X-ray outburst of a radio-loud quasar

Abstract

We report that the XRISM/XTEND Transient Search source XRISM J1826-3651, observed on 2025-04-12 and reported in ATel #17145 was observed again with the Swift X-Ray Telescope (XRT) on 2025-04-22 for a total (non continuous) on-source time of 2642 s. The source is still X-ray luminous, and was detected with a count rate 0.022±0.004 cts/s at this position: alpha=18 26 08.16 and delta=-36 50 46.8, with a position uncertainty of 4.2 arcseconds. The spectrum is relatively hard and can be fitted with a power law, with photon index 1.9(+0.8/-0.6), absorbing column density N(H)=2.2(+3.6/-2.1) cm⁻², absorbed flux of 1.0±0.5 x 10⁻¹² erg/cm/⁻²/s, and unabsorbed flux ~1.3 x 10⁻¹² erg/cm⁻²/s. The most likely counterpart is the radio-loud quasar and blazar 1WGA J1826.1-3650 at redshift z=0.888 (Veron Cetty et al. 2010, A&A, 518, 10), which also corresponds to GAIA source 6728071805422016896, at 2.9 arcsec from the Swift XRT position. This object was serendipitously observed with ROSAT in X-rays as 1WGA J1826.1-3650 at comparable luminosity in 1992 March, so this is not the first X-ray active state, but X-ray observations in the intervening time are missing.