- Email: [email protected]
The most energetic solar flares
Nuclear Physics B (Proc. Suppl.) 196 (2009) 267–272 www.elsevier.com/locate/npbps
The most energetic solar flares - detection of solar neutrons and solar cosmic rays Yasushi Murakia∗ a
Department of Physics, Konan University, Higashinada-ku, Kobe 658-8501, Japan
In this talk, I show a typical example of a solar flare event on April 15, 2001 that clearly suggests the particle acceleration mechanism. Then I propose that solar physics is the easiest way to demonstrate the particle acceleration mechanism. In the flare of April 15, 2001, particles were accelerated beyond 56 GeV. The event is highly consistent with the hypothesis that particles are accelerated by the shock acceleration mechanism. The acceleration site was clearly observed by the Yohkoh X-ray telescope and making it possible to compare the Yohkoh X-ray data with ground-based detector data.
1. Introduction There are several important questions in the field of the physics of cosmic rays. (1) Do cosmic strings really exist and do they produce the highest energy cosmic rays? (2) If not, then what is the acceleration mechanism for protons beyond En ≥ 4 × 1019 ? (3) What are the sources of cosmic rays beyond the knee? Are they accelerated by the original second Fermi acceleration model, i.e. protons passing through over 1000 super nova remnants (SNR) [1]? (4) Are cosmic rays accelerated beyond 10 TeV in the SNR by the first Fermi shock acceleration mechanism [2]? (5) Do weakly interacting massive particles (WIMPs) really exist? Although these interesting questions remain unanswered at present considerable fundamental knowledge regarding cosmic ray phenomena at low energies has been collected. This includes evidence that protons are accelerated (1) by the shock acceleration mechanism in the shock front of the solar wind [3,4], (2) by collisions with the plasma jet above the coronal loop of the Sun [5], and (3) beyond 100 GeV in solar flares [6]. Hillas–Protheroe stated [7], that according to the Hillas plot, the energy of accelerated particles (E) is limited by the product of the distance ∗ contact address:[email protected] [email protected]
and
also
0920-5632/$ – see front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.nuclphysbps.2009.09.051
of the acceleration site (R) and the magnetic field strength (B): E≤ZeBR. When studying the particle acceleration mechanism, there are important points to be clarified: (1) how high are the particles accelerated, and (2) what is the acceleration mechanism? The actual acceleration process may be quite complicated and will depend on the environment where the particles are accelerated. Hence, several cases must be considered. In order to determine the acceleration mechanism for charged particles experimentally, numerous observations must be made of any object. For example, an observational result by a Cherenkov telescope could be combined with data from X-ray observations, radio observations, and gamma-ray observations. By performing a range of observations that span multiple wavelengths, we can conclude that particles are accelerated by the shock acceleration mechanism. This result is similar to the situation for solar cosmic rays. In the study of solar cosmic rays, several instruments are used to collect precise data over a wide range of wavelengths. In addition, particle data collected by the worldwide neutron monitor and worldwide solar neutron telescope are used. Using the data of the solar neutron telescope network (SONTEL), we can obtain important information on when the particles are accelerated beyond 10 GeV at the
268
Y. Muraki / Nuclear Physics B (Proc. Suppl.) 196 (2009) 267–272
solar surface. This information is very important for discriminating the different theories. By using ground-based neutron monitor data of the ground level enhancement (GLE), we can estimate the acceleration limit of solar particles at the Sun. For this, we use the magnetic field of the Earth as a spectrometer, which allows us to reduce the energy spectrum of solar particles up to 15 GV. Beyond this energy, we can estimate the energy of solar cosmic rays either using underground muon detectors or small size air shower detectors located on high mountains. In this talk, I will show a typical example of an event in a solar flare that clearly suggests the acceleration mechanism. I show that solar physics is the easiest way to demonstrate the acceleration mechanism. 2. Experimental technique In this section, I briefly explain the technical points regarding observing solar neutrons. To obtain the energy spectrum of solar particles, we must measure the energy spectrum of the charged solar particles. However, solar particles are transferred to the Earth along the interplanetary magnetic field and therefore the arrival time of the charged solar particles does not always reflect important information on the acceleration time at the solar surface. Current practice is to compare the data of solar cosmic rays with X-ray data which provides good detail of the dynamical development of the magnetic loop associated with a solar flare. Without combining the data of solar comic rays with the observational data of X-rays, we cannot obtain an exact description of the particle acceleration mechanism. Thus, we must use data for neutral particles emitted in solar flares when we study the time profile of the acceleration processes. Two kinds of neutral particles are emitted by the Sun: gammarays and neutrons. However, gamma-rays are also emitted due to the Bremsstrahlung process of electrons, and their energy is usually limited to as low as a few MeV. Therefore, information on the particle acceleration process is only obtained through neutrons. The detection of solar neutrons has several as-
Figure 1. Sierra Negra Solar Neutron Telescope. Central four plastic scintillation counters are covered by an array of proportional counters that acts as the anti-counter for charged particles. Incoming neutrons are converted into protons by the charge exchange process in the scintillator. Total deposit energy in the scintillator is measured, and the pulse height of the plastic scintillator is calibrated by the muon signals.
