949 research outputs found
Strange Star Heating Events as a Model for Giant Flares of Soft Gamma-ray Repeaters
Two giant flares were observed on 5 March 1979 and 27 August 1998 from the
soft gamma-ray repeaters SGR 0526-66 and SGR 1900+14, respectively. The
striking similarity between these remarkable bursts strongly implies a common
nature. We show that the light curves of the giant bursts may be easily
explained in the model where the burst radiation is produced by the bare quark
surface of a strange star heated, for example, by impact of a massive
comet-like object.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. Letter
Viability of primordial black holes as short period gamma-ray bursts
It has been proposed that the short period gamma-ray bursts, which occur at a
rate of , may be evaporating primordial black holes
(PBHs). Calculations of the present PBH evaporation rate have traditionally
assumed that the PBH mass function varies as . This mass
function only arises if the density perturbations from which the PBHs form have
a scale invariant power spectrum. It is now known that for a scale invariant
power spectrum, normalised to COBE on large scales, the PBH density is
completely negligible, so that this mass function is cosmologically irrelevant.
For non-scale-invariant power spectra, if all PBHs which form at given epoch
have a fixed mass then the PBH mass function is sharply peaked around that
mass, whilst if the PBH mass depends on the size of the density perturbation
from which it forms, as is expected when critical phenomena are taken into
account, then the PBH mass function will be far broader than . In this paper we calculate the present day PBH evaporation rate,
using constraints from the diffuse gamma-ray background, for both of these mass
functions. If the PBH mass function has significant finite width, as recent
numerical simulations suggest, then it is not possible to produce a present day
PBH evaporation rate comparable with the observed short period gamma-ray burst
rate. This could also have implications for other attempts to detect
evaporating PBHs.Comment: 5 pages, 2 figures, version to appear in Phys. Rev. D with additional
reference
Gamma-Ray Burst Arrival-Time Localizations: Simultaneous Observations by Ulysses, Pioneer Venus Orbiter, SIGMA, WATCH, and PHEBUS
Between the launch of the Ulysses spacecraft in 1990 October and the entry of
Pioneer Venus Orbiter (PVO) into the atmosphere of Venus in 1992 October,
concurrent coverage by Ulysses, PVO, the WATCH experiments aboard the Granat
and EURECA spacecraft, and the SIGMA and PHEBUS experiments aboard the Granat
spacecraft was obtained for numerous gamma-ray bursts. 15 of them were detected
by 3 or more instruments on spacecraft separated by distances of several AU,
and could therefore be accurately localized by triangulation. In some cases
independent, accurate locations were obtained by SIGMA and/or WATCH. We present
these localizations, which range in area from 0.9 to 530 arcminutes.Comment: Accepted for publication in the Astrophysical Journal Supplements,
May 200
The observational legacy of preon stars - probing new physics beyond the LHC
We discuss possible ways to observationally detect the superdense cosmic
objects composed of hypothetical sub-constituent fermions beneath the
quark/lepton level, recently proposed by us. The characteristic mass and size
of such objects depend on the compositeness scale, and their huge density
cannot arise within a context of quarks and leptons alone. Their eventual
observation would therefore be a direct vindication of physics beyond the
standard model of particle physics, possibly far beyond the reach of the Large
Hadron Collider (LHC), in a relatively simple and inexpensive manner. If relic
objects of this type exist, they can possibly be detected by present and future
x-ray observatories, high-frequency gravitational wave detectors, and
seismological detectors. To have a realistic detection rate, i.e., to be
observable, they must necessarily constitute a significant fraction of cold
dark matter.Comment: 8 pages, 4 figures. Added one reference [24]. Reformulated the
discussion at the end of Section II. Accepted for publication in Phys. Rev.
A giant, periodic flare from the soft gamma repeater SGR1900+14
Soft gamma repeaters are high-energy transient sources associated with
neutron stars in young supernova remnants. They emit sporadic, short (~ 0.1 s)
bursts with soft energy spectra during periods of intense activity. The event
of March 5, 1979 was the most intense and the only clearly periodic one to
date. Here we report on an even more intense burst on August 27, 1998, from a
different soft gamma repeater, which displayed a hard energy spectrum at its
peak, and was followed by a ~300 s long tail with a soft energy spectrum and a
dramatic 5.16 s period. Its peak and time integrated energy fluxes at Earth are
the largest yet observed from any cosmic source. This event was probably
initiated by a massive disruption of the neutron star crust, followed by an
outflow of energetic particles rotating with the period of the star. Comparison
of these two bursts supports the idea that magnetic energy plays an important
role, and that such giant flares, while rare, are not unique, and may occur at
any time in the neutron star's activity cycle.Comment: Accepted for publication in Natur
Three precise gamma-ray burst source locations
The precise source regions of three moderately intense gamma ray bursts are derived. These events were observed with the first interplanetary burst sensor network. The optimum locations of the detectors, widely separated throughout the inner solar system, allowed for high accuracy, over-determined source fields of size 0.7 to 7.0 arc-min(2). All three locations are at fairly high galactic latitude in regions of low source confusion; none can be identified with a steady source object. Archived photographs were searched for optical transients that are able to be associated with these source fields; one such association was made
A second catalog of gamma ray bursts: 1978 - 1980 localizations from the interplanetary network
Eighty-two gamma ray bursts were detected between 1978 September 14 and 1980 February 13 by the experiments of the interplanetary network (Prognoz 7, Venera 11 and 12 SIGNE experiments, Pioneer Venus Orbiter, International Sun-Earth Explorer 3, Helios 2, and Vela). Sixty-five of these events have been localized to annuli or error boxes by the method of arrival time analysis. The distribution of sources is consistent with isotropy, and there is no statistically convincing evidence for the detection of more than one burst from any source position. The localizations are compared with those of two previous catalogs
Data reduction and analysis for ISEE-A and -B energetic particles flux experiment and ISEE-C electron and X-ray experiments
A summary of the data reduction and analysis activities from late 1979 to late 1983 is presented. A bibliography of publications is included
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