7722527
Low-energy line emission from Cygnus X-2 observed by the BeppoSAX LECS
We present a 0.2–10 keV spectrum of the low-mass X-ray binary Cygnus X-2 obtained using the Low Energy Concentrator Spectrometer on-board BeppoSAX. The spectrum can be described by a cut-off power-law model with absorption of (2.28±0.07)×1021 atoms cm−2, a power-law index of 0.78±0.02 and a cut-off energy of 4.30±0.08 keV (68% confidence errors), except at energies near ∼1 keV where excess emission is present. This can be modeled by a broad Gaussian line feature with an energy of 1.02±0.04 keV, a full width half-maximum of 0.47±0.07 keV and an equivalent width of 74±1125 eV. This result confirms earlier reports of line emission near 1 keV and shows the intensity and structure of the feature to be variable. For a more detailed account of these observations we refer to Kuulkers et al. [4].
12042223
THE COMPLEX X-RAY SPECTRUM OF THE LOW-MASS X-RAY BINARY 4U 1626-67
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.
2397132
Gamma-Ray Burst 980329 and Its X-Ray Afterglow
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.
13928123
Soft X-ray observations of the complex warm absorber in MCG-6-30-15 with BeppoSAX
We report on soft X-ray observations of the Seyfert 1 galaxy MCG-6-30-15 with the Low and Medium Energy Concentrator Spectrometers on board BeppoSAX. The time averaged 0.1-4 keV spectrum shows evidence for a complex warm absorber. K-edges of highly ionized oxygen (O vii and O viii) can only partly describe the soft X-ray spectrum below 2 keV. A spectral variability study reveales large and rapid changes in absorption at the energy of the O viii K-edge and in the continuum shape and count rate. These fluctuations are not simply correlated.
17512740
The absorption properties of gamma-ray burst afterglows measured by BeppoSAX
We present an analysis of the X-ray absorption prop- erties of 6 gamma-ray burst (GRB) afterglows measured with BeppoSAX. Between 8 hrs and 20 hrs after the initial GRB trig- ger, individual spectra can be described by a power-law with a photon index of 2 and absorption, NH, marginally consistent with the galactic value. Taken collectively, the data are incon- sistent with zero NH at the >99.999% confidence level. The data are only marginally consistent with a distribution of col- umn densities varying as the total galactic NH in the direction of each of the bursts ( 2 =9.6 for 6 degrees of freedom). The data are consistent with cosmological models in which GRB oc- cur within host galaxies. By simultaneously fitting a power-law spectral model with NH fixed at the galactic value and additional, redshifted, absorption to all 6 afterglow spectra, the best-fit av-
17797650
Iron line signatures in X-ray afterglows of GRB by BeppoSAX
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.
118987428
Camtrac - A high energy gamma-ray telescope utilizing a coded aperture mask and drift chambers