- ID:
- ivo://CDS.VizieR/J/ApJ/811/93
- Title:
- Fermi/GBM GRB minimum timescales
- Short Name:
- J/ApJ/811/93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We constrain the minimum variability timescales for 938 gamma-ray bursts (GRBs) observed by the Fermi/Gamma-ray Burst Monitor instrument prior to 2012 July 11. The tightest constraints on progenitor radii derived from these timescales are obtained from light curves in the hardest energy channel. In the softer bands --or from measurements of the same GRBs in the hard X-rays from Swift-- we show that variability timescales tend to be a factor of two to three longer. Applying a survival analysis to account for detections and upper limits, we find median minimum timescale in the rest frame for long-duration and short-duration GRBs of 45 and 10ms, respectively. Less than 10% of GRBs show evidence for variability on timescales below 2ms. These shortest timescales require Lorentz factors >~400 and imply typical emission radii R~1x10^14^cm for long-duration GRBs and R~3x10^13^cm for short-duration GRBs. We discuss implications for the GRB fireball model and investigate whether or not GRB minimum timescales evolve with cosmic time.
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- ID:
- ivo://CDS.VizieR/J/ApJS/254/35
- Title:
- Fermi GBM GRBs with multiple pulses
- Short Name:
- J/ApJS/254/35
- Date:
- 19 Jan 2022 13:11:51
- Publisher:
- CDS
- Description:
- Gamma-ray bursts (GRBs) are highly variable and exhibit strong spectral evolution. In particular, the emission properties vary from pulse to pulse in multipulse bursts. Here we present a time-resolved Bayesian spectral analysis of a compilation of GRB pulses observed by the Fermi/Gamma-ray Burst Monitor. The pulses are selected to have at least four time bins with a high statistical significance, which ensures that the spectral fits are well determined and spectral correlations can be established. The sample consists of 39 bursts, 117 pulses, and 1228 spectra. We confirm the general trend that pulses become softer over time, with mainly the low-energy power-law index {alpha} becoming smaller. A few exceptions to this trend exist, with the hardest pulse occurring at late times. The first pulse in a burst is clearly different from the later pulses; three-fourths of them violate the synchrotron line of death, while around half of them significantly prefer photospheric emission. These fractions decrease for subsequent pulses. We also find that in two-thirds of the pulses, the spectral parameters ({alpha} and peak energy) track the light-curve variations. This is a larger fraction compared to what is found in previous samples. In conclusion, emission compatible with the GRB photosphere is typically found close to the trigger time, while the chance of detecting synchrotron emission is greatest at late times. This allows for the coexistence of emission mechanisms at late times.
- ID:
- ivo://CDS.VizieR/J/ApJ/756/112
- Title:
- Fermi/GBM GRB time-resolved spectral analysis
- Short Name:
- J/ApJ/756/112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a time-resolved spectral analysis of 51 long and 11 short bright gamma-ray bursts (GRBs) observed with the Fermi/Gamma-Ray Burst Monitor, paying special attention to E_p_ evolution within each burst. Among eight single-pulse long GRBs, five show an evolution from hard to soft, while three show intensity tracking. The multi-pulse long GRBs have more complicated patterns. Statistically, the hard-to-soft evolution pulses tend to be more asymmetric than the intensity-tracking ones, with a steeper rising wing than the falling wing. Short GRBs have E_p_ tracking intensity exclusively with the 16ms time-resolution analysis. We performed a simulation analysis and suggest that for at least some bursts, the late intensity-tracking pulses could be a consequence of overlapping hard-to-soft pulses. However, the fact that the intensity-tracking pattern exists in the first pulse of the multi-pulse long GRBs and some single-pulse GRBs, suggests that intensity tracking is an independent component, which may operate in some late pulses as well. For the GRBs with measured redshifts, we present a time-resolved E_p_-L_{gamma},iso_ correlation analysis and show that the scatter of the correlation is comparable to that of the global Amati/Yonetoku relation. We discuss the predictions of various radiation models regarding E_p_ evolution, as well as the possibility of a precessing jet in GRBs. The data pose a great challenge to each of these models, and hold the key to unveiling the physics behind GRB prompt emission.
