13,103 research outputs found
GRB970228 and the class of GRBs with an initial spikelike emission: do they follow the Amati relation?
On the basis of the recent understanding of GRB050315 and GRB060218, we
return to GRB970228, the first Gamma-Ray Burst (GRB) with detected afterglow.
We proposed it as the prototype for a new class of GRBs with "an occasional
softer extended emission lasting tenths of seconds after an initial spikelike
emission". Detailed theoretical computation of the GRB970228 light curves in
selected energy bands for the prompt emission are presented and compared with
observational BeppoSAX data. From our analysis we conclude that GRB970228 and
likely the ones of the above mentioned new class of GRBs are "canonical GRBs"
have only one peculiarity: they exploded in a galactic environment, possibly
the halo, with a very low value of CBM density. Here we investigate how
GRB970228 unveils another peculiarity of this class of GRBs: they do not
fulfill the "Amati relation". We provide a theoretical explanation within the
fireshell model for the apparent absence of such correlation for the GRBs
belonging to this new class.Comment: 5 pages, 3 figures, in the Proceedings of the "4th Italian-Sino
Workshop on Relativistic Astrophysics", held in Pescara, Italy, July 20-28,
2007, C.L. Bianco, S.-S. Xue, Editor
On the physical processes which lie at the bases of time variability of GRBs
The relative-space-time-transformation (RSTT) paradigm and the interpretation
of the burst-structure (IBS) paradigm are applied to probe the origin of the
time variability of GRBs. Again GRB 991216 is used as a prototypical case,
thanks to the precise data from the CGRO, RXTE and Chandra satellites. It is
found that with the exception of the relatively inconspicuous but
scientifically very important signal originating from the initial ``proper
gamma ray burst'' (P-GRB), all the other spikes and time variabilities can be
explained by the interaction of the accelerated-baryonic-matter pulse with
inhomogeneities in the interstellar matter. This can be demonstrated by using
the RSTT paradigm as well as the IBS paradigm, to trace a typical spike
observed in arrival time back to the corresponding one in the laboratory time.
Using these paradigms, the identification of the physical nature of the time
variablity of the GRBs can be made most convincingly. It is made explicit the
dependence of a) the intensities of the afterglow, b) the spikes amplitude and
c) the actual time structure on the Lorentz gamma factor of the
accelerated-baryonic-matter pulse. In principle it is possible to read off from
the spike structure the detailed density contrast of the interstellar medium in
the host galaxy, even at very high redshift.Comment: 11 pages, 5 figure
The EMBH model in GRB 991216 and GRB 980425
This is a summary of the two talks presented at the Rome GRB meeting by C.L.
Bianco and R. Ruffini. It is shown that by respecting the Relative Space-Time
Transformation (RSTT) paradigm and the Interpretation of the Burst Structure
(IBS) paradigm, important inferences are possible: a) in the new physics
occurring in the energy sources of GRBs, b) on the structure of the bursts and
c) on the composition of the interstellar matter surrounding the source.Comment: 8 pages, 3 figures, in the Proceedings of the "Third Rome Workshop on
Gamma-Ray Bursts in the Afterglow Era", 17-20 September 2002, M. Feroci, F.
