A Luminous Red Optical Flare and Hard X-ray Emission in the Tidal Disruption Event AT2024kmq

TL;DR

This paper reports the discovery of a tidal disruption event, AT2024kmq, exhibiting a luminous red optical flare and concurrent hard X-ray emission, providing insights into the event's multiwavelength properties and possible physical mechanisms.

Contribution

It presents the first detailed multiwavelength observations of AT2024kmq, revealing a complex optical light curve and X-ray behavior, and discusses potential origins of the early red optical peak.

Findings

Two distinct optical peaks with different timescales and colors.

Detection of highly variable, luminous, and hard X-ray emission during the second peak.

Radio emission consistent with an active galactic nucleus, not directly related to the TDE.

Abstract

We present the optical discovery and multiwavelength follow-up observations of AT2024kmq, a likely tidal disruption event (TDE) associated with a supermassive ($M_{\rm BH}\sim 10^{8} M_\odot$) black hole in a massive galaxy at $z=0.192$. The optical light curve of AT2024kmq exhibits two distinct peaks: an early fast (timescale 1 d) and luminous ($M\approx-20$ mag) red peak, then a slower (timescale 1 month) blue peak with a higher optical luminosity ($M\approx-22$ mag) and featureless optical spectra. The second component is similar to the spectroscopic class of "featureless TDEs" in the literature, and during this second component we detect highly variable, luminous ($L_X\approx 10^{44}$ erg s$^{-1}$), and hard ($f_\nu \propto \nu^{-1.5}$) X-ray emission. Luminous ($10^{29} $erg s$^{-1}$ Hz$^{-1}$ at 10 GHz) but unchanging radio emission likely arises from an underlying active galactic nucleus. The luminosity, timescale, and color of the early red optical peak can be explained by synchrotron emission, or alternatively by thermal emission from material at a large radius ($R\approx\mathrm{few}\times10^{15}$ cm). Possible physical origins for this early red component include an off-axis relativistic jet, and shocks from self-intersecting debris leading to the formation of the accretion disk. Late-time radio observations will help distinguish between the two possibilities.