Multiwavelength Study of an X-Ray Tidal Disruption Event Candidate in NGC 5092

Abstract

We present multiwavelength studies of a transient X-ray source, XMMSL1 J131952.3+225958, associated with the galaxy NGC 5092 at z = 0.023 detected in the XMM-Newton SLew survey (XMMSL). The source brightened in the 0.2-2 keV band by a factor of > 20 in 2005 as compared with previous flux limits and then faded by a factor of >200 as observed with XMM-Newton in 2013 and with Swift in 2018. At the flaring state the X-ray spectrum can be modeled with a blackbody at a temperature of ∼60 eV and an overall luminosity of ∼ 1.5× {10}⁴³ erg s^-1. A UV flare and optical flare were also detected with the Galaxy Evolution Explorer and the Sloan Digital Sky Survey, respectively, within several months of the X-ray flare, whose nonstellar UV-optical spectrum can be described with a blackbody at a temperature of ∼ (1-2)× {10}⁴ K and a luminosity of ∼ (2-6)× 10⁴³ erg s^-1. Interestingly, mid-infrared monitoring observations of NGC 5092 with the Wide-field Infrared Survey Explorer 5-13 yr later show a continuous flux decline. These dramatic variability properties, from the X-ray through UV and optical to infrared, appear to be orderly, suggestive of a stellar tidal disruption event (TDE) by a massive black hole, confirming the postulation by Kanner et al. This TDE candidate belongs to a rare sample with contemporaneous bright emission detected in the X-ray, UV, and optical, which are later echoed by dust-reprocessed light in the mid-infrared. The black hole has a mass of ∼ 5 × 10⁷ M_⊙, residing in a galaxy that is dominated by a middle-aged stellar population of 2.5 Gyr.