592 research outputs found
'On the difference between the short and long gamma-ray bursts'
We argue that the distributions of both the intrinsic fluence and the
intrinsic duration of the gamma-ray emission in gamma-ray bursts from the BATSE
sample are well represented by log-normal distributions, in which the intrinsic
dispersion is much larger than the cosmological time dilatation and redshift
effects. We perform separate bivariate log-normal distribution fits to the
BATSE short and long burst samples. The bivariate log-normal behaviour results
in an ellipsoidal distribution, whose major axis determines an overall
statistical relation between the fluence and the duration. We show that this
fit provides evidence for a power-law dependence between the fluence and the
duration, with a statistically significant different index for the long and
short groups. We discuss possible biases, which might affect this result, and
argue that the effect is probably real. This may provide a potentially useful
constraint for models of long and short bursts.Comment: A.A. in press ; significantly revised version of astro-ph/0007438; 16
pages 5 PS figure
Gamma photometric redshifts for long gamma-ray bursts
It is known that the soft tail of the gamma-ray bursts' spectra show excesses
from the exact power-law dependence. In this article we show that this
departure can be detected in the peak flux ratios of different BATSE DISCSC
energy channels. This effect allows to estimate the redshift of the bright long
gamma-ray bursts in the BATSE Catalog. A verification of these redshifts is
obtained for the 8 GRB which have both BATSE DISCSC data and measured optical
spectroscopic redshifts. There is good correlation between the measured and
esti redshifts, and the average error is . The method is
similar to the photometric redshift estimation of galaxies in the optical
range, hence it can be called as "gamma photometric redshift estimation". The
estimated redshifts for the long bright gamma-ray bursts are up to . For the the faint long bursts - which should be up to - the
redshifts cannot be determined unambiguously with this method.Comment: accepted in A&A, 7 pages incl. 7 figure
A Semi-analytic Formulation for Relativistic Blast Waves with a Long-lived Reverse Shock
This paper performs a semi-analytic study of relativistic blast waves in the
context of gamma-ray bursts (GRBs). Although commonly used in a wide range of
analytical and numerical studies, the equation of state (EOS) with a constant
adiabatic index is a poor approximation for relativistic hydrodynamics.
Adopting a more realistic EOS with a variable adiabatic index, we present a
simple form of jump conditions for relativistic hydrodynamical shocks. Then we
describe in detail our technique of modeling a very general class of GRB blast
waves with a long-lived reverse shock. Our technique admits an arbitrary radial
stratification of the ejecta and ambient medium. We use two different methods
to find dynamics of the blast wave: (1) customary pressure balance across the
blast wave and (2) the "mechanical model". Using a simple example model, we
demonstrate that the two methods yield significantly different dynamical
evolutions of the blast wave. We show that the pressure balance does not
satisfy the energy conservation for an adiabatic blast wave while the
mechanical model does. We also compare two sets of afterglow light curves
obtained with the two different methods.Comment: 33 pages, 9 figures, published in Ap
GeV-TeV and X-ray flares from gamma-ray bursts
The recent detection of delayed X-ray flares during the afterglow phase of
gamma-ray bursts (GRBs) suggests an inner-engine origin, at radii inside the
deceleration radius characterizing the beginning of the forward shock afterglow
emission. Given the observed temporal overlapping between the flares and
afterglows, there must be inverse Compton (IC) emission arising from such flare
photons scattered by forward shock afterglow electrons. We find that this IC
emission produces GeV-TeV flares, which may be detected by GLAST and
ground-based TeV telescopes. We speculate that this kind of emission may
already have been detected by EGRET from a very strong burst--GRB940217. The
enhanced cooling of the forward shock electrons by the X-ray flare photons may
suppress the synchrotron emission of the afterglows during the flare period.
