XMM-Newton observations of the eclipsing polar V2301 Oph

TL;DR

This study presents XMM-Newton observations of the low magnetic field polar V2301 Oph, revealing eclipse structure, constraining white dwarf mass, and analyzing X-ray spectral features, with implications for accretion processes in polars.

Contribution

First detailed X-ray analysis of V2301 Oph with constraints on white dwarf mass and accretion characteristics in a low magnetic field polar.

Findings

Eclipse profile shows a 26-second standstill feature.

White dwarf mass is constrained to be less than ~1.2 solar masses.

No evidence of quasi-periodic oscillations or a soft X-ray component.

Abstract

We present XMM-Newton observations of the eclipsing polar V2301 Oph which cover nearly 2.5 binary orbital cycles and 2 eclipses. This polar is believed to have the lowest magnetic field strength (7 MG) of any known polar. We find evidence for structure in the X-ray eclipse profile which shows a `standstill' feature lasting 26+/-4 sec. This allows us to place an upper limit on the mass of the white dwarf of ~1.2 Msun. We find no evidence for QPOs in the frequency range 0.02-10 Hz. This coupled with the absence of QPOs in RXTE data suggest that, if present, any oscillations in the shock front have a minimal effect on the resultant X-ray flux. We find no evidence for a distinct soft X-ray component in its spectrum - it therefore joins another 7 systems which do not show this component. We suggest that those systems which are asynchronous, have low mass transfer rates, or have accretion occurring over a relatively large fraction of the white dwarf are more likely to show this effect. We find that the specific mass transfer rate has to be close to 0.1 g cm^-2 s^-1 to predict masses which are consistent with that derived from our eclipse analysis. This maybe due to the fact that the low magnetic field strength allows accretion to take place along a wide range of azimuth.