816 research outputs found
GLAST observation of high-redshift GRBs
No full textWe compare predicted Type Ib/c supernova (SNIb/c) rates with the observed long-duration Gamma-Ray-Burst (GRB) rates both locally and as a function of redshift, by assuming different star formation histories in galaxies of different morphological types. Due to the high star formation in spheroids at high redshift, we predict a large number of GRBs beyond z > 1. Moreover, based on our studies and on the current LAT performance, an estimate of the detection possibility of this burst population is presented. © 2007 American Institute of Physics
The Fermi gamma-ray burst monitor: results from the first year and spectral analysis of GRB 090323 and GRB 090328
No full textIn the first year since the launch of the Fermi Observatory, the Gamma-ray Burst Monitor (GBM) has detected over 250 gamma-ray bursts (GRBs). Besides GRBs, GBM has triggered on other transient sources, such as soft gamma-ray repeaters and terrestrial gamma-ray flashes. Here we present an overview of the capabilities and scientific goals of the GBM, both by itself and in conjunction with the Large Area Telescope (LAT). The wide energy coverage of the two instruments gives an unprecedented view of the broadband emission and energetics of GRBs, spanning almost 7 decades in energy. Out of a total of 9 LAT GRBs detected up to July 31, 2009, 8 showed extended emission. GBM spectral analysis results from two such events, GRBs 090323 and 090328, are discussed. © 2010 American Institute of Physics
The 52 brightest and hardest GRBs detected with the Gamma‐ray Burst Monitor on Fermi
No full textWe present our results of the temporal and spectral analysis of a sample of 52 bright and hard gamma-ray bursts (GRBs) observed with the Fermi Gamma-ray Burst Monitor (GBM) during its first year of operation (July 2008 - July 2009). Our sample was selected from a total of 253 GBM GRBs based on the event peak count rate measured between 0.2 and 40 MeV. The final sample comprised 34 long and 18 short GRBs. A first by-product of our selection methodology is the determination of a detection threshold from the GBM data alone, above which GRBs most likely will be detected in the MeV/GeV range with the Large Area Telescope (LAT) onboard Fermi. This predictor will be very useful for future multiwavelength GRB follow ups with ground and space based observatories. Further we have estimated the burst durations up to 10MeV and for the first time expanded the duration-energy relationship in the GRB light curves to high energies. Finally, we performed time-integrated spectral analysis of all 52 bursts and compared their spectral parameters with those obtained with the larger data sample of the BATSE data. We find that the two parameter data sets are similar and confirm that short GRBs are in general harder than longer ones. © 2011 American Institute of Physics
GRB 090323 and GRB 090328: two long high-energy GRBs detected with Fermi
No full textWe present the analysis of two long Gamma-Ray Bursts, GRB 090323 and GRB 090328, which triggered the Fermi Gamma-Ray Burst Monitor (GBM) and generated an Autonomous Repoint Request to the Fermi Large Area Telescope. The GBM light curves show multi-peaked structures for both events. Here, we present time-integrated and time-resolved burst spectra fitted with different models by the GBM detectors
The Cerenkov telescope array project status
No full textThe Cherenkov Telescope Array (CTA) represents the next generation ground-based observatory for gamma-ray astronomy at very-high energies. It will be capable of detecting gamma rays in the energy range from 20 GeV to more than 300 TeV with unprecedented precision in energy and directional reconstruction. CTA will be located in the northern hemisphere at La Palma, Spain, and in the southern hemisphere at Paranal, Chile, and will comprise more than 100 telescopes of three different types. CTA will be one of the largest astronomical infrastuctures in the world with open data access and it will address questions in astronomy, astrophysics and fundamental physics in the next decades. In this contribution we will present the status of the CTA construction, discuss the telescope prototypes, highlight the scientific perspectives and the instrument performances
High-redshift gamma-ray burst studies with GLAST