- ID:
- ivo://CDS.VizieR/J/A+A/588/A135
- Title:
- Fermi/GBM GRB time-resolved spectral catalog
- Short Name:
- J/A+A/588/A135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to obtain high-quality time-resolved spectral fits of gamma-ray bursts (GRBs) observed by the Gamma-ray Burst Monitor (GBM) on board the Fermi Gamma-ray Space Telescope. We perform time-resolved spectral analysis with high temporal and spectral resolution of the brightest bursts observed by Fermi GBM in its first 4 years of mission. We present the complete catalog containing 1,491 spectra from 81 bursts with high spectral and temporal resolution. Distributions of parameters, statistics of the parameter populations, parameter-parameter and parameter-uncertainty correlations, and their exact values are obtained and presented as main results in this catalog. We report a criterion that is robust enough to automatically distinguish between different spectral evolutionary trends between bursts. We also search for plausible blackbody emission components and find that only 3 bursts (36 spectra in total) show evidence of a pure Planck function. It is observed that the averaged time-resolved low-energy power-law index and peak energy are slightly harder than the time-integrated values. Time-resolved spectroscopic results should be used when interpreting physics from the observed spectra, instead of the time-integrated results.
- ID:
- ivo://CDS.VizieR/J/ApJ/806/52
- Title:
- 8 Fermi GRB afterglows follow-up
- Short Name:
- J/ApJ/806/52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Fermi Gamma-ray Space Telescope has greatly expanded the number and energy window of observations of gamma-ray bursts (GRBs). However, the coarse localizations of tens to a hundred square degrees provided by the Fermi GRB Monitor instrument have posed a formidable obstacle to locating the bursts' host galaxies, measuring their redshifts, and tracking their panchromatic afterglows. We have built a target-of-opportunity (TOO) mode for the intermediate Palomar Transient Factory (iPTF) in order to perform targeted searches for Fermi afterglows. Here, we present the results of one year of this program: 8 afterglow discoveries out of 35 searches. Two of the bursts with detected afterglows (GRBs 130702A and 140606B) were at low redshift (z=0.145 and 0.384, respectively) and had spectroscopically confirmed broad-line Type Ic supernovae. We present our broadband follow-up including spectroscopy as well as X-ray, UV, optical, millimeter, and radio observations. We study possible selection effects in the context of the total Fermi and Swift GRB samples. We identify one new outlier on the Amati relation. We find that two bursts are consistent with a mildly relativistic shock breaking out from the progenitor star rather than the ultra-relativistic internal shock mechanism that powers standard cosmological bursts. Finally, in the context of the Zwicky Transient Facility, we discuss how we will continue to expand this effort to find optical counterparts of binary neutron star mergers that may soon be detected by Advanced LIGO and Virgo.
- ID:
- ivo://CDS.VizieR/J/ApJ/763/15
- Title:
- Fermi GRB analysis. III. T_90_ distributions
- Short Name:
- J/ApJ/763/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The durations (T_90_) of 315 gamma-ray bursts (GRBs) detected with Fermi/GBM (8-1000keV) up to 2011 September are calculated using the Bayesian Block method. We compare the T_90_ distributions between this sample and those derived from previous/current GRB missions. We show that the T_90_ distribution of this GRB sample is bimodal, with a statistical significance level comparable to those derived from the BeppoSAX/GRBM sample and the Swift/BAT sample, but lower than that derived from the CGRO/BATSE sample. The short-to-long GRB number ratio is also much lower than that derived from the BATSE sample, i.e., 1:6.5 versus 1:3. We measure T_90_ in several bands, i.e., 8-15, 15-25, 25-50, 50-100, 100-350, and 350-1000keV, to investigate the energy-dependence effect of the bimodal T_90_distribution. It is found that the bimodal feature is well observed in the 50-100 and 100-350keV bands, but is only marginally acceptable in the 25-50keV and 350-1000keV bands. The hypothesis of bimodality is confidently rejected in the 8-15 and 15-25keV bands. The T_90_distributions in these bands are roughly consistent with those observed by missions with similar energy bands. The parameter T_90_ as a function of energy follows {overline}{T}_90_{propto}E^-0.20+/-0.02^ for long GRBs. Considering the erratic X-ray and optical flares, the duration of a burst would be even longer for most GRBs. Our results, together with the observed extended emission of some short GRBs, indicate that the central engine activity timescale would be much longer than T_90_ for both long and short GRBs and the observed bimodal T_90_ distribution may be due to an instrumental selection effect.
