A Burst from the Direction of UZ Fornacis with XMM-Newton

Abstract

The XMM-Newton pointing toward the magnetic cataclysmic variable UZ For finds the source to be a factor of greater than 10³ fainter than previous EXOSAT and ROSAT observations. The source was not detected for the majority of a 22 ks exposure with the European Photon Imaging Cameras, suggesting that the accretion rate either decreased or stopped altogether. However, a 1.1 ks burst was detected from UZ For during the observation. Spectral fits favor optically thin, kT=4.4^+7.6_-1.8 keV thermal emission. Detection of the burst by the onboard Optical Monitor indicates that this was most probably an accretion event. The 0.1-10 keV luminosity of 2.1^+0.6_-0.3×10³⁰ ergs s^-1 is typical for accretion shock emission from high-state polars and would result from the potential energy release of ~10¹⁶ g of gas. There is no significant soft excess due to reprocessing in the white dwarf atmosphere.