- Email: [email protected]
HiSCORE: A new detector for astroparticle and particle physics beyond 10 TeV
Nuclear Instruments and Methods in Physics Research A 692 (2012) 246–249
Contents lists available at SciVerse ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
HiSCORE: A new detector for astroparticle and particle physics beyond 10 TeV M. Tluczykont a,n, D. Horns a, D. Hampf a, R. Nachtigall a, U. Einhaus a, M. Kunnas a, T. Kneiske a,1, G.P. Rowell b a b
Institut f¨ ur Experimentalphysik, Universit¨ at Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany University of Adelaide 5005, School of Chemistry & Physics, Australia
a r t i c l e i n f o
a b s t r a c t
Available online 5 January 2012
The new large-area (100 km ) wide-angle (0.9 sr) air Cherenkov detector HiSCORE (Hundred n i Square-km Cosmic ORigin Explorer) aims at the exploration of the cosmic ray and g-ray sky (accelerator sky) in the so far poorly covered energy range from 10 TeV to 1 EeV. The main motivation for observations in this energy regime is to solve the origin of Galactic cosmic rays. Other questions of astroparticle and particle physics can be addressed in this energy regime. Furthermore, new physics questions might arise by opening the last remaining observation window of g-ray astronomy (TeV/PeV). HiSCORE is based on non-imaging Cherenkov light-front sampling with sensitive large-area detector modules of the order of 0:5 m2 . Sampling the lateral photon density and arrival-time distribution allows the reconstruction of the direction, the energy and the type (mainly via the shower depth) of the primary particle. & 2012 Elsevier B.V. All rights reserved.
Keywords: g-Rays: ultra-high energy g-Rays: instrumentation Cosmic-rays: instrumentation
1. Introduction While we are approaching the centennial of the discovery of cosmic rays [1], the question of their origin still remains unsolved. A multi-messenger approach using indirect air-shower observations of ultra high energy g-rays (UHE g-rays, E4 10 TeV) and cosmic rays above 100 TeV is the key to this question. Shell-type Supernova remnants (SNR) are considered as best CR accelerator candidates, and the detections of several shell-type SNR in the VHE regime apparently support this scenario see e.g. Ref. [2]. However, a leptonic origin of the observed emission cannot be excluded with existing data see e.g. Ref. [3] for a review. If cosmic rays are indeed accelerated up to 1017 eV inside our Galaxy, there must be Galactic pevatrons which emit g-rays and neutrinos at energies around 100 TeV and up to few PeV (see Fig. 2). Pevatrons are a crucial building-block for a solution of the mystery of the origin of CRs. So far, all shell-type SNR detected in the VHE regime exhibit a cutoff energy too low by two orders of magnitude as compared to the expectation for a cosmic ray pevatron. Some of the known sources at TeV energies, such as the hard sources from the H.E.S.S. Galactic plane scan, might be pevatrons (also shown in Fig. 2). To date, the continuation of their spectra into the UHE regime
n
Corresponding author. E-mail address: [email protected] (M. Tluczykont). 1 ¨ was, wo, Germany. Now at Fraunhofer Institut, fur
0168-9002/$ - see front matter & 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2011.12.075
2
is unknown. Sensitive measurements in this energy regime will answer this question. A search for cosmic ray pevatrons requires an extension of the currently existing g-ray observation window into the UHE g-ray regime. This extension will be provided by the HiSCORE (Hundred n i Square-km Cosmic ORigin Explorer) detector. With HiSCORE, we plan to open up the last remaining observation window of g-ray astronomy, from 10 TeV to several tens of PeV, and to provide high-statistics data on cosmic rays from 100 TeV to 1 EeV, covering the transition range from a Galactic to an extragalactic origin of cosmic rays.
2. Physics objectives The main motivation for HiSCORE is the search for the origin of cosmic rays, and more specifically, the search for cosmic ray pevatrons in the g-ray regime. At the same time, HiSCORE will be a valuable cosmic ray detector, using the same measurement principle as e.g. the Tunka air shower array [4]. Furthermore, HiSCORE will also provide the possibility to address fundamental questions of particle physics using air-shower data. These particle physics questions might partly have an influence on the interpretation of air shower data. Among these particle physics topics are the measurement of the proton–proton cross-section, search for quark-gluon plasma in airshowers, axion search in the Galactic magnetic field, search for Lorentz invariance violation, and for heavy super-symmetric particles (wimpzillas).
