Supersoft X-ray sources in M31: II. ROSAT-detected supersoft sources in the ROSAT, Chandra and XMM eras

We have performed Chandra observations during the past 3 years of 5 of the M31 supersoft X-ray sources (SSS) discovered with ROSAT. Surprisingly, only one of these sources has been detected, despite a predicted detection of about 20-80 counts. This has motivated a thorough check of the ROSAT M31 survey I data, including a relaxation of the hardness ratio requirement used to select SSS. This increases the number of SSS identified in survey I by 7. We then carried out a comparison with the ROSAT M31 survey II dataset which had hitherto not been explicitly investigated for SSS. We find that most of the ROSAT survey I sources are not detected, and only two new SSS are identified. The low detection rate in the ROSAT survey II and our Chandra observations implies that the variability time scale of SSS is a few months. If the majority of these sources are close-binary SSS with shell hydrogen burning, it further implies that half of these sources predominantly experience large mass transfer rates.Comment: accepted for publ. in ApJ; 2 ps-figures; high-quality figures available at http://www.mpe.mpg.de/~jcg/publis.htm

A Catalog of Transient X-ray Sources in M31

From October 1999 to August 2002, 45 transient X-ray sources were detected in M31 by Chandra and XMM-Newton. We have performed spectral analysis of all XMM-Newton and Chandra ACIS detections of these sources, as well as flux measurements of Chandra HRC detections. The result is absorption-corrected X-ray lightcurves for these sources covering this 2.8 year period, along with spectral parameters for several epochs of the outbursts of most of the transient sources. We supply a catalog of the locations, outburst dates, peak observed luminosities, decay time estimates, and spectral properties of the transient sources, and we discuss similarities with Galactic X-ray novae. Duty cycle estimates are possible for 8 of the transients and range from 40% to 2%; upper limits to the duty cycles are estimated for an additional 15 transients and cover a similar range. We find 5 transients which have rapid decay times and may be ultra-compact X-ray binaries. Spectra of three of the transients suggest they may be faint Galactic foreground sources. If even one is a foreground source, this suggests a surface density of faint transient X-ray sources of >~1 deg$^{-2}$.Comment: 63 pages, 22 figures, 3 tables, accepted for publication in Ap

e-VLBI observations of Circinus X-1: monitoring of the quiescent and flaring radio emission on AU scales

A recent detection of the peculiar neutron star X-ray binary Circinus X-1 with electronic very long baseline interferometry (e-VLBI) prompted the suggestion that compact, non-variable radio emission persists through the entire 16.6-day orbit of the binary system. We present the results of a high angular resolution monitoring campaign conducted with the Australian Long Baseline Array in real-time e-VLBI mode. e-VLBI observations of Circinus X-1 were made on alternate days over a period of 20 days covering the full binary orbit. A compact radio source associated with Circinus X-1 was clearly detected at orbital phases following periastron passage but no compact radio emission was detected at any other orbital phase, ruling out the presence of a persistent, compact emitting region at our sensitivity levels. The jet was not resolved at any epoch of our 1.4-GHz monitoring campaign, suggesting that the ultrarelativistic flow previously inferred to exist in this source is likely to be dark. We discuss these findings within the context of previous radio monitoring of Circinus X-1.Comment: Accepted for publication in MNRAS. 7 pages, 5 figure

The first resolved imaging of milliarcsecond-scale jets in Circinus X-1

We present the first resolved imaging of the milliarcsecond-scale jets in the neutron star X-ray binary Circinus X-1, made using the Australian Long Baseline Array. The angular extent of the resolved jets is ~20 milliarcseconds, corresponding to a physical scale of ~150 au at the assumed distance of 7.8 kpc. The jet position angle is relatively consistent with previous arcsecond-scale imaging with the Australia Telescope Compact Array. The radio emission is symmetric about the peak, and is unresolved along the minor axis, constraining the opening angle to be less than 20 degrees. We observe evidence for outward motion of the components between the two halves of the observation. Constraints on the proper motion of the radio-emitting components suggest that they are only mildly relativistic, although we cannot definitively rule out the presence of the unseen, ultra-relativistic (Lorentz factor >15) flow previously inferred to exist in this system.Comment: Accepted for publication in MNRAS Letters. 6 pages, 4 figure

A Synoptic X-ray Study of M31 with the Chandra-HRC

We have obtained 17 epochs of Chandra High Resolution Camera (HRC) snapshot images, each covering most of the M31 disk. The data cover a total baseline of 2.5 years and contain a mean effective exposure of 17 ks. We have measured the mean fluxes and long-term lightcurves for 166 objects detected in these data. At least 25% of the sources show significant variability. The cumulative luminosity function (CLF) of the disk sources is well-fit by a power-law with a slope comparable to those observed in typical elliptical galaxies. The CLF of the bulge is a broken power law similar to measurements made by previous surveys. We note several sources in the southwestern disk with L_X > 10^{37} erg/s . We cross-correlate all of our sources with published optical and radio catalogs, as well as new optical data, finding counterpart candidates for 55 sources. In addition, 17 sources are likely X-ray transients. We analyze follow-up HST WFPC2 data of two X-ray transients, finding F336W (U-band equivalent) counterparts. In both cases, the counterparts are variable. In one case, the optical counterpart is transient with F336W = 22.3 +/- 0.1 mag. The X-ray and optical properties of this object are consistent with a ~10 solar mass black hole X-ray nova with an orbital period of ~20 days. In the other case, the optical counterpart varies between F336W = 20.82 +/- 0.06 mag and F336W = 21.11 +/- 0.02 mag. Ground-based and HST observations show this object is bright (V = 18.8 +/- 0.1) and slightly extended. Finally, the frequency of bright X-ray transients in the M31 bulge suggests that the ratio of neutron star to black hole primaries in low-mass X-ray binaries (NS/BH) is ~1.Comment: 68 pages (27 text), 8 tables, 16 figures, 1 appendix, accepted by ApJ; accepted version contains reorganized text, new tables and figures, and updated result

