An X-ray view of the Cataclysmic Variable V902 Mon: Discovery of an X-ray eclipse

TL;DR

This study confirms an X-ray eclipse in the cataclysmic variable V902 Mon, revealing high absorption and reprocessing effects consistent with a high-inclination accretion disk corona model, advancing understanding of its accretion geometry.

Contribution

First detection of an X-ray eclipse in V902 Mon, providing detailed spectral analysis that supports a high-inclination accretion disk corona model with significant absorption.

Findings

Confirmed X-ray eclipse coincident with optical eclipse

Detected high local absorption N_H ~ 10^23 cm^-2

Observed strong Fe Kα fluorescence line with EW ~ 0.7 keV

Abstract

V902 Mon is one of a few eclipsing Intermediate Polars (IPs), and show deep eclipses in the optical lightcurves. The presence of a strong Fe K$\alpha$ fluorescence line in its X-ray spectrum and its low X-ray flux compared to other IPs suggests significant absorption, most likely from an accretion disk. In an observation carried out using the Nuclear Spectroscopic Telescope Array (NuSTAR), we confirm the presence of an X-ray eclipse in the energy resolved lightcurves, coincident with the optical AAVSO/CV-band lightcurves. Broadband X-ray spectral analysis using NuSTAR and XMM-Newton observations confirm a strong absorption N$_{H}$ $\sim 10^{23}$ cm$^{-2}$ local to the source, along with a high equivalent width of about 0.7 keV for a Fe K$\alpha$ fluorescence line. We interpret this using a model similar to an Accretion Disk Corona source, which have a very high inclination and the compact object is heavily obscured by the body of the accretion disk. We propose that the primary X-rays from the accretion column in V902 Mon is hidden from our direct view at all times by the accretion disk. In this scenario, the observed scattered X-rays indicate substantial absorption of direct X-rays by the accretion disk. Additionally, a strong Fe fluorescence line suggests reprocessing of the radiation by a more extended region, such as the pre-shock region, which could be located a few white dwarf radii above the orbital plane.