sociated observational difficulties: (1) neutrons decay in flight from the Sun to the Earth, (2) even if they reach the top of the atmosphere, most will be absorbed in the upper part of the atmosphere, and (3) the fact that neutrons have a mass presents one of the greatest difficulties. Therefore, neutrons that are emitted from the Sun at the same time will have observable arrival time differences, that is, they exhibit time dispersion. This dispersion makes it difficult to correctly interpret the time profile of the accelerated particles as it is possible to confuse the production time profile between impulsive production and gradual production. Therefore, to deal with this problem we measure the energy of the neutrons. In this paper, I briefly explain how the above
Y. Muraki / Nuclear Physics B (Proc. Suppl.) 196 (2009) 267–272
observational difficulties can be avoided experimentally. Regarding point (1), when solar neutrons with kinetic energy higher than 100 MeV are observed, the effect of the decay is not considered to be that crucial. The survival probability of solar neutrons of kinetic energy En = 200 MeV in flight for 1 AU is 0.30. The absorption process in the atmosphere is a serious effect for neutrons with energy less than 100 MeV [8](point (2)). For this reason, solar neutron telescopes have been located on high mountains [9–11]. Since it is important to measure the energy of neutrons, solar neutron telescopes employ thick plastic scintillator detectors. Figure 1 shows a typical example of a neutron telescope. The energy of the neutrons can be measured either by the range method or the total energy deposited method. The deposited energy is detected as the pulse height by photomultipliers. Since we cannot measure the deposited energy for each neutron, the data is normally discriminated into 2-4 levels of pulse height. The scintillator can also be used as a kind of threshold counter. 3. Actual event detected on September 7, 2005 In this section, I describe the detection of solar neutron signals by a solar neutron telescope and a classical neutron monitor [12]. As shown in Figure 2, in association with the solar flare of September 7 2005, an event was recorded in detectors located at the Sierra Negra (4,620 m Mexico) (Figure 2) [13] and Chacaltaya observatories (5,250 m, Bolivia) (Figure 3). The detections were made simultaneously so the confidence of the signals is very reliable. In addition, the event was recorded at two stations by two different kinds of detectors: a neutron telescope and a neutron monitor. The energy spectra obtained by the neutron telescopes at the two different observatories gave the same energy spectra with an integral energy index of γ ≈ −2.0 in the neutron energy range En = 30 − 200 MeV. Note that the energy of the neutrons corresponds to the energy inside the detector and does not always correspond to the incident energy of the neutrons at the top of the at-
269
mosphere. The detection efficiency of secondary neutrons inside the detector is about 10% per 10 cm thickness of plastic scintillator. 4. Event observed on April 15, 2001 (the Easter event On April 15, 2001, a very exciting event was observed [5]. The event is called the Easter event, the important features of which can be summarized as follows: (1) the X-ray telescope onboard the Yohkoh satellite observed the development of solar flares from the start time to the peak time of the flare, (2) at the same time the neutron monitor located at the Chacaltaya observatory observed a ≈4σ bump before the arrival of solar energetic particles (charged particles) Figures 4 and 5 , (3) the muon detector located at the Notre Dame university (GRAND) observed a 6.1 enhancement of the signal, corresponding to 56 GeV equivalent proton energy [14], and (4) from the GLE enhancement spectrum, the energy spectrum of solar protons could be written as a single power law with a power index of γ = −2.75 (integral). Figure 6 shows the data for the Easter event together with other solar flares. The solid black circles correspond to the Easter event. The data can be fitted by a straight line with power law index −2.75 in the energy range between 100 MeV and 100 GeV over three orders of magnitude of energy. The event is highly consistent with the hypothesis that particles are accelerated by the shock