To TDE or not to TDE: The luminous transient ASASSN-18jd with TDE-like and AGN-like qualities

TL;DR

ASASSN-18jd is a luminous nuclear transient with both TDE-like and AGN-like features, showing complex UV, X-ray, and optical behaviors that challenge simple classification.

Contribution

This study provides a detailed multi-wavelength analysis of ASASSN-18jd, highlighting its hybrid characteristics and discussing its implications for understanding nuclear transients.

Findings

Transient UV and X-ray emission with blackbody characteristics.

Presence of broad Balmer emission and transient high-ionization lines.

Similarity to both TDEs and faint AGN activity.

Abstract

We present the discovery of ASASSN-18jd (AT 2018bcb), a luminous optical/UV/X-ray transient located in the nucleus of the galaxy 2MASX J22434289--1659083 at $z=0.1192$. Over the year after discovery, Swift UVOT photometry shows the UV SED of the transient to be well modeled by a slowly shrinking blackbody with temperature $T \sim 2.5 \times 10^{4} \rm ~K$, a maximum observed luminosity of $L_\text{max} = 4.5^{+0.6}_{-0.3} \times 10^{44} \rm ~erg ~s^{-1}$, and a radiated energy of $E = 9.6^{+1.1}_{-0.6} \times 10^{51} \rm ~erg$. X-ray data from Swift XRT and XMM-Newton show a transient, variable X-ray flux with blackbody and power-law components that fade by nearly an order of magnitude over the following year. Optical spectra show strong, roughly constant broad Balmer emission as well as transient features attributable to He II, N III-V, O III, and coronal Fe. While ASASSN-18jd shares similarities with Tidal Disruption Events (TDEs), it is also similar to the newly-discovered nuclear transients seen in quiescent galaxies and faint Active Galactic Nuclei (AGNs).