644 research outputs found
INTERPLANETARY NETWORK LOCALIZATIONS OF KONUS SHORT GAMMA-RAY BURSTS
No full textBetween the launch of the Global Geospace Science Wind spacecraft in 1994 November and the end of 2010, the Konus-Wind experiment detected 296 short-duration gamma-ray bursts (including 23 bursts which can be classified as short bursts with extended emission). During this period, the Interplanetary Network (IPN) consisted of up to 11 spacecraft, and using triangulation, the localizations of 271 bursts were obtained. We present the most comprehensive IPN localization data on these events. The short burst detection rate, ~18 yr[superscript –1], exceeds that of many individual experiments.Russian Space AgencyRussian Foundation for Basic Research (Grant 12-02-00032a)Russian Foundation for Basic Research (Grant 13-02-12017-ofi-m
Evidence for Circumburst Extinction of Gamma-Ray Bursts with Dark Optical Afterglows and Evidence for a Molecular Cloud Origin of Gamma-Ray Bursts
No full textFirst, we show that the gamma-ray bursts with dark optical afterglows (DOAs) cannot be explained
by a failure to image deeply enough quickly enough, and argue that circumburst extinction is the most likely
solution. If so, many DOAs will be “revived” with rapid follow up and NIR searches in the HETE-2 and Swift
eras. Next, we consider the effects of dust sublimation and fragmentation, and show that DOAs occur in clouds
of size R ≳ 10L^(1/2)_49 pc and mass M ≳ 3x10^5L_(49) M_⊙, where L is the luminosity of the optical flash. Stability
considerations show that such clouds cannot be diffuse, but must be molecular. Consequently, we compute the
expected column density distribution of bursts that occur in Galactic-like molecular clouds, and show that the
column density measurements from X-ray spectra of afterglows, DOAs and otherwise, satisfy this expectation in
the source frame
GRB 000911: Evidence for an Associated Supernova?
No full textWe present photometric and spectroscopic observations of the late afterglow of GRB 000911. We detect a moderately significant re-brightening in the R, I and J lightcurves, associated with a sizable reddening of the spectrum. This can be explained through the presence of an underlying supernova, outshining the afterglow ~ 30 days after the burst event
THE TRANSITING EXOPLANET SURVEY SATELLITE: SIMULATIONS OF PLANET DETECTIONS AND ASTROPHYSICAL FALSE POSITIVES
No full textThe Transiting Exoplanet Survey Satellite (TESS) is a NASA-sponsored Explorer mission that will perform a wide-field survey for planets that transit bright host stars. Here, we predict the properties of the transiting planets that TESS will detect along with the EB stars that produce false-positive photometric signals. The predictions are based on Monte Carlo simulations of the nearby population of stars, occurrence rates of planets derived from Kepler, and models for the photometric performance and sky coverage of the TESS cameras. We expect that TESS will find approximately 1700 transiting planets from 2 X 10[superscript 5] pre-selected target stars. This includes 556 planets smaller than twice the size of Earth, of which 419 are hosted by M dwarf stars and 137 are hosted by FGK dwarfs. Approximately 130 of the R < 2R[subscript ⊕] planets will have host stars brighter than K[subscript s] = 9. Approximately 48 of the planets with R < 2R[subscript ⊕] lie within or near the habitable zone ($0.2 < S/S[subscript ⊕] < 2); between 2 and 7 such planets have host stars brighter than K[subscript s] = 9. We also expect approximately 1100 detections of planets with radii 2–4 R[subscript ⊕], and 67 planets larger than 4 R[subscript ⊕]. Additional planets larger than 2 R[subscript ⊕] can be detected around stars that are not among the pre-selected target stars, because TESS will also deliver full-frame images at a 30-minute cadence. The planet detections are accompanied by over 1000 astrophysical false positives. We discuss how TESS data and ground-based observations can be used to distinguish the false positives from genuine planets. We also discuss the prospects for follow-up observations to measure the masses and atmospheres of the TESS planets
GRB Afterglows and Other Transients in the SDSS
No full textThe Sloan Digital Sky Survey (SDSS) will image one quarter of the sky centered on the northern galactic cap and produce a 3‐D map of galaxies and quasars found in the sample. An additional 225 deg2 southern survey will be imaged repeatedly on varying timescales. Here we discuss both archival searches in the SDSS catalog (such as SDSS J24602.54+011318.8) and active searches with the SDSS instruments (such as for GRB 010222) for GRB afterglows and other transient objects. © 2003 American Institute of PhysicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87288/2/349_1.pd
