High‐(Energy)‐Lights The Very High Energy Gamma‐Ray Sky

Horns, D.

doi:10.1002/9783527622993.ch8

Cited by 8 publications

(7 citation statements)

References 184 publications

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“…Because relatively little work has been done on the expected properties of such sources in starbursts, it is unclear if they could dominate the γ -ray emission from M82 and NGC 253. A number of star formation phenomena are known to be TeV sources (as reviewed by, e.g., Grenier 2008;Horns 2008;Hinton & Hofmann 2009), including SN remnants, PWNe (Abdo et al 2009b), and possibly star clusters (Aharonian et al 2007). The observed Galactic TeV sources tend to have hard spectra (Γ ≈ 2.2), similar to the observed GeV-to-TeV spectra of M82 and NGC 253.…”

Section: Discrete γ -Ray Sourcessupporting

confidence: 56%

ON THE GeV AND TeV DETECTIONS OF THE STARBURST GALAXIES M82 AND NGC 253

Lacki

Thompson

Quataert

et al. 2011

ApJ

198

277

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The GeV and TeV emission from M82 and NGC 253 observed by Fermi, HESS, and VERITAS constrain the physics of cosmic rays (CRs) in these dense starbursts. We argue that the γ -rays are predominantly hadronic in origin, as expected by previous studies. The measured fluxes imply that pionic losses are efficient for CR protons in both galaxies: we show that a fraction F cal ≈ 0.2-0.4 of the energy injected in high-energy primary CR protons is lost to inelastic proton-proton collisions (pion production) before escape, producing γ -rays, neutrinos, and secondary electrons and positrons. We discuss the factor of ∼2 uncertainties in this estimate, including supernova rate and leptonic contributions to the GeV-TeV emission. We argue that γ -ray data on ULIRGs like Arp 220 can test whether M82 and NGC 253 are truly calorimetric, and we present upper limits on Arp 220 from the Fermi data. We show that the observed ratio of the GeV to GHz fluxes of the starbursts suggests that non-synchrotron cooling processes are important for cooling the CR electron/positron population. We briefly reconsider previous predictions in light of the γ -ray detections, including the starburst contribution to the γ -ray background and CR energy densities. Finally, as a guide for future studies, we list the brightest star-forming galaxies on the sky and present updated predictions for their γ -ray and neutrino fluxes.

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Section: Discrete γ -Ray Sourcessupporting

confidence: 56%

ON THE GeV AND TeV DETECTIONS OF THE STARBURST GALAXIES M82 AND NGC 253

Lacki

Thompson

Quataert

et al. 2011

ApJ

198

277

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“…A coarse estimate of the shower direction can be obtained by fitting a plane to the measured light arrival times 3 . If signals from only three stations are available, only this estimate is used.…”

Section: Direction Of Originmentioning

confidence: 99%

“…More than hundred sources of very high energy (VHE, 30 GeV to 30 TeV) gamma-ray emission are currently known, and detailed spectral, morphological and temporal studies provide a wealth of information on the underlying acceleration and radiation mechanisms of these sources (see e.g. [1], [2] or [3] for reviews).…”

Section: Introductionmentioning

confidence: 99%

Event reconstruction techniques for the wide-angle air Cherenkov detector HiSCORE

Hampf

Tluczykont

Horns

2013

Nuclear Instruments and Methods in Physics Research Section A:

