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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

GRB 990712: First Detection of Polarization Variability in a Gamma-ray Burst Afterglow

We report the detection of significant polarization in the afterglow of GRB 990712 on three instances 0.44-1.45 days after the gamma-ray burst. This polarization is intrinsic to the afterglow. The degree of polarization is not constant, and smallest at the second measurement. The polarization angle does not vary significantly during these observations. We find that none of the existing models predict such polarization variations constant polarization angle, and discuss ways in which these models might be modified to accommodate the observed behavior of this afterglow.

Rol, E.↗
NASA NTRS2005

Terrestrial Ozone Depletion Due to a Milky Way Gamma-Ray Burst

Based on cosmological rates, it is probable that at least once in the last Gy the Earth has been irradiated by a gamma-ray burst in our Galaxy from within 2 kpc. Using a two-dimensional atmospheric model we have computed the effects upon the Earth's atmosphere of one such burst. A ten second burst delivering 100 kJ/sq m to the Earth results in globally averaged ozone depletion of 35%, with depletion reaching 55% at some latitudes. Significant global depletion persists for over 5 years after the burst. This depletion would have dramatic implications for life since a 50% decrease in ozone column density results in approximately three times the normal UVB flux. Widespread extinctions are likely, based on extrapolation from UVB sensitivity of modern organisms.

Thomas, Brian C.↗
NASA NTRS2007

Prompt and Afterglow Emmision Properties of Gamma-ray Bursts with Spectroscopically Identified Supernovae

We present a detailed spectral analysis of the prompt and afterglow emission of four nearby long-soft gamma-ray bursts (GRBs 980425,030329,031203, and 060218) that were spectroscopically found to be associated with Type IC supernovae and compare them to the general GRB population. For each event, we investigate the spectral and luminosity evolution and estimate the total energy budget based on broadband observations. The observational inventory for these events has become rich enough to allow estimates of their energy content in relativistic and subrelativistic form. The result is a global portrait of the effects of the physical processes responsible for producing long-soft GRBs. In particular, we find that the values of the energy released in mildly relativistic out8ows appears to have a sigruficantly smaller scatter than those found in highly relativistic ejecta. This is consistent with a picture in which the energy released inside the progenitor star is roughly standard, while the fracti

Kaneko, Yuki↗
NASA NTRS2007

Prompt and Afterglow Emission Properties of Gamma-Ray Bursts with Spectroscopically Identified Supernovae

We present a detailed spectral analysis of the prompt and afterglow emission of four nearby long-soft gamma-ray bursts (GRBs 980425,030329,031203, and 060218) that were spectroscopically found to be associated with Type Ic supernovae and compare them to the general GRB population. For each event, we investigate the spectral and luminosity evolution and estimate the total energy budget based on broadband observations. The observational inventory for these events has become rich enough to allow estimates of their energy content in relativistic and subrelativistic form. The result is a global portrait of the effects of the physical processes responsible for producing long-soft GRBs. In particular, we find that the values of the energy released in mildly relativistic outflows appears to have a significantly smaller scatter than those found in highly relativistic ejecta. This is consistent with a picture in which the energy released inside the progenitor star is roughly standard, while the fraction of that energy that ends up in highly relativistic ejecta outside the star can vary dramatically between different events.

Kaneko, Yuki↗
NASA NTRS1994

A study of gamma ray burst continuum properties presnting evidence for two spectral states in bursts

Evidence is presented for the existence of two spectral states contributing simultaneously to the total spectrum observed in many gamma-ray bursts (GRB's). An ensemble of 120 GRB's measured by BATSE were studied, using 4 channel spectral data, to determine in which bursts the spectral states can be most effectively resolved. The technique of summing the low intensity spectra together to get an average spectrum allows for precise characterization of the average low intensity spectral behavior. The 4 and 16 channel spectra obtained by the BATSE Large Area Detectors (LAD's) are analyzed using a model-independent spectral inversion technique. The results of these analyses applied to an individual burst are discussed in detail.

