L. Homer

University of Washington Seattle, Seattle, WA, United States

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Publications (63)213.87 Total impact

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    ABSTRACT: We report on follow-up observations of candidate X-ray-bright, radio-quiet isolated neutron stars (INSs) identified from correlations of the ROSAT All-Sky Survey (RASS) and the Sloan Digital Sky Survey (SDSS) Data Release 4 in Agüeros et al. We obtained Chandra X-ray Observatory exposures for 13 candidates in order to pinpoint the source of X-ray emission in optically blank RASS error circles. These observations eliminated 12 targets as good INS candidates. We discuss subsequent observations of the remaining candidate with XMM-Newton, the Gemini North Observatory, and the Apache Point Observatory. We identify this object as a likely extragalactic source with an unusually high log (f X/f opt) ~ 2.4. We also use an updated version of the population synthesis models of Popov et al. to estimate the number of RASS-detected INSs in the SDSS Data Release 7 footprint. We find that these models predict ~3-4 INSs in the 11,000 deg2 imaged by SDSS, which is consistent with the number of known INSs that fall within the survey footprint. In addition, our analysis of the four new INS candidates identified in the SDSS footprint implies that they are unlikely to be confirmed as INSs; together, these results suggest that new INSs are not likely to be found from further correlations of the RASS and SDSS.
    The Astronomical Journal 04/2011; 141(6):176. · 4.97 Impact Factor
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    ABSTRACT: Highly sensitive and precise X-ray imaging from Chandra, combined with the superb spatial resolution of HST optical images, dramatically enhances our empirical understanding of compact binaries such as cataclysmic variables and low mass X-ray binaries, their progeny, and other stellar X-ray source populations deep into the cores of globular clusters. Our Chandra X-ray images of the globular cluster NGC 362 reveal 100 X-ray sources, the bulk of which are likely cluster members. Using HST color-magnitude and color-color diagrams, we quantitatively consider the optical content of the NGC 362 Chandra X-ray error circles, especially to assess and identify the compact binary population in this condensed-core globular cluster. Despite residual significant crowding in both X-rays and optical, we identify an excess population of H{\alpha}-emitting objects that is statistically associated with the Chandra X-ray sources. The X-ray and optical characteristics suggest that these are mainly cataclysmic variables, but we also identify a candidate quiescent low mass X-ray binary. A potentially interesting and largely unanticipated use of observations such as these may be to help constrain the macroscopic dynamic state of globular clusters. Comment: 6 pages, 6 figures, to appear in the proceedings of the conference "Binary Star Evolution: Mass Loss, Accretion, and Mergers," Mykonos, Greece, June 22-25, 2010
    11/2010;
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    ABSTRACT: We present the first pointed X-ray observation of DW Ursae Majoris, a novalike cataclysmic variable (CV) and one of the archetype members of the SW Sextantis class, obtained with the XMM-Newton satellite. These data provide the first detailed look at an SW Sex star in the X-ray regime (with previous X-ray knowledge of the SW Sex stars limited primarily to weak or non-detections in the ROSAT All Sky Survey). It is also one of only a few XMM-Newton observations (to date) of any high mass transfer rate novalike CV, and the only one in the evolutionarily important 3-4 hr orbital period range. The observed X-ray spectrum of DW UMa is very soft, with ~95% of the detected X-ray photons at energies <2 keV. The spectrum can be fit equally well by a one-component cooling flow model, with a temperature range of 0.2-3.5 keV, or a two-component, two-temperature thermal plasma model, containing hard (~5-6 keV) and soft (~0.8 keV) components. The X-ray light curve of DW UMa shows a likely partial eclipse, implying X-ray reprocessing in a vertically extended region, and an orbital modulation, implying a structural asymmetry in the X-ray reprocessing site (e.g., it cannot be a uniform corona). We also obtained a simultaneous near-ultraviolet light curve of DW UMa using the Optical Monitor on XMM-Newton. This light curve is similar in appearance to published optical-UV light curves of DW UMa and shows a prominent deep eclipse. Regardless of the exact nature of the X-ray reprocessing site in DW UMa, the lack of a prominent hard X-ray total eclipse and very low fraction of high energy X-rays point to the presence of an optically and geometrically thick accretion disk that obscures the boundary layer and modifies the X-ray spectrum emitted near the white dwarf.
