Discovery of an X-ray afterglow associated with the γ-ray burst of 28 February 1997
Establishing the nature of γ-ray bursts is one of the greatest challenges in high-energy astrophysics. The distribution of these bursts is isotropic across the sky, but inhomogeneous in space, with a deficit of faint bursts. It is currently unknown whether γ-ray bursts are produced in our Galaxy or at cosmological distances. The detection and identification of counterparts at other wavelengths are seen as crucial for resolving the origin of the events. Here we report the detection by the Beppo-SAX satellite of an X-ray ‘afterglow’, associated with the γ-ray burst of 28 February 1997 (GRB970228; ref. 3)—the first such detection for any γ-ray burst. The X-ray transient was found to contain a significant fraction of the total energy of the γ-ray burst and, following the initial detection eight hours after the main burst, faded within a few days with a power-law decay function. The rapid locating of this γ-ray burst instigated a multi-wavelength observational campaign that culminated in the identification of a fading optical transient in a position consistent with the X-ray transient reported here.

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: 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: SLAC Linac Preparations for FACET
abstract: The SLAC 3km linear electron accelerator has been cut at the two-thirds point to provide beams to two independent programs. The last third provides the electron beam for the Linac Coherent Light Source (LCLS), leaving the first two-thirds available for FACET, the new experimental facility for accelerator science and test beams. In this paper, we describe this separation and projects to prepare the linac for the FACET experimental program.

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: 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: Two-component model for cosmic-ray fluctuations at neutron monitor energies

title: Camtrac - A high energy gamma-ray telescope utilizing a coded aperture mask and drift chambers

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.

title: A Simple Model for Galactic Cosmic Rays which is Consistent with Age and Anisotropy Data

title: The age distribution of galactic cosmic rays
abstract: The general solution for the distribution of ages for primary galactic cosmic rays is given for a class of steady-state, bounded models of cosmic-ray diffusion in the Galaxy. Both one-and threedimensional models are considered, with point sources and distributed sources. In all models, the age distribution, is approximately exponential for ages longer than the average age, although for shorter ages the distribution depends on the details of the model. The leaky-box model, with an exponential age distribution, is thus a good approximation to most diffusive models. It is shown that one-dimensional (‘disk’) models are consistent with both age and anisotropy data for galactic cosmic rays regardless of whether production takes place near the galactic center or throughout the disk.