The detection of GeV-TeV flares combined with low energy observations may help
to constrain the poorly known magnetic field in afterglow shocks. We also
consider the self-IC emission in the context of internal-shock and
external-shock models for X-ray flares. The emission above GeV from internal
shocks is low, while the external shock model can also produce GeV-TeV flares,
but with a different temporal behavior from that caused by IC scattering of
flare photons by afterglow electrons. This suggests a useful approach for
distinguishing whether X-ray flares originate from late central engine activity
or from external shocks.Comment: slightly shortened version, accepted for publication in ApJ Letters,
4 emulateapj pages, no figure
Dependence of the optical brightness on the gamma and X-ray properties of GRBs
The Swift satellite made a real break through with measuring simultaneously
the gamma X-ray and optical data of GRBs, effectively. Although, the satellite
measures the gamma, X-ray and optical properties almost in the same time a
significant fractions of GRBs remain undetected in the optical domain. In a
large number of cases only an upper bound is obtained. Survival analysis is a
tool for studying samples where a part of the cases has only an upper (lower)
limit. The obtained survival function may depend on some other variables. The
Cox regression is a way to study these dependencies. We studied the dependence
of the optical brightness (obtained by the UVOT) on the gamma and X-ray
properties, measured by the BAT and XRT on board of the Swift satellite. We
showed that the gamma peak flux has the greatest impact on the afterglow's
optical brightness while the gamma photon index and the X-ray flux do not. This
effect probably originates in the energetics of the jet launched from the
central engine of the GRB which triggers the afterglow.Comment: 2012 Fermi Symposium proceedings - eConf C12102
Gamma-ray Burst Afterglow with Continuous Energy Injection: Signature of a Highly-Magnetized Millisecond Pulsar
We investigate the consequences of a continuously injecting central engine on
the gamma-ray burst afterglow emission, focusing more specifically on a
highly-magnetized millisecond pulsar engine. For initial pulsar parameters
within a certain region of the parameter space, the afterglow lightcurves are
predicted to show a distinctive achromatic bump feature, the onset and duration
of which range from minutes to months, depending on the pulsar and the fireball
parameters. The detection of or upper limits on such features would provide
constraints on the burst progenitor and on magnetar-like central engine models.
An achromatic bump such as that in GRB 000301C afterglow may be caused by a
millisecond pulsar with P0=3.4 millisecond and Bp=2.7e14 Gauss.Comment: 5 pages, emulateapj style, to appear in ApJ Letters, updated with the
accepted version, a few corrections are mad
Detailed Classification of Swift's Gamma-Ray Bursts
Earlier classification analyses found three types of gamma-ray bursts (short,
long and intermediate in duration) in the BATSE sample. Recent works have shown
that these three groups are also present in the RHESSI and the BeppoSAX
databases. The duration distribution analysis of the bursts observed by the
Swift satellite also favors the three-component model. In this paper, we extend
the analysis of the Swift data with spectral information. We show, using the
spectral hardness and the duration simultaneously, that the maximum likelihood
method favors the three-component against the two-component model. The
likelihood also shows that a fourth component is not needed.Comment: Accepted for publication in The Astrophysical Journa
Temporal-spatial Patterns of Noctuinae Communities (Lep. Noctuidae) in Hungarian Apple Orchards (Apple Ecosystem Research)
In our present study we aimed to recognize the temporal and spatial patterns of Noctuinae communities (Lep.Noctuidae) of four differently managed apple orchards laying in different localities of Hungary. Data were obtained by light trap collection. The quantitative data resulting from our investigations were analyzed by multivariate methods and were also analyzed by their diversity characteristics.As a result connections were found regarding the diversities of species and individuals, the patterns of occurrence and phenological properties. The studies were based on 8497 individuals of 39 species
A possible interrelation between the estimated luminosity distances and internal extinctions of type Ia supernovae
We studied the statistical properties of the luminosity distance and internal extinction data of type Ia supernovae in the lists published by Tonry et al. (2003) and Barris et al. (2004). After selecting the luminosity distance in an empty Universe as a reference level we divided the sample into low and high parts. We further divided these subsamples by the median of the internal extinction. Performing sign tests using the standardized residuals between the estimated logarithmic luminosity distances and those of an empty universe, on the four subsamples separately, we recognized that the residuals were distributed symmetrically in the low redshift region, independently from the internal extinction. On the contrary, the low extinction part of the data of clearly showed an excess of the points with respect to an empty Universe which was not the case in the high extinction region. This diversity pointed to an interrelation between the estimated luminosity distance and internal extinction. To characterize quantitatively this interrelation we introduced a hidden variable making use of the technics of factor analysis. After subtracting that part of the residual which was explained by the hiddenmaking use of the technics of factor analysis. After subtracting that part of the residual which was explained by the hidden variable we obtained luminosity distances which were already free from interrelation with internal extinction. Fitting the corrected luminosity distances with cosmological models we concluded that the SN Ia data alone did not exclude the possibility of the solution
- âŠ