77 research outputs found
Telescope performance and image simulations of the balloon-borne coded-mask protoMIRAX experiment
In this work we present the results of imaging simulations performed with the
help of the GEANT4 package for the protoMIRAX hard X-ray balloon experiment.
The instrumental background was simulated taking into account the various
radiation components and their angular dependence, as well as a detailed mass
model of the experiment. We modeled the meridian transits of the Crab Nebula
and the Galatic Centre region during balloon flights in Brazil ( of latitude and an altitude of km) and
introduced the correspondent spectra as inputs to the imaging simulations. We
present images of the Crab and of three sources in the Galactic Centre region:
1E 1740.7-2942, GRS 1758-258 and GX 1+4. The results show that the protoMIRAX
experiment is capable of making spectral and timing observations of bright hard
X-ray sources as well as important imaging demonstrations that will contribute
to the design of the MIRAX satellite mission.Comment: 9 figure
A common behavior in the late X-ray afterglow of energetic GRB-SN systems
The possibility to divide GRBs in different subclasses allow to understand
better the physics underlying their emission mechanisms and progenitors. The
induced gravitational collapse scenario proposes a binary progenitor to explain
the time-sequence in GRBs-SNe. We show the existence of a common behavior of
the late decay of the X-ray afterglow emission of this subclass of GRBs,
pointing to a common physical mechanism of their late emission, consistent with
the IGC picture.Comment: 3 pages, to appear in the proceedings of the Gamma-Ray Burst
Symposium 2012 - IAA-CSIC - Marbella, editors: Castro-Tirado, A. J.,
Gorosabel, J. and Park, I.
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
GRB 081024B and GRB 140402A: two additional short GRBs from binary neutron star mergers
Theoretical and observational evidences have been recently gained for a
two-fold classification of short bursts: 1) short gamma-ray flashes (S-GRFs),
with isotropic energy ~erg and no BH formation, and 2) the
authentic short gamma-ray bursts (S-GRBs), with isotropic energy
~erg evidencing a BH formation in the binary neutron star
merging process. The signature for the BH formation consists in the on-set of
the high energy (--~GeV) emission, coeval to the prompt emission, in
all S-GRBs. No GeV emission is expected nor observed in the S-GRFs. In this
paper we present two additional S-GRBs, GRB 081024B and GRB 140402A, following
the already identified S-GRBs, i.e., GRB 090227B, GRB 090510 and GRB 140619B.
We also return on the absence of the GeV emission of the S-GRB 090227B, at an
angle of from the \textit{Fermi}-LAT boresight. All the correctly
identified S-GRBs correlate to the high energy emission, implying no
significant presence of beaming in the GeV emission. The existence of a common
power-law behavior in the GeV luminosities, following the BH formation, when
measured in the source rest-frame, points to a commonality in the mass and spin
of the newly-formed BH in all S-GRBs.Comment: 16 pages, submitted to ApJ, second version addressing the comments by
the refere
The protoMIRAX Hard X-ray Imaging Balloon Experiment
The protoMIRAX hard X-ray imaging telescope is a balloon-borne experiment
developed as a pathfinder for the MIRAX satellite mission. The experiment
consists essentially in a coded-aperture hard X-ray (30-200 keV) imager with a
square array (1313) of 2mm-thick planar CZT detectors with a total area
of 169 cm. The total, fully-coded field-of-view is and the angular resolution is 143'. In this paper we
describe the protoMIRAX instrument and all the subsystems of its balloon
gondola, and we show simulated results of the instrument performance. The main
objective of protoMIRAX is to carry out imaging spectroscopy of selected bright
sources to demonstrate the performance of a prototype of the MIRAX hard X-ray
imager. Detailed background and imaging simulations have been performed for
protoMIRAX balloon flights. The 3 sensitivity for the 30-200 keV range
is ~1.9 10 photons cm s for an integration time
of 8 hs at an atmospheric depth of 2.7 g cm and an average zenith angle
of 30. We have developed an attitude control system for the balloon
gondola and new data handling and ground systems that also include prototypes
for the MIRAX satellite. We present the results of Monte Carlo simulations of
the camera response at balloon altitudes, showing the expected background level
and the detailed sensitivity of protoMIRAX. We also present the results of
imaging simulations of the Crab region. The results show that protoMIRAX is
capable of making spectral and imaging observations of bright hard X-ray source
fields. Furthermore, the balloon observations will carry out very important
tests and demonstrations of MIRAX hardware and software in a near space
environment.Comment: 9 pages, 13 figures, accepted for publication in Astronomy &
Astrophysic
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