XMM-Newton observations of OY Car III: OM light curve modelling, X-ray timing and spectral studies

Abstract

Abstract.We revisit the XMM-Newton observations of the dwarf nova OY Car taken in July 2000 which occured shortly after an outburst. Ramsay et al. (2001a) found a prominent energy dependent modulation at a period of 2240 s: this modulation was only seen for ∼1/3 of the observation duration. In our new analysis, we examine this time interval in greater detail. In addition to the 2240 s period we find evidence for other periods, the most prominent being near 3500 s. Both these modulations are most likely due to changes in photoelectric absorption over this period: this is supported by phase-resolved spectroscopy. This may indicate the presence of matter above the accretion disc or a presence of a magnetic accretion curtain. In this case the 2240 s period could represent a spin period of the white dwarf and the 3500 s period a beat period between the spin and orbital periods. We also model the B band and UV eclipse profiles and light curves using a new technique to map the spatial extent of the accretion disc. As a result we find that whilst the optical emission is dominated by both the emission close to the accretion disc boundary layer and the hot spot where the accretion stream hits the disc, the UV emission is mainly dominated by the inner disc/boundary layer only.

XMM-Newton observations of the dwarf nova YZ Cnc in quiescence

“…In particular, the XMM-Newton observations of a similar system OY Car (Ramsay et al 2001a;Hakala & Ramsay 2004) have indicated that the X-ray light curve could contain a significant white dwarf spin period component.…”

“…Based on results of other dwarf novae (for instance OY Car, Ramsay et al 2001a;and VW Hyi, Pandel et al 2003) an UV modulation due to the hot spot on the edge of the disc would be expected. However, recently Hakala & Ramsay (2004) showed using XMM-Newton OM data that even in a high inclination system like OY Car, the hot spot modulation in quiescence is much more prominent in optical band than in UV. This, combined with the presumably low inclination, is the likely reason for nondetection.…”

“…Recently, observations using XMM-Newton of the dwarf nova OY Car showed the X-rays varied on a timescale of 2240 s (Ramsay et al 2001a): the amplitude of this variation was stronger at soft X-rays. A further investigation also showed a period near 3500 s (Hakala & Ramsay 2004). They interpreted the 2240 s period as the spin period of the white dwarf and the 3500 s period as a beat between the spin and the binary orbital period.…”

QPOs in compact binaries from small-scale eruptions in an inner magnetized disc

“…Given the radii at which the disk becomes unstable, QPOs, in our model, would be emitted in the near UV in agreement with observations. However, some QPOs are also detected in X-rays (Remillard et al 1994, Ramsay et al 2001, Hakala & Ramsay 2004. X-rays in DNe come from accretion onto a boundary layer between the inner radius of the disk and the surface of the white dwarf (see Mukai 2017 for a review).…”

Dwarf nova oscillations and quasi-periodic oscillations in cataclysmic variables ��� VII. OY Carinae and oscillations in dwarf novae in quiescence

“…There are also two observations of quiescent QPOs made in the X‐ray region: 290 s in AB Dra (Cordova & Mason 1984), which is possibly also an lpDNO, and a pair at 2193 and 3510 s in OY Car (Ramsay et al 2001; Hakala & Ramsay 2004).…”