    The Astronomical Journal 10/2010; 140(5):1313. · 4.97 Impact Factor
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    ABSTRACT: The combination of highly sensitive and precise X-ray imaging from Chandra and the superb spatial resolution of HST optical images have dramatically enhanced our empirical understanding of compact binaries (e.g., cataclysmic variables and low-mass X-ray binaries), their progeny, and other stellar X-ray source populations deep into the cores of globular clusters. Our Chandra X-ray images toward the globular cluster NGC 362 reveal nearly 100 X-ray sources, the bulk of which are likely associated with the cluster. Using CMD, color-color, and multiepoch imaging data from HST, we quantitatively consider the optical content of the NGC 362 Chandra X-ray error circles, especially to assess and identify the compact binary population in this crowded, possibly core-collapsed, globular cluster.
    01/2009;
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    ABSTRACT: We discuss the nature of the infrared (IR) counterpart of GX 17+2, one of the most luminous of the persistently bright X-ray binaries. Chandra HRC-S astrometry is consistent with either NP Ser (the original counterpart of GX 17+2 proposed by M. Tarenghi & C. Reina in 1972) or star "A" of E. W. Deutsch et al. as the counterpart of the X-ray source. However, we present Keck K-band observations that reveal a bright counterpart in the radio error circle of Deutsch et al. 09 north of NP Ser itself. Furthermore, the position of this counterpart is consistent with that of star A to within 01, implying an amplitude of variation of ~25-33 between the Keck observations and the Hubble Space Telescope (HST) measurements of Deutsch et al. Subsequent Keck imaging also reveals star A in an "IR-faint" state (K = 18.3 mag, with a corresponding amplitude of variability of ~22). In addition, archival Cerro Tololo Inter-American Observatory observations provide evidence for K-band variability, albeit of smaller amplitude. The HST and Keck K-band variations, however, do not appear to be accompanied by any changes in the overall X-ray luminosity of GX 17+2 as measured by contemporaneous (but not simultaneous) Rossi X-Ray Timing Explorer All-Sky Monitor observations. We propose instead that the large radio outbursts observed when the source is in the horizontal branch of its "Z" state are likely to give rise to synchrotron flares in the IR. The amplitude of the radio flares is in agreement with this scenario. Such IR variability, unrelated (directly) to X-ray reprocessing and the gross characteristics of the mass accretion rate, may be present in the IR flux of other low-mass X-ray binaries but harder to see owing to the intrinsically brighter IR fluxes of the longer period systems.
    The Astrophysical Journal 12/2008; 574(2):L143. · 6.73 Impact Factor
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    ABSTRACT: As part of our campaign to determine the nature of the various source populations of the low-luminosity globular cluster X-ray sources, we have obtained a Chandra X-Ray Observatory ACIS-S3 image of the globular cluster NGC 6440. We detect 24 sources to a limiting luminosity of ~2 × 1031 ergs s-1 (0.5-2.5 keV) inside the cluster's half-mass radius, all of which lie within ~2 core radii of the cluster center. We also find excess emission in and around the core that could be due to unresolved point sources. Based on X-ray luminosities and colors, we conclude that there are 4-5 likely quiescent low-mass X-ray binaries and that most of the other sources are cataclysmic variables. We compare these results to Chandra results from other globular clusters and find the X-ray luminosity functions differ among the clusters.
