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Title: Search for gamma-ray emission from the Coma Cluster with six years of Fermi-LAT data

We present results from γ-ray observations of the Coma cluster incorporating 6 years of Fermi-LAT data and the newly released “Pass 8” event-level analysis. Our analysis of the region reveals low-significance residual structures within the virial radius of the cluster that are too faint for a detailed investigation with the current data. Using a likelihood approach that is free of assumptions on the spectral shape we derive upper limits on the γ-ray flux that is expected from energetic particle interactions in the cluster. We also consider a benchmark spatial and spectral template motivated by models in which the observed radio halo is mostly emission by secondary electrons. In this case, the median expected and observed upper limits for the flux above 100MeV are 1.7 x 10 -9 ph cm -2 s -1 and 5.2 x 10 -9 ph cm -2 s -1 respectively (the latter corresponds to residual emission at the level of 1:8σ). These bounds are comparable to or higher than predicted levels of hadronic gamma-ray emission in cosmic-ray models with or without reacceleration of secondary electrons, although direct comparisons are sensitive to assumptions regarding the origin and propagation mode of cosmic rays and magnetic field properties. The minimalmore » expected γ-ray flux from radio and star-forming galaxies within the Coma cluster is roughly an order of magnitude below the median sensitivity of our analysis.« less
Authors:
 [1]
  1. Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 819; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE
Contributing Orgs:
The Fermi-LAT Collaboration
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS
OSTI Identifier:
1355684

Ackermann, M. Search for gamma-ray emission from the Coma Cluster with six years of Fermi-LAT data. United States: N. p., Web. doi:10.3847/0004-637X/819/2/149.
Ackermann, M. Search for gamma-ray emission from the Coma Cluster with six years of Fermi-LAT data. United States. doi:10.3847/0004-637X/819/2/149.
Ackermann, M. 2016. "Search for gamma-ray emission from the Coma Cluster with six years of Fermi-LAT data". United States. doi:10.3847/0004-637X/819/2/149. https://www.osti.gov/servlets/purl/1355684.
@article{osti_1355684,
title = {Search for gamma-ray emission from the Coma Cluster with six years of Fermi-LAT data},
author = {Ackermann, M.},
abstractNote = {We present results from γ-ray observations of the Coma cluster incorporating 6 years of Fermi-LAT data and the newly released “Pass 8” event-level analysis. Our analysis of the region reveals low-significance residual structures within the virial radius of the cluster that are too faint for a detailed investigation with the current data. Using a likelihood approach that is free of assumptions on the spectral shape we derive upper limits on the γ-ray flux that is expected from energetic particle interactions in the cluster. We also consider a benchmark spatial and spectral template motivated by models in which the observed radio halo is mostly emission by secondary electrons. In this case, the median expected and observed upper limits for the flux above 100MeV are 1.7 x 10-9 ph cm-2 s-1 and 5.2 x 10-9 ph cm-2 s-1 respectively (the latter corresponds to residual emission at the level of 1:8σ). These bounds are comparable to or higher than predicted levels of hadronic gamma-ray emission in cosmic-ray models with or without reacceleration of secondary electrons, although direct comparisons are sensitive to assumptions regarding the origin and propagation mode of cosmic rays and magnetic field properties. The minimal expected γ-ray flux from radio and star-forming galaxies within the Coma cluster is roughly an order of magnitude below the median sensitivity of our analysis.},
doi = {10.3847/0004-637X/819/2/149},
journal = {The Astrophysical Journal (Online)},
number = 2,
volume = 819,
place = {United States},
year = {2016},
month = {3}
}