1RXS J214303.7+065419/RBS 1774: A New Isolated Neutron Star Candidate

We report on the identification of a new possible Isolated Neutron Star candidate in archival ROSAT observations. The source 1RXS J214303.7+065419, listed in the ROSAT Bright Survey as RBS 1774, is very soft, exhibits a thermal spectrum well fitted by a blackbody at ${T}\sim 90$ eV and has a low column density, ${N_H}\sim 5\times 10^{20}$ ${cm}^{-2}$. Catalogue searches revealed no known sources in other energy bands close to the X-ray position of RBS 1774. Follow-up optical observations with NTT showed no peculiar object within the X-ray error circle. The absence of any plausible optical counterpart down to ${m_R}\sim 23$ results in an X-ray to optical flux ratio in excess of 1000.Comment: LaTeX (A&A style files), 5 pages, 3 figures. Accepted for publication in Astronomy and Astrophysics Letters. Minor correction

X-Ray Wind Tomography of the highly absorbed HMXB IGR J17252-3616

Our goal is to understand the specificities of highly absorbed sgHMXB and in particular of the companion stellar wind, thought to be responsible for the strong absorption. We have monitored IGR J17252-3616, a highly absorbed system featuring eclipses, with XMM-Newton to study the vari- ability of the column density and of the Fe K{\alpha} emission line along the orbit and during the eclipses. We also built a 3D model of the structure of the stellar wind to reproduce the observed variability. We first derived a refined orbital solution built from INTEGRAL, RXTE and XMM data. The XMM monitoring campaign revealed significant variation of intrinsic absorbing column density along the orbit and of the Fe K{\alpha} line equivalent width around the eclipses. The origin of the soft X-ray absorption is modeled with an dense and extended hydrodynamical tail, trailing the neutron star. This structure extends along most of the orbit, indicating that the stellar wind is strongly disrupted by the neutron star. The variability of the absorbing column density suggests that the terminal velocity of the wind is smaller (~400 km/s) than observed in classical systems. This can also explain the much stronger density perturbation inferred from the observations. Most of the Fe K{\alpha} emission is generated in the most inner region of the hydrodynamical tail. This region, that extends over a few accretion radii, is ionized and does not contribute to the soft X-ray absorption. We have built a qualitative model of the stellar wind of IGR J17252-3616 that can represent the observations and suggest that highly absorbed systems have a lower wind velocity than classical sgHMXB. This proposal could be tested with de- tailed numerical simulations and high-resolution infrared/optical observations. If confirmed, it may turn out that half of the persistent sgHMXB have low stellar wind speeds.Comment: 9 pages, 8 figure

XMM-Newton observations of the INTEGRAL X-ray transient J17544-2619

On 2003 September 17 INTEGRAL discovered a bright transient source 3 degrees from the Galactic Center, IGR J17544-2619. The field containing the transient was observed by XMM-Newton on 2003 March 17 and September 11 and 17. A bright source, at a position consistent with the INTEGRAL location, was detected by the European Photon Imaging Camera (EPIC) during both September observations with mean 0.5-10 keV unabsorbed luminosities of 1.1x10^35 and 5.7x10^35 erg s-1 for an (assumed) distance of 8 kpc. The source was not detected in 2003 March, with a 0.5-10 keV luminosity of < 3.8x10^32 erg s-1. The September 11 and 17 EPIC spectra can be represented by a power-law model with photon indices of 2.25+/-0.15 and 1.42+/-0.17, respectively. Thus, the 0.5-10 keV spectrum hardens with increasing intensity. The low-energy absorption during both September observations is comparable to the interstellar value. The X-ray lightcurves for both September observations show energy dependent flaring which may be modeled by changes in either low-energy absorption or power-law index.Comment: Six pages, five figures; to appear in Astronomy and Astrophysic

Soft band X/K luminosity ratios in late-type galaxies and constraints on the population of supersoft X-ray sources

We study X-ray to K-band luminosity ratios (L_X/L_K) of late-type galaxies in the 0.3-0.7 keV energy range. From the Chandra archive, we selected nine spiral and three irregular galaxies with point source detection sensitivity better than 5 x 10^36 erg/s in order to minimize the contribution of unresolved X-ray binaries. In late-type galaxies cold gas and dust may cause significant interstellar absorption, therefore we also demanded the existence of publicly available HI maps. The obtained L_X/L_K ratios vary between (5.4-68) x 10^27 erg/s/L_K,sun exceeding by factor of 2-20 the values obtained for gas-poor early-type galaxies. Based on these results we constrain the role of supersoft X-ray sources as progenitors of type Ia supernovae (SNe Ia). For majority of galaxies the upper limits range from ~3% to ~15% of the SN Ia frequency inferred from K-band luminosity, but for a few of them no meaningful constraints can be placed. On a more detailed level, we study individual structural components of spiral galaxies: bulge and disk, and, for grand design spiral galaxies, arm and interarm regions.Comment: 10 pages, 2 tables, 6 figures, accepted for publication in MNRAS, minor change

2003--2005 INTEGRAL and XMM-Newton observations of 3C 273

The aim of this paper is to study the evolution of the broadband spectrum of one of the brightest and nearest quasars 3C 273. We analyze the data obtained during quasi-simultaneous INTEGRAL and XMM monitoring of the blazar 3C 273 in 2003--2005 in the UV, X-ray and soft gamma-ray bands and study the results in the context of the long-term evolution of the source. The 0.2-100 keV spectrum of the source is well fitted by a combination of a soft cut-off power law and a hard power law. No improvement of the fit is achieved if one replaces the soft cut-off power law by either a blackbody, or a disk reflection model. During the observation period the source has reached the historically softest state in the hard X-ray domain with a photon index $\Gamma=1.82\pm 0.01$. Comparing our data with available archived X-ray data from previous years, we find a secular evolution of the source toward softer X-ray emission (the photon index has increased by $\Delta\Gamma\simeq 0.3-0.4$ over the last thirty years). We argue that existing theoretical models have to be significantly modified to account for the observed spectral evolution of the source.Comment: 11 pages, accepted to A&