    The Astrophysical Journal 12/2008; 573(1):184. · 6.73 Impact Factor
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    ABSTRACT: We have obtained exposures of the field of X0512-401 in the globular cluster NGC 1851, in X-rays with the Chandra X-Ray Observatory, and in the far-UV with the Hubble Space Telescope. We derive an accurate new X-ray position (within ~1'') for X0512-401, which enables us to confirm that the only plausible candidate for the optical/UV counterpart is star A, which we previously identified from Wide Field Planetary Camera 2 imaging. We find no evidence for X-ray or UV flux modulation on the ultrashort (1 hr) expected binary period, which implies a low system inclination. In addition, we have detected and spatially resolved an X-ray burst event, confirming the association of the burster, quiescent X-ray source, and optical object. The very large LX/Lopt of this object implies an extraordinarily compact system, similar to the sources in NGC 6624 and NGC 6712.
    The Astrophysical Journal 12/2008; 550(2):L155. · 6.73 Impact Factor
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    ABSTRACT: We know from observations that globular clusters are very efficient catalysts in forming unusual short-period binary systems or their offspring, such as low-mass X-ray binaries (LMXBs; neutron stars accreting matter from low-mass stellar companions), cataclysmic variables (white dwarfs accreting matter from stellar companions), and millisecond pulsars (rotating neutron stars with spin periods of a few milliseconds). Although there has been little direct evidence, the overabundance of these objects in globular clusters has been attributed by numerous authors to the high densities in the cores, which leads to an increase in the formation rate of exotic binary systems through close stellar encounters. Many such close binary systems emit X-radiation at low luminosities (LX 1034 ergs s-1) and are being found in large numbers through observations with the Chandra X-Ray Observatory. Here we present conclusive observational evidence of a link between the number of close binaries observed in X-rays in a globular cluster and the stellar encounter rate of the cluster. We also make an estimate of the total number of LMXBs in globular clusters in our Galaxy.
    The Astrophysical Journal 12/2008; 591(2):L131. · 6.73 Impact Factor
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    ABSTRACT: We report on the Chandra X-Ray Observatory ACIS-S3 imaging observation of the Galactic globular cluster M4 (NGC 6121). We detect 12 X-ray sources inside the core and 19 more within the cluster half-mass radius. The limiting luminosity of this observation is LX ≈ 1029 ergs s-1 for sources associated with the cluster, the deepest X-ray observation of a globular cluster to date. We identify six X-ray sources with known objects and use ROSAT observations to show that the brightest X-ray source is variable. Archival data from the Hubble Space Telescope allow us to identify optical counterparts to 16 X-ray sources. Based on the X-ray and optical properties of the identifications and the information from the literature, we classify two (possibly three) sources as cataclysmic variables, one X-ray source as a millisecond pulsar, and 12 sources as chromospherically active binaries. Comparison of M4 with 47 Tuc and NGC 6397 suggests a scaling of the number of active binaries in these clusters with the cluster (core) mass.
    The Astrophysical Journal 12/2008; 609(2):755. · 6.73 Impact Factor
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    ABSTRACT: The cataclysmic variable SDSS J015543.40+002807.2 is confirmed to be a magnetic system of the AM Herculis type. With an orbital period of 87.13 minutes, it is also the shortest period eclipsing Polar known. Monitoring with XMM-Newton finds a high-state light curve dominated by a single X-ray-emitting accretion pole located slightly prograde of the secondary star. The hard X-ray spectrum is typical of radial shocks on magnetic white dwarfs (kT ~ 10 keV), and there is evidence for a soft X-ray component consistent with reprocessing from the stellar surface. The optical circular polarization is weak (v 3%) when the accretion rate is high (mV ~ 15.5), as a result of optically thick cyclotron emission and the apparent competition between two accreting poles. However, in low states (mV ~ 18), the polarization increases smoothly to the blue, reaching 20% at 4200 Å, and the flux spectrum displays a rich set of thermally broadened cyclotron harmonics that indicate a polar field of 29 MG. The phase interval preceding the 6.5 minute eclipse depicts the development of P Cygni components followed by complete absorption reversals in the emission lines. This phenomenon is not unexpected for a strongly accreting magnetic system viewed through the cool base of the funnel, and high-quality spectroscopy through this interval will likely lead to new insights into the dynamics of magnetic coupling and gas flow onto the white dwarf.