Collapsar Disks and Winds
No full textWinds blown from collapsar accretion disks may produce observable stellar explosions independent of any GRB-(and afterglow)-producing jets which may be simultaneously produced. The production of winds is controlled by the accretion disk physics, in particular, the nature of disk cooling via neutrino emission and photo-disintegration of heavy nuclei. These temperature-dependent processes depend on the stellar angular momentum via the depth of the gravitational potential at the Kepler radius where the disk forms. Wind-driven stellar explosions which do not make a GRB (or only a faint one) may occur and constitute a new class of supernova explosion. SN1998bw and 1997ef may be examples. A key feature of collapsar winds is that they are capable of producing the radioactive ^(56)Ni necessary to power a supernova light curve. It is possible to make a GRB in a star without significant production of ^(56)Ni. Such a star would not make an observable supernova and no such component would be expected in the light curve of the optical afterglow
Determining the GRB (Redshift, Luminosity)-Distribution Using Burst Variability
No full textWe use the possible Cepheid-like luminosity estimator for the long-duration gamma-ray bursts (GRBs) developed by Reichart et al. (2000) to estimate the intrinsic luminosity, and thus the redshift, of 907 long-duration GRBs from the BATSE 4B catalog. We describe a method based on Bayesian inference which allows us to infer the intrinsic GRB burst rate as a function of redshift for bursts with estimated intrinsic luminosities and redshifts. We apply this method to the above sample of long-duration GRBs, and present some preliminary results
Determining the Gamma-Ray Burst Rate as a Function of Redshift
No full textWe exploit the 14 gamma-ray bursts (GRBs) with known redshifts z and the 7 GRBs for which there are constraints on z to determine the GRB rate R_(GRB)(z), using a method based on Bayesian inference. We find that, despite the qualitative differences between the observed GRB rate and estimates of the SFR in the universe, current data are consistent with R_(GRB)(z) being proportional to the SFR
Radio, Sub-mm, and X-Ray Studies of Gamma-Ray Burst Host Galaxies
No full textThe study of gamma-ray burst (GRB) host galaxies in the radio, sub-mm, and X-ray wavelength regimes began only recently, in contrast to optical studies. This is mainly due to the long timescale on which the radio afterglow emission decays, and to the intrinsic faintness of radio emission from star-forming galaxies at z ~ 1, as well as source confusion in sub-mm observations; X-ray observations of GRB hosts have simply not been attempted yet. Despite these difficulties, we have recently made the first detections of radio and sub-mm emission from the host galaxies of GRB 980703 and GRB 010222, respectively, using the VLA and the SCUBA instrument on JCMT. In both cases we find that the inferred star formation rates (~ 500 M_☉) and bolometric luminosities (few × 10^(12) L_☉) indicate that these galaxies are possibly analogous to the local population of Ultra-Luminous Infrared Galaxies (ULIRGs) undergoing a starburst. However, there is a modest probability that the observed emission is due to AGN activity rather than star formation, thus requiring observations with Chandra or XMM. The sample of GRB hosts offers a number of unique advantages to the broader question of the evolution of galaxies and star formation from high redshift to the present time since: (i) GRBs trace massive stars, (ii) are detectable to high redshifts, and (iii) have immense dust penetrating power. Therefore, radio/sub-mm/X-ray observations of GRB hosts can potentially provide crucial information both on the nature of the GRB host galaxies, and on the history of star formation
An Observational Evidence for the Difference Between the Short and Long Gamma-Ray Bursts
No full textThe intrinsic fluence and duration distributions of gamma-ray bursts are well represented by log-normal
distributions. This allows a bivariate log-normal distribution fit to be made to the BATSE short and long bursts
separately. A statistically significant difference between the long and short groups is found. We argue that the
effect is probably real. Applying the Cramér’s theorem these results lead to some predictions for models of long
and short bursts
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