M. Tluczykont et al. / Nuclear Instruments and Methods in Physics Research A 692 (2012) 246–249
3. The HiSCORE detector With HiSCORE, we are pursuing the concept of non-imaging air Cherenkov astronomy, based on the collection of Cherenkov photons from air showers on the observation level using wideangle detector stations. The non-imaging technique allows to build a detector with a large field of view (survey instrument) and to equip very large areas with a small number of PMT channels. In the case of HiSCORE as described here, only of the order of 200 channels/km2 are necessary. As opposed to that, a typical imaging air Cherenkov telescope array comes along with 10 000 channels/km2. Therefore, the non-imaging technique is best suited for the UHE g-ray regime, where large detector areas are the most important detector aspect, and for cosmic ray physics. The station concept is shown in Fig. 1. HiSCORE is planned as a distributed array of detector stations, covering an area of 100 km2 (or more), and arranged in a grid with 150 m inter-station separation. Each detector station consists of four photomultiplier tubes equipped with Winston-cones (increasing the light collection area). The sensitive area of one detector station sums up to 0.5 m2 (PMTþWinston-cone area), resulting in a total lightcollection area (100 km2 array, 150 m inter-station distance) of 2300 m2. The chosen Winston-cone geometry results in a field of view of the detector of 301 half-opening angle (0.84 sr). The dynamic range will be increased to the necessary factor of 105 (10 TeV–1 EeV) by reading out one or two dynodes in addition to the anode signal. The usage of four PMT channels is crucial for the maximization of the light collection area of a station and for the suppression of noise induced by night-sky background (NSB) photons. The individual signals of each PMT channel are analogsummed before read-out. Before the trigger is built, the individual PMT signals are clipped to a predefined level. The trigger is built using the sum of the clipped signals, effectively building a fourchannel coincidence. Using signal clipping avoids false triggers induced by very large signals (afterpulses) in a single PMT channel. A full simulation of the HiSCORE detector [5] resulted in an expected cosmic ray trigger rate of 18 kHz (100 km2 array). The event reconstruction of HiSCORE is based on the combination
of information from the lateral photon density distribution (amplitude) and the arrival time distribution of Cherenkov photons [6]. The reconstruction of the longitudinal development using the shower-front arrival-time distribution (at distances from the shower core 4100 m) allows detailed spectral and composition measurements, and g-hadron separation via reconstruction of the shower-depth.
4. Sensitivity to g-rays On the basis of the above-mentioned simulation and reconstruction, the integral sensitivity to g-ray point sources was calculated [5]. The results are shown in Fig. 2. For comparison, the sensitivities of different other experiments are also shown. The final stage of HiSCORE is planned for construction at a southern hemisphere site (likewise CTA), as opposed to the northern experiments HAWC and LHAASO. Already around 50 TeV, the sensitivity of HiSCORE will be comparable to the currently planned imaging air Cherenkov telescope array CTA [7]. Beyond this energy, the sensitive range will be extended deeply into the UHE g-ray regime. When comparing sensitivities between different experiments, one has to keep in mind that HiSCORE is a survey instrument with a very large field of view. Therefore, a source inside the field of view is visible over 200 h per year (for a site at a latitude of 351), i.e. 1000 h after 5 years of survey operation, covering a total area of the sky of p steradian. As opposed to that, Cherenkov telescopes have a comparatively small field of view and always operate in pointed observation mode. When aiming at a sky survey using Cherenkov telescopes, this imposes a scan of the sky in subsequent overlapping short pointings of small parts of the sky. In the UHE g-ray regime, absorption via e þ e pair production becomes relevant for the propagation inside our Galaxy. The interstellar radiation field (ISRF) is dense enough to generate a non-negligible absorption effect. Moskalenko et al. [10] have shown that the absorption of g-rays by pair production in the ISRF reaches a maximum around 100 TeV. At PeV energies the universal cosmic microwave background (CMB) radiation field becomes relevant. Fig. 3 illustrates the impact of this absorption
HiSCORE detector station concept Central DAQ
Total light−collecting area: 0.5 sqm
~500mm
400mm
R/O DRS 4
Winston cone
1024 cells
time sync. USB
clock PlugPC 12V
Summing
PMT ~ 206mm HV divider HV divider HV divider HV divider on/off moni
0..5V
Slow control Arduino
247
clipping
0..2.5kV on/off & moni
12V
low gain − dyn 5 high gain − anode Power−distribution
USB
Fig. 1. The HiSCORE detector station concept. Shown are the four PMT channels equipped with Winston cones, trigger and read-out electronics.