acceleration mechanism. The acceleration site was clearly observed by the Yohkoh X-ray telescope and it should be at the top of the magnetic loop. Furthermore, the X-ray data suggests an interesting feature whereby the acceleration process occurred by different magnetic loops, which gradually increased the average momentum of the particles. Particles accelerated at the first loop were injected into the next loop, which likely had a stronger magnetic field. The accelerated particles at the second loop were then injected into the third and final loop, which had a stronger magnetic field than the second loop. The charged particles could be combined inside the loops. At
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Y. Muraki / Nuclear Physics B (Proc. Suppl.) 196 (2009) 267–272
Figure 2. Solar neutron event observed on September 7, 2005 by the Sierra Negra Solar Neutron Telescope (Mexico). The time profile of the Anti all corresponds to the signals detected by the anti-counters. They must be protons converted in the atmosphere by solar neutrons. The S1 channel represents the minimum energy channel of the SONTEL with energy Ep >30 MeV. The S1 anti channel corresponds to the signals of neutrons. The counting rate of the Layer 1 represents the 5 minutes value of the proportional counter placed at the under part of the plastic scintillator. The vertical dotted line corresponds to the start time of the flare (by the X-ray observation).
Figure 3. Solar neutron event observed by the Chacaltaya Neutron Telescope (Bolivia) on September 7, 2005. The time profiles correspond from the top to the bottom, neutral and charged signals deposited in the scintillator with energy > 40, >80, >160, >240 MeV respectively. The bottom panel shows the time profile of the neutron monitor. A clear spike can be seen. The vertical dotted line corresponds to the departure time of high energy particles from the Sun (17:36:40UT) that are estimated from the Geotail satellite data.
Y. Muraki / Nuclear Physics B (Proc. Suppl.) 196 (2009) 267–272
Counts/ 5.0 min
3
491
× 10
Neutron_Monitor
Chacaltaya 2001/4/15
490 489 488 487 486 485
05:00:00
07:00:00
09:00:00
11:00:00
13:00:00
15:00:00 LT (hour)
Figure 4. The 5 minutes value of the Chacaltaya neutron monitor (Bolivia). An enhancement can be seen around 10:00 Local Time just after a large solar flare. The vertical line corresponds to the maximum time of the intensity of gamma-rays from the Sun (09:45 Local Time or 13:45 UT).
271
the top of the third loop, a high-speed plasma jet may be emitted. This system should be able to accelerate particles to over 56 GeV. Another interesting fact associated with this event is that protons with average energy of 56 GeV were transferred from the Sun to the Earth within the interplanetary magnetic field. By a first approximation, only protons with energy higher than 100 GeV are transferred independent of the interplanetary magnetic field and arrive at the same time as neutrons. However, both the high and low energy charged particles were observed at the same time, implying that the magnetic field of the interplanetary space is sufficiently strong to effect even high energy protons.
5. Summary
Figure 5. The same data as Figure 4, however the background lines were shown. The dotted line corresponds to the deviation from the mean counting rate with 1σ. Daily modulation was seen on the counting rate.
While another candidate, similar to that of April 15, 2001, was observed on October 23, 2003 (The Halloween event), analysis of this event has not been completed. Since only one such event has been recorded and analyzed, it is too early to reach the general conclusion that protons are accelerated by the shock acceleration mechanism at the solar surface. In the forthcoming solar cycle, cycle 24, we are preparing to observe more solar cosmic rays and hope to eventually be able to draw a definite conclusion on the acceleration mechanism. In solar cycle 24, a new solar neutron detector will be available for observations. This new neutron detector will be launched in June 2009 and installed at the International Space Station (ISS SEDA-AP) [15]. A new X-ray telescope (Hinode) is already under operation. It is hoped that it will be possible to obtain valuable results using these instruments and that Sun activity will start soon.
