Gamma-ray burst observations by <i>Fermi</i> Large Area Telescope revisited: new candidates found

Рубцов, Г.; Пширков, М. С.; Tinyakov, P.

doi:10.1111/j.1745-3933.2011.01197.x

Cited by 12 publications

(12 citation statements)

References 33 publications

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“…However there were two other bursts with significant emission: GRB 100207B and GRB 081009A. The latter has also been reported as a candidate for a LAT-detected burst with the same method but with a wider energy range (E > 100 MeV) and longer observations times (t obs = 1500 s) (Rubtsov et al 2012). However, it has not been added to the LAT Burst catalog so far.…”

Section: Detection Significancementioning

confidence: 99%

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The average GeV-band emission from gamma-ray bursts

Lange¹,

Pohl

2013

A&A

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Aims. We analyze the emission in the 0.3-30 GeV energy range of gamma-ray bursts detected with the Fermi Gamma-ray Space Telescope. We concentrate on bursts that were previously only detected with the Gamma-Ray Burst Monitor in the keV energy range. These bursts will then be compared to the bursts that were individually detected with the Large Area Telescope at higher energies. Methods. To estimate the emission of faint GRBs we used nonstandard analysis methods and sum over many GRBs to find an average signal that is significantly above background level. We used a subsample of 99 GRBs listed in the Burst Catalog from the first two years of observation. Results. Although most are not individually detectable, the bursts not detected by the Large Area Telescope on average emit a significant flux in the energy range from 0.3 GeV to 30 GeV, but their cumulative energy fluence is only 8% of that of all GRBs. Likewise, the GeV-to-MeV flux ratio is less and the GeV-band spectra are softer. We confirm that the GeV-band emission lasts much longer than the emission found in the keV energy range. The average allsky energy flux from GRBs in the GeV band is 6.4 × 10 −4 erg cm −2 yr −1 or only ∼4% of the energy flux of cosmic rays above the ankle at 10 18.6 eV.

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Section: Detection Significancementioning

confidence: 99%

“…Abdo et al 2009;Rubtsov et al 2012), mandating that the GRBs be monitored for long time intervals after the prompt emission phase. The duration of GRBs is characterized by T 90 , the mid time in which 90% of the fluence is observed in the BATSE energy range (50 keV to 300 keV).…”

Section: Time Intervalsmentioning

confidence: 99%

The average GeV-band emission from gamma-ray bursts

Lange¹,

Pohl

2013

A&A

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“…We hope that this has begun to address the mysterious nature of the relation between the very large number of GBM events and the much smaller subset at higher energies. Given the low statistics of the latter, we hope every effort will be made to encourage the most efficient search techniques of the available data stream (see also Rubtsov et al 2012). …”

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confidence: 99%

GRB 110709A, 111117A, AND 120107A: FAINT HIGH-ENERGY GAMMA-RAY PHOTON EMISSION FROMFERMI-LAT OBSERVATIONS AND DEMOGRAPHIC IMPLICATIONS

Zheng¹,

Akerlof²,

McKay³

et al. 2012

ApJ

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Launched on 2008 June 11, the Large Area Telescope (LAT) instrument on board the Fermi Gamma-ray Space Telescope has provided a rare opportunity to study high-energy photon emission from gamma-ray bursts (GRBs). Although the majority of such events (27) have been identified by the Fermi-LAT Collaboration, four were uncovered by using more sensitive statistical techniques. In this paper, we continue our earlier work by finding three more GRBs associated with high-energy photon emission, GRB 110709A, 111117A, and 120107A. To systematize our matched filter approach, a pipeline has been developed to identify these objects in nearly real time. GRB 120107A is the first product of this analysis procedure. Despite the reduced threshold for identification, the number of GRB events has not increased significantly. This relative dearth of events with low photon number prompted a study of the apparent photon number distribution. We find an extremely good fit to a simple power law with an exponent of −1.8 ± 0.3 for the differential distribution. As might be expected, there is a substantial correlation between the number of lower energy photons detected by the Gamma-ray Burst Monitor (GBM) and the number observed by LAT. Thus, high-energy photon emission is associated with some but not all of the brighter GBM events. Deeper studies of the properties of the small population of high-energy emitting bursts may eventually yield a better understanding of these entire phenomena.

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“…We use trilinear interpolation to compute exposures for all energies and locations. Knowing the exposures, we use the method introduced in the appendix of [11] to estimate the background for low and high-energy bands. Note, that the "TRANSIENT" class photons are not included in the analysis due to the strong dependence of the background on the spacecraft position.…”

Section: Exposure Maps and Background Estimationmentioning

confidence: 99%

“…The photons during the burst and the photons for 24 hours before the burst are downloaded from the LAT Data Server 1 . The latter are used for the background estimation in both energy bands with the technique introduced in [11]. In order to have enough statistics we require that at least 10 photons are detected with the energy greater than 1 GeV.…”

Section: Introductionmentioning

confidence: 99%

TIME STRETCHING OF THE GeV EMISSION OF GRBs: FERMI-LAT DATA VERSUS GEOMETRICAL MODEL

Piskunov

Рубцов

2016

ApJ

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It is known that the high energy (> 100 MeV) emission of gamma-ray bursts is delayed with respect to the low energy emission. However, the dependence of light curves on energy has not been studied for the high energy bands. In this paper we consider the bursts observed by Fermi LAT from 2008 August 4 to 2011 August 1, for which at least 10 photons were observed with the energy greater than 1 GeV. These include 4 bursts: GRB 080916C, GRB 090510, GRB 090902B, and GRB 090926A. We use the Kolmogorov-Smirnov test to compare the light curves in the two bands, 100 MeV < E < 1 GeV and E > 1 GeV. For GRB 080916C and GRB 090510 the light curves in the two bands are statistically compatible. However, for GRB 090926A, the higher-energy light curve is stretched compared to the lower-energy one with a statistical significance of 3.3σ and, for GRB 090902B, on the contrary, the lower-energy curve is stretched with 2.3σ significance. We argue that the observed diversity of stretching factors may be explained in a simple geometrical model. The model assumes that the jet opening angle depends on the emission energy in a way that the most energetic photons are radiated near the axis of the jet. All the bursts are considered equivalent in their rest frames and the observed light curves differ only due to different redshifts and view directions. The model conforms to the total burst energy constraint and matches the Fermi-LAT observations of the fraction of GRBs visible in 100 MeV < E < 1 GeV band, which may be observed at higher energies. The model predicts the distribution of observable stretching factors, which may be tested in the future data. Finally, we propose a method to estimate observer's off-axis angle based on the stretching factor and the fraction of the high-energy photons. The code for modeling is open source and is publicly available on GitHub (https:

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Gamma-ray burst observations by Fermi Large Area Telescope revisited: new candidates found

Cited by 12 publications

References 33 publications

The average GeV-band emission from gamma-ray bursts

The average GeV-band emission from gamma-ray bursts

GRB 110709A, 111117A, AND 120107A: FAINT HIGH-ENERGY GAMMA-RAY PHOTON EMISSION FROMFERMI-LAT OBSERVATIONS AND DEMOGRAPHIC IMPLICATIONS

TIME STRETCHING OF THE GeV EMISSION OF GRBs: FERMI-LAT DATA VERSUS GEOMETRICAL MODEL

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