Evidence for Dust-related X-Ray Emission from Comet C/1995 O1 (Hale-Bopp)
We report the discovery of X-ray emission from comet C/1995 O1 (Hale-Bopp) by the LECS instrument on board BeppoSAX on 1996 September 10-11. The 0.1-2.0 keV luminosity decayed by a factor of 2 on a timescale of ~10 hr with a mean value of 5×1016 ergs s−1. The spectrum is well fitted by a thermal bremsstrahlung model with a temperature of 0.29±0.06 keV or a power law with a photon index of 3.1+ 0.6−0.2. The lack of detected C and O line emission places severe constraints on many models for cometary X-ray emission, especially those that involve X-ray production in cometary gas. The luminosity is a factor of at least 3.4 greater than measured by the Extreme Ultraviolet Explorer (EUVE) 4 days later. This difference may be related to the emergence from the nucleus on 1996 September 9 of a dust-rich cloud. Over the next few days, the cloud continued to expand, becoming increasingly tenuous until it had reached an extent of ~3×105 km (or ~2') by the start of the EUVE observation. We speculate that the observed reduction in X-ray intensity is evidence for dust fragmentation. These results support the view that cometary X-ray emission arises from the interaction between solar X-rays and cometary dust.

title: A BeppoSAX observation of the massive x-ray binary 4U1700-37
abstract: A 0.5-200 keV BeppoSAX spectrum of the non- pulsating high-mass X-ray binary 4U 1700-37 is presented. The spectrum is well characterized by the standard accret- ing pulsar model of an absorbed power-law with a photon in- dex of 1:07 0:02 0:03 , sharply modified by an exponential cutoff above 5:9 0:2 keV. The e-folding energy of the cutoff is 23:9 0:5 keV. A soft bremsstrahlung component with a tem- perature of0:20:1 keV is also required, together with a narrow iron line at 6.5 keV. Both continuum components are absorbed by a column of (5:1 0:2) 10 22 atom cm 2 . There is some evidence for the presence of a broad cyclotron absorption fea- ture at 37 keV, although we cannot exclude the possibility that this is due to an incorrect modeling of the continuum, or instrumental effects. The hypothesis that the compact object is a neutron star rather than a black hole seems most likely.

title: Iron line signatures in X-ray afterglows of GRB by BeppoSAX
abstract: We report the possible detection (99.3% of sta- tistical signicance) of redshifted Fe iron line emission in the X-ray afterglow of Gamma-ray burst GRB 970508 ob- served by BeppoSAX. Its energy is consistent with the redshift of the putative host galaxy determined from op- tical spectroscopy. In contrast to the fairly clean environ- ment expected in the merging of two neutron stars, the observed line properties would imply that the site of the burst is embedded in a large mass of material (> 0:5M), consistent with pre-explosion ejecta of a very massive star. This material could be related with the outburst observed in the afterglow 1 day after the GRB and with the spectral variations measured during this phase. We did not nd ev- idence of Fe line in two other GRB with known redshift (GRB 971214 and GRB 980613), but we note that the up- per limits are of the same order of the intensity measured in GRB 97508 and that none of these afterglows shows rebursting activity.

title: Gamma-Ray Burst 980329 and Its X-Ray Afterglow
abstract: The gamma-ray burst (GRB) 980329 is the brightest gamma-ray burst detected so far with the Wide Field Cameras aboard BeppoSAX, in both gamma rays and X-rays. With respect to its fluence (2.6×10−5 ergs s−1 cm−2 in 50-300 keV), it would be in the top 4% of gamma-ray bursts in the 4B catalog (Meegan et al.). The time-averaged burst spectrum from 2 to 20 keV and from 70 to 650 keV can be well described by the empirical model of Band et al. The resulting photon index above the break energy is exceptionally hard at -1.32±0.03. An X-ray afterglow was detected with the narrow-field instruments aboard BeppoSAX 7 hr after the event within the error box as determined with the Wide Field Cameras. Its peak flux is (1.4±0.2)×10−12 ergs s−1 cm−2 (2-10 keV). The afterglow decayed according to a power-law function with an index of -1.35±0.03. GRB 980329 is characterized by being bright and hard and by lacking strong spectral evolution.

title: THE COMPLEX X-RAY SPECTRUM OF THE LOW-MASS X-RAY BINARY 4U 1626-67
abstract: We report on observations of the X-ray pulsar 4U 1626-67 by the LECS instrument on-board Bepposax. We confirm the recent ASCA discovery of excess emission near 1 keV (Angelini et al. 1995). The pulse period of 7.66794 +/- 0.00004 s indicates that the source continues to spin-down. The phase averaged spectrum is well fit by an absorbed power-law of photon index 0.61 +/- 0.02 and a blackbody of temperature 0.33 +/- 0.02 keV, together with an emission feature at 1.05 +/- 0.02 keV. This spectral shape is similar to that observed by ASCA during the spin-down phase, but significantly different from measurements during spin-up. This suggests that the change in spectrum observed by ASCA may be a stable feature during spin-down intervals. The source intensity is a factor ~2 lower than observed by ASCA three years earlier, confirming that 4U 1626-67 continues to become fainter with time.

title: BeppoSAX observations of GRB970402
abstract: GRB970402 is the fourth gamma-ray burst detected by BeppoSAX simultaneously in the Gamma Ray Burst Monitor (GRBM) and one of the two Wide Field Cameras (WFCs). A rapid pointing of the BeppoSAX Narrow Field Instruments (NFIs) 8 hours after the GRB led to the identification of an unknown weak X-ray source: 1SAX J1450.1-6920. Its position was approximately at the center of the 3 arcmin error circle derived from the WFC image. Both the Medium Energy (MECS, 2-10 keV) and Low Energy (LECS, 0.1-10 keV) concentrators detected the source. A follow-up observation performed 1.5 days later and lasting 54 ks showed that the source had faded almost to, but not below the detectability threshold. The flux decrease between the two observations was a factor ~= 2.5. 1SAX J1450.1-6920 was the second X-ray afterglow associated with a GRB. Searches promptly started at other wavelengths (optical, IR, radio) did not reveal any transient event within the 3 arcmin error circle.

title: Simple technique for determining the mean lifetime of the cosmic ray μ meson
abstract: A single scintillation counter is used for determining the lifetime of cosmic ray μ mesons. The experimental arrangement has a greater detection rate and a higher detection efficiency than the conventional multidetector delayed coincidence technique.