298 research outputs found
The peak luminosity - peak energy correlation in GRBs
We derive the peak luminosity - peak energy (L_iso - E_peak) correlation
using 22 long Gamma-Ray Bursts (GRBs) with firm redshift measurements. We find
that its slope is similar to the correlation between the time integrated
isotropic emitted energy E_iso and E_peak (Amati et al. 2002). For the 15 GRBs
in our sample with estimated jet opening angle we compute the collimation
corrected peak luminosity L_gamma, and find that it correlates with E_peak.
This has, however, a scatter larger than the correlation between E_peak and
E_gamma (the time integrated emitted energy, corrected for collimation;
Ghirlanda et al. 2004), which we ascribe to the fact that the opening angle is
estimated through the global energetics. We have then selected a large sample
of 442 GRBs with pseudo--redshifts, derived through the lag-luminosity
relation, to test the existence of the L_iso-E_peak correlation. With this
sample we also explore the possibility of a correlation between time resolved
quantities, namely L_iso,p and the peak energy at the peak of emission
E_peak,p.Comment: 5 pages, 5 figures, 2 tables - MNRAS Letters submitte
Black-body components in Gamma-Ray Bursts spectra?
We study 7 Gamma Ray Bursts (GRBs), detected both by the BATSE instrument,
on-board the Compton Gamma Ray Observatory, and by the Wide Field Camera (WFC),
on-board BeppoSAX. These bursts have measured spectroscopic redshifts and are a
sizeable fraction of the bursts defining the correlation between the peak
energy E_peak (i.e. the peak of the vFv spectrum) and the total prompt
isotropic energy E_iso (the so called "Amati" relation). Recent theoretical
interpretations of this correlation assume that black-body emission dominates
the time resolved spectra of GRBs, even if, in the time integrated spectrum,
its presence may be hidden by the change of its temperature and by the dilution
of a possible non-thermal power law component. We perform a time resolved
spectral analysis, and show that the sum of a power-law and a black-body gives
acceptable fits to the time dependent spectra within the BATSE energy range,
but overpredicts the flux in the WFC X-ray range. Moreover, a fit with a cutoff
power-law plus a black-body is consistent with the WFC data, but the black-body
component contributes a negligible fraction of the total flux. On the contrary,
we find that fitting the spectra with a Band model or a simple cutoff power-law
model yields an X-ray flux and spectral slope which well matches the WFC
spectra.Comment: 14 pages, 13 figures, accepted for publication in MNRA
The spectral catalogue of INTEGRAL gamma-ray bursts: results of the joint IBIS/SPI spectral analysis
We present the updated INTEGRAL catalogue of gamma-ray bursts (GRBs) observed
between December 2002 and February 2012. The catalogue contains the spectral
parameters for 59 GRBs localized by the INTEGRAL Burst Alert System (IBAS). We
used the data from the two main instruments on board the INTEGRAL satellite:
the spectrometer SPI (SPectrometer on INTEGRAL) nominally covering the energy
range 18 keV - 8 MeV, and the imager IBIS (the Imager on Board the INTEGRAL
Satellite) operating in the range from 15 keV to 10 MeV. For the spectral
analysis we applied a new data extraction technique, developed in order to
explore the energy regions of highest sensitivity for both instruments, SPI and
IBIS. It allowed us to perform analysis of the GRB spectra over a broad energy
range and to determine the bursts' spectral peak energies. The spectral
analysis was performed on the whole sample of GRBs triggered by IBAS, including
all the events observed in period December 2002 - February 2012. The catalogue
contains the trigger times, burst coordinates, positional errors, durations and
peak fluxes for 28 unpublished GRBs observed between September 2008 and
February 2012. The light curves in 20 - 200 keV energy band of these events
were derived using IBIS data. We compare the prompt emission properties of the
INTEGRAL GRB sample with the BATSE and Fermi samples.Comment: 16 pages, 40 figures, accepted for publication in Astronomy &
Astrophysic
Are GRB 980425 and GRB 031203 real outliers or twins of GRB 060218?
GRB 980425 and GRB 031203 are apparently two outliers with respect to the
correlation between the isotropic equivalent energy E_iso emitted in the prompt
radiation phase and the peak frequency E_peak of the spectrum in a vF(v)
representation (the so-called Amati relation). We discuss if these two bursts
are really different from the others or if their location in the E_iso-E_peak
plane is the result of other effects, such as viewing them off-axis, or through
a scattering screen, or a misinterpretation of their spectral properties. The
latter case seems particularly interesting after GRB 060218, that, unlike GRB
031203 and GRB 980425, had a prompt emission detected both in hard and soft
X-rays which lasted ~2800 seconds. This allowed to determine its E_peak and
total emitted energy. Although it shares with GRB 031203 the total energetics,
it is not an outlier with respect to the Amati correlation. We then investigate
if a hard-to-soft spectral evolution in GRB 031203 and GRB 980425, consistent
with all the observed properties, can give rise to a time integrated spectrum
with an E_peak consistent with the Amati relation.Comment: 13 pages, 9 figures, 2 tables. Accepted for publication in MNRA
GRB 990413: Insight into the thermal phase evolution
GRB 990413 shows a very hard spectrum (with a low energy spectral component
F(E) \propto E^{2.49}) which is well represented by a black body model with
characteristic temperature ~70 keV. It thus belongs to the subset of GRBs which
might be revealing a thermal phase. We find that the temperature/luminosity
evolution is consistent with that found in the other ``thermal'' GRBs. The time
resolved spectral analysis indicates the presence of a second non--thermal
component contributing (for about 1 s) up to 30 per cent of the total flux.
Differently from the other thermal GRBs, GRB 990413 shows significantly high
level of variability and the evolution of the thermal/non--thermal spectral
components is strongly correlated with the flux variations. This GRB thus
offers the unique opportunity to test the standard fireball photospheric and
internal shock phases and their reciprocal influence. GRB 990413 was not
selected on the basis of its spectrum and thus hints to the possibility that
this early behavior might be more common than currently known.Comment: 6 pages, 5 figures, 2 tables. Accepted for publication in MNRAS
Lette
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