geophysics 15, 397. Newton, R.R., 1972. Medieval Chronicles and the Rotation of the Earth. John Hopkins University Press, Baltimore. Pudovkin, M.I., Raspopov, O.M., 1992. Geomagnetic Aeronomy 32, 593. Pudovkin, M.I., Veretenenko, S.V., 1995. Journal of Atmospheric and Solar-Terrestrial Physics 57, 1349. Raisbeck, G.M., Yiou, F., Bourles, D., et al., 1987. Nature 326, 273. Rees, M.H., Roble, R.G., 1975. Review of Geophysics & Space Physics 13, 201. Reid, G.C., 1999. Journal of Atmospheric and Solar-Terrestrial Physics 61, 3. Reid, G.C., McAfee, J.R., Crutzen, P.J., 1978. Nature 275, 489. Rood, R.T., Sarazin, C.L., Zeller, E.J., Parker, B.C., 1979. Nature 282, 701. Ruderman, M., 1974. Science 184, 1079. Ruderman, M., Chamberlain, J.W., 1975. Planetary Space Science 23, 247. Shepherd, G.G., Cogger, L.L., Burrows, J.R., 1976. Journal of Geophysical Research 81, 4597. Silverman, S.M., 1992. Review of Geophysics 30, 333. Siscoe, G.L., 1980. Review of Geophysics & Space Physics 18, 647. Sonett, C.P., MorLll, G.E., Jokipii, J.R., 1987. Nature 330, 458. Stephenson, J.A.E., ScourLeld, M.W.J., 1991. Nature 352, 137. Strickland, D.J., Meier, R.R., Hecht, J.H., Christensen, A.B., 1989. Journal of Geophysical Research 94, 13,527. Svensmark, H., Frijs-Christensen, E., 1997. Journal of Atmospheric and Solar-Terrestrial Physics 59, 1225. Svensmark, H., 1998. Physics Review Letters 81, 5027. Terry, K.D., Tucker, W.H., 1968. Science 159, 421. Warneck, P., 1972. Journal of Geophysical Research 77, 6589. Whitten, R.C., Borucci, W.J., Turco, R.P., 1975. Nature 257, 38. Whitten, R.C., Cuzzi, J., Borucci, W.J., Wolfe, J.H., 1976. Nature 263, 398. Wol1, E.W., 1995 In: Delmas, R.J. (Ed.), Ice Core Studies of Global Geochemical Cycles, NATO ASI Series, Vol. 130. Springer, Berlin=Heidelberg, p. 195. Zeller, E.J., Parker, B.C., 1981. Geophysical Research Letters 8, 895. Zeller, E.J., Dreschho1, G.A.M., Laird, C.M., 1986. Geophysical Research Letters 13, 1264. Zhang, Zh., 1985. Journal of British Astronomical Association 95, 205.