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Y. Muraki / Nuclear Physics B (Proc. Suppl.) 196 (2009) 267–272
6. Acknowledgments The author thanks his colleagues, Drs. Y. Matsubara, T. Sako, K. Watanabe, Y. Tsunesada and Rolf Buetikofer for providing him valuable data. He also acknowledges Profs. E. Flueckiger, Valdes-Galicia, Ashot Chlingalian, T. Terasawa and J.L. Zhang for valuable discussions. Finally he thanks Jean Noel Capdevielle who provided him an oppotunity to present the talk in the conference. REFERENCES
Figure 6. The integral flux of solar protons are shown with the intensity of the galactic cosmic rays. The solar flare event observed on Easter day is shown by the large black circles (•). The four black points with the energies lower than 100 MeV were detected by the GOES satellite, while the other three points were measured by the neutron monitors located at various rigidities. The point of GRAND has just come on the extension of those points by a straight line on the logarithmic scale graph. This implies that particles may be accelerated by the shock acceleration model.
1. W.I. Axford, Proceed. of the ICRR international symposium (1991) 406, edited by Nagano and Takahara (World Scientific). 2. C.J. Cesarsky, Raportuer paper for the 15th ICRC (Plovdiv), 10(1977) 196. 3. T. Terasawa et al., Advances in Space Research, 37 (2006) 1408. 4. N. Shimada et al., Astrophys. Space Sci, 264 (1999) 481. 5. Y. Muraki et al, Astroparticle Physics, 28 (2007) 119. 6. Y. Muraki et al, Astroparticle Physics, 29 (2008) 229. 7. R.J. Protheroe, Astroph (2004) 0401523. 8. S. Shibata, J.G.R., 99 (1994) A4, 6651. 9. E.O. Flueckiger et al., Proceed. 27th ICRC, 8 (2001) 3044. 10. K. Watanabe et al., Proceed. 29th ICRC, 1 (2005) 37. 11. Y. Matsubara et al., Proceed. 30the ICRC, (2007) paper number 191 (in press). 12. T. Sako et al., ApJ, 651 (2006) L69. 13. J.F. Valdes-Galicia et al., Nucl.Instr. Meth., Phys. Res., A535 (2004) 656. 14. C.DAndrea and J. Poirier, Proceed. of the 28th ICRC (Tsukuba), 6 (2003) 3423. 15. K. Koga et al, Proceed 21st ECRS (2008) paper # 2.16 (in press).
The most energetic solar flares - detection of solar neutrons and solar cosmic rays Yasushi Murakia∗ a
Department of Physics, Konan University, Higashinada-ku, Kobe 658-8501, Japan
In this talk, I show a typical example of a solar flare event on April 15, 2001 that clearly suggests the particle acceleration mechanism. Then I propose that solar physics is the easiest way to demonstrate the particle acceleration mechanism. In the flare of April 15, 2001, particles were accelerated beyond 56 GeV. The event is highly consistent with the hypothesis that particles are accelerated by the shock acceleration mechanism. The acceleration site was clearly observed by the Yohkoh X-ray telescope and making it possible to compare the Yohkoh X-ray data with ground-based detector data.
1. Introduction There are several important questions in the field of the physics of cosmic rays. (1) Do cosmic strings really exist and do they produce the highest energy cosmic rays? (2) If not, then what is the acceleration mechanism for protons beyond En ≥ 4 × 1019 ? (3) What are the sources of cosmic rays beyond the knee? Are they accelerated by the original second Fermi acceleration model, i.e. protons passing through over 1000 super nova remnants (SNR) [1]? (4) Are cosmic rays accelerated beyond 10 TeV in the SNR by the first Fermi shock acceleration mechanism [2]? (5) Do weakly interacting massive particles (WIMPs) really exist? Although these interesting questions remain unanswered at present considerable fundamental knowledge regarding cosmic ray phenomena at low energies has been collected. This includes evidence that protons are accelerated (1) by the shock acceleration mechanism in the shock front of the solar wind [3,4], (2) by collisions with the plasma jet above the coronal loop of the Sun [5], and (3) beyond 100 GeV in solar flares [6]. Hillas–Protheroe stated [7], that according to the Hillas plot, the energy of accelerated particles (E) is limited by the product of the distance ∗ contact address:[email protected] [email protected]
and
also
0920-5632/$ – see front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.nuclphysbps.2009.09.051
