ABSTRACT We present a method to estimate the jet opening angles of long duration gamma-ray bursts (GRBs) using the prompt gamma-ray energetics and an inversion of the Ghirlanda relation, which is a ...correlation between the time-integrated peak energy of the GRB prompt spectrum and the collimation-corrected energy in gamma-rays. The derived jet opening angles using this method and detailed assumptions match well with the corresponding inferred jet opening angles obtained when a break in the afterglow is observed. Furthermore, using a model of the predicted long GRB redshift probability distribution observable by the Fermi Gamma-ray Burst Monitor (GBM), we estimate the probability distributions for the jet opening angle and rest-frame energetics for a large sample of GBM GRBs for which the redshifts have not been observed. Previous studies have only used a handful of GRBs to estimate these properties due to the paucity of observed afterglow jet breaks, spectroscopic redshifts, and comprehensive prompt gamma-ray observations, and we potentially expand the number of GRBs that can be used in this analysis by more than an order of magnitude. In this analysis, we also present an inferred distribution of jet breaks which indicates that a large fraction of jet breaks are not observable with current instrumentation and observing strategies. We present simple parameterizations for the jet angle, energetics, and jet break distributions so that they may be used in future studies.
The federally threatened American crocodile (Crocodylus acutus) is a flagship species and ecological indicator of hydrologic restoration in the Florida Everglades. We conducted a long-term ...capture-recapture study on the South Florida population of American crocodiles from 1978 to 2015 to evaluate the effects of restoration efforts to more historic hydrologic conditions. The study produced 10,040 crocodile capture events of 9,865 individuals and more than 90% of captures were of hatchlings. Body condition and growth rates of crocodiles were highly age-structured with younger crocodiles presenting with the poorest body condition and highest growth rates. Mean crocodile body condition in this study was 2.14±0.35 SD across the South Florida population. Crocodiles exposed to hypersaline conditions (> 40 psu) during the dry season maintained lower body condition scores and reduced growth rate by 13% after one year, by 24% after five years, and by 29% after ten years. Estimated hatchling survival for the South Florida population was 25% increasing with ontogeny and reaching near 90% survival at year six. Hatchling survival was 34% in NE Florida Bay relative to a 69% hatchling survival at Crocodile Lake National Wildlife Refuge and 53% in Flamingo area of Everglades National Park. Hypersaline conditions negatively affected survival, growth and body condition and was most pronounced in NE Florida Bay, where the hydrologic conditions have been most disturbed. The American crocodile, a long-lived animal, with relatively slow growth rate provides an excellent model system to measure the effects of altered hydropatterns in the Everglades landscape. These results illustrate the need for continued long-term monitoring to assess system-wide restoration outcomes and inform resource managers.
We present a systematic spectral analysis of 350 bright gamma-ray bursts (GRBs) observed with the Burst and Transient Source Experiment (BATSE; 630 keV-2 MeV) with high temporal and spectral ...resolution. Our sample was selected from the complete set of 2704 BATSE GRBs based on their energy fluence or peak photon flux values to assure good statistics and included 17 short GRBs. To obtain well-constrained spectral parameters, several photon models were used to fit each spectrum. We compared spectral parameters resulting from the fits using different models, and the spectral parameters that best represent each spectrum were statistically determined, taking into account the parameterization differences among the models. A thorough analysis was performed on 350 time-integrated and 8459 time-resolved burst spectra, and the effects of integration times in determining the spectral parameters were explored. Using the results, we studied correlations among spectral parameters and their evolution pattern within each burst. The resulting spectral catalog is the most comprehensive study of spectral properties of GRB prompt emission to date and is available electronically from the High-Energy Astrophysics Science Archive Research Center (HEASARC). The catalog provides reliable constraints on particle acceleration and emission mechanisms in GRBs.
HOW LONG DOES A BURST BURST? Zhang, Bin-Bin; Zhang, Bing; Murase, Kohta ...
The Astrophysical journal,
05/2014, Volume:
787, Issue:
1
Journal Article
Peer reviewed
Open access
Several gamma-ray bursts (GRBs) last much longer (~hours) in gamma-rays than typical long GRBs (~minutes), and it has recently been proposed that these "ultra-long GRBs" may form a distinct ...population, probably with a different (e.g., blue supergiant) progenitor than typical GRBs. We perform a comprehensive study on a large sample of Swift GRBs with X-Ray Telescope observations to investigate GRB central engine activity duration and to determine whether ultra-long GRBs are unusual events. We define burst duration t sub(burst) based on both gamma-ray and X-ray light curves rather than using gamma-ray observations alone. We find that t sub(burst) can be reliably measured in 343 GRBs. Within this "good" sample, 21.9% GRBs have t sub(burst) gap 10 super(3) s and 11.5% GRBs have t sub(burst) gap 10 super(4) s. There is an apparent bimodal distribution of t sub(burst) in this sample. We found that the existing evidence for a separate ultra-long GRB population is inconclusive, and further multi-wavelength observations are needed to draw a firmer conclusion.
