More than fifty years have elapsed from the first discovery of gamma-ray bursts (GRBs) with American Vela satellites, and more than twenty-five years from the discovery with the BeppoSAX satellite of ...the first X-ray afterglow of a GRB. Thanks to the afterglow discovery and to the possibility given to the optical and radio astronomers to discover the GRB optical counterparts, the long-time mystery about the origin of these events has been solved. Now we know that GRBs are huge explosions, mainly ultra relativistic jets, in galaxies at cosmological distances. Starting from the first GRB detection with the Vela satellites, I will review the story of these discoveries, those obtained with BeppoSAX, the contribution to GRBs by other satellites and ground experiments, among them being Venera, Compton Gamma Ray Observatory, HETE-2, Swift, Fermi, AGILE, MAGIC, H.E.S.S., which were, and some of them are still, very important for the study of GRB properties. Then, I will review the main results obtained thus far and the still open problems and prospects of GRB astronomy.
The key role of BeppoSAX in the GRB history Frontera, Filippo
Atti della Accademia nazionale dei Lincei. Rendiconti Lincei. Scienze fisiche e naturali,
12/2019, Letnik:
30, Številka:
Suppl 1
Journal Article
Recenzirano
Twenty years have already been elapsed from the
BeppoSAX
discovery of the first afterglow of a Gamma-Ray Burst (GRB) in February 28, 1997. Thanks to this discovery, it was possible to unveil the 30 ...year mystery about GRB origin: GRBs are huge explosions in galaxies at cosmological distances. Starting from the first GRB detection with Vela satellites, I will review the main results obtained before
BeppoSAX
, the story of the
BeppoSAX
discovery of the GRB afterglow with the consequent cosmological distance determination, the main
BeppoSAX
results, and those obtained after the
BeppoSAX
era until nowadays with the still open problems and prospects.
ABSTRACT
Gamma-ray bursts (GRBs) are known to be highly collimated events, and are mostly detectable when they are seen on-axis or very nearly on-axis. However, GRBs can be seen from off-axis angles, ...and the recent detection of a short GRB associated with a gravitational wave event has conclusively shown such a scenario. The observer viewing angle plays an important role in the observable spectral shape and the energetic of such events. We present a numerical model that is based on the single-pulse approximation with emission from a top-hat jet and has been developed to investigate the effects of the observer viewing angle. We assume a conical jet parametrized by a radius Rjet, half-opening angle θjet, a comoving-frame emissivity law and an observer viewing angle θobs, and then study the effects for the conditions θobs < θjet and θobs > θjet. We present results considering a smoothly broken power-law emissivity law in jet comoving frame, albeit the model implementation easily allows to consider other emissivity laws. We find that the relation $E^{\rm i}_{\rm p}\propto E_{\rm iso}^{0.5}$ (Amati relation) is naturally obtained from pure relativistic kinematic when $\Gamma \gtrsim 10$ and θobs < θjet; on the contrary, when θobs > θjet it results $E^{\rm i}_{\rm p}\propto E_{\rm iso}^{0.25}$. Using data from literature for a class of well-know sub-energetic GRBs, we show that their position in the $E^{\rm i}_{\rm p}\!-\!E_{\rm iso}$ plane is consistent with event observed off-axis. The presented model is developed as a module to be integrated in spectral fitting software package xspec and can be used by the scientific community.
We have developed a new model for the X-ray spectral fitting package XSPEC that takes into account the effects of both thermal and dynamical (i.e., bulk) Comptonization. The model consists of two ...components: one is the direct blackbody-like emission due to seed photons that are not subjected to effective Compton scattering, while the other is a convolution of the Green's function of the energy operator with a blackbody-like seed photon spectrum. When combined thermal and bulk effects are considered, the analytical form of the Green's function may be obtained as a solution of the diffusion equation describing Comptonization. Using data from the BeppoSAX, INTEGRAL, and RXTE satellites, we test our model on the spectra of a sample of six bright neutron star low-mass X-ray binaries with low magnetic fields, covering three different spectral states. Particular attention is given to the transient power-law-like hard X-ray (image30 keV) tails, which we interpret in the framework of the bulk motion Comptonization process. We show that the values of the best-fit delta -parameter, which represents the importance of bulk with respect to thermal Comptonization, can be physically meaningful and can at least qualitatively describe the physical conditions of the environment in the innermost part of the system. Moreover, we show that in fitting the thermal Comptonization spectra to the X-ray spectra of these systems, the best-fit parameters of our model are in excellent agreement with those from compTT, a broadly used and well-established XSPEC model.
