Search FOR extended gamma-ray emission from the Virgo galaxy cluster with Fermi-LAT

Journal Article · Tue Oct 20 04:00:00 EDT 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/812/2/159· OSTI ID:22882467

Ackermann, M.; Buehler, R. ^[1]; Ajello, M. ^[2]; Albert, A.; Baldini, L.; Bloom, E. D.; Bottacini, E.; Caliandro, G. A.; Cameron, R. A. ^[3]; Atwood, W. B. ^[4]; Barbiellini, G. ^[5]; Bastieri, D.; Buson, S. ^[6]; Bechtol, K. ^[7]; Bellazzini, R. ^[8]; Bissaldi, E. ^[9]; Bonino, R. ^[10]; Brandt, T. J. ^[11]; Bregeon, J. ^[12]; others, and

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1. Deutsches Elektronen Synchrotron DESY, D-15738 Zeuthen (Germany)
2. Department of Physics and Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC 29634d-0978 (United States)
3. W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States)
4. Santa Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064 (United States)
5. Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste (Italy)
6. Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova (Italy)
7. Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637 (United States)
8. Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy)
9. Istituto Nazionale di Fisica Nucleare, Sezione di Bari, I-70126 Bari (Italy)
10. Istituto Nazionale di Fisica Nucleare, Sezione di Torino, I-10125 Torino (Italy)
11. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
12. Laboratoire Univers et Particules de Montpellier, Université Montpellier, CNRS/IN2P3, Montpellier (France)

Galaxy clusters are one of the prime sites to search for dark matter (DM) annihilation signals. Depending on the substructure of the DM halo of a galaxy cluster and the cross sections for DM annihilation channels, these signals might be detectable by the latest generation of γ-ray telescopes. Here we use three years of Fermi-Large Area Telescope data, which are the most suitable for searching for very extended emission in the vicinity of the nearby Virgo galaxy cluster. Our analysis reveals statistically significant extended emission which can be well characterized by a uniformly emitting disk profile with a radius of 3° that moreover is offset from the cluster center. We demonstrate that the significance of this extended emission strongly depends on the adopted interstellar emission model (IEM) and is most likely an artifact of our incomplete description of the IEM in this region. We also search for and find new point source candidates in the region. We then derive conservative upper limits on the velocity-averaged DM pair annihilation cross section from Virgo. We take into account the potential γ-ray flux enhancement due to DM sub-halos and its complex morphology as a merging cluster. For DM annihilating into b b-bar , assuming a conservative sub-halo model setup, we find limits that are between 1 and 1.5 orders of magnitude above the expectation from the thermal cross section for m{sub DM} ≲ 100 GeV. In a more optimistic scenario, we exclude 〈σv〉∼3×10{sup −26} cm{sup 3} s{sup −1} for m{sub DM} ≲ 40 GeV for the same channel. Finally, we derive upper limits on the γ-ray-flux produced by hadronic cosmic-ray interactions in the inter cluster medium. We find that the volume-averaged cosmic-ray-to-thermal pressure ratio is less than ∼6%.

• OSTI ID: 22882467
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 812; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United Kingdom
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COSMIC RADIATION
CROSS SECTIONS
EMISSION
GALAXY CLUSTERS
GAMMA RADIATION
GEV RANGE 10-100
HADRONS
NONLUMINOUS MATTER
POINT SOURCES
TELESCOPES
VELOCITY