M. Tluczykont et al. / Nuclear Instruments and Methods in Physics Research A 692 (2012) 246–249
integral flux sensitivity / erg cm-2 s-1
248
10-10
H.E.S.S. survey sensitivity, 6 years
HAWC point-source, 5 years
CTA point-source, 50 hours
LHAASO point-source, 1 year
Milagro point-source, 5 years
H.E.S.S. survey hard sources
10-11
KASKADE U.L.
10-12
HiSCORE
10-13
10-14 -1 10
1
102
10
103
104
log (energy/TeV) Fig. 2. Point source sensitivity of the HiSCORE detector (5 years) as compared to data from the H.E.S.S. Galactic plane survey [8], and an upper limit from KASKADE [9]. Also shown are a model spectrum of a pevatron (thin solid line) and sensitivities of other experiments. Milagro and the planned experiments HAWC and LHAASO are northernhemisphere experiments. The final stage of HiSCORE is envisaged to be built in the southern hemisphere for optimal view of the Galactic plane.
Pevatron cutoff regime RXJ 1713.7-3946, extrapolation from H.E.S.S. data
E2 dN/dE / erg cm-2 s-1
10-11 "strong pevatron" MGRO J2019+37
no absorption
strong absorption
10-12 "weak pevatron"
10-13 HiSCORE
CTA
1
10
102 energy / TeV
103
Fig. 3. The HiSCORE sensitivity as compared to pevatron model curves and the CTA sensitivity. Pevatron curves are shown for two different flux levels (labeled strong and weak pevatrons respectively) in the case of strong absorption (thin solid) and no Galactic absorption at all (thin dashed). (1) strong pevatron case: obtained from scaling a hadronic emission model to the flux observed by Milagro from MGRO J2019þ 37 (data point) and (2) weak pevatron case: arbitrarily scaled to be at the edge of the HiSCORE sensitivity. The pevatron spectra after correction for the absorption in the ISRF and CMB were obtained using the optical depth from Moskalenko et al. [10]. Also shown is an extrapolation of the H.E.S.S. spectrum of the shell-type Supernova remnant RXJ 1713.7-3946.
effect on the g-ray spectrum of cosmic ray pevatrons. To be conservative, the transmittance curve for the strongest absorption from Moskalenko et al. [10] was used, corresponding to a location of the object at the other side of the Galaxy, at 28.5 kpc from Earth. The pevatron curves are shown using two different scalings and for the cases of absorption (thin solid lines) and no absorption (thin dashed lines). The curve labeled strong pevatron is scaled to the observed flux from the extended (11) Milagro source MGRO J2019þ37 [11], located in the Cygnus region. This object was detected by Milagro at a median energy of 12 TeV. If MGRO J2019þ37 were a pevatron, its emission would extend into the UHE regime as shown, and would be easily and fully resolved by HiSCORE. The lower thin solid and thin dashed curves (labeled
weak pevatron) illustrate the case of a hypothetical pevatron that could be detected by CTA up to 70 TeV, and by HiSCORE beyond 70 TeV, thus being fully covered by both experiments. In both scenarios, HiSCORE would resolve the cutoff regime of the pevatron spectrum.
5. Hardware deployment plans The PMTs including trigger and read-out electronics, a highvoltage supply and distribution, and a slow-control system are installed in a station box equipped with a sliding lid. A first prototype station was developed and is currently being tested at
M. Tluczykont et al. / Nuclear Instruments and Methods in Physics Research A 692 (2012) 246–249
the University of Hamburg. For more flexibility, we chose to first construct half stations consisting of only two channels. One such half station is underway to the site of the Tunka air shower array in Russia [4]. Field tests and cross calibration measurements are planned in the coming months, after deployment in October 2011. For these measurements, the HiSCORE prototype station will be integrated to the Tunka data acquisition system. In the coming year, the deployment of an engineering array (of up to 1 km2 instrumented area) is planned at the Tunka site. Furthermore, we plan the deployment of a prototype station at the AUGER site. Southern hemisphere sites are interesting due to the better visibility of the Galactic plane. Relative timing accuracy can be a limiting factor for the quality of the reconstruction. We aim at a 1 ns relative time resolution. An already existing time-calibration will be available on the Tunka site, based on the usage of the carrier frequency of optical fibers (also used for read-out). An improvement of the Tunka method to an accuracy of 1 ns is planned. Furthermore, an investigation of alternative time-calibration methods, such as radio-beacon usage [12], or timecalibration using light sources is planned.