We analyze the X-ray spectra and their timing properties of the compact X-ray binary 4U 1820-30. We establish spectral transitions in this source seen with BeppoSAX and the Rossi X-ray Timing ...Explorer (RXTE). During the RXTE observations (1996-2009), the source was in the soft state approximately ~75% of the time making the lower banana and upper banana transitions combined with long-term low-high state transitions. We reveal that all of the X-ray spectra of 4U 1820-30 are fit by a combination of a thermal (Blackbody) component, a Comptonization component (COMPTB), and a Gaussian-line component. Thus, using this spectral analysis, we find that the photon power-law index Gamma of the Comptonization component is almost unchangeable (Gamma ~ 2), while the electron temperature kTe changes from 2.9 to 21 keV during these spectral events. We also establish that for these spectral events the normalization of the COMPTB component (which is proportional to the mass accretion rate M) increases by a factor of eight when kTe decreases from 21 keV to 2.9 keV. Previously, this index stability effect was also found analyzing X-ray data for the Z-source GX 340+0 and for the atolls 4U 1728-34 and GX 3+1. Thus, we can suggest that this spectral stability property is a spectral signature of an accreting neutron star source. On the other hand, in a black hole binary Gamma monotonically increases with M and ultimately its value saturates at large M.
Broadband power density spectra offer a window to understanding turbulent behavior in the emission mechanism and, at the highest frequencies, in the putative inner engines powering long gamma-ray ...bursts (GRBs). We describe a chirp search method alongside Fourier analysis for signal detection in the Poisson noise-dominated, 2 kHz sampled, BeppoSAX light curves. An efficient numerical implementation is described in O(Nn log n) operations, where N is the number of chirp templates and n is the length of the light-curve time series, suited for embarrassingly parallel processing. For the detection of individual chirps over a 1 s duration, the method is one order of magnitude more sensitive in signal-to-noise ratio than Fourier analysis. The Fourier-chirp spectra of GRB 010408 and GRB 970816 show a continuation of the spectral slope with up to 1 kHz of turbulence identified in low-frequency Fourier analysis. The same continuation is observed in an average spectrum of 42 bright, long GRBs. An outlook on a similar analysis of upcoming gravitational wave data is included.
We report on an accurate measurement of the CXB in the 15-50 keV range performed with the Phoswich Detection System (PDS) instrument aboard the BeppoSAX satellite. We establish that the most likely ...CXB intensity level at its emission peak (26-28 keV) is approximately 40 keV cm super(-2) s super(-1) sr super(-1), a value consistent with that derived from the best available CXB measurement obtained over 25 years ago with the first High Energy Astronomical Observatory (HEAO-1) satellite mission (Gruber et al.), whose intensity, lying well below the extrapolation of some lower energy measurements performed with focusing telescopes, was questioned in recent years. We find that 90% of the acceptable solutions of our best-fit model to the PDS data give a 20-50 keV CXB flux lower than 6.5 x 10 super(-8) ergs cm super(-2) s super(-1) sr super(-1), which is 12% higher than that quoted by Gruber et al. when we use our best calibration scale. In combination with the CXB synthesis models we infer that about 25% of the intensity at similar to 30 keV arises from extremely obscured, Compton-thick AGNs (absorbing column density N sub(H) > 10 super(24) cm super(-2)), while a much larger population would be implied by the highest intensity estimates. We also infer a mass density of supermassive black holes of similar to 3 x 10 super(5) M unk Mpc super(-3). The summed contribution of resolved sources (Moretti et al.) in the 2-10 keV band exceeds our best-fit CXB intensity extrapolated to lower energies, but it is within our upper limit, so that any significant contribution to the CXB from sources other than AGNs, such as star-forming galaxies and diffuse warm-hot intergalactic medium (WHIM), is expected to be mainly confined below a few keV.
Low-inclination, low altitude Earth orbits (LEO) are of increasing importance for astrophysical satellites, due to their low background environment. Here, the South Atlantic Anomaly (SAA) is the ...region with the highest amount of radiation. We study the radiation environment in a LEO (500–600 km altitude, 4
∘
inclination) through the particle background measured by the Particle Monitor (PM) experiment onboard the
BeppoSAX
satellite, between 1996 and 2002. Using time series of particle count rates measured by PM we construct intensity maps and derive SAA passage times and fluences. The low-latitude SAA regions are found to have an intensity strongly decreasing with altitude and dependent on the magnetic rigidity. The SAA extent, westward drift and strength vs altitude is shown.
Starting from 1960s, a great number of missions and experiments have been performed for the study of the high-energy sky. This review gives a wide vision of the most important space missions and ...balloon experiments that have operated in the 10–600 keV band, a crucial window for the study of the most energetic and violent phenomena in the Universe. Thus it is important to take the stock of the achievements to better establish what we have still to do with future missions in order to progress in this field, to establish which are the technologies required to solve the still open issues and to extend our knowledge of the Universe.
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