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For the second time in 27 years a bright transient X-ray source has been detected coincident with the globular cluster NGC 6440. It was found to be active in August, 1998, with the Wide Field Camera and the narrow field instruments on the BeppoSAX spacecraft, and with the All-Sky Monitor and the Proportional Counter Array on the RossiXTE spacecraft. Four X-ray bursts were detected, at least one of which shows the characteristics of a thermonuclear flash on a neutron star, in analogy with some ~20 optically identified low-mass X-ray binaries. The broad-band spectrum is hard as is common among low-mass X-ray binaries of lower luminosity (>~10^37 erg/s) and can be explained by a Comptonized model. During the burst the >30 keV emission brightened, consistent with part of the burst emission being Compton up scattered within ~10^11 cm., 10 pages, accepted for publication in A&A

The results of a BeppoSAX TOO observation of the BL Lac object Mkn421 during a high intensity state are reported and compared with monitoring X-ray data collected with the BeppoSAX Wide Field Cameras (WFC) and the RXTE All Sky Monitor(ASM). The 0.1-100 keV spectrum of Mkn421 shows continuous convex curvature that can be interpreted as the high-energy end of the synchrotron emission. The source shows significant short-term temporal and spectral variability, which can be interpreted in terms of synchrotron cooling. The comparison of our results with those of previous observations when the source was a factor 3-5 fainter shows evidence for strong spectral variability, with the maximum of the synchrotron power shifting to higher energy during high states. This behaviour suggest an increase in the number of energetic electrons during high states., Comment: 6 pages, LaTeX, plus 8 .ps figures, accepted by MNRAS

The BeppoSAX satellite has recently opened a new way towards the solution of the long standing gamma-ray bursts' (GRBs) enigma, providing accurate coordinates few hours after the event thus allowing for multiwavelength follow-up observational campaigns. The BeppoSAX Narrow Field Instruments observed the region of sky containing GRB970111 16 hours after the burst. In contrast to other GRBs observed by BeppoSAX no bright afterglow was unambiguously observed. A faint source (1SAXJ1528.1+1937) is detected in a position consistent with the BeppoSAX Wide Field Camera position, but unconsistent with the IPN annulus. Whether 1SAXJ1528.1+1937 is associated with GRB970111 or not, the X-ray intensity of the afterglow is significantly lower than expected, based on the properties of the other BeppoSAX GRB afterglows. Given that GRB970111 is one of the brightest GRBs observed, this implies that there is no obvious relation between the GRB gamma-ray peak flux and the intensity of the X-ray afterglow., Comment: 5 pages, LaTeX A&A style, 3 postscript figures; A&A Letters accepted

Two type I X-ray bursts were detected from a position consistent with the transient X-ray source in NGC 6652 with the Wide Field Camera of the BeppoSAX satellite, strongly suggesting that this transient is a neutron star. Our detection brings to ten the number of X-ray sources in globular clusters in which a type I X-ray burst has been seen, out of twelve known bright sources. The statistical evidence that the fraction of low-mass X-ray binaries which contain a black hole accretor is smaller in globular clusters than in the galactic disk is suggestive, but as yet not compelling., Comment: Published in A&A, 1998, vol. 329, L37; 5 pages, 3 figures

Four or five new outbursts were detected of the bright X-ray transient GRS 1747-312 in the globular cluster Terzan 6 between 1996 and 1999, through monitoring campaigns with the Wide Field Cameras (WFCs) on BeppoSAX and the Proportional Counter Array (PCA) on RossiXTE. This is the first time that the source is seen to exhibit recurrent outbursts after the discovery in September 1990 with ART-P on Granat. Three target-of-opportunity observations in 1998 and 1999, with the narrow-field instruments on BeppoSAX and the PCA, revealed one sharp drop in the flux which we identify as an eclipse of the compact X-ray source by the companion star. A detailed analysis of WFC data identifies further eclipses and we measure the orbital period at 12.360+/-0.009 hr. This is consistent with an identification as a low-mass X-ray binary, as suggested already by the association with a globular cluster. The eclipse duration is 0.72+/-0.06 hr. This implies that the inclination angle is larger than 74 deg. The 0.1-200 keV unabsorbed peak luminosity is 7X10^36 erg/s. The nature of the compact object is unclear., replaced with accepted version

SAX J1819.3-2525 is a nearby X-ray transient which exhibited a fast and large X-ray outburst on Sep. 15, 1999 (Smith et al. 1999). The Wide Field Cameras and the Narrow Field Instruments (NFI) on board BeppoSAX observed SAX J1819.3-2525 at various stages of its activity before that, in the spring and fall of 1999. The fluxes range between 0.012 and 0.3 Crab units (2-10 keV). The NFI observation is unique because it is the longest semi-continuous observation of SAX J1819.3-2525 so far, and it offers a study of the spectrum at a relatively high resolution of 8% full width at half maximum at 6 keV. We discuss the observations with emphasis on the X-ray spectrum. A strong Fe-K emission line was detected in SAX J1819.3-2525 with an equivalent width between 0.3 and 1 keV. The line energy is up to 6.85 +/- 0.02 keV and suggests the presence of highly ionized iron. We identify this as fluorescent emission from a photo-ionized plasma. The continuum spectrum is typical for a low-mass X-ray binary in which emission from an accretion disk corona plays an important role. There is no sign of an eclipse or periodic signal due to the binary orbit in this exposure, despite the fact that the twin jets seen at radio wavelengths suggest a high inclination angle., 8 pages, accepted for publication in A&A Main Journal

