AT2018lqh and the nature of the emerging population of day-scale duration optical transients

Abstract

We report on the discovery of AT2018lqh (ZTF18abfzgpl) -- a rapidly-evolving extra-galactic transient in a star-forming host at 242 Mpc. The transient g-band light curve's duration above half-maximum light is about 2.1 days, where 0.4/1.7 days are spent on the rise/decay, respectively. The estimated bolometric light curve of this object peaked at about 7x10^42 erg/s -- roughly seven times brighter than AT2017gfo. We show that this event can be explained by an explosion with a fast (v~0.08 c) low-mass (~0.07 Msun) ejecta, composed mostly of radioactive elements. For example, ejecta dominated by Ni-56 with a time scale of t_0=1.6 days for the ejecta to become optically thin for gamma-rays fits the data well. Such a scenario requires burning at densities that are typically found in the envelopes of neutron stars or the cores of white dwarfs. A combination of circumstellar material (CSM) interaction power at early times and shock cooling at late times is consistent with the photometric observations, but the observed spectrum of the event may pose some challenges for this scenario. The observations are not consistent with a shock breakout from a stellar envelope, while a model involving a low-mass ejecta ramming into low-mass CSM cannot explain both the early- and late-time observations.

10 pages, ApJ in press

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• A common envelope jets supernova (CEJSN) impostor scenario for fast blue optical transients
• The Large Array Survey Telescope -- Science Goals
• On the nature of Fast Blue Optical Transients
• Simulating the tidal disruption of stars by stellar-mass black holes using moving-mesh hydrodynamics
• The thermalization of $\gamma$-rays in radioactive expanding ejecta: A simple model and its application for Kilonovae and Ia SNe
• Gravitational Collapse of White Dwarfs to Neutron Stars. I. From Initial Conditions to Explosions with Neutrino-radiation Hydrodynamics Simulations
• A precursor interpretation for the Crab supernova 1054 A.D. very early light curve
• Science with a large field-of-view polarization survey: The Large Array Survey Telescope Polarization Node (LAST-P)