Abstract
The Universe is largely transparent to \(\gamma \)-rays in the GeV energy range, making these high-energy photons valuable for exploring energetic processes in the cosmos. After 7 years of operation, the Fermi Gamma-ray Space Telescope has produced a wealth of information about the high-energy sky. This review focuses on extragalactic \(\gamma \)-ray sources: what has been learned about the sources themselves and about how they can be used as cosmological probes. Active galactic nuclei (blazars, radio galaxies, Seyfert galaxies) and star-forming galaxies populate the extragalactic high-energy sky. Fermi observations have demonstrated that these powerful non-thermal sources display substantial diversity in energy spectra and temporal behavior. Coupled with contemporaneous multifrequency observations, the Fermi results are enabling detailed, time-dependent modeling of the energetic particle acceleration and interaction processes that produce the \(\gamma \)-rays, as well as providing indirect measurements of the extragalactic background light and intergalactic magnetic fields. Population studies of the \(\gamma \)-ray source classes compared to the extragalactic \(\gamma \)-ray background place constraints on some models of dark matter. Ongoing searches for the nature of the large number of \(\gamma \)-ray sources without obvious counterparts at other wavelengths remain an important challenge.
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Abbreviations
- AGN(s):
-
Active galactic nucleus(i)
- AGU:
-
Active galaxy of uncertain type
- BCU:
-
Blazar candidate of uncertain type
- CGRO:
-
Compton Gamma-Ray Observatory
- CSS:
-
Compact steep spectrum radio source
- DM:
-
Dark matter
- EBL:
-
Extragalactic gamma-ray background light
- EGB:
-
Extragalactic gamma-ray background
- EC:
-
External Compton
- FR:
-
Fanaroff–Riley radio source class
- FSRQ:
-
Flat-spectrum radio quasar
- GRB:
-
Gamma-ray burst
- HBL:
-
High-frequency peaked BL Lac object
- HSP:
-
High-synchrotron peaked BL Lac object
- QSO:
-
Quasi-stellar object (a.k.a. quasar)
- RG:
-
Radio galaxy
- RLNLSy1:
-
Radio-loud narrow-line Seyfert of type 1
- SED:
-
Spectral energy distribution
- SFR:
-
Star formation rate
- SSC:
-
Synchrotron self-Compton
- SSRQ:
-
Steep spectrum radio quasar
- UGS:
-
Unidentified/unassociated gamma-ray source
- 1FGL:
-
First Fermi gamma-ray LAT point source catalog
- 2FGL:
-
Second Fermi gamma-ray LAT point source catalog
- 3FGL:
-
Third Fermi gamma-ray LAT point source catalog
- 1LAC:
-
First Fermi LAT AGN catalog
- 2LAC:
-
Second Fermi LAT AGN catalog
- 3LAC:
-
Third Fermi LAT AGN catalog
- 2PC:
-
Second LAT pulsar catalog
- 3EG:
-
Third EGRET catalog
- CRATES:
-
The combined radio all-sky targeted eight GHz survey
- LBAS:
-
LAT bright AGN sample
- Roma-BZCAT:
-
Roma-multifrequency blazar catalog
- WGS:
-
WISE gamma-ray strip
- WIBRaLS:
-
WISE blazar-like radio-loud source catalog
- AGILE:
-
Astrorivelatore Gamma a Immagini Leggero
- ATCA:
-
Australia Telescope Compact Array
- BAT :
-
Burst Alert Telescope
- CGRH:
-
Cosmic gamma-ray horizon
- COS-B:
-
Celestial Observation Satellite-B
- CTA:
-
Cherenkov Telescope Array
- EGRET:
-
Energetic Gamma-Ray Experiment Telescope
- FAVA:
-
Fermi all-sky variability analysis
- FoV:
-
Field of view
- GASP:
-
GLAST-AGILE support program
- GBM:
-
Gamma-Ray Burst Monitor
- GLAST:
-
Gamma-Ray Large Area Space Telescope
- HESS:
-
High-Energy Stereoscopic System
- IBIS:
-
Imager on-Board the INTEGRAL Satellite
- INTEGRAL:
-
INTErnational Gamma-Ray Astrophysics Laboratory
- IR:
-
Infrared energy range
- LAT:
-
Large Area Telescope
- LR:
-
Likelihood ratio
- MAGIC:
-
Major Atmospheric Gamma-Ray Imaging Cherenkov Telescope
- MOJAVE:
-
Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments
- OSO-3:
-
Orbiting Solar Observatory-3
- PSF:
-
Point spread function
- SAS-2:
-
Small Astronomy Satellite-2
- SMARTS:
-
Small and Medium Aperture Research Telescope System
- SOAR:
-
Southern Astrophysical Research Telescope
- UV:
-
Ultraviolet energy range
- VERITAS:
-
Very Energetic Radiation Imaging Telescope Array System
- VLA:
-
Very Large Array
- VLBA:
-
Very Long Baseline Array
- VLBI:
-
Very long baseline interferometry
- WEBT:
-
Whole Earth Blazar Telescope
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Acknowledgments
This review would not have been possible without the dedicated efforts of scientists, engineers, and technicians who have made the Fermi Gamma-ray Space Telescope mission so successful. We extend thanks to all those who contributed. Special thanks to Justin Finke, Filippo D’Ammando and Seth Digel for valuable comments on the manuscript. F. Massaro wishes to thank M. Ajello, R. D’Abrusco, D. Gasparrini, M. Giroletti, L. Latronico, N. Masetti, A. Paggi, H. Smith and G. Tosti for their support during the last 4 years spent working on Fermi blazars. The work by is supported by the Programma Giovani Ricercatori—Rita Levi Montalcini—Rientro dei Cervelli (2012). This review is also supported by the NASA grants NNX12AO97G and NNX13AP20G. Part of this work is based on archival data, software or on-line services provided by the ASI Science Data Center. This research has made use of data obtained from the high-energy Astrophysics Science Archive Research Center (HEASARC) provided by NASA’s Goddard Space Flight Center; the SIMBAD database operated at CDS, Strasbourg, France; the NASA/IPAC Extragalactic Database (NED) operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. TOPCAT (http://www.star.bris.ac.uk/~mbt/topcat/) (Taylor 2005) for the preparation and manipulation of the tabular data and the images. The Aladin Java applet (http://aladin.u-strasbg.fr/aladin.gml) was used to create the finding charts reported in this paper (Bonnarel 2000). It can be started from the CDS (Strasbourg, France), from the CFA (Harvard, USA), from the ADAC (Tokyo, Japan), from the IUCAA (Pune, India), from the UKADC (Cambridge, UK), or from the CADC (Victoria, Canada).
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Massaro, F., Thompson, D.J. & Ferrara, E.C. The extragalactic gamma-ray sky in the Fermi era. Astron Astrophys Rev 24, 2 (2016). https://doi.org/10.1007/s00159-015-0090-6
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DOI: https://doi.org/10.1007/s00159-015-0090-6