Extreme ultra-soft X-ray variability in an eROSITA observation of the Narrow-Line Seyfert 1 Galaxy 1H 0707-495

TL;DR

This study reports extreme ultra-soft X-ray variability in the Seyfert galaxy 1H 0707-495 observed by eROSITA, revealing flux changes up to 58 times, likely caused by ionized partial covering absorption affecting the soft X-ray emission.

Contribution

First eROSITA observation of 1H 0707-495 demonstrating extreme ultra-soft X-ray variability and modeling it with relativistic reflection and ionized partial covering absorber.

Findings

Flux decreased by a factor of 58 in soft X-rays.

Variability primarily in the soft band, less in the hard band.

Spectral modeling suggests ionized partial covering absorber explains variability.

Abstract

The ultra-soft narrow-line Seyfert 1 galaxy 1H 0707-495 is a well-known and highly variable active galactic nucleus (AGN), with a complex, steep X-ray spectrum, and has been studied extensively with XMM-Newton. 1H 0707-495 was observed with the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) aboard the Spectrum-Roentgen-Gamma (SRG) mission on October 11, 2019, for about 60,000 seconds as one of the first calibration and pointed verification phase (CalPV) observations. The eROSITA light curves show significant variability in the form of a flux decrease by a factor of 58 with a 1 sigma error confidence interval between 31 and 235. This variability is primarily in the soft band, and is much less extreme in the hard band. No strong ultraviolet variability has been detected in simultaneous XMM-Newton Optical Monitor observations. The UV emission is about 10^44 erg s^-1, close to the Eddington limit. 1H 0707-495 entered the lowest hard flux state seen in 20 years of XMM-Newton observations. In the eROSITA All-Sky Survey (eRASS) observations taken in April 2020, the X-ray light curve is still more variable in the ultra-soft band, but with increased soft and hard band count rates more similar to previously observed flux states. A model including relativistic reflection and a variable partial covering absorber is able to fit the spectra and provides a possible explanation for the extreme light-curve behaviour. The absorber is probably ionised and therefore more transparent to soft X-rays. This leaks soft X-rays in varying amounts, leading to large-amplitude soft-X-ray variability.