Research Topics
My PhD Thesis
My PhD with Natalie Webb was entitled
"Revealing the transient Universe: Multi-wavelength perspectives on super-Eddington accretion"
Projects
Long-term transient live detection
A part of my PhD has been dedicated to writing the STONKS algorithm. STONKS uses our archival knowledge of X-ray emission from a region, compares it to new detections, and automatically sends out an alert in the case of a new transient.
It turns XMM-Newton into a transient detection survey ! You can find details in the submitted paper.
The STONKS alert system is being embedded in the XMM-Newton pipeline at the CDS, with the help of Laurent Michel. You can find it here !
Example of the lightcurve of a transient object, appearing for the first time, with past upper limits (see more details in the STONKS paper)
One of the transient sources that was found lying in the archives, NGC 7793 ULX-4. You can find more details in the paper !
Archival transients in the X-ray archives
A by-product of the development of STONKS is a comprehensive, multi-instrument catalog of the X-ray sky, spanning three decades and containing ~1 million sources.
Archival search for past long-term transients can be performed in this catalog, using tailored selection criteria depending on the targeted object.
Short-term
transient detection
XMM-Newton observations rely on stacking entire exposures to detect sources. However, a fast and faint transient might be drowned out by the noise of an entire observation.
The aim of EXOD is to tackle this issue, by performing carefully designed search for short-term transients in the entire XMM-Newton archive !
Map of the short-term variability of all pixels of a XMM-Newton EPIC observation. The red regions are flagged as variable objects
Astrophysical objects
of interest (to me)
Schematic view of a TDE (adapted from Kramer+21), showing the inbound star being disrupted, its infalling debris later interacting and resulting in the visible flare
Tidal Disruption
Events (TDEs)
TDEs correspond to the destruction of a star by the tidal forces around a Super-Massive Black Hole, (usually) at the center of a galaxy. These events are rare and poorly understood.
My work on TDEs has mainly been motivated by observational considerations. I have worked on unearthing archival TDEs that we had missed, as well as applying STONKS to detect X-ray TDE flares in quasi-real time.
I have also collaborated with the FINK broker for the Vera C. Rubin Observatory, in order to quickly detect optical TDEs during their rise.
Quasi-Periodic
Eruptions (QPEs)
QPEs are mysterious objects, characterized by bright eruptions of soft X-rays lasting about an hour and recurring every ~10h. They are a very recent addition to the ever-growing family of X-ray transients, the first one having been found in 2019. No clear explanation is accepted yet.
My work has focused on improving our ability to detect them and ensuring a proper long-term monitoring. They seem to be linked to TDEs, so monitoring new TDEs in their decay might provide us with new QPEs !
Normalized lightcurves of some known QPE sources.
Artist view of an accreting system (source: Kurzgesagt)
Ultra-Luminous
X-ray sources (ULXs)
ULXs are anomalously bright X-ray binaries. While they were first thought to host the elusive Intermediate Mass Black Holes, the discovery in 2014 of coherent accelerated pulsation led to the conclusion that at least some of them hosted neutron stars, and were thus bona fide super-Eddington accretors.
My work has focused on finding new candidate pulsating ULXs in the archives, and studying the overall long-term behaviour of these sources in order to better understand their nature(s?)