A search for X-ray flares in the nuclei of galaxies

Abstract

Observations of the giant elliptical galaxy NCG 4552 at ultraviolet wavelengths during the early 1990’s showed sharply peaked emission within ~2pc of its centre which initially brightened and then faded. The features of this flare in emission around the nucleus made it one of the few candidates for a stellar tidal disruption event not identified at X-ray energies. In order to compare its X-ray properties with the existing flare candidates a detailed analysis of the X-ray history of NGC 4552 was carried out. No correlation was found between the UV and X-ray variability and the limits placed on the X-ray output from any faint flare component imply th a t the mass accreted must have been less than 10-5/ε0.1M⊙.