Pendleton, Geoffrey N.↗
NASA NTRS2007

SWIFT Discovery of Gamma-ray Bursts without Jet Break Feature in their X-ray Afterglows

We analyze Swift gamma-ray bursts (GRBs) and X-ray afterglows for three GRBs with spectroscopic redshift determinations - GRB 050401, XRF 050416a, and GRB 050525a. We find that the relation between spectral peak energy and isotropic energy of prompt emissions (the Amati relation) is consistent with that for the bursts observed in pre-Swift era. However, we find that the X-ray afterglow lightcurves, which extend up to 10 - 70 days, show no sign of the jet break that is expected in the standard framework of collimated outflows. We do so by showing that none of the X-ray afterglow lightcurves in our sample satisfies the relation between the spectral and temporal indices that is predicted for the phase after jet break. The jet break time can be predicted by inverting the tight empirical relation between the peak energy of the spectrum and the collimation-corrected energy of the prompt emission (the Ghirlanda relation). We find that there are no temporal breaks within the predicted time intervals in X-ray band. This requires either that the Ghirlanda relation has a larger scatter than previously thought, that the temporal break in X-rays is masked by some additional source of X-ray emission, or that it does not happen because of some unknown reason.

Sato, G.↗
NASA NTRS1995

Resonant Compton scattering and gamma-ray burst continuum spectra

The Thomson limit of resonant inverse Compton scattering in the strong magnetic fields of neutron stars is considered as a mechanism for producing gamma-ray burst continuum spectra. Photon production spectra and electron cooling rates are presented using the full magnetic Thomson cross-section. Model emission spectra are obtained as self-consistent solutions of a set of photon and electron kinetic equations, displaying spectral breaks and other structure at gamma-ray energies.

Baring, M. G.↗
NASA NTRS1990

The Energetic Transient Array ETA - A network of 'space buoys' in solar orbit for observations of gamma-ray bursts

The Energetic Transient Array (ETA) is a concept for a dedicated interplanetary network of about 40 microsatellites ('space buoys') deployed in an about 1 AU radius solar orbit for the observation of cosmic gamma ray bursts (GRBs). Such a network is essential for the determination of highly accurate (about 0.1 arcsec) error boxes for GRBs. For each of about 100 bursts which would be detectable per year of observation by such a network, high resolution spectra could be obtained through the use of passively-cooled Ge gamma-ray detectors. Stabilization of each microsatellite would be achieved by a novel technique based on the radiation pressure exerted on 'featherable' solar paddles. It should be possible to have a fully functional array of satellites in place before the end of the decade for a total cost of about $20M, exclusive of launcher fees.

Ricker, George R.↗
NASA NTRS2012

The Prompt-afterglow Connection in Gamma-ray Bursts: a Comprehensive Statistical Analysis of Swift X-ray Light-curves

We present a comprehensive statistical analysis of Swift X-ray light-curves of Gamma- Ray Bursts (GRBs) collecting data from more than 650 GRBs discovered by Swift and other facilities. The unprecedented sample size allows us to constrain the rest-frame X-ray properties of GRBs from a statistical perspective, with particular reference to intrinsic time scales and the energetics of the different light-curve phases in a common rest-frame 0.3-30 keV energy band. Temporal variability episodes are also studied and their properties constrained. Two fundamental questions drive this effort: i) Does the X-ray emission retain any kind of "memory" of the prompt γ-ray phase? ii) Where is the dividing line between long and short GRB X-ray properties? We show that short GRBs decay faster, are less luminous and less energetic than long GRBs in the X-rays, but are interestingly characterized by similar intrinsic absorption. We furthermore reveal the existence of a number of statistically significant relations that link the X-ray to prompt γ-ray parameters in long GRBs; short GRBs are outliers of the majority of these 2-parameter relations. However and more importantly, we report on the existence of a universal 3-parameter scaling that links the X-ray and the γ-ray energy to the prompt spectral peak energy of both long and short GRBs: E(sub X,iso)∝ E(sup 1.00+/-0.06)(sub γ,iso) /E(sup 0.60+/-0.10)(sub pk).