of the acceleration site (R) and the magnetic field strength (B): E≤ZeBR. When studying the particle acceleration mechanism, there are important points to be clarified: (1) how high are the particles accelerated, and (2) what is the acceleration mechanism? The actual acceleration process may be quite complicated and will depend on the environment where the particles are accelerated. Hence, several cases must be considered. In order to determine the acceleration mechanism for charged particles experimentally, numerous observations must be made of any object. For example, an observational result by a Cherenkov telescope could be combined with data from X-ray observations, radio observations, and gamma-ray observations. By performing a range of observations that span multiple wavelengths, we can conclude that particles are accelerated by the shock acceleration mechanism. This result is similar to the situation for solar cosmic rays. In the study of solar cosmic rays, several instruments are used to collect precise data over a wide range of wavelengths. In addition, particle data collected by the worldwide neutron monitor and worldwide solar neutron telescope are used. Using the data of the solar neutron telescope network (SONTEL), we can obtain important information on when the particles are accelerated beyond 10 GeV at the
268
Y. Muraki / Nuclear Physics B (Proc. Suppl.) 196 (2009) 267–272
solar surface. This information is very important for discriminating the different theories. By using ground-based neutron monitor data of the ground level enhancement (GLE), we can estimate the acceleration limit of solar particles at the Sun. For this, we use the magnetic field of the Earth as a spectrometer, which allows us to reduce the energy spectrum of solar particles up to 15 GV. Beyond this energy, we can estimate the energy of solar cosmic rays either using underground muon detectors or small size air shower detectors located on high mountains. In this talk, I will show a typical example of an event in a solar flare that clearly suggests the acceleration mechanism. I show that solar physics is the easiest way to demonstrate the acceleration mechanism. 2. Experimental technique In this section, I briefly explain the technical points regarding observing solar neutrons. To obtain the energy spectrum of solar particles, we must measure the energy spectrum of the charged solar particles. However, solar particles are transferred to the Earth along the interplanetary magnetic field and therefore the arrival time of the charged solar particles does not always reflect important information on the acceleration time at the solar surface. Current practice is to compare the data of solar cosmic rays with X-ray data which provides good detail of the dynamical development of the magnetic loop associated with a solar flare. Without combining the data of solar comic rays with the observational data of X-rays, we cannot obtain an exact description of the particle acceleration mechanism. Thus, we must use data for neutral particles emitted in solar flares when we study the time profile of the acceleration processes. Two kinds of neutral particles are emitted by the Sun: gammarays and neutrons. However, gamma-rays are also emitted due to the Bremsstrahlung process of electrons, and their energy is usually limited to as low as a few MeV. Therefore, information on the particle acceleration process is only obtained through neutrons. The detection of solar neutrons has several as-
Figure 1. Sierra Negra Solar Neutron Telescope. Central four plastic scintillation counters are covered by an array of proportional counters that acts as the anti-counter for charged particles. Incoming neutrons are converted into protons by the charge exchange process in the scintillator. Total deposit energy in the scintillator is measured, and the pulse height of the plastic scintillator is calibrated by the muon signals.
sociated observational difficulties: (1) neutrons decay in flight from the Sun to the Earth, (2) even if they reach the top of the atmosphere, most will be absorbed in the upper part of the atmosphere, and (3) the fact that neutrons have a mass presents one of the greatest difficulties. Therefore, neutrons that are emitted from the Sun at the same time will have observable arrival time differences, that is, they exhibit time dispersion. This dispersion makes it difficult to correctly interpret the time profile of the accelerated particles as it is possible to confuse the production time profile between impulsive production and gradual production. Therefore, to deal with this problem we measure the energy of the neutrons. In this paper, I briefly explain how the above
Y. Muraki / Nuclear Physics B (Proc. Suppl.) 196 (2009) 267–272
