Ultraluminous X-ray Source Correlations with Star-Forming Regions

Maps of low-inclination nearby galaxies in Sloan Digitized Sky Survey u-g, g-r and r-i colors are used to determine whether Ultraluminous X-ray sources (ULXs) are predominantly associated with star-forming regions of their host galaxies. An empirical selection criterion is derived from colors of HII regions in M81 and M101 that differentiates between the young, blue stellar component and the older disk and bulge population. This criterion is applied to a sample of 58 galaxies of Hubble type S0 and later and verified through an application of Fisher's linear discriminant analysis. It is found that 60% (49%) of ULXs in optically-bright environments are within regions blueward of their host galaxy's HII regions compared to only 27% (0%) of a control sample according to the empirical (Fisher) criterion. This is an excess of 3-sigma above the 32% (27%) expected if the ULXs were randomly distributed within their galactic hosts. This indicates a ULX preference for young, approximately <10 Myr, OB associations. However, none of the ULX environments have the morphology and optical brightness suggestive of a massive young super star cluster though several are in extended or crowded star-forming (blue) environments that may contain clusters unresolved by Sloan imaging. Ten of the 12 ULX candidates with estimated X-ray luminosities in excess of 3e39 erg/s are equally divided among the group of ULX environments redward of HII regions and the group of optically faint regions. This likely indicates that the brightest ULXs turn on at a time somewhat later than typical of HII regions; say 10-20 Myr after star formation has ended. This would be consistent with the onset of an accretion phase as the donor star ascends the giant branch if the donor is a <20 solar-mass star.Comment: 13 pages, accepted to Ap

A New Ultraluminous X-ray Source in the Nearby Edge-on Spiral NGC 891

We report the discovery of a new candidate ultraluminous X-ray source (ULX) in the nearby edge-on spiral galaxy NGC 891. The source, which has an absorbed flux of F_X ~ 10^-12 erg/s/cm^2 (corresponding to L_X > 10^40 erg/s at 9 Mpc), must have begun its outburst in the past 5 years as it is not detected in prior X-ray observations between 1986 and 2006. We try empirical fits to the XMM-Newton spectrum, finding that the spectrum is fit very well as emission from a hot disk, a cool irradiated disk, or blurred reflection from the innermost region of the disk. The simplest physically motivated model with an excellent fit is a hot disk around a stellar-mass black hole (a super-Eddington outburst), but equally good fits are found for each model. We suggest several follow-up experiments that could falsify these models.Comment: 6 pages, 4 figures, 1 table. Accepted to ApJ Letter

Comparison Of Abdominal Compression Devices In Persons With Abdominal Paralysis Due To Spinal Cord Injury

Comparison of abdominal compression devices in persons with abdominal paralysis due to spinal cord injury. Michaela de Groot, MA, SPT; Jennifer Swartz, MA, SPT; Jennifer Hastings PT, PhD, NCS University of Puget Sound, Tacoma WA Objective: In the United States the incidence of spinal cord injury (SCI) is approximately 17,000 new cases a year and there are estimated to be 282,000 persons living with SCI. Approximately 80% of those injured sustain neurologic lesions that impair the function of the abdominal musculature. In the non-disabled population it is well understood that the strength of the abdominal wall is key to prevention of musculoskeletal pain and improving postural control. The abdominal wall functions to maintain intra-abdominal cavity pressure which in a healthy system works in coordination with intra-thoracic cavity pressure. Paralysis of the abdominal musculature impairs the function of the diaphragm. Use of an abdominal binder is a common intervention following acute SCI.However, the long term daily use of abdominal binders is not common among individuals living with SCI. The purpose of this study is to compare the effectiveness and usability of alternative commercial abdominal compression garments with the usual medical device. Design/Methods: This study follows a single subject design with 5 participants. Inclusion: SCI T6 or above, currently using abdominal binder when seated in the wheelchair, able to don the binder independently or with caregiver assistance. Exclusion: Unable to speak English and communicate either written or electronically, or current skin breakdown. Data was collected over 3 periods of 1 week at a time; participants wore the compression garment for 5 days followed by a rest period of 2 days. In week 1, the participant wore their current abdominal binder. In weeks 2 and 3, an alternative compression device was worn. The alternatives were a compressive tank top and a compressive unisuit (shorts and tank). Physiological measurements and photographs were taken with the current binder, then after a 5 minute acclimation period each without any binder and then the alternative garment. Outcome measures: blood pressure, blood oxygen saturation, forced exhalation volume in 1 second, and heart rate. A daily log was completed twice daily for 5 days per garment with questions asking about participants’ experience. Results: The use of a personal binder resulted in significant increases in systolic blood pressure (SBP) and forced expiratory volume in 1 second (FEV1). The other parameters were not significantly different with or without the personal binder. There was no difference in SBP between the test garments and the personal binders, but the test garments’ support of FEV1 was significantly less. Graphic analysis of experiential trends will be presented. Conclusion: Abdominal compression improves respiratory function and supports BP. The alternative devices provided similar BP support, but less respiratory support. Alternative devices required caregiver assistance. Lack of full UE ROM made the tank option unfeasible. The unisuit offended sensibilities and therefore is not an acceptable device. Support: This study received support from the University of Puget Sound