    The Astrophysical Journal 12/2008; 620(1):422. · 6.73 Impact Factor
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    ABSTRACT: We report follow-up XMM-Newton and optical observations of three new polars found in the Sloan Digital Sky Survey. Simple modeling of the X-ray spectra, and consideration of the details of the X-ray and optical light curves corroborate the polar nature of these three systems and provide further insights into their accretion characteristics. During the XMM-Newton observation of SDSS J072910.68+365838.3, X-rays are undetected apart from a probable flare event, during which we find both the typical hard X-ray bremsstrahlung component and a very strong O VII (E = 0.57 keV) line, but no evidence of a soft blackbody contribution. In SDSS J075240.45+362823.2 we identify an X-ray eclipse at the beginning of the observation, roughly in phase with the primary minimum of the optical broadband curve. The X-ray spectra require the presence of both hard and soft X-ray components, in a luminosity ratio consistent with that found in other recent XMM-Newton results on polars. SDSS J170053.30+400357.6 appears optically as a very typical polar; however, its large-amplitude optical modulation is 180° out of phase with the variation in our short X-ray light curve.
    The Astrophysical Journal 12/2008; 620(2):929. · 6.73 Impact Factor
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    ABSTRACT: We report the results of a 45 ks Chandra observation of the cataclysmic variable (CV) V426 Ophiuchus. The high-resolution spectrum from the high-energy transmission grating spectrometer is most consistent with a cooling flow model, placing V426 Oph among the group of CVs including U Gem and EX Hya. An uninterrupted light curve was also constructed, in which we detect a significant 4.2 hr modulation together with its first harmonic at 2.1 hr. Reanalysis of archival Ginga and ROSAT X-ray light curves also reveals modulations at periods consistent with 4.2 and/or 2.1 hr. Furthermore, optical photometry in V, simultaneous with the Chandra observation, indicates a modulation anticorrelated with the X-ray, and later more extensive R-band photometry finds a signal at ~2.1 hr. The earlier reported X-ray periods at ~0.5 and 1 hr appear to be only transient and quasi-periodic in nature. In contrast, the 4.2 hr period or its harmonic is stable and persistent in X-ray/optical data from 1988 to 2003. This periodicity is clearly distinct from the 6.85 hr orbit and could be due to the spin of the white dwarf. If this is the case, V426 Oph would be the first long-period intermediate polar with a ratio Pspin/Porb of 0.6. However, this interpretation requires unreasonable values of magnetic field strength and mass accretion rate.
    The Astrophysical Journal 12/2008; 610(2):991. · 6.73 Impact Factor
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    ABSTRACT: We report on the Chandra X-Ray Observatory observations of the globular cluster NGC 288. We detect four X-ray sources within the core radius and seven additional sources within the half-mass radius down to a limiting luminosity of LX = 7 × 1030 ergs s-1 (assuming cluster membership) in the 0.3-7 keV band. We also observed the cluster with the Hubble Space Telescope Advanced Camera for Surveys and identify optical counterparts to seven X-ray sources out of the nine sources within the HST field of view. Based on the X-ray and optical properties, we find 2-5 candidates of cataclysmic variables (CVs) or chromospherically active binaries and 2-5 background galaxies inside the half-mass radius. Since the core density of NGC 288 is very low, the number of faint X-ray sources of NGC 288 found in the Chandra and HST observations is higher than the prediction on the basis of the collision frequency. We suggest that the CVs and chromospherically active binaries are primordial in origin, in agreement with the theoretical expectation.
