Discovering periodic and repeating nuclear transients in the XMM-Newton archives

TL;DR

This paper introduces methods for detecting periodic and repeating nuclear transients in X-ray data from the XMM-Newton archives, including new candidate tidal disruption events and black hole binaries.

Contribution

It presents a novel pipeline and real-time alert system for identifying and following up on transient X-ray sources in archival data.

Findings

Discovery of new candidate TDEs and black hole binaries.

Implementation of the STONKS pipeline in the XMM-Newton data processing.

Successful identification of fading and periodic X-ray sources.

Abstract

The regions around massive black holes can show X-ray variability on timescales from seconds to decades. Observing many black holes over different timescales can enhance our chances of detecting variability coming from (partial) tidal disruption events, massive black hole binaries, changing state AGN, blazar activity and much more. X-ray catalogues with hundreds of thousands of detections are treasure troves of such sources, which require innovative methods to identify these black holes. We present the current XMM-Newton catalogues available and describe several examples of tidal disruption events (TDEs) and quasi-periodic eruption sources that have been found whilst mining this data. We describe preliminary work on a search for periodic variables in the XMM-Newton EPIC archival data, with the example of finding new massive black hole binaries. We also describe the STONKS pipeline that is now in the XMM-Newton automatic reduction pipeline and the near real-time alert system that allows the follow-up of new and fading transients. We provide examples of fading sources that are newly identified candidate TDEs.