Phenothiazine-mediated rescue of cognition in tau transgenic mice requires neuroprotection and reduced soluble tau burden

Abstract Background It has traditionally been thought that the pathological accumulation of tau in Alzheimer's disease and other tauopathies facilitates neurodegeneration, which in turn leads to cognitive impairment. However, recent evidence suggests that tau tangles are not the entity responsible for memory loss, rather it is an intermediate tau species that disrupts neuronal function. Thus, efforts to discover therapeutics for tauopathies emphasize soluble tau reductions as well as neuroprotection. Results Here, we found that neuroprotection alone caused by methylene blue (MB), the parent compound of the anti-tau phenothiaziazine drug, Rember&#8482;, was insufficient to rescue cognition in a mouse model of the human tauopathy, progressive supranuclear palsy (PSP) and fronto-temporal dementia with parkinsonism linked to chromosome 17 (FTDP17): Only when levels of soluble tau protein were concomitantly reduced by a very high concentration of MB, was cognitive improvement observed. Thus, neurodegeneration can be decoupled from tau accumulation, but phenotypic improvement is only possible when soluble tau levels are also reduced. Conclusions Neuroprotection alone is not sufficient to rescue tau-induced memory loss in a transgenic mouse model. Development of neuroprotective agents is an area of intense investigation in the tauopathy drug discovery field. This may ultimately be an unsuccessful approach if soluble toxic tau intermediates are not also reduced. Thus, MB and related compounds, despite their pleiotropic nature, may be the proverbial "magic bullet" because they not only are neuroprotective, but are also able to facilitate soluble tau clearance. Moreover, this shows that neuroprotection is possible without reducing tau levels. This indicates that there is a definitive molecular link between tau and cell death cascades that can be disrupted.http://deepblue.lib.umich.edu/bitstream/2027.42/78314/1/1750-1326-5-45.xmlhttp://deepblue.lib.umich.edu/bitstream/2027.42/78314/2/1750-1326-5-45.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/78314/3/1750-1326-5-45-S1.PDFPeer Reviewe

XMM-Newton observations of IGRJ18410-0535: The ingestion of a clump by a supergiant fast X-ray transient

IGRJ18410-0535 is a supergiant fast X-ray transients. This subclass of supergiant X-ray binaries typically undergoes few- hour-long outbursts reaching luminosities of 10^(36)-10^(37) erg/s, the occurrence of which has been ascribed to the combined effect of the intense magnetic field and rotation of the compact object hosted in them and/or the presence of dense structures ("clumps") in the wind of their supergiant companion. IGR J18410-0535 was observed for 45 ks by XMM-Newton as part of a program designed to study the quiescent emission of supergiant fast X-ray transients and clarify the origin of their peculiar X-ray variability. We carried out an in-depth spectral and timing analysis of these XMM-Newton data. IGR J18410-0535 underwent a bright X-ray flare that started about 5 ks after the beginning of the observation and lasted for \sim15 ks. Thanks to the capabilities of the instruments on-board XMM-Newton, the whole event could be followed in great detail. The results of our analysis provide strong convincing evidence that the flare was produced by the accretion of matter from a massive clump onto the compact object hosted in this system. By assuming that the clump is spherical and moves at the same velocity as the homogeneous stellar wind, we estimate a mass and radius of Mcl \simeq1.4\times10^(22) g and Rcl \simeq8\times10^(11) cm. These are in qualitative agreement with values expected from theoretical calculations. We found no evidence of pulsations at \sim4.7 s after investigating coherent modulations in the range 3.5 ms-100 s. A reanalysis of the archival ASCA and Swift data of IGR J18410-0535, for which these pulsations were previously detected, revealed that they were likely to be due to a statistical fluctuation and an instrumental effect, respectively.Comment: Accepted for publication on A&A. V2: Inserted correct version of Fig.1

The Swift-BAT survey reveals the orbital period of three high-mass X-ray binaries

A growing number of previously hidden Galactic X-ray sources are now detected with recent surveys performed by the Integral and Swift satellites. Most of these new sources eluded past surveys due to their large local X-ray extinction and consequent low soft X-ray flux. The Swift-BAT performs daily monitoring of the sky in an energy band (15-150 keV) which is only marginally affected by X-ray extinction, thus allowing for the search of long periodicities in the light curve and identification of the nature of the X-ray sources. We performed a period search using the folding technique in the Swift-BAT light curves of three Integral sources: IGR J05007-7047, IGR J13186-6257 and IGR J17354-3255. Their periodograms show significant peaks at 30.77$\pm$0.01 d, 19.994$\pm$0.01 d and 8.448$\pm$0.002 d, respectively. We estimate the significance of these features from the chi squared distribution of all the trials, finding a probability less than 1.5$\times10^{-4}$ that the detections occurred due to chance. We complement our analysis with the study of their broadband X-ray emission. We identify the periodicities with the orbital periods of the sources. The periods are typical for the wind accretors X-ray binaries and we support this identification showing that also their energy spectra are compatible with an X-ray spectral emission characteristic of high-mass X-ray binaries. The spectrum of IGR J05007-704 that resides in the Large Magellanic Cloud, does not show any intrinsic local absorption, whereas the spectra of the Galactic sources IGR J17354-3255 and IGR J13186-6257 may be affected by a local absorber. The folded light curve for IGR J13186-6257 suggests a possible Be companion star.Comment: 10 pages, 14 figures. Accepted for publication in A&