6. Summary HiSCORE is a new detector aiming at UHE g-ray astronomy ðE4 10 TeVÞ, allowing a search for the origin of cosmic rays from the most energetic Galactic cosmic ray accelerators and cosmic ray physics from 100 TeV to 1 EeV, covering the transition range from a supposed Galactic to an extragalactic origin of cosmic rays. Many other questions of astroparticle and particle physics can also be addressed by HiSCORE.
249
A full detector simulation has shown that HiSCORE will open up the last remaining observation window of g-ray astronomy by extending the energy range of currently existing and planned instruments into the UHE g-ray regime. References [1] V. Hess, Physikalische Zeitschrift 13 (1912) 1084. ¨ [2] H.J. Volk, Shell-type supernova remnants, in: G.F.B. Degrange (Ed.), ‘‘Cherenkov 2005’’, Towards a Network of Atmospheric Cherenkov Detectors VII, at Ecole Polytechnique, Palaiseau, France, pp. 233–245. Preprint arXiv:astro-ph/ 0603502. [3] G. Morlino, E. Amato, P. Blasi, Gamma Ray Emission from SNR RX J1713.73946 and the Origin of Galactic Cosmic Rays, arXiv e-prints, 2008. ArXiv:as tro-ph/0810.0094. [4] N. Budnev, D. Chernov, O. Gress, et al., The Tunka experiment: towards a 1-km2 Cherenkov EAS array in the Tunka Valley, in: Proceedings of the International Cosmic Ray Conference, vol. 8, p. 255. [5] M. Tluczykont, et al., The ground-based large-area wide-angle gamma-ray and cosmic-ray experiment HiSCORE, Journal of Advances in Space Research (2011), doi:10.1016/j.asr.2011.08.004. [6] D. Hampf, M. Tluczykont, D. Horns, Event reconstruction with the proposed large area Cherenkov air shower detector score, in: Proceedings of the ICRC, Lodz, Poland, 2009. ArXiv:astro-ph/0909.0663H. [7] T. CTA Consortium, Design Concepts for the Cherenkov Telescope Array, 2010. ArXiv:eprint astro-ph.IM 1008.3703. [8] F. Aharonian, A. Akhperjanian, K.-M. Aye, et al., The Astrophysical Journal 636 (2006) 777. [9] T. Antoni, W.D. Apel, A.F. Badea, et al., The Astrophysical Journal 608 (2004) 865. [10] I.V. Moskalenko, T.A. Porter, A.W. Strong, The Astrophysical Journal Letters 640 (2006) L155. [11] A.A. Abdo, Discovery of TeV gamma-rays from the Cygnus region with Milagro using a new background rejection technique, in: S. Ritz, et al. (Eds.), 1st GLAST Symposium, AIP, vol. 921, pp. 127–129. ¨ ¨ [12] F.G. Schroder, T. Asch, L. Bahren, et al., Nuclear Instruments and Methods in Physics Research Section A 615 (2010) 277.
Contents lists available at SciVerse ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
HiSCORE: A new detector for astroparticle and particle physics beyond 10 TeV M. Tluczykont a,n, D. Horns a, D. Hampf a, R. Nachtigall a, U. Einhaus a, M. Kunnas a, T. Kneiske a,1, G.P. Rowell b a b
Institut f¨ ur Experimentalphysik, Universit¨ at Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany University of Adelaide 5005, School of Chemistry & Physics, Australia
a r t i c l e i n f o
a b s t r a c t
Available online 5 January 2012
The new large-area (100 km ) wide-angle (0.9 sr) air Cherenkov detector HiSCORE (Hundred n i Square-km Cosmic ORigin Explorer) aims at the exploration of the cosmic ray and g-ray sky (accelerator sky) in the so far poorly covered energy range from 10 TeV to 1 EeV. The main motivation for observations in this energy regime is to solve the origin of Galactic cosmic rays. Other questions of astroparticle and particle physics can be addressed in this energy regime. Furthermore, new physics questions might arise by opening the last remaining observation window of g-ray astronomy (TeV/PeV). HiSCORE is based on non-imaging Cherenkov light-front sampling with sensitive large-area detector modules of the order of 0:5 m2 . Sampling the lateral photon density and arrival-time distribution allows the reconstruction of the direction, the energy and the type (mainly via the shower depth) of the primary particle. & 2012 Elsevier B.V. All rights reserved.
