X-ray Observations of Historical Classical Nova Counterparts with eROSITA Telescope Onboard the SRG Orbital Observatory during the All-Sky Survey

Abstract

Abstract: The X-ray emission from the counterparts of historical classical novae (CNe) in our Galaxy is studied. For this purpose, we use data from three SRG/eROSITA sky surveys in the half of the sky for the processing of which the Russian SRG/eROSITA consortium is responsible. Out of 309 historical CNe, X-ray emission has been detected from 52 sources with 0.3–2.3 keV luminosities (Formula presented.) erg -1. Among them, two sources with supersoft spectra are associated with the post-nova supersoft X-ray emission. X-ray spectroscopy suggests that systems with magnetized white dwarfs (WDs) may account for some fraction in our sample of CN counterparts detected in X-rays. This suggestion will be checked during further SRG/eROSITA sky surveys. The CN counterparts represent a bona fide sample of accreting WDs with non-steady thermonuclear hydrogen burning on their surface, while their X-ray luminosity in quiescence is a good indicator of the accretion rate in a binary system. Using this fact, we have constructed the accretion rate distribution of WDs with non-steady hydrogen burning and compared it with the accretion rate distribution of known steady supersoft X-ray sources in our Galaxy and nearby external galaxies. There is a pronounced dichotomy between these two distributions—the CN counterparts and the steady supersoft sources are in different regions, in accordance with the predictions of the theory of thermonuclear hydrogen burning on the WD surface.