ROSAT All-Sky Survey observations of IRAS galaxies; I. Soft X-ray and far-infrared properties

The 120,000 X-ray sources detected in the RASS II processing of the ROSAT All-Sky Survey are correlated with the 14,315 IRAS galaxies selected from the IRAS Point Source Catalogue: 372 IRAS galaxies show X-ray emission within a distance of 100 arcsec from the infrared position. By inspecting the structure of the X-ray emission in overlays on optical images we quantify the likelihood that the X-rays originate from the IRAS galaxy. For 197 objects the soft X-ray emission is very likely associated with the IRAS galaxy. Their soft X-ray properties are determined and compared with their far-infrared emission. X-ray contour plots overlaid on Palomar Digitized Sky Survey images are given for each of the 372 potential identifications. All images and tables displayed here are also available in electronic form.Comment: accepted for publication in A&AS, complete version including all figures and tables available at http://www.rosat.mpe-garching.mpg.de/~bol/iras_rassI

Detection of [OI] 6300 and Other Diagnostic Emission Lines in the Diffuse Ionized Gas of M33 with Gemini-North

We present spectroscopic observations of diffuse ionized gas (DIG) in M33 near the HII region NGC 604. We present the first detection of [OI] 6300 in the DIG of M33, one of the critical lines for distinguishing photo- from shock ionization models. We measure [OI]/Ha in the range of 0.04 to 0.10 and an increase in this ratio with decreasing emission measure. Our measurements of [SII]/Ha and [NII]/Ha also rise with decreasing emission measure, while our [OIII]/Hb measurements remain fairly constant. We have one tentative detection of He I in the region of brightest emission measure, with a ratio of He I/Ha = 0.033 +- 0.019, indicating that the helium is at least partially ionized. We compare our observed emission line ratios to photoionization models and find that field star ionization models do not fit our data well. Leaky HII region models are consistent with our data, without the need to invoke additional ionization mechanisms to fit our [OI] or [OIII] measurements. The closest large HII region is NGC 604 and is therefore a likely candidate for the source of the ionizing photons for the gas in this region.Comment: 12 pages, 4 figures, accepted by ApJ

SDSS AGNs with X-ray Emission from ROSAT PSPC Pointed Observations

We present a sample of 1744 type 1 active galactic nuclei (AGNs) from the Sloan Digital Sky Survey (SDSS DR4) spectroscopic catalog with X-ray counterparts in the White-Giommi-Angelini Catalog (WGACAT) of ROSAT PSPC pointed observations. Of 1744 X-ray sources, 1410 (80.9%) are new AGN identifications. Of 4574 SDSS DR4 AGNs for which we found radio matches in the catalog of radio sources from the FIRST catalog, 224 turned up in our sample of SDSS X-ray AGNs. The sample objects are given in a catalog that contains optical and X-ray parameters along with radio emission parameters where available. We illustrate the content of our catalog and its potential for AGN science by providing statistical relationships for the catalog data. The potential of the morphological information is emphasized by confronting the statistics of optically resolved and unresolved AGNs. The immediate properties of the catalog objects include significant correlation of X-ray and optical fluxes, which is consistent with expectations. Also expected is the decrease of X-ray flux toward higher redshifts. The X-ray to optical flux ratio for the unresolved AGNs exhibits a decline toward higher redshifts, in agreement with previous results. The resolved AGNs, however, display the opposite trend. At a given optical brightness, X-ray fluxes of radio-quiet AGNs by a factor of 2. We caution, however, that because of the variety of selection effects present in both the WGACAT and the SDSS, the interpretation of any relationships based on our sample of X-ray AGNs requires a careful analysis of these effects.Comment: 34 pages, 18 figure

Optical variability of the strong-lined and X-ray bright source 1WGA J0447.9-0322

We present the historic light curve of 1WGA J0447.9-0322, spanning the time interval from 1962 to 1991, built using the Asiago archive plates. The source shows small fluctuations of about 0.3 mag around B=16 until 1986 and a fast dimming of its average level by about 0.5 mag after that date, again with small short term variations. The variability pattern is within the values shown by other QSOs with long term monitoring, notwithstanding its high X-ray/optical ratio. We present also its overall SED using literature data and recent UV-optical SWIFT observations.Comment: 17 pages, 4 figures, accepted by The Astronomical Journal. Table 2 available upon reques