    The Astrophysical Journal 12/2008; 647(2):1065. · 6.73 Impact Factor
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    ABSTRACT: We present Chandra X-ray Observatory ACIS-S3 X-ray imaging observations and VLT/FORS2 and Hubble Space Telescope optical observations of two low-density Galactic globular clusters; NGC 6366 and M55. We detect 16 X-ray sources with 0.5–6.0 keV luminosities above LX = 4 × 1030 erg s−1 within the half-mass radius of M55, of which 8 or 9 are expected to be background sources, and 5 within the half-mass radius of NGC6366, of which 4 are expected to be background sources. Optical counterparts are identified for several X-ray sources in both clusters and from these we conclude that 3 of the X-ray sources in M55 and 2 or 3 of the X-ray sources in NGC 6366 are probably related to the cluster. Combining these results with those for other clusters, we find the best fit for a predicted number of X-ray sources in a globular cluster μc = 1.2Γ + 1.1 Mh, where Γ is the collision number and Mh is (half of) the cluster mass, both normalized to the values for the globular cluster M4. Some sources tentatively classified as magnetically active binaries are more luminous in X-rays than the upper limit of LX= 0.001 Lbol of such binaries in the solar neighbourhood. Comparison with XMM and ROSAT observations lead us to conclude that the brightest X-ray source in M55, a dwarf nova, becomes fainter in X-rays during the optical outburst, in accordance with other dwarf novae. The brightest X-ray source in NGC6366 is a point source surrounded by a slightly offset extended source. The absence of galaxies and Hα emission in our optical observations argues against a cluster of galaxies and against a planetary nebula, and we suggest that the source may be an old nova.
    Astronomy and Astrophysics 01/2008; · 5.08 Impact Factor
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    ABSTRACT: This paper continues the series that identifies new cataclysmic variables found in the Sloan Digital Sky Survey (SDSS). We present 36 cataclysmic variables and one possible symbiotic star from Sloan spectra obtained during 2002, of which 34 are new discoveries, two are known dwarf novae (BC UMa and KS UMa), and one is a known cataclysmic variable identified from the Two-Degree Field survey. The positions, colors, and spectra of all 37 systems are presented, along with follow-up spectroscopic/photometric observations of 10 systems. As in the past 2 yr of data, the new SDSS systems show a large variety of characteristics based on their inclination and magnetic fields, including three eclipsing systems, four with prominent He II emission, and 15 systems showing features of the underlying stars.
    The Astronomical Journal 12/2007; 128(4):1882. · 4.97 Impact Factor
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    ABSTRACT: XMM-Newton observations of the polar SDSS J155331.12+551614.5 reveal that all the X-ray flux emerges at energies less than 2 keV. The best fit to the spectrum is with a thermal plasma with kT = 0.8 keV plus a 20–90 eV black body, yielding a thermal X-ray luminosity of (8.0–9.5) × 1028 ergs s-1. The low temperature and X-ray luminosity, together with the lack of variation of the X-ray flux during the observations, are all consistent with an extremely low accretion rate that puts the system in the bombardment regime of accretion, rather than accretion involving a standoff shock. It is likely that the observed X-rays originate from the M dwarf secondary star, thus providing a base activity level for late main-sequence stars in close binaries. SDSS J132411.57+032050.5 is detected by XMM-Newton at the faint EPIC pn count rate of 0.0012 ± 0.0003 counts s-1, giving an upper limit to the X-ray luminosity of ~7 × 1028 ergs s-1 for a distance of 300 pc, which is also consistent with the above scenario.