Keywords: g-Rays: ultra-high energy g-Rays: instrumentation Cosmic-rays: instrumentation
1. Introduction While we are approaching the centennial of the discovery of cosmic rays [1], the question of their origin still remains unsolved. A multi-messenger approach using indirect air-shower observations of ultra high energy g-rays (UHE g-rays, E4 10 TeV) and cosmic rays above 100 TeV is the key to this question. Shell-type Supernova remnants (SNR) are considered as best CR accelerator candidates, and the detections of several shell-type SNR in the VHE regime apparently support this scenario see e.g. Ref. [2]. However, a leptonic origin of the observed emission cannot be excluded with existing data see e.g. Ref. [3] for a review. If cosmic rays are indeed accelerated up to 1017 eV inside our Galaxy, there must be Galactic pevatrons which emit g-rays and neutrinos at energies around 100 TeV and up to few PeV (see Fig. 2). Pevatrons are a crucial building-block for a solution of the mystery of the origin of CRs. So far, all shell-type SNR detected in the VHE regime exhibit a cutoff energy too low by two orders of magnitude as compared to the expectation for a cosmic ray pevatron. Some of the known sources at TeV energies, such as the hard sources from the H.E.S.S. Galactic plane scan, might be pevatrons (also shown in Fig. 2). To date, the continuation of their spectra into the UHE regime
n
Corresponding author. E-mail address: [email protected] (M. Tluczykont). 1 ¨ was, wo, Germany. Now at Fraunhofer Institut, fur
0168-9002/$ - see front matter & 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2011.12.075
2
is unknown. Sensitive measurements in this energy regime will answer this question. A search for cosmic ray pevatrons requires an extension of the currently existing g-ray observation window into the UHE g-ray regime. This extension will be provided by the HiSCORE (Hundred n i Square-km Cosmic ORigin Explorer) detector. With HiSCORE, we plan to open up the last remaining observation window of g-ray astronomy, from 10 TeV to several tens of PeV, and to provide high-statistics data on cosmic rays from 100 TeV to 1 EeV, covering the transition range from a Galactic to an extragalactic origin of cosmic rays.
2. Physics objectives The main motivation for HiSCORE is the search for the origin of cosmic rays, and more specifically, the search for cosmic ray pevatrons in the g-ray regime. At the same time, HiSCORE will be a valuable cosmic ray detector, using the same measurement principle as e.g. the Tunka air shower array [4]. Furthermore, HiSCORE will also provide the possibility to address fundamental questions of particle physics using air-shower data. These particle physics questions might partly have an influence on the interpretation of air shower data. Among these particle physics topics are the measurement of the proton–proton cross-section, search for quark-gluon plasma in airshowers, axion search in the Galactic magnetic field, search for Lorentz invariance violation, and for heavy super-symmetric particles (wimpzillas).
