Journal article
CONSTRAINTS ON COSMIC RAYS, MAGNETIC FIELDS, AND DARK MATTER FROM GAMMA-RAY OBSERVATIONS OF THE COMA CLUSTER OF GALAXIES WITH VERITAS AND FERMI
The Astrophysical journal, Vol.757(2), 123
10/01/2012
DOI: 10.1088/0004-637X/757/2/123
Abstract
Observations of radio halos and relics in galaxy clusters indicate efficient electron acceleration. Protons should likewise be accelerated and, on account of weak energy losses, can accumulate, suggesting that clusters may also be sources of very high energy (VHE; E > 100 GeV) gamma-ray emission. We report here on VHE gamma-ray observations of the Coma galaxy cluster with the VERITAS array of imaging Cerenkov telescopes, with complementing Fermi Large Area Telescope observations at GeV energies. No significant gamma-ray emission from the Coma Cluster was detected. Integral flux upper limits at the 99% confidence level were measured to be on the order of (2-5) Multiplication-Sign 10{sup -8} photons m {sup -2} s {sup -1} (VERITAS, >220 GeV) and {approx}2 Multiplication-Sign 10{sup -6} photons m {sup -2} s {sup -1} (Fermi, 1-3 GeV), respectively. We use the gamma-ray upper limits to constrain cosmic rays (CRs) and magnetic fields in Coma. Using an analytical approach, the CR-to-thermal pressure ratio is constrained to be <16% from VERITAS data and <1.7% from Fermi data (averaged within the virial radius). These upper limits are starting to constrain the CR physics in self-consistent cosmological cluster simulations and cap the maximum CR acceleration efficiency at structure formation shocks to be <50%. Alternatively, this may argue for non-negligible CR transport processes such as CR streaming and diffusion into the outer cluster regions. Assuming that the radio-emitting electrons of the Coma halo result from hadronic CR interactions, the observations imply a lower limit on the central magnetic field in Coma of {approx}(2-5.5) {mu}G, depending on the radial magnetic field profile and on the gamma-ray spectral index. Since these values are below those inferred by Faraday rotation measurements in Coma (for most of the parameter space), this renders the hadronic model a very plausible explanation of the Coma radio halo. Finally, since galaxy clusters are dark matter (DM) dominated, the VERITAS upper limits have been used to place constraints on the thermally averaged product of the total self-annihilation cross section and the relative velocity of the DM particles, ({sigma}v).
Details
- Title: Subtitle
- CONSTRAINTS ON COSMIC RAYS, MAGNETIC FIELDS, AND DARK MATTER FROM GAMMA-RAY OBSERVATIONS OF THE COMA CLUSTER OF GALAXIES WITH VERITAS AND FERMI
- Creators
- T Arlen - University of California, Los AngelesT Aune - University of California, Santa CruzA Bouvier - University of California, Santa CruzM Beilicke - Washington University in St. LouisJ. H Buckley - Washington University in St. LouisV Bugaev - Washington University in St. LouisR Dickherber - Washington University in St. LouisW Benbow - Harvard UniversityK Byrum - Argonne National LaboratoryA Cannon - University College DublinE Collins-Hughes - University College DublinA Cesarini - Ollscoil na Gaillimhe – University of GalwayM. P Connolly - Ollscoil na Gaillimhe – University of GalwayL Ciupik - Adler PlanetariumW Cui - Purdue University West LafayetteQ Feng - Purdue University West LafayetteJ. P Finley - Purdue University West LafayetteJ Dumm - University of MinnesotaA Falcone - Pennsylvania State UniversityP Kaaret - University of Iowa, Physics and AstronomyS Federici - University of Potsdam
- Resource Type
- Journal article
- Publication Details
- The Astrophysical journal, Vol.757(2), 123
- DOI
- 10.1088/0004-637X/757/2/123
- ISSN
- 0004-637X
- eISSN
- 1538-4357
- Publisher
- Institute of Physics (IOP)
- Language
- English
- Date published
- 10/01/2012
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984200047202771
Metrics
4 Record Views