262 research outputs found
Observational properties of cosmic gamma-ray bursts
A brief overview of the major observational results obtained in gamma-ray burst studies is presented. Also discussed is to what extent the thermonuclear model, which appears at present to be the most plausible, can account for the observed properties of the bursts. The investigation of gamma-ray bursts should cover observations of the time histories of events, energy spectra, and their variablility, source localization, and inspection of the localization regions during the active and quiescent phases of the source in other wavelengths, as well as, evaluation of the statistical distributions of the data obtained
Reactivation and Precise IPN Localization of the Soft Gamma Repeater SGR1900+14
In 1998 May, the soft gamma repeater SGR1900+14 emerged from several years of
quiescence and emitted a series of intense bursts, one with a time history
unlike any previously observed from this source. Triangulation using Ulysses,
BATSE, and KONUS data give a 1.6 square arcminute error box near the galactic
supernova remnant G42.8+0.6. This error box contains a quiescent soft X-ray
source which is probably a neutron star associated with the soft repeater.Comment: Accepted for publication in the Astrophysical Journal Letter
Experimental data as evidence against the hypothesis on the earth's dust cloud
Cosmos and Explorer satellite data used to reject hypothesis of terrestrial meteoroid and dust cloud
The Giant Flare of 1998 August 27 from SGR 1900+14: II. Radiative Mechanism and Physical Constraints on the Source
(ABBREVIATED) The extraordinary 1998 August 27 giant flare places strong
constraints on the physical properties of its source, SGR 1900+14. We make
detailed comparisons of the published data with the magnetar model. The giant
flare evolved through three stages, whose radiative mechanisms we address in
turn. A triggering mechanism is proposed, whereby a helical distortion of the
core magnetic field induces large-scale fracturing in the crust and a twisting
deformation of the crust and exterior magnetic field. The envelope of the
pulsating tail of the August 27 flare can be accurately fit, after ~40 s, by
the contracting surface of a relativistically hot, but inhomogeneous, trapped
fireball. We quantify the effects of direct neutrino-pair emission, thereby
deducing a lower bound ~ 10^{32} G-cm^3 to the magnetic moment of the confining
field. The radiative flux during the intermediate ~40 s of the burst appears to
exceed the trapped fireball fit. The spectrum and lightcurve of this smooth
tail are consistent with heating in an extended pair corona, possibly powered
by continuing seismic activity in the star. We consider in detail the critical
luminosity, below which a stable balance can be maintained between heating and
radiative cooling in a confined, magnetized pair plasma; but above which the
confined plasma runs away to local thermodynamic equilibrium. In the later
pulsating tail, the best fit temperature equilibrates at a value which agrees
well with the regulating effect of photon splitting. The remarkable four-peaked
substructure within each 5.16-s pulse provides strong evidence for the presence
of higher magnetic multipoles in SGR 1900+14. The corresponding collimation of
the X-ray flux is related to radiative transport in a super-QED magnetic field.Comment: 11 July 2001, accepted for publication in the Astrophysical Journa
Konus catalog of SGR activity to 2000
Observational data on the bursting activity of all five known Soft Gamma
Repeaters are presented. This information was obtained with Konus gamma-ray
burst experiments on board Venera 11-14, Wind, and Kosmos-2326 spacecraft in
the period from 1978 to 2000. These data on appearance rates, time histories,
and energy spectra of repeated soft bursts obtained with similar instruments
and collected together in a comparable form should be useful for further
studies of SGRs. (available at http://www.ioffe.rssi.ru/LEA/SGR/Catalog/).Comment: 20 pages, including 5 tables, LaTeX AASTeX5.0, with 50 PNG-files of
reduced size figures. Catalog with full size figures is available at
http://www.ioffe.rssi.ru/LEA/SGR/Catalog/ To be submitted to ApJ Supp
Unusual Burst Emission from the New Soft Gamma Repeater SGR1627-41
In June-July,1998 the Konus-Wind burst spectrometer observed a series of
bursts from the new soft gamma repeater SGR1627-41. Time histories and energy
spectra of the bursts have been studied, revealing fluences and peak fluxes in
the ranges of 3x10^{-7} - 7.5x10^{-6} erg cm^{-2} and 10^{-5} - 10^{-4}erg
cm^{-2}/s respectively. One event, 18 June 6153.5sUT stands out dramatically
from this series. Its fluence is ~7x10^{-4} erg cm^{-2} and peak flux
~2x10^{-2} erg cm^{-2}/s. These values from a source at a distance of 5.8 kpc
yield an energy output of ~3x10^{42}erg and maximum luminosity of ~8x10^{43}
erg/s, similar to the values for the famous March 5, 1979 and August27,1998
events. In terms of energy, this event is another giant outburst seen in a
third SGR! However, this very energetic burst differs significantly from the
other giant outbursts. It exhibits no separate initial pulse with a fast rise
time, no extended tail, and no pulsations. It is rather similar to ordinary
repeated bursts but is a few hundred times stronger in intensity. According to
the magnetar model by Thompson and Duncan (1995) such a burst may be initiated
by a strong starquake when a crust fracture propagates over the whole surface
of a neutron star.Comment: 7 pages, 5 figures. To be appeared in ApJ
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