M. Tluczykont et al. / Nuclear Instruments and Methods in Physics Research A 692 (2012) 246–249
3. The HiSCORE detector With HiSCORE, we are pursuing the concept of non-imaging air Cherenkov astronomy, based on the collection of Cherenkov photons from air showers on the observation level using wideangle detector stations. The non-imaging technique allows to build a detector with a large field of view (survey instrument) and to equip very large areas with a small number of PMT channels. In the case of HiSCORE as described here, only of the order of 200 channels/km2 are necessary. As opposed to that, a typical imaging air Cherenkov telescope array comes along with 10 000 channels/km2. Therefore, the non-imaging technique is best suited for the UHE g-ray regime, where large detector areas are the most important detector aspect, and for cosmic ray physics. The station concept is shown in Fig. 1. HiSCORE is planned as a distributed array of detector stations, covering an area of 100 km2 (or more), and arranged in a grid with 150 m inter-station separation. Each detector station consists of four photomultiplier tubes equipped with Winston-cones (increasing the light collection area). The sensitive area of one detector station sums up to 0.5 m2 (PMTþWinston-cone area), resulting in a total lightcollection area (100 km2 array, 150 m inter-station distance) of 2300 m2. The chosen Winston-cone geometry results in a field of view of the detector of 301 half-opening angle (0.84 sr). The dynamic range will be increased to the necessary factor of 105 (10 TeV–1 EeV) by reading out one or two dynodes in addition to the anode signal. The usage of four PMT channels is crucial for the maximization of the light collection area of a station and for the suppression of noise induced by night-sky background (NSB) photons. The individual signals of each PMT channel are analogsummed before read-out. Before the trigger is built, the individual PMT signals are clipped to a predefined level. The trigger is built using the sum of the clipped signals, effectively building a fourchannel coincidence. Using signal clipping avoids false triggers induced by very large signals (afterpulses) in a single PMT channel. A full simulation of the HiSCORE detector [5] resulted in an expected cosmic ray trigger rate of 18 kHz (100 km2 array). The event reconstruction of HiSCORE is based on the combination
of information from the lateral photon density distribution (amplitude) and the arrival time distribution of Cherenkov photons [6]. The reconstruction of the longitudinal development using the shower-front arrival-time distribution (at distances from the shower core 4100 m) allows detailed spectral and composition measurements, and g-hadron separation via reconstruction of the shower-depth.
4. Sensitivity to g-rays On the basis of the above-mentioned simulation and reconstruction, the integral sensitivity to g-ray point sources was calculated [5]. The results are shown in Fig. 2. For comparison, the sensitivities of different other experiments are also shown. The final stage of HiSCORE is planned for construction at a southern hemisphere site (likewise CTA), as opposed to the northern experiments HAWC and LHAASO. Already around 50 TeV, the sensitivity of HiSCORE will be comparable to the currently planned imaging air Cherenkov telescope array CTA [7]. Beyond this energy, the sensitive range will be extended deeply into the UHE g-ray regime. When comparing sensitivities between different experiments, one has to keep in mind that HiSCORE is a survey instrument with a very large field of view. Therefore, a source inside the field of view is visible over 200 h per year (for a site at a latitude of 351), i.e. 1000 h after 5 years of survey operation, covering a total area of the sky of p steradian. As opposed to that, Cherenkov telescopes have a comparatively small field of view and always operate in pointed observation mode. When aiming at a sky survey using Cherenkov telescopes, this imposes a scan of the sky in subsequent overlapping short pointings of small parts of the sky. In the UHE g-ray regime, absorption via e þ e pair production becomes relevant for the propagation inside our Galaxy. The interstellar radiation field (ISRF) is dense enough to generate a non-negligible absorption effect. Moskalenko et al. [10] have shown that the absorption of g-rays by pair production in the ISRF reaches a maximum around 100 TeV. At PeV energies the universal cosmic microwave background (CMB) radiation field becomes relevant. Fig. 3 illustrates the impact of this absorption
HiSCORE detector station concept Central DAQ
Total light−collecting area: 0.5 sqm
~500mm
400mm
R/O DRS 4
Winston cone
1024 cells
time sync. USB
clock PlugPC 12V
Summing
PMT ~ 206mm HV divider HV divider HV divider HV divider on/off moni
0..5V
Slow control Arduino
247
clipping
0..2.5kV on/off & moni
12V
low gain − dyn 5 high gain − anode Power−distribution
USB
Fig. 1. The HiSCORE detector station concept. Shown are the four PMT channels equipped with Winston cones, trigger and read-out electronics.
M. Tluczykont et al. / Nuclear Instruments and Methods in Physics Research A 692 (2012) 246–249
integral flux sensitivity / erg cm-2 s-1
248
10-10
H.E.S.S. survey sensitivity, 6 years
HAWC point-source, 5 years
CTA point-source, 50 hours
LHAASO point-source, 1 year
Milagro point-source, 5 years
H.E.S.S. survey hard sources
10-11
KASKADE U.L.