    The Astronomical Journal 12/2007; 128(5):2443. · 4.97 Impact Factor
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    ABSTRACT: We describe further results of a program aimed at yielding ~104 fully characterized optical identifications of ROSAT X-ray sources. Our program employs X-ray data from the ROSAT All Sky Survey (RASS) and both optical imaging and spectroscopic data from the Sloan Digital Sky Survey (SDSS). RASS/SDSS data from 5740 deg2 of sky spectroscopically covered in SDSS Data Release 5 provide an expanded catalog of 7000 confirmed quasars and other active galactic nuclei (AGNs) that are probable RASS identifications. Again, in our expanded catalog the identifications as X-ray sources are statistically secure, with only a few percent of the SDSS AGNs likely to be randomly superposed on unrelated RASS X-ray sources. Most identifications continue to be quasars and Seyfert 1 galaxies with 15 < m < 21 and 0.01 < z < 4, but the total sample size has grown to include very substantial numbers of even quite rare AGNs, e.g., it now includes several hundreds of candidate X-ray-emitting BL Lac objects and narrow-line Seyfert 1 galaxies. In addition to exploring rare subpopulations, such a large total sample may be useful when considering correlations between the X-ray and the optical and may also serve as a resource list from which to select the "best" object (e.g., X-ray-brightest AGN of a certain subclass at a preferred redshift or luminosity) for follow-up X-ray spectral or alternate detailed studies.
    The Astronomical Journal 12/2007; 133(1):313. · 4.97 Impact Factor
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    ABSTRACT: We have obtained Hubble Space Telescope/Space Telescope Imaging Spectrograph low-resolution ultraviolet spectra of the X-ray pulsar 4U 1626-67 (=KZ TrA); 4U 1626-67 is unusual even among X-ray pulsars because of its ultrashort binary period (P = 41.4 minutes) and remarkably low mass function (≤1.3 × 10-6 M). The far-UV spectrum was exposed for a total of 32 ks and has sufficient signal-to-noise ratio to reveal numerous broad emission and prominent narrower absorption lines. Most of the absorption lines are consistent in strength with a purely interstellar origin. However, there is evidence that both C I and C IV require additional absorbing gas local to the system. In emission, the usual prominent lines of N V and He II are absent, while both O IV and O V are relatively strong. We further identify a rarely seen feature at ~1660 Å as the O III] multiplet. Our ultraviolet spectra therefore provide independent support for the recent suggestion that the mass donor is the chemically fractionated core of either a CONe or ONeMg white dwarf; this was put forward to explain the results of Chandra high-resolution X-ray spectroscopy. The velocity profiles of the ultraviolet lines are in all cases broad and/or flat topped or perhaps even double peaked for the highest ionization cases of O; in either case, the ultraviolet line profiles are in broad agreement with the Doppler pairs found in the X-ray spectra. Both the X-ray and far-UV lines are plausibly formed in (or in an corona just above) a Keplerian accretion disk; the combination of ultraviolet and X-ray spectral data may provide a rich data set for follow-on detailed models of the disk dynamics and ionization structure in this highly unusual low-mass X-ray pulsar system.
    The Astronomical Journal 12/2007; 124(6):3348. · 4.97 Impact Factor
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    ABSTRACT: Many open questions in X-ray astronomy are limited by the relatively small number of objects in uniform optically identified and observed samples, especially when rare subclasses are considered or when subsets are isolated to search for evolution or correlations between wavebands. We describe the initial results of a new program aimed to ultimately yield ~104 fully characterized X-ray source identifications—a sample about an order of magnitude larger than earlier efforts. The technique is detailed and employs X-ray data from the ROSAT All-Sky Survey (RASS) and optical imaging and spectroscopic follow-up from the Sloan Digital Sky Survey (SDSS); these two surveys prove to be serendipitously very well matched in sensitivity. As part of the SDSS software pipelines, optical objects in the SDSS photometric catalogs are automatically positionally cross-correlated with RASS X-ray sources. Then priorities for follow-on SDSS optical spectra of candidate counterparts are automatically assigned using an algorithm based on the known ratios of fx/fopt for various classes of X-ray emitters at typical RASS fluxes of ~10-13 ergs cm-2 s-1. SDSS photometric parameters for optical morphology, magnitude, and colors, plus FIRST radio information, serve as proxies for object class. Initial application of this approach to RASS/SDSS data from 1400 deg2 of sky provides a catalog of more than 1200 spectroscopically confirmed quasars and other AGNs that are probable RASS identifications. Most of these are new identifications, and only a few percent of the AGN counterparts are likely to be random superpositions. The magnitude and redshift ranges of the counterparts are very broad, extending over 15 < m < 21 and 0.03 < z < 3.6, respectively. Although most identifications are quasars and Seyfert 1 galaxies, a variety of other AGN subclasses are also sampled. Substantial numbers of rare AGN types are found, including more than 130 narrow-line Seyfert 1 galaxies and 45 BL Lac candidates. These early results already provide a very sizable set of source identifications, demonstrate the utility of the sample in multiwaveband investigations, and show the capability of the joint RASS/SDSS approach to efficiently proceed toward the largest homogeneously selected/observed sample of X-ray–emitting quasars and other kinds of AGNs.
