Rapid soft X-ray variability in a newly discovered active galaxy : EXO 1128+691.

Abstract

A previously unknown active galaxy has been discovered, and has been tentatively identified as a Seyfert type 1. 1t is possibly a member of the UMa I cluster. The X-ray emission differs from that for 'normal' Seyferts in that it is very soft and also shows rapid variability (~15 min to 2 hr). Assuming the galactic value N_H_~1.5x10^20^ cm^-2^ for the column density leads to a power-law spectral index α_E_~4, or T~6x10^5^ K for a thermal spectrum (with a substantial uncertainty in these values because of the variability of EXO 1128+691), for single component models. A separate soft component is suggested by such values. EXO 1125+691 has L_x_~1-3x10^43^ erg s^-1^ (0.05-2 kev) for N_H_~1.5x10^20^ cm^-2^, using the measured redshift z=0.043+/-0.002.