Delayed and fast rising radio flares from an optical and X-ray detected tidal disruption event in the center of a dwarf galaxy

Abstract: AT2018cqh is a unique tidal disruption event (TDE) candidate discovered in a dwarf galaxy. Both the light curve fitting and galaxy scaling relationships suggest a central black hole mass in the range of 5.9<logM_BH/M_sun\<6.4. A delayed X-ray brightening was found around 590 days after the optical discovery, but shows unusual long-time rising to peak over at least 558 days, which could be coming from delayed accretion of a newly forming debris disk. We report the discovery of delayed radio flares around 1105 days since its discovery, characterized by an initial steep rise of ~\>175 days, a flattening lasting about 544 days, and a phase with another steep rise. The rapid rise in radio flux coupled with the slow decay in the X-ray emission points to a delayed launching of outflow, perhaps due to a transition in the accretion state. However, known accretion models can hardly explain the origins of the secondary radio flare that is rising even more rapidly in comparison with the initial one. If confirmed, AT2018cqh would be a rare TDE in a dwarf galaxy exhibiting optical, X-ray and radio flares. We call for continued multi-frequency radio observations to monitor its spectral and temporal evolution, which may help to reveal new physical processes that are not included in standard TDE models.