Unveiling the nature of an X-ray flare from 3XMM* J014528.9+610729: a candidate spiral galaxy

Abstract

We report an X-ray flare from 3XMM J014528.9+610729, serendipitously detected during the observation of the open star cluster NGC 663. The colour–colour space technique using optical and infrared data reveals the X-ray source as a candidate spiral galaxy. The flare shows fast rise and exponential decay shape with a ratio of the peak and the quiescent count rates of ∼60 and duration of ∼5.4 ks. The spectrum during the flaring state is well fitted with a combination of thermal (apec) model with a plasma temperature of 1.3 ± 0.1 keV and non-thermal (power-law) model with power-law index of 1.9 ± 0.2. However, no firm conclusion can be made for the spectrum during the quiescent state. The temporal behaviour, plasma temperature and spectral evolution during flare suggest that the flare from 3XMM J014528.9+610729 cannot be associated with tidal disruption events.