ChAInGeS: The Chandra Arp Interacting Galaxies Survey

We have conducted a statistical analysis of the ultra-luminous X-ray point sources (ULXs; L(X) >= 10^39 erg/s) in a sample of galaxies selected from the Arp Atlas of Peculiar Galaxies. We find a possible enhancement of a factor of ~2-4 in the number of ULXs per blue luminosity for the strongly interacting subset. Such an enhancement would be expected if ULX production is related to star formation, as interacting galaxies tend to have enhanced star formation rates on average. For most of the Arp galaxies in our sample, the total number of ULXs compared to the far-infrared luminosity is consistent with values found earlier for spiral galaxies. This suggests that for these galaxies, ULXs trace recent star formation. However, for the most infrared-luminous galaxies, we find a deficiency of ULXs compared to the infrared luminosity. For these very infrared-luminous galaxies, AGNs may contribute to powering the far-infrared; alternatively, ULXs may be highly obscured in the X-ray in these galaxies and therefore not detected by these Chandra observations. We determined local UV/optical colors within the galaxies in the vicinity of the candidate ULXs using GALEX UV and SDSS optical images. In most cases, the distributions of colors are similar to the global colors of interacting galaxies. However, the u - g and r - i colors at the ULX locations tend to be bluer on average than these global colors, suggesting that ULXs are preferentially found in regions with young stellar populations. In the Arp sample there is a possible enhancement of a factor of ~2 - 5 in the fraction of galactic nuclei that are X-ray bright compared to more normal spirals.Comment: 28 pages, 7 figures, Astronomical Journal, in pres

The Effect of Starburst Metallicity on Bright X-Ray Binary Formation Pathways

We investigate the characteristics of young ( 1e36 erg/s) High-Mass X-ray Binaries (HMXBs) and find the population to be strongly metallicity-dependent. We separate the model populations among two distinct formation pathways: (1) systems undergoing active Roche Lobe Overflow (RLO), and (2) wind accretion systems with donors in the (super)giant (SG) stage, which we find to dominate the HMXB population. We find metallicity to primarily affect the number of systems which move through each formation pathway, rather than the observable parameters of systems which move through each individual pathway. We discuss the most important model parameters affecting the HMXB population at both low and high metallicities. Using these results, we show that (1) the population of ultra-luminous X-Ray sources can be consistently described by very bright HMXBs which undergo stable Roche Lobe overflow with mild super-Eddington accretion and (2) the HMXB population of the bright starburst galaxy NGC~1569 is likely dominated by one extremely metal-poor starburst cluster.Comment: 12 pages, 10 figures, Accepted by Ap

A census of X-ray nuclear activity in nearby galaxies

We have studied the X-ray nuclear activity of 187 nearby (distance < 15 Mpc) galaxies observed with Chandra/ACIS. We found that 86 of them have a point-like X-ray core, consistent with an accreting black hole (BH). We argue that the majority of them are nuclear BHs, rather than X-ray binaries. The fraction of galaxies with an X-ray detected nuclear BH is higher (~60 per cent) for ellipticals and early-type spirals (E to Sb), and lower (~30 per cent) for late-type spirals (Sc to Sm). There is no preferential association of X-ray cores with a large-scale bar; in fact, strongly barred galaxies appear to have slightly lower detection fraction and luminosity for their nuclear X-ray sources, compared with non-barred or weakly barred galaxies of similar Hubble types. The cumulative luminosity distribution of the nuclear sources in the 0.3-8 keV band is a power-law with slope ~-0.5, from ~2 x 10^{38} erg/s to ~10^{42} erg/s. The Eddington ratio is lower for ellipticals (L_{X}/L_{Edd} ~ 10^{-8}) and higher for late-type spirals (up to L_{X}/L_{Edd} ~ 10^{-4}), but in all cases, the accretion rate is low enough to be in the radiatively-inefficient regime. The intrinsic NH is generally low, especially for the less luminous sources: there appear to be no Type-2 nuclear BHs at luminosities <~ 10^{39} erg/s. The lack of a dusty torus or of other sources of intrinsic absorption (e.g., an optically-thick disk wind) may be directly related to the lack of a standard accretion disk around those faint nuclear BHs. The fraction of obscured sources increases with the nuclear BH luminosity: 2/3 of the sources with L_{X} > 10^{40} erg/s have a fitted NH > 10^{22} cm^{-2}. This is contrary to the declining trend of the obscured fraction with increasing luminosities, observed in more luminous AGN and quasars.Comment: 27 pages, 353 kB, accepted by Ap

Reflections on Including Disability in Social Protection Programmes

This article presents reflections on including disability in social protection and, specifically, in social assistance programmes. The main considerations for including disability in such programmes are: (a) the factors associated with disability that create vulnerabilities for people with disabilities and their household (e.g. social exclusion, the need for care and extra costs); (b) the nature of disability targeting within social protection and social assistance programmes; and (c) the measurement of disability – a complex but key factor in ensuring accurate targeting and monitoring of impact. This article describes these considerations in relation to experiences in three African countries – Uganda, Zambia and South Africa – and concludes with recommendations on recognition of disability as a vulnerability factor, and how targeting and measurement can and should be addressed for inclusion of disability in social assistance programmes

The factor structure of the Edinburgh Postnatal Depression scale in a South African peri-urban settlement

The factor structure of the Edinburgh Postnatal Depression scale (EPDS) and similar instruments have received little attention in the literature. The researchers set out to investigate the construct validity and reliability of the EPDS amongst impoverished South African women. The EPDS was translated into isiXhosa (using Brislin's back translation method) and administered by trained interviewers to 147 women in Khayelitsha, South Africa. Responses were subjected to maximum likelihood confirmatory factor analysis. A single factor structure was found, consistent with the theory on which the EPDS was based. Internal consistency was satisfactory (a =0.89)