Multifrequency nature of the 0.75 mHz feature in the X-ray light curves of the nova V4743 Sgr

TL;DR

This study analyzes the multifrequency and time-evolving nature of a 0.75 mHz feature in X-ray light curves of nova V4743 Sgr, revealing pulsation modulation, frequency changes, and evidence of the white dwarf's rotation in an intermediate polar system.

Contribution

It provides the first detailed multifrequency timing analysis of V4743 Sgr across different phases, identifying pulsation modulation and linking the observed frequency to white dwarf rotation.

Findings

Detected a double peak and overtone in the 0.75 mHz feature during early phases.

Observed frequency and amplitude variations linked to pulsations and system evolution.

Identified the late frequency as the white dwarf's rotation, supporting the intermediate polar classification.

Abstract

We present timing analyses of eight X-ray light curves and one optical/UV light curve of the nova V4743 Sgr (2002) taken by CHANDRA and XMM on days after outburst: 50 (early hard emission phase), 180, 196, 302, 371, 526 (super soft source, SSS, phase), and 742 and 1286 (quiescent emission phase). We have studied the multifrequency nature and time evolution of the dominant peak at ~0.75 mHz using the standard Lomb-Scargle method and a 2-D sine fitting method. We found a double structure of the peak and its overtone for days 180 and 196. The two frequencies were closer together on day 196, suggesting that the difference between the two peaks is gradually decreasing. For the later observations, only a single frequency can be detected, which is likely due to the exposure times being shorter than the beat period between the two peaks, especially if they are moving closer together. The observations on days 742 and 1286 are long enough to detect two frequencies with the difference found for day 196, but we confidently find only a single frequency. We found significant changes in the oscillation frequency and amplitude. We have derived blackbody temperatures from the SSS spectra, and the evolution of changes in frequency and blackbody temperature suggests that the 0.75-mHz peak was modulated by pulsations. Later, after nuclear burning had ceased, the signal stabilised at a single frequency, although the X-ray frequency differs from the optical/UV frequency obtained consistently from the OM onboard XMM and from ground-based observations. We believe that the late frequency is the white dwarf rotation and that the ratio of spin/orbit period strongly supports that the system is an intermediate polar.