Gamma-Ray Bursts↗
NASA NTRS1981

The spectra and light curves of two gamma-ray bursts

Observations made by the Hard X-ray and Low Energy Gamma-Ray Experiment on board HEAO-1 of the spectra and light curves of two gamma-ray bursts for which localized arrival directions will become available are presented. The burst of October 20, 1977 is found to exhibit a fluence of 0.000031 + or - 0.000005 erg/sq cm over the energy range 0.135-2.05 MeV and a duration of 38.7 sec, while that of November 10, 1977 is found to have a fluence of 0.000021 + or - 0.000008 erg/sq cm between 0.125 and 3 MeV over 2.8 sec. The light curves of both bursts exhibit time fluctuations down to the limiting time resolution of the detectors. The spectrum of the October burst can be fit by a power law of index -1.93 + or -0.16, which is harder than any other gamma-burst spectrum yet reported. The spectrum of the second burst is softer (index -2.4 + or - 0.7), and is consistent with the upper index in the double power law fit to the burst of April 27, 1972.

Knight, F. K.↗
DOE OSTI2020

Constraints on cosmological parameters from gamma-ray burst peak photon energy and bolometric fluence measurements and other data

ABSTRACT We use measurements of the peak photon energy and bolometric fluence of 119 gamma-ray bursts (GRBs) extending over the redshift range of 0.3399 ≤ z ≤ 8.2 to simultaneously determine cosmological and Amati relation parameters in six different cosmological models. The resulting Amati relation parameters are almost identical in all six cosmological models, thus validating the use of the Amati relation in standardizing these GRBs. The GRB data cosmological parameter constraints are consistent with, but significantly less restrictive than, those obtained from a joint analysis of baryon acoustic oscillation and Hubble parameter measurements.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Explaining Nonmerger Gamma-Ray Bursts and Broad-lined Supernovae with Close Binary Progenitors with Black Hole Central Engines

For over 25 yr, the origin of long-duration gamma-ray bursts (lGRBs) has been linked to the collapse of rotating massive stars. However, we have yet to pinpoint the stellar progenitor powering these transients. Moreover, the dominant engine powering the explosions remains open to debate. Observations of both lGRBs, supernovae associated with these GRBs, such as broad-line (BL) stripped-envelope (type Ic) supernovae (hereafter, Ic-BL), supernovae (SNe), and perhaps superluminous SNe, fast blue optical transients, and fast x-ray transients, may provide clues to both engines and progenitors. In this paper, we conduct a detailed study of the tight-binary formation scenario for lGRBs, comparing this scenario to other leading progenitor models. Combining this progenitor scenario with different lGRB engines, we can compare to existing data and make predictions for future observational tests. We find that the combination of the tight-binary progenitor scenario with the black hole accretion disk engine can explain lGRBs, low-luminosity GRBs, ultra-long GRBs, and Ic-BL. We discuss the various progenitor properties required for these different subclasses and note such systems would be future gravitational-wave merger sources. We show that the current literature on other progenitor-engine scenarios cannot explain all of these transient classes with a single origin, motivating additional work. We find that the tight-binary progenitor with a magnetar engine is excluded by existing observations. The observations can be used to constrain the properties of stellar evolution, the nature of the GRB, and the associated SN engines in lGRBs and Ic-BL. We discuss the future observations needed to constrain our understanding of these rare, but powerful, explosions.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1997

Observing gamma-ray bursts with the INTEGRAL spectrometer SPI

The spectrometer for INTEGRAL (SPI) is a germanium spectrometer with a wide field of view and will provide the International Gamma Ray Astrophysics Laboratory (INTEGRAL) mission with the opportunity of studying gamma ray bursts. Simulations carried out to assess the response of the instrument using data from real burst data as input are reported on. It is shown that, despite the angular resolution of 3 deg, it is possible to locate the direction of bursts with an accuracy of a few arcmin, while offering the high spectral resolution of the germanium detectors. It is remarked that the SPI field of view is similar to the size of the halo of bursts expected around M 31 on galactic models. The detectability of bursts with such a halo is discussed.

