The Rapid X-ray and UV Evolution of ASASSN-14ko

TL;DR

This study investigates the rapid, multi-wavelength evolution of the periodically flaring transient ASASSN-14ko in a dual-AGN system, revealing detailed UV, optical, and X-ray behaviors during two major flares.

Contribution

It provides the first detailed multi-wavelength analysis of ASASSN-14ko's flares, highlighting the complex X-ray spectral evolution and UV/optical correlation in a post-merger AGN system.

Findings

UV/optical emission rises and falls in unison with luminosity changes.

X-ray flux exhibits rapid drops and rises with different spectral behaviors.

Flares originate from the brighter nucleus in a dual-AGN system.

Abstract

ASASSN-14ko is a recently discovered periodically flaring transient at the center of the AGN ESO 253-G003 with a slowly decreasing period. Here we show that the flares originate from the northern, brighter nucleus in this dual-AGN, post-merger system. The light curves for the two flares that occurred in May 2020 and September 2020 are nearly identical over all wavelengths. For both events, Swift observations showed that the UV and optical wavelengths brightened in unison. The effective temperature of the UV/optical emission rises and falls with the increase and subsequent decline in the luminosity. The X-ray flux, in contrast, first rapidly drops over $\sim$2.6 days, rises for $\sim$5.8 days, drops again over $\sim$4.3 days and then recovers. The X-ray spectral evolution of the two flares differ, however. During the May 2020 peak the spectrum softened with increases in the X-ray luminosity, while we observed the reverse for the September 2020 peak.