XMM-Newton reveals ~100 new LMXBs in M31 from variability studies

We have conducted a survey of X-ray sources in XMM-Newton observations of M31, examining their power density spectra (PDS) and spectral energy distributions (SEDs). Our automated source detection yielded 535 good X-ray sources; to date, we have studied 225 of them. In particular, we examined the PDS because low mass X-ray binaries (LMXBs) exhibit two distinctive types of PDS. At low accretion rates, the PDS is characterised by a broken power law, with the spectral index changing from ~0 to ~1 at some frequency in the range \~0.01--1 Hz; we refer to such PDS as Type A. At higher accretion rates, the PDS is described by a simple power law; we call these PDS Type B. Of the 225 sources studied to date, 75 exhibit Type A variability, and are almost certainly LMXBs, while 6 show Type B but not Type A, and are likely LMXBs. Of these 81 candidate LMXBs, 71 are newly identified in this survey; furthermore, they are mostly found near the centre of M31. Furthermore, most of the X-ray population in the disc are associated with the spiral arms, making them likely high mass X-ray binaries (HMXBs). In general these HMXBs do not exhibit Type A variability, while many central X-ray sources (LMXBs) in the same luminosity range do. Hence the PDS may distinguish between LMXBs and HMXBs in this luminosity range.Comment: 4 pages, 2 figures. To appear in proceedings of IAUS230: "Populations of High Energy Sources in Galaxies", 14-19 August 2005, Dublin, Eds E.J.A. Meurs and G. Fabbian

Statistics and characteristics of MgII absorbers along GRB lines of sight observed with VLT-UVES

We analyse the properties of MgII absorption systems detected along the sightlines toward GRBs using a sample of 10 GRB afterglow spectra obtained with VLT-UVES over the past six years. The S/N ratio is sufficiently high that we can extend previous studies to smaller equivalent widths (typically Wr>0.3A). Over a pathlength of Delta(z)~14 the number of weak absorbers detected is similar along GRB and QSO lines of sight, while the number of strong systems is larger along GRB lines of sight with a 2-sigma significance. Using intermediate and low resolution observations reported in the literature, we increase the absorption length for strong systems to Delta(z)=31.5 (about twice the path length of previous studies) and find that the number density of strong MgII systems is a factor of 2.1+/-0.6 higher (about 3-sigma significance) toward GRBs as compared to QSOs, about twice smaller however than previously reported. We divide the sample in three redshift bins and we find that the number density of strong MgII is larger in the low redshift bins. We investigate in detail the properties of strong MgII systems observed with UVES. Both the estimated dust extinction in strong GRB MgII systems and the equivalent width distribution are consistent with what is observed for standard QSO systems. We find also that the number density of (sub)-DLAs per unit redshift in the UVES sample is probably twice larger than what is expected from QSO sightlines which confirms the peculiarity of GRB lines of sight. These results indicate that neither a dust extinction bias nor different beam sizes of the sources are viable explanations for the excess. It is still possible that the current sample of GRB lines of sight is biased by a subtle gravitational lensing effect. More data and larger samples are needed to test this hypothesis. (abridged)Comment: 12 pages, 10 figures; accepted for publication in A&A (12 June 2009

Trends in Space Astronomy and Cosmic Vision 2015-2025

To be published in the proceedings of the 2005 ESLAB Symposium "Trends in Space Science and Cosmic Vision 2020", held at ESTEC, 19-21 April 2005, F. Favata (ed)As a short introduction to the astronomy session, the response of the community to the Call for Themes issued by ESA and the specific themes selected by the Astronomy Working Group are briefly presented in connection with the four grand themes finally selected for the ESA Science Programme. They are placed in the context of the main discoveries of the past decade and the astronomy projects currently in their development or definition phase. Finally, possible strategies for their implementation are summarised

Decreased systemic IL-7 and soluble IL-7R alpha in multiple sclerosis patients

Polymorphisms (single-nucleotide polymorphism (SNP)) in the interleukin-7 receptor-alpha (IL-7R alpha)/IL-7 pathway are associated with an increased risk to develop multiple sclerosis (MS). The rs6897932 SNP in the IL-7R alpha leads to increased soluble IL-7R alpha production. Given the functional interaction between sIL-7R alpha, membrane-bound IL-7R alpha and IL-7, we assessed IL-7, mIL-7R alpha and sIL-7R alpha levels in MS patients and healthy controls (HCs). One-hundred and twenty eight MS patients had significantly lower sIL-7R alpha levels compared with 73 HCs. The levels of sIL-7R alpha increased dose-dependent upon rs6897932 [C] risk allele carriership in both HCs and MS. Next, we hypothesized that lower sIL-7R alpha could result in a higher mIL-7R alpha to soluble IL-7R alpha ratio. Indeed, 52 MS patients had significantly increased mIL-7R alpha to sIL-7R alpha ratio for both CD4 and CD8 T cells compared with 44 HCs. Given the supposed role of IL-7 in autoimmunity, we determined whether sIL-7R alpha influences IL-7 levels. IL-7 levels were significantly decreased in 40 MS patients compared with 40 HCs. In conclusion, MS patients had lower free IL-7 and a higher membrane to soluble IL-7R alpha ratio. The soluble IL-7R alpha levels correlate with the rs6897932 [C] risk allele carriership. The skew at the IL-7 and IL-7R alpha level may influence responsiveness of IL-7R alpha(+) cells