10-12
HiSCORE
10-13
10-14 -1 10
1
102
10
103
104
log (energy/TeV) Fig. 2. Point source sensitivity of the HiSCORE detector (5 years) as compared to data from the H.E.S.S. Galactic plane survey [8], and an upper limit from KASKADE [9]. Also shown are a model spectrum of a pevatron (thin solid line) and sensitivities of other experiments. Milagro and the planned experiments HAWC and LHAASO are northernhemisphere experiments. The final stage of HiSCORE is envisaged to be built in the southern hemisphere for optimal view of the Galactic plane.
Pevatron cutoff regime RXJ 1713.7-3946, extrapolation from H.E.S.S. data
E2 dN/dE / erg cm-2 s-1
10-11 "strong pevatron" MGRO J2019+37
no absorption
strong absorption
10-12 "weak pevatron"
10-13 HiSCORE
CTA
1
10
102 energy / TeV
103
Fig. 3. The HiSCORE sensitivity as compared to pevatron model curves and the CTA sensitivity. Pevatron curves are shown for two different flux levels (labeled strong and weak pevatrons respectively) in the case of strong absorption (thin solid) and no Galactic absorption at all (thin dashed). (1) strong pevatron case: obtained from scaling a hadronic emission model to the flux observed by Milagro from MGRO J2019þ 37 (data point) and (2) weak pevatron case: arbitrarily scaled to be at the edge of the HiSCORE sensitivity. The pevatron spectra after correction for the absorption in the ISRF and CMB were obtained using the optical depth from Moskalenko et al. [10]. Also shown is an extrapolation of the H.E.S.S. spectrum of the shell-type Supernova remnant RXJ 1713.7-3946.
effect on the g-ray spectrum of cosmic ray pevatrons. To be conservative, the transmittance curve for the strongest absorption from Moskalenko et al. [10] was used, corresponding to a location of the object at the other side of the Galaxy, at 28.5 kpc from Earth. The pevatron curves are shown using two different scalings and for the cases of absorption (thin solid lines) and no absorption (thin dashed lines). The curve labeled strong pevatron is scaled to the observed flux from the extended (11) Milagro source MGRO J2019þ37 [11], located in the Cygnus region. This object was detected by Milagro at a median energy of 12 TeV. If MGRO J2019þ37 were a pevatron, its emission would extend into the UHE regime as shown, and would be easily and fully resolved by HiSCORE. The lower thin solid and thin dashed curves (labeled
weak pevatron) illustrate the case of a hypothetical pevatron that could be detected by CTA up to 70 TeV, and by HiSCORE beyond 70 TeV, thus being fully covered by both experiments. In both scenarios, HiSCORE would resolve the cutoff regime of the pevatron spectrum.
5. Hardware deployment plans The PMTs including trigger and read-out electronics, a highvoltage supply and distribution, and a slow-control system are installed in a station box equipped with a sliding lid. A first prototype station was developed and is currently being tested at
M. Tluczykont et al. / Nuclear Instruments and Methods in Physics Research A 692 (2012) 246–249
the University of Hamburg. For more flexibility, we chose to first construct half stations consisting of only two channels. One such half station is underway to the site of the Tunka air shower array in Russia [4]. Field tests and cross calibration measurements are planned in the coming months, after deployment in October 2011. For these measurements, the HiSCORE prototype station will be integrated to the Tunka data acquisition system. In the coming year, the deployment of an engineering array (of up to 1 km2 instrumented area) is planned at the Tunka site. Furthermore, we plan the deployment of a prototype station at the AUGER site. Southern hemisphere sites are interesting due to the better visibility of the Galactic plane. Relative timing accuracy can be a limiting factor for the quality of the reconstruction. We aim at a 1 ns relative time resolution. An already existing time-calibration will be available on the Tunka site, based on the usage of the carrier frequency of optical fibers (also used for read-out). An improvement of the Tunka method to an accuracy of 1 ns is planned. Furthermore, an investigation of alternative time-calibration methods, such as radio-beacon usage [12], or timecalibration using light sources is planned.
6. Summary HiSCORE is a new detector aiming at UHE g-ray astronomy ðE4 10 TeVÞ, allowing a search for the origin of cosmic rays from the most energetic Galactic cosmic ray accelerators and cosmic ray physics from 100 TeV to 1 EeV, covering the transition range from a supposed Galactic to an extragalactic origin of cosmic rays. Many other questions of astroparticle and particle physics can also be addressed by HiSCORE.
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