Analysis of a State Changing Supersoft X-ray Source in M31

TL;DR

This paper reports on the spectral state changes of a luminous supersoft X-ray source in M31, revealing a new class of state-changing phenomena that could indicate unusual black hole or neutron star accretors.

Contribution

It documents the first observed spectral transitions in a supersoft X-ray source, highlighting their implications for understanding the nature of these sources.

Findings

Spectral changes from supersoft to harder X-ray states observed.

Discovery of quasisoft states as a new phenomenon.

Implications for identifying black hole or neutron star accretors.

Abstract

We report on observations of a luminous supersoft X-ray source (SSS) in M31, r1-25, that has exhibited spectral changes to harder X-ray states. We document these spectral changes. In addition, we show that they have important implications for modeling the source. Quasisoft states in a source that has been observed as an SSS represent a newly- discovered phenomenon. We show how such state changers could prove to be examples of unusual black hole or neutron star accretors. Future observations of this and other state changers can provide the information needed to determine the nature(s) of these intriguing new sources.