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Register a new userXMM-Newton and optical follow-up observations of SDSS J093249.57+472523.0 and SDSS J102347.67+003841.2
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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 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= 2453081.8546(3) + E* 0.198094(1) d. It is easily detected in X-rays at an unabsorbed flux (0.01-10.0 keV) of 5x10e-13 erg/cm^2/s. Fitting a variety of models we find that: (i) 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; (ii) these models prefer a low column density ~10e19 cm^-2; (iii) 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), though only for a much higher column of about 4x10e20 cm^-2 and a very cool atmosphere kT<~50eV. These results support the case that SDSS J1023 is a transient LMXB, and indeed places 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 an high inclination eclipsing system. Combined with its optical characteristics -- high excitation emission lines, and brightness, yielding a large F_X/F_opt ratio -- its 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. (abridged)
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In the latest in our series of papers on XMM-Newton and ground-based optical follow-up of new candidate magnetic cataclysmic variables (mCVs) found in the Sloan Digital Sky Survey, we report classifications of three systems: SDSS J144659.95+025330.3, SDSS J205017.84-053626.8, and SDSS J210131.26+105251.5. Both the X-ray and optical fluxes of SDSS J1446+02 are modulated on a period of 48.7+/-0.5 min, with the X-ray modulation showing the characteristic energy dependence of photo-electric absorption seen in many intermediate polars (IP). A longer period modulation and radial velocity variation is also seen at a period around 4 hrs, though neither dataset set is long enough to constrain this longer, likely orbital, period well. SDSS J2050-05 appears to be an example of the most highly magnetized class of mCV, a disk-less, stream-fed polar. Its 1.57 hr orbital period is well-constrained via optical eclipse timings; in the X-ray it shows both eclipses and an underlying strong, smooth modulation. In this case, broadly phase-resolved spectral fits indicate that this change in flux is the result of a varying normalization of the dominant component (a 41 keV MEKAL), plus the addition of a partial covering absorber during the lower flux interval. SDSS J2101+10 is a more perplexing system to categorize: its X-ray and optical fluxes exhibit no large periodic modulations; there are only barely detectable changes in the velocity structure of its optical emission lines; the X-ray spectra require only absorption by the interstellar medium; and the temperatures of the MEKAL fits are low, with maximum temperature components of either 10 or 25 keV. We conclude that SDSS J2101+10 can not be an IP, nor likely a polar, but is rather most likely a disc accretor-- a low inclination SW Sex star.
We report on XMM-Newton and optical results for 6 cataclysmic variables that were selected from Sloan Digital Sky Survey spectra because they showed strong HeII emission lines, indicative of being candidates for containing white dwarfs with strong magnetic fields. While high X-ray background rates prevented optimum results, we are able to confirm SDSSJ233325.92+152222.1 as an intermediate polar from its strong pulse signature at 21 min and its obscured hard X-ray spectrum. Ground-based circular polarization and photometric observations were also able to confirm SDSSJ142256.31-022108.1 as a polar with a period near 4 hr. Photometry of SDSSJ083751.00+383012.5 and SDSSJ093214.82+495054.7 solidifies the orbital period of the former as 3.18 hrs and confirms the latter as a high inclination system with deep eclipses.
We have analyzed the {it XMM-Newton} and {it Chandra} data overlapping $sim$16.5 deg$^2$ of Sloan Digital Sky Survey Stripe 82, including $sim$4.6 deg$^2$ of proprietary {it XMM-Newton} data that we present here. In total, 3362 unique X-ray sources are detected at high significance. We derive the {it XMM-Newton} number counts and compare them with our previously reported {it Chandra} Log$N$-Log$S$ relations and other X-ray surveys. The Stripe 82 X-ray source lists have been matched to multi-wavelength catalogs using a maximum likelihood estimator algorithm. We discovered the highest redshift ($z=5.86$) quasar yet identified in an X-ray survey. We find 2.5 times more high luminosity (L$_x geq 10^{45}$ erg s$^{-1}$) AGN than the smaller area {it Chandra} and {it XMM-Newton} survey of COSMOS and 1.3 times as many identified by XBootes. Comparing the high luminosity AGN we have identified with those predicted by population synthesis models, our results suggest that this AGN population is a more important component of cosmic black hole growth than previously appreciated. Approximately a third of the X-ray sources not detected in the optical are identified in the infrared, making them candidates for the elusive population of obscured high luminosity AGN in the early universe.
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 lightcurves 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 line O VII (E=0.57 keV), 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 broad band curve. The X-ray spectra require the presence of both hard and soft X-ray components, with their luminosity ratio consistent with that found in other recent XMM-Newton results on polars. Lastly, SDSS J170053.30+400357.6 appears optically as a very typical polar, however its large amplitude optical modulation is 180 degrees out of phase with the variation in our short X-ray lightcurve.
In this paper we combine archival and proprietary XMM-Newton observations (about 5deg^2) that overlap with the Sloan Digital Sky Survey to explore the nature of the moderate-z X-ray population. We focus on X-ray sources with optically red colours (g-r>0.4), which we argue are important for understanding the origin of the X-ray background. Firstly, these systems constitute a significant fraction, about 2/3, of the z<1 X-ray population to the limit f(2-8keV)~2e-14cgs. Secondly, their luminosity function under evolution of the form ~(1+z)^3 suggests that they could be responsible for about 17 per cent of the diffuse X-ray background to z=1. Thirdly, their stacked X-ray spectrum in the range 1-8keV is consistent with a power-law distribution with Gamma~1.4 (without fitting intrinsic absorption), i.e. similar to the diffuse X-ray background. We find that the optically red X-ray population comprises a mixed bag of objects, both obscured (N_H>1e22 cm^{-2}) and unobscured (N_H<1e22 cm^{-2}), with a wide range of X-ray luminosities up L_X~1e44cgs. We argue that dilution of the AGN light by the host galaxy may play a role in shaping the continuum optical emission of this population. Finally, we explore a possible association of these sources and the moderate-z red (J-Ks>2mag) AGNs identified in the Two Micron All Sky Survey (2MASS). The median N_H of the red X-ray sources studied here is ~1e21cm^{-2}, lower than that found for the 2MASS AGNs, suggesting different populations.
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