In the context of the LAUE project devoted to build a long focal length focusing optics for soft gamma-ray astronomy (70/100 keV to $>$600 keV), we present results of simulation of a Laue lens, based on bent crystals in different assembling configura
tions (quasi-mosaic and reflection-like geometries). The main aim is to significantly overcome the sensitivity limits of the current generation of gamma-ray telescopes and improve the imaging capability.
We propose a model for the spectral formation of Gamma Ray Burst (GRB) prompt emission, where the phenomenological Bands function is usually applied to describe the GRB prompt emission. We suggest that the GRB prompt emission is mainly a result of tw
o upscattering processes. The first process is the Comptonization of relatively cold soft photons of the star off electrons of a hot shell of plasma of temperature T_e of the order of 10^{9} K (or kT_e~100 keV) that moves sub-relativistically with the bulk velocity V_b substantially less than the speed of light c. In this phase, the Comptonization parameter Y is high and the interaction between a blackbody-like soft seed photon population and hot electrons leads to formation of a saturated Comptonization spectrum modified by the sub-relativistic bulk outflow. The second process is an upscattering of the previously Comptonized spectrum by the plasma outflow once it becomes relativistic. This process gives rise to the high-energy power-law component above the peak in the EF(E)-diagram where F(E) is the energy flux. The latter process can be described by a convolution of the Comptonized spectrum with a broken-power-law Green function. Possible physical scenarios for this second upscattering process are discussed. In the framework of our model, we give an interpretation of the Amati relation between the intrinsic spectral peak photon energy and radiated energy or luminosity, and we propose a possible explanation of the GRB temporal variability.
The transient 500 s X-ray pulsar MAXI J1409-619 was discovered by the slit cameras aboard MAXI on October 17, 2010, and soon after accurately localized by Swift. We found that the source position was serendipitously observed in 2000 during BeppoSAX o
bservations of the Galactic plane. Two sources are clearly detected in the MECS: one is consistent with the position of IGR J14043-6148 and the other one with that of MAXI J1409-619. We report on the analysis of this archival BeppoSAX/MECS observation integrated with newly analyzed observation from ASCA and a set of high-energy observations obtained from the offset fields of the BeppoSAX/PDS instrument. For the ON-source observation, the 1.8-100 keV spectrum is fit by an absorbed power law with a photon index Gamma = 0.87_{-0.19}^{+0.29}, corresponding to 2-10 and 15-100 keV unabsorbed fluxes of 2.7E-12 and 4E-11 erg/cm2/s, respectively, and a 2-10 keV luminosity of 7E+34 erg/s for a 15 kpc distance. For a PDS offset field observation, performed about one year later and showing a 15-100 keV flux of 7E-11 erg/cm2/s, we clearly pinpoint three spectral absorption features at 44, 73, and 128 keV, resolved both in the spectral fit and in the Crab ratio. We interpret these not harmonically spaced features as due to cyclotron resonances. The fundamental energy of 44 +/- 3 keV corresponds to a magnetic field strength at the neutron star surface of 3.8E12 (1+z) G, where z is the gravitational redshift. We discuss the nature of the source in the light of its possible counterpart.
We study the time variability and spectral evolution of the Black Hole Candidate source XTE J1650-500 using the BeppoSax wide energy range (0.12-200 keV) observations performed during the 2001 X-ray outburst. The source evolves from a low/hard state
(LHS) toward a high/soft state (HSS). In all states the emergent photon spectrum is described by the sum of Comptonization and soft (disk) blackbody components. In the LHS, the Comptonization component dominates in the resulting spectrum. On the other hand, during the HSS the soft (disk) component is already dominant. In this state the Comptonization part of the spectrum is much softer than that in the LHS (photon index is ~ 2.4 in the HSS vs. that is ~1.7 in the LHS). In the BeppoSAX data we find a strong signature of the index saturation with the mass accretion rate which can be considered as an observational evidence of the converging flow (black hole) in XTE J1650-500. We derive power spectra (PS) of the source time variability in different spectral states as a function of energy band. When the source undergoes a transition to softer states, the PS as a whole is shifted to higher frequencies which can be interpreted as a contraction of the Compton cloud during hard-soft spectral evolution. It is worthwhile to emphasize a detection of a strong low-frequency red noise component in the HSS PS which can be considered a signature of the presence of the strong extended disk in the HSS. Also as a result of our data analysis, we find a very weak sign of K_alpha line appearance in these BeppoSAX data. This finding does not confirm previous claims by Miniutti et al. on the presence of a broad and strongly relativistic iron emission line in this particular set of the BeppoSAX data.