observational difficulties can be avoided experimentally. Regarding point (1), when solar neutrons with kinetic energy higher than 100 MeV are observed, the effect of the decay is not considered to be that crucial. The survival probability of solar neutrons of kinetic energy En = 200 MeV in flight for 1 AU is 0.30. The absorption process in the atmosphere is a serious effect for neutrons with energy less than 100 MeV [8](point (2)). For this reason, solar neutron telescopes have been located on high mountains [9–11]. Since it is important to measure the energy of neutrons, solar neutron telescopes employ thick plastic scintillator detectors. Figure 1 shows a typical example of a neutron telescope. The energy of the neutrons can be measured either by the range method or the total energy deposited method. The deposited energy is detected as the pulse height by photomultipliers. Since we cannot measure the deposited energy for each neutron, the data is normally discriminated into 2-4 levels of pulse height. The scintillator can also be used as a kind of threshold counter. 3. Actual event detected on September 7, 2005 In this section, I describe the detection of solar neutron signals by a solar neutron telescope and a classical neutron monitor [12]. As shown in Figure 2, in association with the solar flare of September 7 2005, an event was recorded in detectors located at the Sierra Negra (4,620 m Mexico) (Figure 2) [13] and Chacaltaya observatories (5,250 m, Bolivia) (Figure 3). The detections were made simultaneously so the confidence of the signals is very reliable. In addition, the event was recorded at two stations by two different kinds of detectors: a neutron telescope and a neutron monitor. The energy spectra obtained by the neutron telescopes at the two different observatories gave the same energy spectra with an integral energy index of γ ≈ −2.0 in the neutron energy range En = 30 − 200 MeV. Note that the energy of the neutrons corresponds to the energy inside the detector and does not always correspond to the incident energy of the neutrons at the top of the at-
269
mosphere. The detection efficiency of secondary neutrons inside the detector is about 10% per 10 cm thickness of plastic scintillator. 4. Event observed on April 15, 2001 (the Easter event On April 15, 2001, a very exciting event was observed [5]. The event is called the Easter event, the important features of which can be summarized as follows: (1) the X-ray telescope onboard the Yohkoh satellite observed the development of solar flares from the start time to the peak time of the flare, (2) at the same time the neutron monitor located at the Chacaltaya observatory observed a ≈4σ bump before the arrival of solar energetic particles (charged particles) Figures 4 and 5 , (3) the muon detector located at the Notre Dame university (GRAND) observed a 6.1 enhancement of the signal, corresponding to 56 GeV equivalent proton energy [14], and (4) from the GLE enhancement spectrum, the energy spectrum of solar protons could be written as a single power law with a power index of γ = −2.75 (integral). Figure 6 shows the data for the Easter event together with other solar flares. The solid black circles correspond to the Easter event. The data can be fitted by a straight line with power law index −2.75 in the energy range between 100 MeV and 100 GeV over three orders of magnitude of energy. The event is highly consistent with the hypothesis that particles are accelerated by the shock acceleration mechanism. The acceleration site was clearly observed by the Yohkoh X-ray telescope and it should be at the top of the magnetic loop. Furthermore, the X-ray data suggests an interesting feature whereby the acceleration process occurred by different magnetic loops, which gradually increased the average momentum of the particles. Particles accelerated at the first loop were injected into the next loop, which likely had a stronger magnetic field. The accelerated particles at the second loop were then injected into the third and final loop, which had a stronger magnetic field than the second loop. The charged particles could be combined inside the loops. At
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Y. Muraki / Nuclear Physics B (Proc. Suppl.) 196 (2009) 267–272
Figure 2. Solar neutron event observed on September 7, 2005 by the Sierra Negra Solar Neutron Telescope (Mexico). The time profile of the Anti all corresponds to the signals detected by the anti-counters. They must be protons converted in the atmosphere by solar neutrons. The S1 channel represents the minimum energy channel of the SONTEL with energy Ep >30 MeV. The S1 anti channel corresponds to the signals of neutrons. The counting rate of the Layer 1 represents the 5 minutes value of the proportional counter placed at the under part of the plastic scintillator. The vertical dotted line corresponds to the start time of the flare (by the X-ray observation).
Figure 3. Solar neutron event observed by the Chacaltaya Neutron Telescope (Bolivia) on September 7, 2005. The time profiles correspond from the top to the bottom, neutral and charged signals deposited in the scintillator with energy > 40, >80, >160, >240 MeV respectively. The bottom panel shows the time profile of the neutron monitor. A clear spike can be seen. The vertical dotted line corresponds to the departure time of high energy particles from the Sun (17:36:40UT) that are estimated from the Geotail satellite data.
