New fast X-ray transient IGR J18462-0223 discovered by the INTEGRAL observatory

Details of the discovery of a new X-ray source, IGR J18462-0223, on October 12, 2007, during a short (several hours), intense (~ 35 mCrab at the peak) outburst of hard radiation by the IBIS/ISGRI gamma-ray telescope onboard the INTEGRAL observatory are given. The detection of another earlier outburst from this source occurred on April 28, 2006, in the archival data of the telescope is reported. We present the results of the source's localization and our spectral/timing analysis of the observational data. The source may turn out to be yet another representative of the continuously growing population of fast X-ray transients, which are the focus of attention because of the identification of their optical counterparts with early-type supergiants

Observing GRBs with the LOFT Wide Field Monitor

LOFT (Large Observatory For X-ray Timing) is one of the four candidate missions currently under assessment study for the M3 mission in ESAs Cosmic Vision program to be launched in 2024. LOFT will carry two instruments with prime sensitivity in the 2-30 keV range: a 10 m2 class large area detector (LAD) with a <1° collimated field of view and a wide field monitor (WFM) instrument. The WFM is based on the coded mask principle, and 5 camera units will provide coverage of more than 1/3 of the sky. The prime goal of the WFM is to detect transient sources to be observed by the LAD. With its wide field of view and good energy resolution of <500 eV, the WFM will be an excellent instrument for detecting and studying GRBs and X-ray flashes. The WFM will be able to detect ~150 gamma ray bursts per year, and a burst alert system will enable the distribution of ~100 GRB positions per year with a ~1 arcmin location accuracy within 30 s of the burst

XMM-Newton observation of 4U 1820-30: Broad band spectrum and the contribution of the cold interstellar medium

We present the analysis of the bright X-ray binary 4U 1820-30, based mainly on XMM-Newton-RGS data, but using complementary data from XMM-Epic, Integral, and Chandra-HETG, to investigate different aspects of the source. The broad band continuum is well fitted by a classical combination of black body and Comptonized emission. The continuum shape and the high flux of the source (L/L_Edd\sim0.16) are consistent with a "high state" of the source. We do not find significant evidence of iron emission at energies >=6.4 keV. The soft X-ray spectrum contain a number of absorption features. Here we focus on the cold-mildly ionized gas. The neutral gas column density is N_H\sim1.63x10^21 cm^-2. The detailed study of the oxygen and iron edge reveals that those elements are depleted, defined here as the ratio between dust and the total ISM cold phase, by a factor 0.20\pm0.02 and 0.87\pm0.14, respectively. Using the available dust models, the best fit points to a major contribution of Mg-rich silicates, with metallic iron inclusion. Although we find that a large fraction of Fe is in dust form, the fit shows that Fe-rich silicates are disfavored. The measured Mg:Fe ratio is 2.0\pm0.3. Interestingly, this modeling may point to a well studied dust constituent (GEMS), sometimes proposed as a silicate constituent in our Galaxy. Oxygen and iron are found to be slightly over- and under-abundant, respectively (1.23 and 0.85 times the solar value) along this line of sight. We also report the detection of two absorption lines, tentatively identified as part of an outflow of mildly ionized gas (\xi\sim-0.5) at a velocity of \sim1200 km/s.Comment: 13 pages, 10 figures. Accepted for publication in Astronomy and Astrophysic