804 research outputs found
A Robust Filter for the BeppoSAX Gamma Ray Burst Monitor Triggers
The BeppoSAX Gamma Ray Burst Monitor (GRBM) is triggered any time a
statistically significant counting excess is simultaneously revealed by at
least two of its four independent detectors. Several spurious effects,
including highly ionizing particles crossing two detectors, are recorded as
onboard triggers. In fact, a large number of false triggers is detected, in the
order of 10/day. A software code, based on an heuristic algorithm, was written
to discriminate between real and false triggers. We present the results of the
analysis on an homogeneous sample of GRBM triggers, thus providing an estimate
of the efficiency of the GRB detection system consisting of the GRBM and the
software.Comment: Proc. 5th Huntsville GRB Symposiu
The complex time behaviour of the microquasar GRS 1915+105 in the \rho-class observed with BeppoSAX. III: The hard X-ray delay and limit cycle mapping
The microquasar GRS1915+105 was observed by BeppoSAX in October 2000 for
about ten days while the source was in \rho-mode, which is characterized by a
quasi-regular type I bursting activity. This paper presents a systematic
analysis of the delay of the hard and soft X-ray emission at the burst peaks.
The lag, also apparent from the comparison of the [1.7-3.4] keV light curves
with those in the [6.8-10.2] keV range, is evaluated and studied as a function
of time, spectral parameters, and flux. We apply the limit cycle mapping
technique, using as independent variables the count rate and the mean photon
rate. The results using this technique were also cross-checked using a more
standard approach with the cross-correlation methods. Data are organized in
runs, each relative to a continuous observation interval. The detected
hard-soft delay changes in the course of the pointing from about 3 s to about
10 s and presents a clear correlation with the baseline count rate.Comment: accepted for publication in A&
Comparative study of the two large flares from SGR1900+14 with the BeppoSAX Gamma-Ray Burst Monitor
We report on spectral and temporal results of the 40-700 keV observations,
obtained with the Gamma-Ray Burst Monitor (GRBM) on board BeppoSAX, of the two
large flares from the Soft Gamma-ray Repeater SGR1900+14 occurred on August 27,
1998 and April 18, 2001. From their intensity, fluence and duration, the first
one was classified as "giant" and the second as "intermediate". The spectral
results have been obtained with an improved response function of the GRBM. We
find that the two events have similar spectral properties, but different
temporal properties. The major difference concerns the time profiles of the
light curves, whereas the lack of evidence in the 2001 flare for the erratic
time variability found at high frequencies (10-1000 Hz) in the 1998 flare could
be ascribed to lower counting statistics. We discuss these results in the light
of the magnetar model proposed for SGR sources.Comment: 15 pages, 20 figures, accepted for publication in A&
The Gamma--Ray Burst catalog obtained with the Gamma Ray Burst Monitor aboard BeppoSAX
We report on the catalog of Gamma--Ray Bursts (GRBs) detected with the Gamma
Ray Burst Monitor aboard the BeppoSAX satellite. It includes 1082 GRBs with
40--700 keV fluences in the range from to erg cm, and with 40--700 keV peak fluxes from to erg cms. We report in the catalog
some relevant parameters of each GRB and discuss the derived statistical
properties.Comment: 48 pages, 14 figures, 4 Tables. Accepted for publication in The
Astrophysical Journal Supplemen
Wo3 and ionic liquids: A synergic pair for pollutant gas sensing and desulfurization
This review deals with the notable results obtained by the synergy between ionic liquids (ILs) and WO3 in the field of pollutant gas sensing and sulfur removal pretreatment of fuels. Starting from the known characteristics of tungsten trioxide as catalytic material, many authors have proposed the use of ionic liquids in order to both direct WO3 production towards controllable nanostructures (nanorods, nanospheres, etc.) and to modify the metal oxide structure (incorporating ILs) in order to increase the gas adsorption ability and, thus, the catalytic efficiency. Moreover, ionic liquids are able to highly disperse WO3 in composites, thus enhancing the contact surface and the catalytic ability of WO3 in both hydrodesulfurization (HDS) and oxidative desulfurization (ODS) of liquid fuels. In particular, the use of ILs in composite synthesis can direct the hydrogenation process (HDS) towards sulfur compounds rather than towards olefins, thus preserving the octane number of the fuel while highly reducing the sulfur content and, thus, the possibility of air pollution with sulfur oxides. A similar performance enhancement was obtained in ODS, where the high dispersion of WO3 (due to the use of ILs during the synthesis) allows for noteworthy results at very low temperatures (50◦ C)
The complex behaviour of the microquasar GRS 1915+105 in the rho class observed with BeppoSAX. I: Timing analysis
GRS 1915+105 was observed by BeppoSAX for about 10 days in October 2000. For
about 80% of the time, the source was in the variability class ,
characterised by a series of recurrent bursts. We describe the results of the
timing analysis performed on the MECS (1.6--10 keV) and PDS (15--100 keV) data.
The X-ray count rate from \grss showed an increasing trend with different
characteristics in the various energy bands. Fourier and wavelet analyses
detect a variation in the recurrence time of the bursts, from 45--50 s to about
75 s, which appear well correlated with the count rate. From the power
distribution of peaks in Fourier periodograms and wavelet spectra, we
distinguished between the {\it regular} and {\it irregular} variability modes
of the class, which are related to variations in the count rate in the
3--10 keV range. We identified two components in the burst structure: the slow
leading trail, and the pulse, superimposed on a rather stable level. We found
that the change in the recurrence time of the regular mode is caused by the
slow leading trails, while the duration of the pulse phase remains far more
stable. The evolution in the mean count rates shows that the time behaviour of
both the leading trail and the baseline level are very similar to those
observed in the 1.6--3 and 15--100 keV ranges, while that of the pulse follows
the peak number. These differences in the time behaviour and count rates at
different energies indicate that the process responsible for the pulses must
produce the strongest emission between 3 and 10 keV, while that associated with
both the leading trail and the baseline dominates at lower and higher energiesComment: Astronomy and Astrophysics, in pres
- …