ABSTRACT We perform a time-resolved spectral analysis of GRB 130606B within the framework of a fast-cooling synchrotron radiation model with magnetic field strength in the emission region decaying ...with time, as proposed by Uhm & Zhang. The data from all time intervals can be successfully fit by the model. The same data can be equally well fit by the empirical Band function with typical parameter values. Our results, which involve only minimal physical assumptions, offer one natural solution to the origin of the observed GRB spectra and imply that, at least some, if not all, Band-like GRB spectra with typical Band parameter values can indeed be explained by synchrotron radiation.
Radio emissions continue to provide insight into the production of terrestrial gamma ray flashes (TGFs) by thunderstorms, including the critical question of the conditions under which they are ...generated. We have identified several TGF‐associated lightning radio emissions in which the altitudes of in‐cloud lightning leader pulses that precede and follow the TGF can be measured. We combine these with high absolute timing accuracy TGF observations from the Fermi satellite to determine the development of the lightning channel before, during, and after the TGF production. All of these TGFs were produced several milliseconds after the leader had initiated and when the leaders reached 1–2 km in length. After the TGFs, the leaders all continued to ascend for several more kilometers with no dramatic change in their characteristics, although they all exhibited high average velocities of 0.8–1.0 × 106 m/s. Implications in the context of TGF models are discussed. These results paint the first clear picture of the lightning processes that occur before, during, and after TGF production.
Key Points
TGFs are produced when a lightning leader is near the midpoint of its ascent
Lightning leaders associated with TGFs are fast moving but otherwise ordinary
Why TGFs are not produced at other times in the leader ascent is not clear
PCORnet: turning a dream into reality Collins, Francis S; Hudson, Kathy L; Briggs, Josephine P ...
Journal of the American Medical Informatics Association : JAMIA,
07/2014, Volume:
21, Issue:
4
Journal Article
Many details of how thunderstorms generate terrestrial gamma ray flashes (TGFs) and other forms of high‐energy radiation remain uncertain, including the basic question of where they are produced. We ...exploit the association of distinct low‐frequency radio emissions with generation of terrestrial gamma ray flashes (TGFs) to directly measure for the first time the TGF source altitude. Analysis of two events reveals source altitudes of 11.8 ± 0.4 km and 11.9 ± 0.9 km. This places the source region in the interior of the thunderstorm between the two main charge layers and implies an intrinsic TGF brightness of approximately 1018 runaway electrons. The electric current in this nontraditional lightning process is found to be strong enough to drive nonlinear effects in the ionosphere, and in one case is comparable to the highest peak current lightning processes on the planet.
Key Points
TGFs are produced near 12 km between the charge layers of a thunderstormTGFs contain approximately 1018 runaway electronsThe electric current in the TGF generation process can be very strong
The BATSE 5B Gamma-Ray Burst Spectral Catalog Goldstein, A; Preece, R D; Mallozzi, R S ...
The Astrophysical journal. Supplement series,
10/2013, Volume:
208, Issue:
2
Journal Article
Peer reviewed
Open access
We present systematic spectral analyses of GRBs detected with the Burst and Transient Source Experiment (BATSE) onboard the Compton Gamma-Ray Observatory (CGRO) during its entire nine years of ...operation. This catalog contains two types of spectra extracted from 2145 GRBs and fitted with five different spectral models resulting in a compendium of over 19000 spectra. The models were selected based on their empirical importance to the spectral shape of many GRBs, and the analysis performed was devised to be as thorough and objective as possible. We describe in detail our procedures and criteria for the analyses, and present the bulk results in the form of parameter distributions. This catalog should be considered an official product from the BATSE Science Team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center (HEASARC).
This is the second of a series of catalogs of gamma-ray bursts (GRBs) observed with the Fermi Gamma-ray Burst Monitor (GBM). It extends the first two-year catalog by two more years, resulting in an ...overall list of 953 GBM triggered GRBs. The intention of the GBM GRB catalog is to provide information to the community on the most important observables of the GBM detected GRBs. For each GRB the location and main characteristics of the prompt emission, the duration, peak flux and fluence are derived. Uie latter two quantities are calculated for the 50-300 keV energy band, where the maximum energy release of GRBs in the instrument reference system is observed and also for a broader energy band from 10-1000 keV, exploiting the full energy range of GBMs low-energy detectors. Furthermore, information is given on the settings and modifications of the triggering criteria and exceptional operational conditions during years three and four in the mission. This second catalog is an official product of the Fermi GBM science team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center.
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