During more than 3 years (August 1996-October 1999) monitoring of a 40x40 degree sky region around the Galactic Centre by the Wide Field Cameras on board BeppoSAX, a total of 8 type-I bursts have been detected from a sky position consistent with that of 4U 1812-12, a likely neutron-star low-mass X-ray binary. We present the results of a detailed study of the bursts of 4U 1812-12, about 15 years after the last reported observations of X-ray bursts from this source (Murakami et al. 1983). Clear evidence for photospheric radius expansion due to Eddington-limited burst luminosity is present in most of the observed events, allowing an accurate estimate of the source distance (~4 kpc) and its burst parameters., Comment: 6 pages, 3 figures, accepted for publication in A&A main journal

We report the X/gamma-ray spectrum of GRB971214 and of its afterglow. The afterglow was measured few hours after the main event and for an elapsed time of more than two days. The measure of this GRB and afterglow is relevant due to its extreme, cosmological distance (z=3.42). The prompt event shows a hard photon spectrum, consistent with a broken power law with photon indices Gamma_X~0.1 below ~20 keV and Gamma_g~1.3 above 60 keV. The afterglow spectrum, measured with the MECS and LECS BeppoSAX telescopes, is consistent with a power law with spectral photon index Gamma=1.6. Within the statistical accuracy of our measure no spectral evolution is detected during the observation of the afterglow. When integrated during the time span covered by BeppoSAX observations, the power in the afterglow emission, even with very conservative assumptions, is at least comparable with the power in the main event. The IR-to-X rays broad band spectrum is also presented, collecting data from the literature and adding them to the BeppoSAX measure. It shows that the predictions from synchrotron emission models is qualitatively confirmed. The BeppoSAX measurement of the X and gamma ray spectrum of this GRB/afterglow is discussed in the framework of current theoretical models., Comment: 8 pages, 4 figures. To be published in Astronomy and Astrophysics. Uses aa, epsf and times LaTeX macros

In this paper we present the observations performed by the BeppoSAX Gamma-Ray Burst Monitor (GRBM) and Wide Field Cameras (WFC) of GB960720. We derive a precise localization (3 arcmin radius) and fast broad band (2-700 keV) spectral evolution of the event. A search in the catalogues at all wavelengths in the error box yields a unique outstanding source: the bright radio quasar 4C 49.29. Although the probability of finding such a source by chance is very low (0.0002), the absence of similar counterparts in other small error boxes suggests a chance occurrence. We also find that the duration-energy relationship for bursts previously observed above 25keV (Fenimore et al. 1995) extends down to 1.5 keV. This result suggests that the same radiation mechanism is operating from X-rays to gamma-rays and is in agreement with radiative cooling by synchotron emission. A fast evolution of the spectrum is found, in which the ratio of X- to gamma-ray intensities varies over three orders of magnitude. Furthermore, the spectrum in the initial phase of the event betrays the presence of an optically thick source rapidly evolving in a thin configuration.No other class of sources in the universe shows such a fast and extreme evolution. These results pose new and tighter constraints on theoretical models for gamma-ray bursts., 5 pages, LaTeX, 5 postscript figures; A&A, Accepted 15 July 1997, updated reference Costa 1997b

We report the discovery of a fairly bright transient during observations with the Wide Field Cameras on board the BeppoSAX satellite in September 1996. It was detected at a peak intensity of 0.1 Crab (2 to 10 keV) and lasted between 6 and 40 days above a detection threshold of 2 mCrab. Two very bright type I X-ray bursts were detected from this transient in the same observations. These almost certainly identify this X-ray transient as a low-mass X-ray binary with a neutron star as compact component. The double-peaked time history of both bursts at high energies suggests a peak luminosity close to the Eddington limit. Assuming this to be true implies a distance to this object of 4 kpc., Comment: 4 pages, 4 figures, published in A&A March II 1998 issue

Two mAb specific for the potent toxin II of the scorpion Androctonus australis Hector have been produced. One of them shows both high affinity binding to the toxin (Kd) = 0.8 nM) and in vivo and in vitro neutralizing properties. The mechanism by which the antibody neutralizes toxin binding to its receptor was shown to be of the competitive type, the epitope overlapping or being close to the receptor-binding region of the toxin. Several residues of the toxin clustered in the C-terminal region were shown likely to be part of the discontinuous epitope recognized by the antibody. The positive charge of the N epsilon-Lys-58 seems to play a pivotal role in the binding of the toxin to both the mAb and the sodium channel receptor.

We report on the BeppoSAX/WFC observation of a strong type-I X-ray burst from the recently discovered transient source SAX J1810.8-2609. The observed event showed evidence of photospheric radius expansion due to super-Eddington burst luminosity. Burst detection identifies the source as a probable low-mass X-ray binary harbouring a neutron star., 4 pages, 3 figures, proc. 3rd INTEGRAL Workshop - Taormina 1998