Skinner, G. K.↗
NASA NTRS2004

Probing a Gamma-Ray Burst Progenitor at a Redshift of z = 2: A Comprehensive Observing Campaign Campaign of the Afterglow of GRB 030226

We report results from a comprehensive follow-up observing campaign of the afterglow of GRB 030226 including VLT spectroscopy, VLT polarimetry, and Chandra X-ray observations. In addition, we present BOOTES-1 wide-field observations at the time of the occurrence of the burst. First observations at ESO started 0.2 days after the event when the gamma ray burst (GRB) afterglow was at a magnitude of R approximately 19 and continued until the afterglow had faded below the detection threshold (R greater than 26). No underlying host galaxy was found. The optical light curve shows a break around 0.8 days after the burst, which is achromatic within the observational errors, supporting the view that it was due to a jetted explosion. Close to the break time the degree of linear polarization of the afterglow light was less than 1.1%, which favors a uniform-jet model rather than a structured one. VLT spectra show two absorption line systems at redshifts z = 1.962 plus or minus 0.001 and 1.986 plus or minus 0.001, placing the lower limit for the redshift of the GRB close to 2. We emphasize that the kinematics and the composition of the absorbing clouds responsible for these line systems are very similar to those observed in the afterglow of GRB 021004. This corroborates the picture in which at least some GRBs are physically related to the explosion of a Wolf-Rayet star.

Klose, S.↗
DOE OSTI2021

GRB 191016A: A Long Gamma-Ray Burst Detected by TESS

The Transiting Exoplanet Survey Satellite (TESS) exoplanet-hunting mission detected the rising and decaying optical afterglow of GRB 191016A, a long gamma-ray burst (GRB) detected by Swift-BAT but without prompt XRT or UVOT follow-up due to proximity to the Moon. The afterglow has a late peak at least 1000 s after the BAT trigger, with a brightest-detected TESS data point at 2589.7 s post-trigger. The burst was not detected by Fermi-LAT, but was detected by Fermi-GBM without triggering, possibly due to the gradual nature of the rising light curve. Using ground-based photometry, we estimate a photometric redshift of z phot = 3.29 ± 0.40. Combined with the high-energy emission and optical peak time derived from TESS, estimates of the bulk Lorentz factor Γ BL range from 90 to 133. The burst is relatively bright, with a peak optical magnitude in ground-based follow-up of R = 15.1 mag. Using published distributions of GRB afterglows and considering the TESS sensitivity and sampling, we estimate that TESS is likely to detect ~1 GRB afterglow per year above its magnitude limit.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1983

Corequake and shock heating model of the 5 March 1979 gamma-ray burst

Ramaty et al. (1980) have proposed a model of a neutron-star corequake and subsequent shock heating of the atmosphere to account for the gamma-ray burst of March 5, 1979. This model is elaborated by examining the overall energetics and characteristics of the radiation-dominated gas shocks under the assumption of thermodynamic equilibrium, taking into account the electron-positron pair production behind the shock. Using values for the density typical of those expected for neutron-star crusts (100-10,000 g/cu cm) and shock velocities characteristic of the sound speed (40,000-100,000), shock luminosities are obtained comparable to those required if the burst originated in the LMC. In addition, the fraction of energy deposited in electron-positron pairs is in good agreement with observation. Uneven shock heating between the polar and equatorial regions of the neutron star due to the presence of a dipole magnetic field, coupled with a rotation rate of 8 s, can also naturally account for the pulsating phase of the burst.

Ellison, D. C.↗
NASA NTRS2005

Tomography of a Gamma-ray Burst Progenitor and its Host Galaxy

We have obtained near-infrared and high-resolution optical spectroscopy of the bright afterglow of the very intense gamma-ray burst recorded on 2002, October 4 (GRB 021004). Besides of line emission in the near-IR allowing an independent measurement of the systemic redshift (z = 2.3304 plus or minus 0.0005), we find several absorption line groups spanning a range of about 3,000 kilometers per second in velocity relative to the redshift of the host galaxy. The absorption profiles are very complex with both velocity-broadened components extending over several 100 kilometers per second and narrow lines with velocity widths of only approximately 20 kilometers per second. By analogy with QSO absorption line studies, the relative velocities, widths, and degrees of ionization of the lines ("line-locking", "ionization-velocity correlation") show that the progenitor had both an extremely strong radiation field and several distinct mass loss phases (winds). These results are consistent with GRB progenitors being massive stars, such as Luminous Blue Variables (LBVs) or Wolf-Rayet stars, providing a detailed picture of the spatial and velocity structure of the GRB progenitor star at the time of explosion. The host galaxy is a prolific star-forming galaxy with a SFR of approximately 10 solar mass yr(sup -l).

Castro-Tirado, Alberto J.↗