[en] We present 0.1-10 keV observations of Her X-1 obtained with the Low-Energy Spectrometer Concentrator instrument onboard the BeppoSAX satellite during the main on-state of the 35 day cycle. We confirm the existence of an intense 0.093 keV blackbody component and a broad emission feature at 0.94 keV. The pulse phase dependence of these components is similar, suggesting a common origin. This is most likely fluorescent excitation of moderately ionized (ξ ∼ 10-100) material located at the inner edge of the accretion disk

[en] Results of a search for X-ray counterparts of radio pulsars with the EPIC-PN instrument on board XMM-Newton are presented. Despite the mostly relatively short exposure times (<8 ks, PSR B0823+26 was observed for 50 ks) these observations have resulted in much improved upper limits over previous work and, in the case of PSR B1719-37, a first detection in X-rays. The obtained upper limits and detection are found to be consistent with the empirical relation as found by Verbunt et al. and Becker and Truemper

[en] The 7 s X-ray pulsar 1E 2259+586 and the supernova remnant (SNR) G109.1-1.0 (CTB 109) were observed by BeppoSAX in 1996 November. We confirm the ASCA discovery of an additional low-energy spectral component from 1E 2259+586. This can be modeled as a 0.44 keV blackbody, but we cannot exclude that some, or all, of this emission arises from the part of the SNR that lies within the pulsar's extraction region. The G109.1-1.0 spectrum is well fit with a non-equilibrium ionization plasma model with a best-fit temperature of 0.95 keV. The derived mass for the X-ray emitting plasma (∼15-20 M_[odot]) and its near cosmic abundances imply that the X-ray emission comes mainly from mildly enriched, swept-up circumstellar material. The spectrum is strongly out of equilibrium with an ionization age of only 3000 yr

[en] We report on observations of the low-mass X-ray binary 4U1626-67 performed during the BeppoSAX Science Verification Phase. We present the broad-band 0.1-100 keV pulse averated spectrum, that is well fit by a two-component function: a 0.27 ± 0.02 keV blackbody and an absorbed power law with a photon index of 0.89 ± 0.02. A very deep and narrow absorption feature at 38 keV, attributable to electron cyclotron resonance, is clearly visible in the broad-band spectrum. It corresponds to a neutron star magnetic field strength of 3.3 x 10¹² G. The 4U1626-67 pulse profiles show a dramatic dependence on energy: the transition between the low energy (E < 10 keV) bi-horned shape to the high-energy (E > 10 keV) sinusoidal profile is clearly visible in our data. The modulation index shows a monotonic increase with energy

[en] We report the detection of soft X-rays from comet C/1995 O1 (Hale-Bopp) by the LECS instrument on-board BeppoSAX on 1996 September 10-11. After correcting for the comets motion, a 7σ enhancement was found within 2' of the expected location of the nucleus at much greater than 99.99% confidence. A weak 1.3σ enhancement was also found in MECS data at the same location. The extracted LECS spectrum is well fit by a thermal bremsstrahlung model of temperature of 0.29 ± 0.06 keV - consistent with that observed in other comets. The 0.1-2.0 keV luminosity has a mean value of 5x10¹⁶ erg s^-1 and is a factor of ∼ 8 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 which continued to expand rapidly over the next few days becoming tenuous by the start of the EUVE observation. There is no evidence for fluorescent carbon or oxygen emission with 95% confidence limits of 1.0x10¹⁵ and 7.8x10¹⁵ erg s^-1 to narrow line emission at 0.28 and 0.53 keV, respectively. This implies that if such lines are present, their total luminosity must be must be <18% of the 0.1-2.0 keV continuum luminosity

