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

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

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

Search for X-ray Afterglows from Gamma-Ray Bursts in the RASS

We report on a search for X-ray afterglows from gamma-ray bursts using the ROSAT all-sky survey (RASS) data. If the emission in the soft X-ray band is significantly less beamed than in the gamma-ray band, we expect to detect many afterglows in the RASS. Our search procedure generated 23 afterglow candidates, where about 4 detections are predicted. Follow-up spectroscopy of several counterpart candidates strongly suggests a flare star origin of the RASS events in many, if not all, cases. Given the small number of events we conclude that the data are consistent with comparable beaming angles in the X-ray and gamma-ray bands. Models predicting a large amount of energy emerging as a nearly isotropic X-ray component, and a so far undetected class of ``dirty fireballs'' and re-bursts are constrained.Comment: 5 pages, LATEX with aipproc.sty, incl. 1 ps-Fig., Proc. of the 5th Huntsville Gamma Ray Burst Symposium, Oct. 1999, ed. R.M. Kippen, AIP; also available at http://www.aip.de/~jcg/publis.htm

Nothing to hide: An X-ray survey for young stellar objects in the Pipe Nebula

We have previously analyzed sensitive mid-infrared observations to establish that the Pipe Nebula has a very low star-formation efficiency. That study focused on YSOs with excess infrared emission (i.e, protostars and pre-main sequence stars with disks), however, and could have missed a population of more evolved pre-main sequence stars or Class III objects (i.e., young stars with dissipated disks that no longer show excess infrared emission). Evolved pre-main sequence stars are X-ray bright, so we have used ROSAT All-Sky Survey data to search for diskless pre-main sequence stars throughout the Pipe Nebula. We have also analyzed archival XMM-Newton observations of three prominent areas within the Pipe: Barnard 59, containing a known cluster of young stellar objects; Barnard 68, a dense core that has yet to form stars; and the Pipe molecular ring, a high-extinction region in the bowl of the Pipe. We additionally characterize the X-ray properties of YSOs in Barnard 59. The ROSAT and XMM-Newton data provide no indication of a significant population of more evolved pre-main sequence stars within the Pipe, reinforcing our previous measurement of the Pipe's very low star formation efficiency.Comment: Accepted for publication in Ap

Numerical Investigation of the Phase Evolution in Polymer Blends under External Mechanical Loadings

The influences on the development of polymer blend microstructures are not yet fully understood in the manufacturing processes. The purpose of this paper is to give a closer look at the effect of the elastic energy on the decomposition process. The decomposition process of a melt consisting of two polymers with different shear moduli is investigated. Due to the resulting heterogeneous material behavior and deformations, the generated energy field is heterogeneous as well. This energy causes changes in the local stability of the mixture, which yields phases consisting of both the polymers. Additionally, possible large deformations result in dominating diffusion directions

The Effect of Hot Gas in WMAP's First Year Data

By cross-correlating templates constructed from the 2 Micron All Sky Survey (2MASS) Extended Source (XSC) catalogue with WMAP's first year data, we search for the thermal Sunyaev-Zel'dovich signature induced by hot gas in the local Universe. Assuming that galaxies trace the distribution of hot gas, we select regions on the sky with the largest projected density of galaxies. Under conservative assumptions on the amplitude of foreground residuals, we find a temperature decrement of -35 $\pm$ 7 $\mu$K ($\sim 5\sigma$ detection level, the highest reported so far) in the $\sim$ 26 square degrees of the sky containing the largest number of galaxies per solid angle. We show that most of the reported signal is caused by known galaxy clusters which, when convolved with the average beam of the WMAP W band channel, subtend a typical angular size of 20--30 arcmins. Finally, after removing from our analyses all pixels associated with known optical and X-ray galaxy clusters, we still find a tSZ decrement of -96 $\pm$ 37 $\mu$K in pixels subtending about $\sim$ 0.8 square degrees on the sky. Most of this signal is coming from five different cluster candidates in the Zone of Avoidance (ZoA), present in the Clusters In the ZoA (CIZA) catalogue. We found no evidence that structures less bound than clusters contribute to the tSZ signal present in the WMAP data.Comment: 10 pages, 4 figures, matches accepted version in ApJ Letter

The North Ecliptic Pole Supercluster

We have used the ROSAT All-Sky Survey to detect a known supercluster at z=0.087 in the North Ecliptic Pole region. The X-ray data greatly improve our understanding of this supercluster's characteristics, approximately doubling our knowledge of the structure's spatial extent and tripling the cluster/group membership compared to the optical discovery data. The supercluster is a rich structure consisting of at least 21 galaxy clusters and groups, 12 AGN, 61 IRAS galaxies, and various other objects. A majority of these components were discovered with the X-ray data, but the supercluster is also robustly detected in optical, IR, and UV wavebands. Extending 129 x 102 x 67 (1/h50 Mpc)^3, the North Ecliptic Pole Supercluster has a flattened shape oriented nearly edge-on to our line-of-sight. Owing to the softness of the ROSAT X-ray passband and the deep exposure over a large solid angle, we have detected for the first time a significant population of X-ray emitting galaxy groups in a supercluster. These results demonstrate the effectiveness of X-ray observations with contiguous coverage for studying structure in the Universe.Comment: Accepted for publication in The Astrophysical Journal; 5 pages with 2 embedded figures; uses emulateapj.sty; For associated animations, see http://www.ifa.hawaii.edu/~mullis/nep3d.html; A high-resolution color postscript version of the full paper is available at http://www.ifa.hawaii.edu/~mullis/papers/nepsc.ps.g

The 1 keV to 200 keV X-ray Spectrum of NGC 2992 and NGC 3081

The Seyfert 2 galaxies NGC 2992 and NGC 3081 have been observed by INTEGRAL and Swift. We report about the results and the comparison of the spectrum above 10 keV based on INTEGRAL IBIS/ISGRI, Swift/BAT, and BeppoSAX/PDS. A spectrum can be extracted in the X-ray energy band ranging from 1 keV up to 200 keV. Although NGC 2992 shows a complex spectrum below 10 keV, the hard tail observed by various missions exhibits a slope with photon index = 2, independent on the flux level during the observation. No cut-off is detectable up to the detection limit around 200 keV. In addition, NGC 3081 is detected in the INTEGRAL and Swift observation and also shows an unbroken Gamma = 1.8 spectrum up to 150 keV. These two Seyfert galaxies give further evidence that a high-energy cut-off in the hard X-ray spectra is often located at energies E_C >> 100 keV. In NGC 2992 a constant spectral shape is observed over a hard X-ray luminosity variation by a factor of 11. This might indicate that the physical conditions of the emitting hot plasma are constant, while the amount of plasma varies, due to long-term flaring activity.Comment: 8 pages, 4 figures, accepted for publication in Ap