FERMI LAT STACKING ANALYSIS OF SWIFT LOCALIZED GRBs
- Deutsches Elektronen Synchrotron DESY, D-15738 Zeuthen (Germany)
- Department of Physics and Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC 29634-0978 (United States)
- 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)
- Department of Physics, KTH Royal Institute of Technology, AlbaNova, SE-106 91 Stockholm (Sweden)
- Università di Pisa and Istituto Nazionale di Fisica Nucleare, Sezione di Pisa I-56127 Pisa (Italy)
- Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste (Italy)
- Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova (Italy)
- Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy)
- Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, Huntsville, AL 35899 (United States)
- Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari (Italy)
- Istituto Nazionale di Fisica Nucleare, Sezione di Torino, I-10125 Torino (Italy)
- 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)
- NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
- Laboratoire Univers et Particules de Montpellier, Université Montpellier, CNRS/IN2P3, Montpellier (France)
- Laboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau (France)
We perform a comprehensive stacking analysis of data collected by the Fermi Large Area Telescope (LAT) of γ -ray bursts (GRBs) localized by the Swift spacecraft, which were not detected by the LAT but which fell within the instrument’s field of view at the time of trigger. We examine a total of 79 GRBs by comparing the observed counts over a range of time intervals to that expected from designated background orbits, as well as by using a joint likelihood technique to model the expected distribution of stacked counts. We find strong evidence for subthreshold emission at MeV to GeV energies using both techniques. This observed excess is detected during intervals that include and exceed the durations typically characterizing the prompt emission observed at keV energies and lasts at least 2700 s after the co-aligned burst trigger. By utilizing a novel cumulative likelihood analysis, we find that although a burst’s prompt γ -ray and afterglow X-ray flux both correlate with the strength of the subthreshold emission, the X-ray afterglow flux measured by Swift ’ s X-ray Telescope at 11 hr post trigger correlates far more significantly. Overall, the extended nature of the subthreshold emission and its connection to the burst’s afterglow brightness lend further support to the external forward shock origin of the late-time emission detected by the LAT. These results suggest that the extended high-energy emission observed by the LAT may be a relatively common feature but remains undetected in a majority of bursts owing to instrumental threshold effects.
- OSTI ID:
- 22663062
- Journal Information:
- Astrophysical Journal, Vol. 822, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Unbiased Long-Term Monitoring at TeV Energies
|
text | January 2019 |
The High Energy View of FR0 Radio Galaxies
|
journal | September 2019 |
Unbiased Long-Term Monitoring at TeV Energies
|
journal | April 2019 |
| The High Energy View of FR0 Radio Galaxies | preprint | January 2019 |
Similar Records
Fermi and Swift Observations of GRB 190114C: Tracing the Evolution of High-energy Emission from Prompt to Afterglow
GRB 050717: A Long, Short-Lag Burst Observed by Swift and Konus