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Wide-angle, non-imaging air Cherenkov detectors provide a way to observe cosmic gamma-rays which is complementary to observations by imaging Cherenkov telescopes. Their particular strength lies in the multi-TeV to ultra high energy range (E γ > 30 TeV), where large effective areas, yet small light sensitive areas per detector station are needed. To exploit this potential to full extent, a large station spacing is required to achieve a large effective area at a reasonable effort.In such a detector, the low number of signals per event, the absence of imaging information, and the poor signal to noise ratio of Cherenkov light to night sky brightness pose considerable challenges for the event reconstruction, especially the gamma hadron separation. The event reconstruction presented in this paper has been developed for the wide-angle detector HiSCORE, but the concepts may be applied more generically. It is tested on simulated data in the 10 TeV to 5 PeV energy range using the air shower simulation CORSIKA and the HiSCORE detector simulation sim score. For the tests, a regular grid of 22 × 22 detector stations with a spacing of 150 m is assumed, covering an area of 10 km 2 . The angular resolution of individual events is found to be about 0.3• near the energy threshold, improving to below 0.1 • at higher energies. The relative energy resolution is 20% at the threshold and improves to 10% at higher energies. Several parameters for gamma hadron separation are described. With a combination of these parameters, 80% to 90% of the hadronic background can be suppressed, while about 60% of the gamma-ray events are retained. The point source sensitivity to gamma-ray sources is estimated, using conservative assumptions, to be about 8 × 10 −13 erg s −1 cm −2 at 100 TeV gamma-ray energy for a 10 km 2 array. With more optimistic assumptions, and a 100 km 2 array, a sensitivity of about 1 × 10 −13 erg s −1 cm −2 can be achieved (at 100 TeV). Even in the former case the detector is sensitive enough to measure the continuation of currently known gamma-ray spectra into the ultra high energy domain. Due to its large field of view of 0.6 sr it also offers a great potential for the discovery of new gamma-ray sources at the so far largely unexplored energies of 100 TeV and above.

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“…[71] has allowed to constrain the EBL density. At large optical depth, τ 2, however, there are hints that the Universe is anomalously transparent to gamma-rays [72][73][74][75][76]. This may be explained by photon ↔ ALP oscillations: the conversion of gamma rays into ALPs in the magnetic fields around AGNs or in the intergalactic medium, followed by their unimpeded travel towards our galaxy and the consequent reconversion into photons in the galactic/intergalactic magnetic fields [77][78][79][80][81].…”

Section: Jhep06(2014)037mentioning

confidence: 99%

The quest for an intermediate-scale accidental axion and further ALPs

Dias

Machado

Nishi

et al. 2014

J. High Energ. Phys.

143

147

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Abstract:The recent detection of the cosmic microwave background polarimeter experiment BICEP2 of tensor fluctuations in the B-mode power spectrum basically excludes all plausible axion models where its decay constant is above 10 13 GeV. Moreover, there are strong theoretical, astrophysical, and cosmological motivations for models involving, in addition to the axion, also axion-like particles (ALPs), with decay constants in the intermediate scale range, between 10 9 GeV and 10 13 GeV. Here, we present a general analysis of models with an axion and further ALPs and derive bounds on the relative size of the axion and ALP photon (and electron) coupling. We discuss what we can learn from measurements of the axion and ALP photon couplings about the fundamental parameters of the underlying ultraviolet completion of the theory. For the latter we consider extensions of the Standard Model in which the axion and the ALP(s) appear as pseudo Nambu-Goldstone bosons from the breaking of global chiral U(1) (Peccei-Quinn (PQ)) symmetries, occurring accidentally as low energy remnants from exact discrete symmetries. In such models, the axion and the further ALP are protected from disastrous explicit symmetry breaking effects due to Planck-scale suppressed operators. The scenarios considered exploit heavy right handed neutrinos getting their mass via PQ symmetry breaking and thus explain the small mass of the active neutrinos via a seesaw relation between the electroweak and an intermediate PQ symmetry breaking scale. For a number of explicit models, we determine the parameters of the low-energy effective field theory describing the axion, the ALPs, and JHEP06 (2014)037 their interactions with photons and electrons, in terms of the input parameters, in particular the PQ symmetry breaking scales. We show that these models can accommodate simultaneously an axion dark matter candidate, an ALP explaining the anomalous transparency of the universe for γ-rays, and an ALP explaining the recently reported 3.55 keV gamma line from galaxies and clusters of galaxies, if the respective decay constants are of intermediate scale. Moreover, they do not suffer severely from the domain wall problem.

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High‐(Energy)‐Lights The Very High Energy Gamma‐Ray Sky

Cited by 8 publications

References 184 publications

ON THE GeV AND TeV DETECTIONS OF THE STARBURST GALAXIES M82 AND NGC 253

ON THE GeV AND TeV DETECTIONS OF THE STARBURST GALAXIES M82 AND NGC 253

Event reconstruction techniques for the wide-angle air Cherenkov detector HiSCORE

The quest for an intermediate-scale accidental axion and further ALPs

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