Frontera, N. Masetti, L. Piro (editors
The Amati relation in the "fireshell" model
(Shortened) CONTEXT: [...] AIMS: Motivated by the relation proposed by Amati
and collaborators, we look within the ``fireshell'' model for a relation
between the peak energy E_p of the \nu F_\nu total time-integrated spectrum of
the afterglow and the total energy of the afterglow E_{aft}, which in our model
encompasses and extends the prompt emission. METODS: [...] Within the fireshell
model [...] We can then build two sets of ``gedanken'' GRBs varying the total
energy of the electron-positron plasma E^{e^\pm}_{tot} and keeping the same
baryon loading B of GRB050315. The first set assumes for the effective CBM
density the one obtained in the fit of GRB050315. The second set assumes
instead a constant CBM density equal to the average value of the GRB050315
prompt phase. RESULTS: For the first set of ``gedanken'' GRBs we find a
relation E_p\propto (E_{aft})^a, with a = 0.45 \pm 0.01, whose slope strictly
agrees with the Amati one. Such a relation, in the limit B \to 10^{-2},
coincides with the Amati one. Instead, in the second set of ``gedanken'' GRBs
no correlation is found. CONCLUSIONS: Our analysis excludes the Proper-GRB
(P-GRB) from the prompt emission, extends all the way to the latest afterglow
phases and is independent on the assumed cosmological model, since all
``gedanken'' GRBs are at the same redshift. The Amati relation, on the other
hand, includes also the P-GRB, focuses on the prompt emission only, and is
therefore influenced by the instrumental threshold which fixes the end of the
prompt emission, and depends on the assumed cosmology. This may well explain
the intrinsic scatter observed in the Amati relation.Comment: 4 pages, 5 figures, to appear on A&A Letter
A Robust Filter for the BeppoSAX Gamma Ray Burst Monitor Triggers
The BeppoSAX Gamma Ray Burst Monitor (GRBM) is triggered any time a
statistically significant counting excess is simultaneously revealed by at
least two of its four independent detectors. Several spurious effects,
including highly ionizing particles crossing two detectors, are recorded as
onboard triggers. In fact, a large number of false triggers is detected, in the
order of 10/day. A software code, based on an heuristic algorithm, was written
to discriminate between real and false triggers. We present the results of the
analysis on an homogeneous sample of GRBM triggers, thus providing an estimate
of the efficiency of the GRB detection system consisting of the GRBM and the
software.Comment: Proc. 5th Huntsville GRB Symposiu
On the thermal and double episode emissions in GRB 970828
Following the recent theoretical interpretation of GRB 090618 and GRB 101023,
we here interpret GRB 970828 in terms of a double episode emission: the first
episode, observed in the first 40 s of the emission, is interpreted as the
proto-black-hole emission; the second episode, observed after t+50 s, as a
canonical gamma ray burst. The transition between the two episodes marks the
black hole formation. The characteristics of the real GRB, in the second
episode, are an energy of erg, a
baryon load of and a bulk Lorentz factor at transparency
of . The clear analogy with GRB 090618 would require also in
GRB 970828 the presence of a possible supernova. We also infer that the GRB
exploded in an environment with a large average particle density part/cm and dense clouds characterized by typical dimensions
of cm and . Such an environment
is in line with the observed large column density absorption, which might have
darkened both the supernova emission and the GRB optical afterglow.Comment: 7 pages, 10 figures, submitted to Ap
Induced gravitational collapse at extreme cosmological distances: the case of GRB 090423
CONTEXT: The induced gravitational collapse (IGC) scenario has been
introduced in order to explain the most energetic gamma ray bursts (GRBs),
Eiso=10^{52}-10^{54}erg, associated with type Ib/c supernovae (SNe). It has led
to the concept of binary-driven hypernovae (BdHNe) originating in a tight
binary system composed by a FeCO core on the verge of a SN explosion and a
companion neutron star (NS). Their evolution is characterized by a rapid
sequence of events: [...]. AIMS: We investigate whether GRB 090423, one of the
farthest observed GRB at z=8.2, is a member of the BdHN family. METHODS: We
compare and contrast the spectra, the luminosity evolution and the
detectability in the observations by Swift of GRB 090423 with the corresponding
ones of the best known BdHN case, GRB 090618. RESULTS: Identification of
constant slope power-law behavior in the late X-ray emission of GRB 090423 and
its overlapping with the corresponding one in GRB 090618, measured in a common
rest frame, represents the main result of this article. This result represents
a very significant step on the way to using the scaling law properties, proven
in Episode 3 of this BdHN family, as a cosmological standard candle.
CONCLUSIONS: Having identified GRB 090423 as a member of the BdHN family, we
can conclude that SN events, leading to NS formation, can already occur already
at z=8.2, namely at 650 Myr after the Big Bang. It is then possible that these
BdHNe originate stem from 40-60 M_{\odot} binaries. They are probing the
Population II stars after the completion and possible disappearance of
Population III stars.Comment: 9 pages, 9 figures, to appear on A&
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