    The Astronomical Journal 12/2007; 126(5):2209. · 4.97 Impact Factor
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    ABSTRACT: We report follow-up XMM-Newton and ground-based optical observations of the unusual X-ray binary SDSS J102347.67+003841.2 (=FIRST J102347.6+003841) and a new candidate intermediate polar (IP) found in the Sloan Digital Sky Survey: SDSS J093249.57+472523.0. SDSS J1023 was observed in its low state, with similar magnitude/color (V = 17.4 and B = 17.9) and smooth orbital modulation as seen in most previous observations. We further refine the ephemeris (for photometric minimum) to HJD(TT)min = 2,453,081.8546(3) + E0.198094(1) days. It is easily detected in X-rays at an unabsorbed flux (0.01–10.0 keV) of 5 × 10-13 ergs cm-2 s-1. Fitting a variety of models we find that (1) either a hot (kT 15 keV) optically thin plasma emission model (bremsstrahlung or MEKAL) or a simple power law can provide adequate fits to the data; (2) these models prefer a low column density ~1019 cm-2; (3) a neutron star atmosphere plus power-law model (as found for quiescent low-mass X-ray binaries) can also produce a good fit (for plausible distances), although only for a much higher column ≈4 × 1020 cm-2 and a very cool atmosphere (kT 50 eV). These results support the case that SDSS J1023 is a transient LMXB and indeed place it in the subclass of such systems whose quiescent X-ray emission is dominated by a hard power-law component. Our optical photometry of SDSS J0932 reveals that it is a high-inclination eclipsing system. From our two epochs of data and seven eclipse times, we are able to derive a best-fit ephemeris for minimum light: HJD(TT)min = 2,453,122.2324(1) + E0.0661618(4) days, although aliases, with one cycle count different between epochs, are acceptable. The X-ray spectrum is well fit by either a hard bremsstrahlung or power law, with a partial covering absorption model, with a high covering fraction ~0.9 and column ≈1023 cm-2. Combined with its optical characteristics—high excitation emission lines and its brightness, yielding a large FX/Fopt ratio—this highly absorbed X-ray spectrum argues that SDSS J0932 is a strong IP candidate. However, only more extensive optical photometry and a detection of its spin or spin-orbit beat frequency can confirm this classification.
    The Astronomical Journal 12/2007; 131(1):562. · 4.97 Impact Factor

Publication Stats

621 Citations
213.87 Total Impact Points

Institutions

  • 2001–2011
    • University of Washington Seattle
      • Department of Astronomy
      Seattle, WA, United States
    • University of Oxford
      Oxford, England, United Kingdom
  • 2000
    • Universiteit Utrecht
      • Astronomical Institute
      Utrecht, Provincie Utrecht, Netherlands
  • 1998
    • South African Astronomical Observatory
      Kaapstad, Western Cape, South Africa