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Search for Gamma-Ray Emission from the Coma Cluster with Six Years of Fermi-LAT DataWe present results from gamma-ray observations of the Coma cluster incorporating six 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 gamma-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 100 MeV are 1.7 x 10(exp -9) ph cm(exp -2) s(exp -1) and 5.2 x 10(exp -9) ph cm(exp -2) s(exp -1) respectively (the latter corresponds to residual emission at the level of 1.8sigma). These bounds are comparable to or higher than predicted levels of hadronic gamma-ray emission in cosmic-ray (CR) models with or without reacceleration of secondary electrons, although direct comparisons are sensitive to assumptions regarding the origin and propagation mode of CRs and magnetic field properties. The minimal expected gamma-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.
Document ID
20170003557
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Ackermann, M.
(Deutsches Elektronen-Synchrotron Zeuthen, Germany)
Ajello, M.
(Clemson Univ. SC, United States)
Albert, A.
(Stanford Univ. Stanford, CA, United States)
Atwood, W. B.
(California Univ. Santa Cruz, CA, United States)
Baldini, L.
(Stanford Univ. Stanford, CA, United States)
Ballet, J.
(Universite Paris Diderot Paris, France)
Barbiellini, G.
(Istituto Nazionale di Fisica Nucleare Trieste, Italy)
Bastieri, D.
(Istituto Nazionale di Fisica Nucleare Padova, Italy)
Bechtol, K.
(Wisconsin Univ. Madison, WI, United States)
Bellazzini, R.
(Istituto Nazionale di Fisica Nucleare Pisa, Italy)
Guiriec, S.
(Maryland Univ. College Park, MD, United States)
Hays, E.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Date Acquired
April 17, 2017
Publication Date
March 8, 2016
Publication Information
Publication: The Astrophysical Journal
Publisher: American Astronomical Society
Volume: 819
Issue: 2
ISSN: 0004-637X
e-ISSN: 1538-4357
Subject Category
Astrophysics
Report/Patent Number
GSFC-E-DAA-TN41702
Distribution Limits
Public
Copyright
Other
Keywords
galaxies: clusters: individual (Coma) – gamma rays: galaxies: clusters

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