Discovery and follow-up of ASASSN-19dj: an X-ray and UV luminous TDE in an extreme post-starburst galaxy. Issue 2 (15th October 2020)

• Record Type: Journal Article
• Authors: Hinkle, Jason T; Holoien, T W-S; Auchettl, K; Shappee, B J; Neustadt, J M M; Payne, A V; Brown, J S; Kochanek, C S; Stanek, K Z; Graham, M J; Tucker, M A; Do, A; Anderson, J P; Bose, S; Chen, P; Coulter, D A; Dimitriadis, G; Dong, Subo; Foley, R J; Huber, M E; Hung, T; Kilpatrick, C D; Pignata, G; Piro, A L; Rojas-Bravo, C; Siebert, M R; Stalder, B; Thompson, Todd A; Tonry, J L; Vallely, P J; Wisniewski, J P;
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 500:Issue 2(2021)
• Page Start: 1673
• Page End: 1696
• Publication Date: 2020-10-15
• Subjects: accretion, accretion discs -- black hole physics -- galaxies: nuclei; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa3170
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We present observations of ASASSN-19dj, a nearby tidal disruption event (TDE) discovered in the post-starburst galaxy KUG 0810+227 by the All-Sky Automated Survey for Supernovae (ASAS-SN) at a distance of d ≃ 98 Mpc. We observed ASASSN-19dj from −21 to 392 d relative to peak ultraviolet (UV)/optical emission using high-cadence, multiwavelength spectroscopy and photometry. From the ASAS-SN g -band data, we determine that the TDE began to brighten on 2019 February 6.8 and for the first 16 d the rise was consistent with a flux ∝ t 2 power law. ASASSN-19dj peaked in the UV/optical on 2019 March 6.5 (MJD = 58548.5) at a bolometric luminosity of L = (6.2 ± 0.2) × 10 44 erg s −1 . Initially remaining roughly constant in X-rays and slowly fading in the UV/optical, the X-ray flux increased by over an order of magnitude ∼225 d after peak, resulting from the expansion of the X-ray emitting region. The late-time X-ray emission is well fitted by a blackbody with an effective radius of ∼1 × 10 12 cm and a temperature of ∼6 × 10 5 K. The X-ray hardness ratio becomes softer after brightening and then returns to a harder state as the X-rays fade. Analysis of Catalina Real-Time Transient Survey images reveals a nuclear outburst roughly 14.5 yr earlier with a smooth decline and a luminosity of LV ≥ 1.4 × 10 43 erg s −1, although the nature of the flare is unknown. ASASSN-19dj occurred in the most extreme post-starburst galaxy yet to host a TDE, with Lick Hδ A = 7.67 ± 0.17 Å.