Observations of GRB 100724B with the Fermi Gamma-Ray Burst Monitor find that the spectrum is dominated by the typical Band functional form, which is usually taken to represent a non-thermal emission ...component, but also includes a statistically highly significant thermal spectral contribution. The simultaneous observation of the thermal and non-thermal components allows us to confidently identify the two emission components. The fact that these seem to vary independently favors the idea that the thermal component is of photospheric origin while the dominant non-thermal emission occurs at larger radii. Our results imply either a very high efficiency for the non-thermal process or a very small size of the region at the base of the flow, both quite challenging for the standard fireball model. These problems are resolved if the jet is initially highly magnetized and has a substantial Poynting flux.
From 2008 July to 2009 October, the Gamma-ray Burst Monitor (GBM) on board the Fermi Gamma-ray Space Telescope has detected 320 gamma-ray bursts (GRBs). About 20% of these events are classified as ...short based on their T 90 duration below 2 s. We present here for the first time time-resolved spectroscopy at timescales as short as 2 ms for the three brightest short GRBs observed with GBM. The time-integrated spectra of the events deviate from the Band function, indicating the existence of an additional spectral component, which can be fit by a power law with index ~--1.5. The time-integrated E peak values exceed 2 MeV for two of the bursts and are well above the values observed in the brightest long GRBs. Their E peak values and their low-energy power-law indices ( Delta *a) confirm that short GRBs are harder than long ones. We find that short GRBs are very similar to long ones, but with light curves contracted in time and with harder spectra stretched toward higher energies. In our time-resolved spectroscopy analysis, we find that the E peak values range from a few tens of keV up to more than 6 MeV. In general, the hardness evolutions during the bursts follow their flux/intensity variations, similar to long bursts. However, we do not always see the E peak leading the light-curve rises and confirm the zero/short average light-curve spectral lag below 1 MeV, already established for short GRBs. We also find that the time-resolved low-energy power-law indices of the Band function mostly violate the limits imposed by the synchrotron models for both slow and fast electron cooling and may require additional emission processes to explain the data. Finally, we interpreted these observations in the context of the current existing models and emission mechanisms for the prompt emission of GRBs.
Spinal cord injuries (SCIs) are often the result of traumatic accidents, which also produce multiple other injuries (polytrauma). Nociceptive input from associated injuries has been shown to ...significantly impair recovery post-SCI. Historically, work in our laboratory has focused exclusively on male animals; however, increasing incidence of SCI in females requires research to determine whether pain (nociceptive) input poses the same risk to their recovery. Some animal studies have shown that females demonstrate greater tissue preservation and better locomotor recovery post-SCI. Given this, we examined the effect of sex on SCI recovery in two pain models—intermittent electrical stimulation (shock) to the tail or capsaicin injection to the hindpaw. Female rats received a lower thoracic contusion injury and were exposed to noxious stimulation the next day. The acute effect of noxious input on cardiovascular function, locomotor performance, and hemorrhage were assessed. Treatment with capsaicin or noxious electrical stimulation disrupted locomotor performance, increased blood pressure, and disrupted stepping. Additional experiments examined the long-term consequences of noxious input, demonstrating that both noxious electrical stimulation and capsaicin impair long-term recovery in female rats. Interestingly, injury had a greater effect on behavioral performance when progesterone and estrogen were low (metestrus). Conversely, nociceptive input led to a greater disruption in locomotor performance and produced a greater rise in blood pressure in animals injured during estrus.
We present our results of the temporal and spectral analysis of a sample of 52 bright and hard gamma-ray bursts (GRBs) observed with the Fermi Gamma-ray Burst Monitor (GBM) during its first year of ...operation (2008 July-2009 July).Our sample was selected from a total of 253 GBM GRBs based on the event peak count rate measured between 0.2 and 40 MeV. The final sample comprised of 34 long and 18 short GRBs. These numbers show that the GBM sample contains a much larger fraction of short GRBs than the CGRO/BATSE data set, which we explain as the result of our (different) selection criteria, which favor collection of short, bright GRBs over BATSE. A first by-product of our selection methodology is the determination of a detection threshold from the GBM data alone, above which GRBs most likely will be detected in the MeV/GeV range with the Large Area Telescope on board Fermi. This predictor will be very useful for future multi-wavelength GRB follow-ups with ground- and space-based observatories. Further, we have estimated the burst durations up to 10 MeV and for the first time expanded the duration-energy relationship in the GRB light curves to high energies. We confirm that GRB durations decline with energy as a power law with index approximately --0.4, as was found earlier with the BATSE data and we also notice evidence of a possible cutoff or break at higher energies. Finally, we performed time-integrated spectral analysis of all 52 bursts and compared their spectral parameters with those obtained with the larger data sample of the BATSE data. We find that the two parameter data sets are similar and confirm that short GRBs are in general harder than longer ones.