No full textWe compare predicted Type Ib/c supernova (SN) rates with the observed long-duration gamma-ray burst (GRB) rates both locally and as a function of redshift. To do that, we assume different star formation histories in galaxies of different morphological type: ellipticals, spirals and irregulars. In particular, the predicted Type Ib/c SN rate (SNRIb/c) is always higher than the GRB rate, as expected, suggesting that only a small fraction (0.1-1%) of them become GRBs. We predict a ratio between the cosmic GRB rate and the cosmic SNRIb/c in the range 10-2 - 10-3, in agreement with previous estimates. Finally, due to the high star formation in spheroids at high redshift, we predict more GRBs at high redshift than previous estimates, a prediction which awaits to be proven by future observations by GLAST. Based on our studies and on the current LAT performance, an estimate of the detection possibility of this high-redshift burst population is finally presented. © 2007 American Institute of Physics
Modeling of New High Density NUV Sensitive Silicon Photomultiplier
No full textIn recent years, Silicon Photomultipliers (SiPMs) have proven to be very performing devices, especially for those applications where high sensitivity to low intensity light and fast responses are required. A SiPM consists of a system of hundreds or even thousands of p-n junctions connected in parallel and operating in Geiger mode. We performed a modeling of the Near Ultraviolet High Density (NUV-HD) devices produced by Fondazione Bruno Kessler (FBK), trying to infer on the cell capacitance, quenching resistance and parasitic capacitances values. We measured the I-V and C-V responses and carefully studied waveforms acquired from sensors conditioned by a simple trans-impedance amplifier, thus obtaining information on the microscopic characteristic of the device. Results regarding the modeling as a function of the overvoltage will be presented and compared with simulations
Exploring the low-energy domain of LAT-detected GRBs
No full textIn preparation for the Second LAT Gamma-Ray Burst (GRB) catalog, we explore the use of the LAT low-energy (LLE) data selection to detect bursts with gamma-ray energy below 100 MeV. Here we present the sample of GRBs that are detected at these energies through a Bayesian Block analysis of all Fermi Gamma-ray Burst Monitor (GBM) triggers collected in 8 years of Fermi mission. In particular, we compare the temporal characteristics of this sample of GRBs with those of the brightest bursts detected above 1 MeV by the GBM. Finally, we examine the properties of a subset of events which are not detected above 100 MeV (LLE-only GRBs)
The connection between gamma-ray bursts and supernovae Ib/c
No full textContext. It has been established that Gamma-Ray Bursts (GRBs) are connected to Supernovae (SNe) explosions of type Ib/c. Aims. We intend to test whether the hypothesis of type Ib/c SNe from different massive progenitors can reproduce the local GRB rate as well as the GRB rate as a function of redshift. We aim to predict the GRB rate at very high redshift under different assumptions about galaxy formation and star formation histories in galaxies. Methods. We assume different star formation histories in galaxies of different morphological types: ellipticals, spirals and irregulars, which have already been tested in self-consistent galaxy models reproducing both chemical and photometrical properties of galaxies. We explore different hypotheses concerning the progenitors of type Ib/c SNe: i) single massive stars (M > 25 M ⊙, Wolf-Rayet stars), ii) massive close binaries (12-20 M ⊙), and iii) both Wolf-Rayet stars and massive binaries. We conclude that the mixed scenario (iii) is preferable to reproduce the local type Ib/c SN rates in galaxies and we adopt this scenario for comparison with the GRB rates. Results. We find an excellent agreement between the observed GRB local rate and the predicted type Ib/c SN rate in irregular galaxies, when a range for single Wolf-Rayet stars of 40-100 M⊙ is adopted. We also predict the cosmic type Ib/c SN rate by taking into account all the galaxy types in a unitary volume of the Universe and we compare it with the observed cosmic GRB rate as a function of redshift. By assuming the formation of spheroids at high redshift, we predict a cosmic type Ib/c SN rate, which is always higher than the GRB rate, suggesting that only a small fraction (0.1-1%) of type Ib/c SNe become GRBs. In particular, we find a ratio between the cosmic GRB rate and the cosmic type Ib/c rate in the range 10-2-10 -3, in agreement with previous estimates. Finally, due to the high rate of star formation in spheroids at high redshift, which is our preferred scenario for galaxy formation, we predict more GRBs at high redshift than in the hierarchical scenario for galaxy formation, a prediction which remains to be proven by future observations. © ESO 2007
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