Showing papers by "F. Frontera published in 2003"
TL;DR: In this paper, the authors examined the complete set of X-ray afterglow observations of dark and optically bright gamma-ray bursts (GRBs) performed by BeppoSAX through 2001 February.
Abstract: We have examined the complete set of X-ray afterglow observations of dark and optically bright gamma-ray bursts (GRBs) performed by BeppoSAX through 2001 February. X-ray afterglows are detected in ~90% of the cases. We do not find significant differences in the X-ray spectral shape, in particular no increased X-ray absorption in GRBs without optical transient (dark GRBs) compared to GRBs with optical transient (OTGRBs). Rather, we find that the 1.6-10 keV flux of OTGRBs is on average about 5 times larger than that of the dark GRBs. A Kolmogorov-Smirnov test shows that this difference is significant at 99.8% probability. Under the assumption that dark and OTGRBs have similar spectra, this could suggest that the first are uncaught in the optical band because they are just faint sources. In order to test this hypothesis, we have determined the optical-to-X-ray flux ratios of the sample. OTGRBs show a remarkably narrow distribution of flux ratios, which corresponds to an average optical-to-X-ray spectral index = 0.794 ? 0.054. We find that, while 75% of dark GRBs have flux ratio upper limits still consistent with those of OT GRBs, the remaining 25% are 4-10 times weaker in optical than in X-rays. The significance of this result is ?2.6 ?. If this subpopulation of dark GRBs were constituted by objects assimilable to OTGRBs, they should have shown optical fluxes higher than upper limits actually found. We discuss the possible causes of their behavior, including a possible occurrence in high-density clouds or origin at very high redshift and a connection with ancient, Population III stars.
79 citations
19 Oct 2003
TL;DR: In this paper, a biparametric method based on a hybrid HW and SW technique that utilizes a twin pulse shaping active filter (one slow and one fast) to analyze the same signal is presented.
Abstract: The performance of high Z solid state detectors has been significantly improved over the last decade: one of the most promising materials for X and gamma ray detectors is CdTe/CdZnTe, which combines high detection efficiency, no requirement for cooling to cryogenic temperatures, good spectroscopic performances, good time response and imaging capabilities. Unfortunately some important features of semiconductor detectors (pulse height, energy resolution, photopeak efficiency) are affected by the charge collection efficiency: the low mobility of the charge carriers (particularly the holes) and trapping/detrapping phenomena can degrade the CdTe/CdZnTe detectors' response, depending on the distance between the charge formation position and the collecting electrodes. The deterioration of the spectroscopic performances can be reduced by using either hardware or software techniques. The biparametric method herein described is based on a hybrid HW and SW technique that utilizes a twin pulse shaping active filter (one "slow" and one "fast") to analyze the same signal. This technique could be particularly suitable for implementation in a readout integrated circuit for multipixel detectors. The experimental results obtained with the application of this biparametric technique with CdZnTe detectors are presented in order to assess the reliability and the efficiency of this compensation method as a function of bias voltage, primary photon energy and shaping time pairs.
14 citations
14 May 2003
TL;DR: In this article, preliminary results of BeppoSAX measurements of the prompt (2-700 keV) and afterglow (0.1 -10 keV), emission of the dark GRB 001109 were presented.
Abstract: We present here preliminary results of BeppoSAX measurements of the prompt (2–700 keV) and afterglow (0.1 – 10 keV) emission of the ‘dark’ GRB 001109. The burst light curves show indication of pulse broadening with the decrease of the energy band and its average spectrum is well described by the standard Band function from X to gamma‐rays. The X‐ray afterglow emission shows a monotonic power‐law decay and its spectrum can be satisfactorily fitted with a photo‐electrically absorbed power‐law. Both the decay index and the photon index are inside the range of common values found in GRBs afterglows. More detailed data analysis and interpretation is in progress.
6 citations
14 May 2003
TL;DR: The 3rd Interplanetary Network (IPN) has been operating since April 2001 with two distant spacecraft, Ulysses and Mars Odyssey, and numerous near-Earth spacecraft, such as BeppoSAX, Wind, and HETEII.
Abstract: The 3rd Interplanetary Network (IPN) has been operating since April 2001 with two distant spacecraft, Ulysses and Mars Odyssey, and numerous near‐Earth spacecraft, such as BeppoSAX, Wind, and HETE‐II. Mars Odyssey is presently in orbit about Mars, and the network has detected approximately 30 cosmic, SGR, and solar bursts. We discuss the results obtained to date and use them to predict the future performance of the network.
5 citations
Posted Content•
TL;DR: In this article, a grid of spectral templates were used to fit the SED of the dark GRB 000210 host galaxy to its Spectral Energy Distribution (SED) and derived a photometric redshift (z=0.842\+0.0540) which is in excellent agreement with the spectroscopic one (z = 0.8463+/-0.0002).
Abstract: We report on UBVRIZJsHKs-band photometry of the dark GRB 000210 host galaxy. Fitting a grid of spectral templates to its Spectral Energy Distribution (SED), we derived a photometric redshift (z=0.842\+0.0540.042) which is in excellent agreement with the spectroscopic one (z=0.8463+/-0.0002; Piro et al. 2002). The best fit to the SED is obtained with a blue starburst template with an age of 0.181\+0.0370.026 Gyr. We discuss the implications of the inferred low value of Av and the age of the dominant stellar population for the non detection of the GRB 000210 optical afterglow.
1 citations