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Register a new userFirst XMM-Newton observations of a Cataclysmic Variable I: Timing studies of OY Car
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Authors
Gavin Ramsay
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We present XMM-Newton observations of the eclipsing, disc accreting, cataclysmic variable OY Car which were obtained as part of the performance verification phase of the mission. The star was observed 4 days after an outburst and then again 5 weeks later when it was in a quiescent state. There is a quasi-stable modulation of the X-rays at ~2240 sec, which is most prominent at the lowest energies. We speculate that this may be related to the spin period of the white dwarf. The duration of the eclipse ingress and egress in X-rays is 20--30 sec. This indicates that the bulk of the X-ray emission originates from the boundary layer which has a negligible height above the surface of the white dwarf. The eclipse profile implies a white dwarf of mass M_{1}=0.9-1.1Msun and a secondary star of M_{2}=0.08-0.11Msun.
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XMM-Newton was used to observe two eclipsing, magnetic cataclysmic variables, DP Leo and WW Hor, continuously for three orbital cycles each. Both systems were in an intermediate state of accretion. For WW Hor we also obtained optical light curves with the XMM-Newton Optical Monitor and from ground-based observations. Our analysis of the X-ray and optical light curves allows us to constrain physical and geometrical parameters of the accretion regions and derive orbital parameters and eclipse ephemerides of the systems. For WW Hor we directly measure horizontal and vertical temperature variations in the accretion column. From comparisons with previous observations we find that changes in the accretion spot longitude are correlated with the accretion rate. For DP Leo the shape of the hard X-ray light curve is not as expected for optically thin emission, showing the importance of optical depth effects in the post-shock region. We find that the spin period of the white dwarf is slightly shorter than the orbital period and that the orbital period is decreasing faster than expected for energy loss by gravitational radiation alone.
XMM-Newton observations of the accreting, pulsating white dwarf in the quiescent dwarf nova GW Librae were conducted to determine if the non-radial pulsations present in previous UV and optical data affect the X-ray emission. The non-radial pulsations are evident in the simultaneous Optical Monitor data but are not detected in X-ray with an upper limit on the pulsation amplitude of 0.092 mags. The best fits to the X-ray spectrum are with a low temperature diffuse gas model or a multi-temperature cooling flow model, with a strong OVIII line, similar to other short period dwarf novae, but with a lower temperature range than evident in normal short period dwarf novae. The lack of pulsations and the spectrum likely indicate that the boundary layer does not extend to the surface of the white dwarf.
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V405 Peg is a low-luminosity cataclysmic variable (CV) that was identified as the optical counterpart of the bright, high-latitude ROSAT all-sky survey source RBS1955. The system was suspected to belong to a largely undiscovered population of hibernating CVs. Despite intensive optical follow-up its subclass however remained undetermined. We want to further classify V405 Peg and understand its role in the CV zoo via its long-term behaviour, spectral properties, energy distribution and accretion luminosity. We perform a spectral and timing analysis of textit{XMM-Newton} X-ray and ultra-violet data. Archival WISE, HST, and Swift observations are used to determine the spectral energy distribution and characterize the long-term variability. The X-ray spectrum is characterized by emission from a multi-temperature plasma. No evidence for a luminous soft X-ray component was found. Orbital phase-dependent X-ray photometric variability by $sim50%$ occurred without significant spectral changes. No further periodicity was significant in our X-ray data. The average X-ray luminosity during the XMM-Newton observations was L_X, bol simeq 5e30 erg/s but, based on the Swift observations, the corresponding luminosity varied between 5e29 erg/s and 2e31 erg/son timescales of years. The CV subclass of this object remains elusive. The spectral and timing properties show commonalities with both classes of magnetic and non-magnetic CVs. The accretion luminosity is far below than that expected for a standard accreting CV at the given orbital period. Objects like V405 Peg might represent the tip of an iceberg and thus may be important contributors to the Galactic Ridge X-ray Emission. If so they will be uncovered by future X-ray surveys, e.g. with eROSITA.
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