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Needle in a Poissonian haystack -- An X-ray astronomer's guide to QPE fishing

E. Quintin, N. Khan, N. A. Webb, R. Webbe, R. D. Saxton, G. Miniutti, M. Giustini

TL;DR

The paper tackles the bias and incompleteness in current QPE detection by outlining two complementary observational strategies to expand the QPE sample. The first strategy focuses on following up X-ray-detected TDEs to efficiently allocate observing time and reduce biases, leveraging existing and upcoming X-ray alert capabilities. The second strategy introduces EXOD, a time-resolved, 3D-binning search in the XMM-Newton archive to reveal faint, short-lived bursts that elude standard stacking methods, potentially uncovering QPE-like events at greater distances. Together, these approaches aim to broaden the population of QPEs, enable more robust model testing, and mitigate reliance on any single discovery pathway.

Abstract

After six years of studies following the discovery of GSN069, a link is starting to appear between the elusive Quasi-Periodic Eruptions (QPEs) and other types of nuclear transients, among which are Tidal Disruption Events (TDEs). As such, observing strategies are adapting, with a current trend focusing on late-time X-ray follow-ups of (optical) TDEs. While these campaigns are so far proving quite successful, the inherent confirmation bias they introduce in our sample could lead the community to hasty, and perhaps erroneous, conclusions. It is thus important to still pursue the search for nuclear transients in other, more agnostic directions. In this work, we focus on the observational aspects of our field, and lay out two different methods that can be deployed in order to reveal new QPE sources. These complementary methods enable the detection of long-term ($\sim$years) and short term ($\sim$minutes) transient events, that would have otherwise been missed by the standard detection pipelines. Both of these methods can be used either for data mining in the 25 years worth of XMM-Newton archive, or to trigger real-time follow-ups upon a more recent discovery.

Needle in a Poissonian haystack -- An X-ray astronomer's guide to QPE fishing

TL;DR

The paper tackles the bias and incompleteness in current QPE detection by outlining two complementary observational strategies to expand the QPE sample. The first strategy focuses on following up X-ray-detected TDEs to efficiently allocate observing time and reduce biases, leveraging existing and upcoming X-ray alert capabilities. The second strategy introduces EXOD, a time-resolved, 3D-binning search in the XMM-Newton archive to reveal faint, short-lived bursts that elude standard stacking methods, potentially uncovering QPE-like events at greater distances. Together, these approaches aim to broaden the population of QPEs, enable more robust model testing, and mitigate reliance on any single discovery pathway.

Abstract

After six years of studies following the discovery of GSN069, a link is starting to appear between the elusive Quasi-Periodic Eruptions (QPEs) and other types of nuclear transients, among which are Tidal Disruption Events (TDEs). As such, observing strategies are adapting, with a current trend focusing on late-time X-ray follow-ups of (optical) TDEs. While these campaigns are so far proving quite successful, the inherent confirmation bias they introduce in our sample could lead the community to hasty, and perhaps erroneous, conclusions. It is thus important to still pursue the search for nuclear transients in other, more agnostic directions. In this work, we focus on the observational aspects of our field, and lay out two different methods that can be deployed in order to reveal new QPE sources. These complementary methods enable the detection of long-term (years) and short term (minutes) transient events, that would have otherwise been missed by the standard detection pipelines. Both of these methods can be used either for data mining in the 25 years worth of XMM-Newton archive, or to trigger real-time follow-ups upon a more recent discovery.

Paper Structure

This paper contains 5 sections, 2 figures.

Table of Contents

  1. Introduction
  2. Current methods of QPE detection, and their limits
  3. First alternative: Following up on X-ray TDEs
  4. Second alternative: Dedicated faint bursts search
  5. Conclusions

Figures (2)

  • Figure 1: Illustration of the philosophy behind EXOD. The top panel shows a single frame, and the bottom panel an entire stacked observation. In both, we compare the appearance of a constant source (light blue circle) and a transient source (dark blue circle). This shows clearly that stacking over the whole exposure increases the signal-to-noise ratio of constant sources, but drowns out transient objects.
  • Figure 2: Illustration of the potential of EXOD for QPEs. The left panel depicts the current sample found in the archive, where the source is typically above the background at all times, or at least for a significant fraction of the eruptions. The right panel shows a much fainter sample of QPEs, where the source is only visible a few times above the background, such that it does not appear clearly in a stacked image.