In this catalog we present the updated set of spectral analyses of gamma-ray bursts (GRBs) detected by the Fermi Gamma-Ray Burst Monitor during its first four years of operation. It contains two ...types of spectra, time-integrated spectral fits and spectral fits at the brightest time bin, from 943 triggered GRBs. Four different spectral models were fitted to the data, resulting in a compendium of more than 7500 spectra. The analysis was performed similarly but not identically to Goldstein et al. All 487 GRBs from the first two years have been re-fitted using the same methodology as that of the 456 GRBs in years three and four. We describe, in detail, our procedure and criteria for the analysis and present the results in the form of parameter distributions both for the observer-frame and rest-frame quantities. The data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center.
Abstract GW230529 is the first compact binary coalescence detected by the LIGO–Virgo–KAGRA collaboration with at least one component mass confidently in the lower mass gap, corresponding to the range ...3–5 M ⊙ . If interpreted as a neutron star–black hole merger, this event has the most symmetric mass ratio detected so far and therefore has a relatively high probability of producing electromagnetic (EM) emission. However, no EM counterpart has been reported. At the merger time t 0 , Swift-BAT and Fermi-GBM together covered 100% of the sky. Performing a targeted search in a time window t 0 − 20 s, t 0 + 20 s, we report no detection by the Swift-BAT and Fermi-GBM instruments. Combining the position-dependent γ -ray flux upper limits and the gravitational-wave posterior distribution of luminosity distance, sky localization, and inclination angle of the binary, we derive constraints on the characteristic luminosity and structure of the jet possibly launched during the merger. Assuming a top-hat jet structure, we exclude at 90% credibility the presence of a jet that has at the same time an on-axis isotropic luminosity ≳10 48 erg s −1 in the bolometric band 1 keV–10 MeV and a jet opening angle ≳15°. Similar constraints are derived by testing other assumptions about the jet structure profile. Excluding GRB 170817A, the luminosity upper limits derived here are below the luminosity of any GRB observed so far.
GW230529 is the first compact binary coalescence detected by the
LIGO-Virgo-KAGRA collaboration with at least one component mass confidently in
the lower mass-gap, corresponding to the range ...3-5$M_{\odot}$. If interpreted
as a neutron star-black hole merger, this event has the most symmetric mass
ratio detected so far and therefore has a relatively high probability of
producing electromagnetic (EM) emission. However, no EM counterpart has been
reported. At the merger time $t_0$, Swift-BAT and Fermi-GBM together covered
100$\%$ of the sky. Performing a targeted search in a time window $t_0-20
\text{s},t_0+20 \text{s}$, we report no detection by the Swift-BAT and the
Fermi-GBM instruments. Combining the position-dependent $\gamma-$ray flux upper
limits and the gravitational-wave posterior distribution of luminosity
distance, sky localization and inclination angle of the binary, we derive
constraints on the characteristic luminosity and structure of the jet possibly
launched during the merger. Assuming a top-hat jet structure, we exclude at
90$\%$ credibility the presence of a jet which has at the same time an on-axis
isotropic luminosity $\gtrsim 10^{48}$ erg s$^{-1}$, in the bolometric band 1
keV-10 MeV, and a jet opening angle $\gtrsim 15$ deg. Similar constraints are
derived testing other assumptions about the jet structure profile. Excluding
GRB 170817A, the luminosity upper limits derived here are below the luminosity
of any GRB observed so far.
GW230529 is the first compact binary coalescence detected by the LIGO-Virgo-KAGRA collaboration with at least one component mass confidently in the lower mass-gap, corresponding to the range ...3-5\(M_{\odot}\). If interpreted as a neutron star-black hole merger, this event has the most symmetric mass ratio detected so far and therefore has a relatively high probability of producing electromagnetic (EM) emission. However, no EM counterpart has been reported. At the merger time \(t_0\), Swift-BAT and Fermi-GBM together covered 100\(\%\) of the sky. Performing a targeted search in a time window \(t_0-20 \text{s},t_0+20 \text{s}\), we report no detection by the Swift-BAT and the Fermi-GBM instruments. Combining the position-dependent \(\gamma-\)ray flux upper limits and the gravitational-wave posterior distribution of luminosity distance, sky localization and inclination angle of the binary, we derive constraints on the characteristic luminosity and structure of the jet possibly launched during the merger. Assuming a top-hat jet structure, we exclude at 90\(\%\) credibility the presence of a jet which has at the same time an on-axis isotropic luminosity \(\gtrsim 10^{48}\) erg s\(^{-1}\), in the bolometric band 1 keV-10 MeV, and a jet opening angle \(\gtrsim 15\) deg. Similar constraints are derived testing other assumptions about the jet structure profile. Excluding GRB 170817A, the luminosity upper limits derived here are below the luminosity of any GRB observed so far.
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