- ID:
- ivo://CDS.VizieR/J/ApJ/757/25
- Title:
- Fermi/LAT AGN at 5GHz
- Short Name:
- J/ApJ/757/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The parsec-scale radio properties of 232 active galactic nuclei, most of which are blazars, detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed contemporaneously by the Very Long Baseline Array (VLBA) at 5GHz. Data from both the first 11 months (1FGL) and the first 2 years (2FGL) of the Fermi mission were used to investigate these sources' {gamma}-ray properties. We use the ratio of the {gamma}-ray-to-radio luminosity as a measure of {gamma}-ray loudness. We investigate the relationship of several radio properties to {gamma}-ray loudness and to the synchrotron peak frequency. There is a tentative correlation between {gamma}-ray loudness and synchrotron peak frequency for BL Lac objects in both 1FGL and 2FGL, and for flat-spectrum radio quasars (FSRQs) in 2FGL. We find that the apparent opening angle tentatively correlates with {gamma}-ray loudness for FSRQs, but only when we use the 2FGL data. We also find that the total VLBA flux density correlates with the synchrotron peak frequency for BL Lac objects and FSRQs. The core brightness temperature also correlates with synchrotron peak frequency, but only for the BL Lac objects. The low-synchrotron-peaked (LSP) BL Lac object sample shows indications of contamination by FSRQs which happen to have undetectable emission lines. There is evidence that the LSP BL Lac objects are more strongly beamed than the rest of the BL Lac object population.
- ID:
- ivo://CDS.VizieR/J/ApJS/183/46
- Title:
- Fermi/LAT bright gamma-ray source list (0FGL)
- Short Name:
- J/ApJS/183/46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Following its launch in 2008 June, the Fermi Gamma-ray Space Telescope (Fermi) began a sky survey in August. The Large Area Telescope (LAT) on Fermi in three months produced a deeper and better resolved map of the {gamma}-ray sky than any previous space mission. We present here initial results for energies above 100MeV for the 205 most significant (statistical significance greater than ~10{sigma}) {gamma}-ray sources in these data. These are the best characterized and best localized point-like (i.e., spatially unresolved) {gamma}-ray sources in the early mission data.
- ID:
- ivo://CDS.VizieR/J/ApJ/700/597
- Title:
- FERMI LAT detected blazars
- Short Name:
- J/ApJ/700/597
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The first three months of sky-survey operation with the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope reveal 132 bright sources at |b|>10{deg} with test statistic greater than 100 (corresponding to about 10{sigma}). Two methods, based on the CGRaBS, CRATES, and BZCat catalogs, indicate high-confidence associations of 106 of these sources with known active galactic nuclei (AGNs). This sample is referred to as the LAT Bright AGN Sample (LBAS). It contains two radio galaxies, namely, Centaurus A and NGC 1275, and 104 blazars consisting of 58 flat spectrum radio quasars (FSRQs), 42 BL Lac objects, and 4 blazars with unknown classification. Four new blazars were discovered on the basis of the LAT detections. Remarkably, the LBAS includes 10 high-energy-peaked BL Lacs (HBLs), sources which were previously difficult to detect in the GeV range. Another 10 lower-confidence associations are found. Only 33 of the sources, plus two at |b|<10{deg}, were previously detected with Energetic Gamma-Ray Experiment Telescope (EGRET), probably due to variability.
- ID:
- ivo://CDS.VizieR/J/ApJ/722/L7
- Title:
- Fermi/LAT detected MOJAVE AGNs
- Short Name:
- J/ApJ/722/L7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the detection of a non-zero time delay between radio emission measured by the VLBA at 15.4GHz and {gamma}-ray radiation ({gamma}-ray leads radio) registered by the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope for a sample of 183 radio and {gamma}-ray bright active galactic nuclei. For the correlation analysis, we used 0.1-100GeV {gamma}-ray photon fluxes, taken from monthly binned measurements from the first Fermi LAT catalog (1FGL; Abdo et al. 2010, Cat. J/ApJS/188/405), and 15.4GHz radio flux densities from the MOJAVE VLBA program (Lister et al. 2009, Cat. J/AJ/137/3718). The correlation is most pronounced if the core flux density is used, strongly indicating that the {gamma}-ray emission is generated within the compact region of the 15GHz VLBA core. Determining the Pearson's r and Kendall's {tau} correlation coefficients for different time lags, we find that for the majority of sources the radio/{gamma}-ray delay ranges from 1 to 8 months in the observer's frame and peaks at approximately 1.2 months in the source's frame. We interpret the primary source of the time delay to be synchrotron opacity in the nuclear region.