Y. Muraki / Nuclear Physics B (Proc. Suppl.) 196 (2009) 267–272
Counts/ 5.0 min
3
491
× 10
Neutron_Monitor
Chacaltaya 2001/4/15
490 489 488 487 486 485
05:00:00
07:00:00
09:00:00
11:00:00
13:00:00
15:00:00 LT (hour)
Figure 4. The 5 minutes value of the Chacaltaya neutron monitor (Bolivia). An enhancement can be seen around 10:00 Local Time just after a large solar flare. The vertical line corresponds to the maximum time of the intensity of gamma-rays from the Sun (09:45 Local Time or 13:45 UT).
271
the top of the third loop, a high-speed plasma jet may be emitted. This system should be able to accelerate particles to over 56 GeV. Another interesting fact associated with this event is that protons with average energy of 56 GeV were transferred from the Sun to the Earth within the interplanetary magnetic field. By a first approximation, only protons with energy higher than 100 GeV are transferred independent of the interplanetary magnetic field and arrive at the same time as neutrons. However, both the high and low energy charged particles were observed at the same time, implying that the magnetic field of the interplanetary space is sufficiently strong to effect even high energy protons.
5. Summary
Figure 5. The same data as Figure 4, however the background lines were shown. The dotted line corresponds to the deviation from the mean counting rate with 1σ. Daily modulation was seen on the counting rate.
While another candidate, similar to that of April 15, 2001, was observed on October 23, 2003 (The Halloween event), analysis of this event has not been completed. Since only one such event has been recorded and analyzed, it is too early to reach the general conclusion that protons are accelerated by the shock acceleration mechanism at the solar surface. In the forthcoming solar cycle, cycle 24, we are preparing to observe more solar cosmic rays and hope to eventually be able to draw a definite conclusion on the acceleration mechanism. In solar cycle 24, a new solar neutron detector will be available for observations. This new neutron detector will be launched in June 2009 and installed at the International Space Station (ISS SEDA-AP) [15]. A new X-ray telescope (Hinode) is already under operation. It is hoped that it will be possible to obtain valuable results using these instruments and that Sun activity will start soon.
272
Y. Muraki / Nuclear Physics B (Proc. Suppl.) 196 (2009) 267–272
6. Acknowledgments The author thanks his colleagues, Drs. Y. Matsubara, T. Sako, K. Watanabe, Y. Tsunesada and Rolf Buetikofer for providing him valuable data. He also acknowledges Profs. E. Flueckiger, Valdes-Galicia, Ashot Chlingalian, T. Terasawa and J.L. Zhang for valuable discussions. Finally he thanks Jean Noel Capdevielle who provided him an oppotunity to present the talk in the conference. REFERENCES
Figure 6. The integral flux of solar protons are shown with the intensity of the galactic cosmic rays. The solar flare event observed on Easter day is shown by the large black circles (•). The four black points with the energies lower than 100 MeV were detected by the GOES satellite, while the other three points were measured by the neutron monitors located at various rigidities. The point of GRAND has just come on the extension of those points by a straight line on the logarithmic scale graph. This implies that particles may be accelerated by the shock acceleration model.
1. W.I. Axford, Proceed. of the ICRR international symposium (1991) 406, edited by Nagano and Takahara (World Scientific). 2. C.J. Cesarsky, Raportuer paper for the 15th ICRC (Plovdiv), 10(1977) 196. 3. T. Terasawa et al., Advances in Space Research, 37 (2006) 1408. 4. N. Shimada et al., Astrophys. Space Sci, 264 (1999) 481. 5. Y. Muraki et al, Astroparticle Physics, 28 (2007) 119. 6. Y. Muraki et al, Astroparticle Physics, 29 (2008) 229. 7. R.J. Protheroe, Astroph (2004) 0401523. 8. S. Shibata, J.G.R., 99 (1994) A4, 6651. 9. E.O. Flueckiger et al., Proceed. 27th ICRC, 8 (2001) 3044. 10. K. Watanabe et al., Proceed. 29th ICRC, 1 (2005) 37. 11. Y. Matsubara et al., Proceed. 30the ICRC, (2007) paper number 191 (in press). 12. T. Sako et al., ApJ, 651 (2006) L69. 13. J.F. Valdes-Galicia et al., Nucl.Instr. Meth., Phys. Res., A535 (2004) 656. 14. C.DAndrea and J. Poirier, Proceed. of the 28th ICRC (Tsukuba), 6 (2003) 3423. 15. K. Koga et al, Proceed 21st ECRS (2008) paper # 2.16 (in press).