[en] BeppoSAX observed several galactic binary X-ray pulsars during the Science Verification Phase and in the first year of the regular program. The complex emission spectra of these sources are an ideal target for the BeppoSAX instrumentation, that can measure the emission spectra in an unprecedented broad energy band. Using this capability of BeppoSAX a detailed observational work can be done on the galactic X-ray pulsars. In particular the 0.1-200 keV energy band allows the shape of the continuum emission to be tightly constrained. A better determination of the underlying continuum allows an easier detection of features superimposed onto it, both at low energy (Fe K and L, Ne lines) and at high energies (cyclotron features). We report on the spectral properties of a sample of X-ray pulsars observed with BeppoSAX comparing the obtained results. Some ideas of common properties are also discussed and compared with our present understanding of the emission mechanisms and processes

[en] The transient X-ray pulsar GS 1843+009 was observed by BeppoSAX satellite on 1997 April 4, while it was at flux level of 50 mCrab in the 20-200 keV energy band. Using the MECS and LECS concentrators, the source position was measured with unprecedented accuracy of 30''. In this poster we present results on both spectral and temporal analysis

[en] We present broad band timing and spectral analysis of Beppo-SAX data of the Seyfert galaxy NGC 4151, and propose multi-component models to explain the complex spectrum of this source and the observed, energy dependent, spectral variability. Many different components are needed to model SAX NGC 4151 spectra. The intrinsic continuum is well described by a simple power law with energy spectral index slightly correlated with intensity (α ∼ 0.4 - 0.5) up to ∼ 15 keV. At higher energies an exponential cutoff is clearly detected in the PDS spectra (E_c = 50±5 keV). There is also an evidence for a flattening of the spectrum above ∼ 15 keV which is well described by a reflection model. A non-variable, complex soft component becomes dominant below ∼ 1 keV. Between 1 keV and ∼ 5 keV, a complicate absorption structure reveals the presence of either a cold absorber partially covering the nuclear continuum or a very thick warm absorber, or both. Finally, a strong Iron line at 6.4 keV is clearly detected, with varying equivalent width, becoming stronger as continuum intensity drops

[en] From a statistical study of X-ray bursts observed with EXOSAT from 4U/MXB 1636-53 and EXO 0748-67, we find a strong correlation between the burst duration and the blackbody temperature, kT_bb, as measured at the moment that the flux has decayed to 10 per cent of the Eddington flux. We find no correlation between the persistent flux near the burst and this temperature nor with the duration of the burst. Since the burst duration probably depends on the chemical composition of the bursting layers, these results suggest that: (i) burst spectra show deviations from a Planckian spectrum, which depend on the chemical composition of the bursting layer, and (ii) this composition is not a simple function of the persistent flux and consequently of the accretion rate. (author)

[en] Aims. The study of the observational properties of uncommonly long bursts from low luminosity sources is important when investigating the transition from a hydrogen - rich bursting regime to a pure helium regime and from helium burning to carbon burning as predicted by current burst theories. On a few occasions X-ray bursts have been observed with extended decay times up to several tens of minutes, intermediate between usual type I X-ray bursts and so-called super-bursts. Methods. IGR J17254-3257 is a recently discovered X-ray burster of which only two bursts have been recorded: an ordinary short type I X-ray burst, and a 15 min long burst. The properties of the X-ray bursts observed from IGR J17254-3257 are investigated. The broad-band spectrum of the persistent emission in the 0.3-100 keV energy band is studied using contemporaneous INTEGRAL and XMM-Newton data. Results. A refined position of IGR J17254-3257 is given and an upper limit to its distance is estimated to about 14.5 kpc. The persistent bolometric flux of 1.1 * 10^-10 erg cm^-2 s^-1 corresponds, at the canonical distance of 8 kpc, to L(pers) ≅ 8.4 * 10³⁵ erg s^-1 between 0.1-100 keV, which translates to a mean accretion rate of about 7 * 10^-11 M-(circle dot) yr^-1. Conclusions. The low X-ray persistent luminosity of IGR J17254-3257 seems to indicate the source may be in a state of low accretion rate usually associated with a hard spectrum in the X-ray range. The nuclear burning regime may be intermediate between pure He and mixed H/He burning. The long burst is the result of the accumulation of a thick He layer, while the short one is a pre-maturate H-triggered He burning burst at a slightly lower accretion rate. (authors)