The XMM-Newton Optical/UV Monitor Telescope

The XMM-OM instrument extends the spectral coverage of the XMM-Newton observatory into the ultraviolet and optical range. It provides imaging and time-resolved data on targets simultaneously with observations in the EPIC and RGS. It also has the ability to track stars in its field of view, thus providing an improved post-facto aspect solution for the spacecraft. An overview of the XMM-OM and its operation is given, together with current information on the performance of the instrument

Rms-flux relation of Cyg X-1 with RXTE: dipping and nondipping cases

The rms (root mean square) variability is the parameter for understanding the emission temporal properties of X-ray binaries (XRBs) and active galactic nuclei (AGN). The rms-flux relation with Rossi X-ray Timing Explorer (RXTE) data for the dips and nondip of black hole Cyg X-1 has been investigated in this paper. Our results show that there exist the linear rms-flux relations in the frequency range 0.1-10 Hz for the dipping light curve. Moreover, this linear relation still remains during the nondip regime, but with the steeper slope than that of the dipping case in the low energy band. For the high energy band, the slopes of the dipping and nondipping cases are hardly constant within errors. The explanations of the results have been made by means of the ``Propagating Perturbation'' model of Lyubarskii (1997).Comment: 15 pages, 12 figures, Accepted for publication in Astrophysics & Space Scienc

Suicidal Ideation is Associated with Limited Engagement in HIV Care

PHQ-9 data from persons living with HIV (PLWH, n = 4099) being screened for depression in three clinics in the southeastern USA were used to determine the prevalence of suicidal ideation (SI). SI was reported by 352 (8.6 %); associated with 50 copies/ml (1.70, 95 %CI 1.35, 2.14). Data from PLWH enrolled in a depression treatment study were used to determine the association between moderate-to-high risk SI (severity) and SI frequency reported on PHQ-9 screening. Over forty percent of persons reporting that SI occurred on “more than half the days” (by the PHQ-9) were assessed as having a moderate-to-high risk for suicide completion during the Mini International Neuropsychiatric Interview. SI, including moderate-to-high risk SI, remains a significant comorbid problem for PLWH who are not fully stabilized in care (as indicated by detectable HIV RNA or HIV diagnosis for less than 3 years)

Trauma history and depression predict incomplete adherence to antiretroviral therapies in a low income country.

As antiretroviral therapy (ART) for HIV becomes increasingly available in low and middle income countries (LMICs), understanding reasons for lack of adherence is critical to stemming the tide of infections and improving health. Understanding the effect of psychosocial experiences and mental health symptomatology on ART adherence can help maximize the benefit of expanded ART programs by indicating types of services, which could be offered in combination with HIV care. The Coping with HIV/AIDS in Tanzania (CHAT) study is a longitudinal cohort study in the Kilimanjaro Region that included randomly selected HIV-infected (HIV+) participants from two local hospital-based HIV clinics and four free-standing voluntary HIV counselling and testing sites. Baseline data were collected in 2008 and 2009; this paper used data from 36 month follow-up interviews (N = 468). Regression analyses were used to predict factors associated with incomplete self-reported adherence to ART. INCOMPLETE ART ADHERENCE WAS SIGNIFICANTLY MORE LIKELY TO BE REPORTED AMONGST PARTICIPANTS WHO EXPERIENCED A GREATER NUMBER OF CHILDHOOD TRAUMATIC EVENTS: sexual abuse prior to puberty and the death in childhood of an immediate family member not from suicide or homicide were significantly more likely in the non-adherent group and other negative childhood events trended toward being more likely. Those with incomplete adherence had higher depressive symptom severity and post-traumatic stress disorder (PTSD). In multivariable analyses, childhood trauma, depression, and financial sacrifice remained associated with incomplete adherence.\ud This is the first study to examine the effect of childhood trauma, depression and PTSD on HIV medication adherence in a low income country facing a significant burden of HIV. Allocating spending on HIV/AIDS toward integrating mental health services with HIV care is essential to the creation of systems that enhance medication adherence and maximize the potential of expanded antiretroviral access to improve health and reduce new infections

The central region of M31 observed with XMM-Newton (I. Group properties and diffuse emission)

We present the results of a study based on an XMM-Newton Performance Verification observation of the central 30 arcmin of the nearby spiral galaxy M31. In the 34-ks European Photon Imaging Camera (EPIC) exposure, we detect 116 sources down to a limiting luminosity of 6 x 10^35 erg/s (0.3--12 keV, d = 760 kpc). The luminosity distribution of the sources detected with XMM-Newton flattens at luminosities below ~ 2.5 x 10^37 erg/s. We make use of hardness ratios for the detected sources in order to distinguish between classes of objects such as super-soft sources and intrinsically hard or highly absorbed sources. We demonstrate that the spectrum of the unresolved emission in the bulge of M31 contains a soft excess which can be fitted with a ~ 0.35-keV optically-thin thermal-plasma component clearly distinct from the composite point-source spectrum. We suggest that this may represent diffuse gas in the centre of M31, and we illustrate its extent in a wavelet-deconvolved image.Comment: to appear in the XMM-Newton special issue of A&A (Vol 365, January 2001). High-resolution versions of fig. 1 and fig. 6 available on reques