THE FIRST FERMI -LAT GAMMA-RAY BURST CATALOG

Abstract

In three years of observations since the beginning of nominal science operations in 2008 August, the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope has observed high-energy (20 MeV) γ-ray emission from 35 gamma-ray bursts (GRBs). Among these, 28 GRBs have been detected above 100 MeV and 7 GRBs above ∼20 MeV. The first Fermi-LAT catalog of GRBs is a compilation of these detections and provides a systematic study of high-energy emission from GRBs for the first time. To generate the catalog, we examined 733 GRBs detected by the Gamma-Ray Burst Monitor (GBM) on Fermi and processed each of them using the same analysis sequence. Details of the methodology followed by the LAT collaboration for the GRB analysis are provided. We summarize the temporal and spectral properties of the LAT-detected GRBs. We also discuss characteristics of LAT-detected emission such as its delayed onset and longer duration compared with emission detected by the GBM, its power-law temporal decay at late times, and the fact that it is dominated by a power-law spectral component that appears in addition to the usual Band model.

Surprise in simplicity: an unusual spectral evolution of a single pulse GRB 151006A

“…1 shows the photons to be associated to the GRB with probability > 0.9 in red filled circle, otherwise in open circles (using gtsrcprob of Fermi science tool 1 ). The delayed onset of the LAT events with respect to GBM emission is consistent with that observed for long bursts as reported in Ackermann et al (2013). We note that high energy emission in the energy range, 100 keV -30 MeV and 30 MeV -100 MeV, peaks nearly simultaneously at ∼ 1.4 s, whereas the low energy emission in the energy range, 8 keV -100 keV, peaks later at ∼ 5.4 s. The BAT light curve also shows a single FRED like pulse with a T 90 (15 -350 keV) of 203.9 ± 41.6 s (Cummings et al 2015).…”

“…The emission consists of a narrow pulse accompanied by two other smaller pulses towards the end. Thus, LLE emission does not show the typical delay that is observed in its onset with respect to the GBM observations (Ackermann et al 2013). The LAT LLE data bridges the gap between the BGO and LAT detections, and thereby helps in constraining high MeV spectral peaks (Axelsson et al 2012;Moretti & Axelsson 2016).…”

“…As the n3 has the highest count rate among the chosen NaI detectors, we use it to define the time intervals for time resolved spectroscopy. We apply a signal-to-noise ratio (S/N) of 20 and find 14 time bins in the interval −2.0 − 88.1 s. The LAT LLE data is also extracted in these time bins until ∼ 27 s, following the standard procedure described in Ackermann et al (2013). The LAT P8R2 source class events, > 100 MeV, events were selected within a 12 deg region centred around the Swift XRT position.…”

The Arcminute Microkelvin Imager catalogue of gamma-ray burst afterglows at 15.7 GHz

“…These include GRB 120729A, GRB 121011A, GRB 130427A, GRB 130702A, GRB 130907A, and GRB 150314A (Ackermann et al 2013). Of these 6 Fermi-LAT GRBs, three were detected with AMI, including GRB 130427A and GRB 130702A, which were the two least radio luminous AMI detected GRBs (see Figure 10), and GRB 130907A, which was only detected at early times and also radio faint (as previously mentioned both GRB 130427A and GRB 130907A have the earliest radio afterglow detections with AMI).…”

Evaluating the Bulk Lorentz Factors of Outflow Material: Lessons Learned from the Extremely Energetic Outburst GRB 160625B

“…Area Corr. term in RMFIT (Ackermann et al 2013). The correction factors are allowed to vary from 0.9 to 1.2 for NaI and BGO detectors, while fixed to 1 for LAT LLE.…”