Sep 8 – 13, 2019
Europe/Rome timezone
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The unusual broadband X-ray continuum variability seen from Ultraluminous X-ray Sources

Speaker

Dominic Walton (University of Cambridge)

Description

Observational studies of Ultraluminous X-ray Sources (ULXs, L > 1e39 erg/s) have taken on greater siginficance since the discovery that this population is (primarily) made up of X-ray binaries accreting at super-Eddington rates, a result that has been spectacularly confirmed with the detection of coherent pulsations from a growing number of ULXs (requiring neutron star accretors, despite their extreme luminosities). The NuSTAR observatory has played a major role in this effort, initially providing the first view of ULXs in the hard X-ray band (E > 10 keV), contributing the first detection of pulsations in a ULX (M82 X-2), and now allowing broadband spectral variability studies to be undertaken. Throughout 2017 we undertook a major, multi-epoch observing campaign on the well-known 'extreme' ULX (L ~ 1e40 erg/s) NGC1313 X-1, combining XMM-Newton (800 ks), Chandra (500 ks) and NuSTAR (500 ks). I will present early results from this large coordinated campaign, focusing on the unusual broadband spectral variability exhibited. Remarkably, we find evidence that the thermal emission that dominates the ~2-10 keV band exhibits two distinct L ~ T^4 tracks, implying the presence of two stable radii in the inner accretion flow, separated by a factor of ~4. The source appears to jump between these different radii at different epochs. I will discuss possible interpretations for this strange behaviour, and place the broadband variability seen from NGC1313 X-1 in the context of that seen from the broader ULX sample to date.

Affiliation University of Cambridge
Topic Compact and diffuse sources in galaxies and in the Galactic Center

Primary authors

Dominic Walton (University of Cambridge) Dr Pinto Ciro (Cambridge University) Dr Mike Nowak (Washington University in St. Louis) Tim Roberts (Durham University) Mr Rajath Sathyaprakash (Durham University) Dr Matteo Bachetti (Osservatorio Astronomico di Cagliari) Dr Felix Fürst (ESA) Dr Will Alston (University of Cambridge ) Dr Erin Kara (University of Maryland) Peter Kosec (Institute of Astronomy, University of Cambridge) Prof. Andy Fabian (University of Cambridge) Roberto Soria (UCAS) Dr Hannah Earnshaw (Caltech) Matthew Middleton (University of Southampton) Dr Ryan Urquhart Dr Matteo Guainazzi (European Space Agency) Prof. Fiona Harrison Dr Daniel Stern (Jet Propulsion Laboratory) Didier Barret (IRAP) Natalie Webb (IRAP) Prof. Claude Canizares (MIT)

Presentation materials