399 research outputs found
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
The second Konus-Wind catalog of short gamma-ray bursts
In this catalog, we present the results of a systematic study of 295 short
gamma-ray bursts (GRBs) detected by Konus-Wind (KW) from 1994 to 2010. From the
temporal and spectral analyses of the sample, we provide the burst durations,
the spectral lags, the results of spectral fits with three model functions, the
total energy fluences and the peak energy fluxes of the bursts. We discuss
evidence found for an additional power-law spectral component and the presence
of extended emission in a fraction of the KW short GRBs. Finally, we consider
the results obtained in the context of the Type I (merger-origin) / Type II
(collapsar-origin) classifications.Comment: Accepted to the Astrophysical Journal Supplement Series (7 Figures, 8
Tables
Heterogeneity in Short Gamma-ray Bursts
We analyze the Swift/BAT sample of short gamma-ray bursts, using an objective
Bayesian Block procedure to extract temporal descriptors of the bursts' initial
pulse complexes (IPCs). The sample comprises 12 and 41 bursts with and without
extended emission (EE) components, respectively. IPCs of non-EE bursts are
dominated by single pulse structures, while EE bursts tend to have two or more
pulse structures. The medians of characteristic timescales - durations, pulse
structure widths, and peak intervals - for EE bursts are factors of ~ 2-3
longer than for non-EE bursts. A trend previously reported by Hakkila and
colleagues unifying long and short bursts - the anti-correlation of pulse
intensity and width - continues in the two short burst groups, with non-EE
bursts extending to more intense, narrower pulses. In addition we find that
preceding and succeeding pulse intensities are anti-correlated with pulse
interval. We also examine the short burst X-ray afterglows as observed by the
Swift/XRT. The median flux of the initial XRT detections for EE bursts (~ 6 x
10^-10 erg cm^-2 s^-1) is ~> 20 x brighter than for non-EE bursts, and the
median X-ray afterglow duration for EE bursts (~ 60,000 s) is ~ 30 x longer
than for non-EE bursts.
The tendency for EE bursts toward longer prompt-emission timescales and
higher initial X-ray afterglow fluxes implies larger energy injections powering
the afterglows. The longer-lasting X-ray afterglows of EE bursts may suggest
that a significant fraction explode into more dense environments than non-EE
bursts, or that the sometimes-dominant EE component efficiently powers the
afterglow. Combined, these results favor different progenitors for EE and
non-EE short bursts.Comment: 30 pages, 11 figures, 3 tables; accepted to The Astrophysical Journa
An Extended Burst Tail from SGR 1900+14 with a Thermal X-ray Spectrum
The Soft Gamma Repeater, SGR 1900+14, entered a new phase of activity in
April 2001 initiated by the intermediate flare recorded on April 18. Ten days
following this flare, we discovered an abrupt increase in the source flux
between consecutive RXTE orbits. This X-ray flux excess decayed over the next
several minutes and was subsequently linked to a high fluence burst from SGR
1900+14 recorded by other spacecraft (Ulysses and KONUS) while the SGR was
Earth-occulted for RXTE. We present here spectral and temporal analysis of both
the burst of 28 April and the long X-ray tail following it. We find strong
evidence of an exclusively thermal X-ray tail in this event and bring this
evidence to bear on other bursts and flares from SGR 1900+14 which have shown
extended X-ray excesses (e.g. 1998 August 29). We include in this comparison a
discussion of the physical origins of SGR bursts and extended X-ray tails.Comment: 27 pages, 13 figures, ApJ submissio
How Advanced Change Patterns Impact the Process of Process Modeling
Process model quality has been an area of considerable research efforts. In
this context, correctness-by-construction as enabled by change patterns
provides promising perspectives. While the process of process modeling (PPM)
based on change primitives has been thoroughly investigated, only little is
known about the PPM based on change patterns. In particular, it is unclear what
set of change patterns should be provided and how the available change pattern
set impacts the PPM. To obtain a better understanding of the latter as well as
the (subjective) perceptions of process modelers, the arising challenges, and
the pros and cons of different change pattern sets we conduct a controlled
experiment. Our results indicate that process modelers face similar challenges
irrespective of the used change pattern set (core pattern set versus extended
pattern set, which adds two advanced change patterns to the core patterns set).
An extended change pattern set, however, is perceived as more difficult to use,
yielding a higher mental effort. Moreover, our results indicate that more
advanced patterns were only used to a limited extent and frequently applied
incorrectly, thus, lowering the potential benefits of an extended pattern set
Precise interplanetary network localization of a new soft gamma repeater, SGR 1627-41
We present Ulysses, KONUS-WIND, and BATSE observations of bursts from a new
soft gamma repeater which was active in 1998 June and July. Triangulation of
the bursts results in a ~ 1.8 degree by 16 '' error box whose area is ~ 7.6
arcminutes^2, which contains the Galactic supernova remnant G337.0-0.1. This
error box intersects the position of a BeppoSAX X-ray source which is also
consistent with the position of G337.0-0.1 (Woods et al. 1999), and is thought
to be the quiescent counterpart to the repeater. If so, the resulting error box
is ~ 2 ' by 16 '' and has an area of ~ 0.6 arcminutes^2. The error box location
within the supernova remnant suggests that the neutron star has a transverse
velocity of ~ 200 - 2000 km/s.Comment: 15 pages, 2 figures, submitted to ApJ Letter
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