A ROSAT Survey of Contact Binary Stars

Contact binary stars are common variable stars which are all believed to emit relatively large fluxes of x-rays. In this work we combine a large new sample of contact binary stars derived from the ROTSE-I telescope with x-ray data from the ROSAT All-Sky Survey (RASS) to estimate the x-ray volume emissivity of contact binary stars in the galaxy. We obtained x-ray fluxes for 140 contact binaries from the RASS, as well as 2 additional stars observed by the XMM-Newton observatory. From these data we confirm the emission of x-rays from all contact binary systems, with typical luminosities of approximately 1.0 x 10^30 erg s^-1. Combining calculated luminosities with an estimated contact binary space density, we find that contact binaries do not have strong enough x-ray emission to account for a significant portion of the galactic x-ray background.Comment: 19 pages, 5 figures, accepted by A

Risk and resiliency factors in posttraumatic stress disorder

BACKGROUND: Not everyone who experiences a trauma develops posttraumatic stress disorder (PTSD). The aim of this study was to determine the risk and resiliency factors for this disorder in a sample of people exposed to trauma. METHOD: Twenty-five people who had developed PTSD following a trauma and 27 people who had not were asked to complete the Posttraumatic Stress Diagnostic Scale, the Coping Inventory for Stressful Situations, and the State-Trait Anxiety Inventory. In addition, they completed a questionnaire to provide information autobiographic and other information. ANALYSIS: Five variables that discriminated significantly between the two groups using chi-square analysis or t-tests were entered into a logistic regression equation as predictors, namely, being female, perceiving a threat to one's life, having a history of sexual abuse, talking to someone about the event, and the "intentionality" of the trauma. RESULTS: Only being female and perceiving a threat to one's life were significant predictors of PTSD. Taking base rates into account, 96.0% of participants with PTSD were correctly classified as having the disorder and 37.0% of participants without PTSD were correctly classified as not having the disorder, for an overall success rate of 65.4% CONCLUSIONS: Because women are more likely than men to develop PTSD, more preventive measures should be directed towards them. The same is true for trauma victims (of both sexes) who feel that their life was in dange

Source Matching in the SDSS and RASS: Which Galaxies are Really X-ray Sources?

The current view of galaxy formation holds that all massive galaxies harbor a massive black hole at their center, but that these black holes are not always in an actively accreting phase. X-ray emission is often used to identify accreting sources, but for galaxies that are not harboring quasars (low-luminosity active galaxies), the X-ray flux may be weak, or obscured by dust. To aid in the understanding of weakly accreting black holes in the local universe, a large sample of galaxies with X-ray detections is needed. We cross-match the ROSAT All Sky Survey (RASS) with galaxies from the Sloan Digital Sky Survey Data Release 4 (SDSS DR4) to create such a sample. Because of the high SDSS source density and large RASS positional errors, the cross-matched catalog is highly contaminated by random associations. We investigate the overlap of these surveys and provide a statistical test of the validity of RASS-SDSS galaxy cross-matches. SDSS quasars provide a test of our cross-match validation scheme, as they have a very high fraction of true RASS matches. We find that the number of true matches between the SDSS main galaxy sample and the RASS is highly dependent on the optical spectral classification of the galaxy; essentially no star-forming galaxies are detected, while more than 0.6% of narrow-line Seyferts are detected in the RASS. Also, galaxies with ambiguous optical classification have a surprisingly high RASS detection fraction. This allows us to further constrain the SEDs of low-luminosity active galaxies. Our technique is quite general, and can be applied to any cross-matching between surveys with well-understood positional errors.Comment: 10 pages, 10 figures, submitted to The Astronomical Journal on 19 June 200

Discovery of a new cataclysmic variable through optical variability and X-ray emission

Aims: We present discovery observations of the new cataclysmic variable star (CV) 1RXS J092737.4-191529, as well as spectra and photometry of SY Vol. The selection technique that turned up these two CVs is described; it should be efficient for finding dwarf novae with high outburst duty cycles. Methods: Two very common observational features of CVs, namely optical variability and X-ray emission, are combined to select targets for follow-up observations. Long-slit spectra were taken to identify CVs in the sample. Results: Two out of three objects selected in this way are CVs. One of these is the known dwarf nova SY Vol, while the second system, 1RXS J092737.4-191529, is a new discovery. We present medium resolution spectra, $UBVRI$ magnitudes, and high-speed photometry for both these CVs. Rapid flickering in the light curve of 1RXS J092737.4-191529 confirms the mass transferring binary nature of this object; it is probably a dwarf nova that was in quiescence during our observations.Comment: 4 pages, 5 figures, accepted to A&