Speaker
Patrizia Romano
(INAF)
Description
We present the results of the Swift Supergiant Fast X-ray Transients project,
which has been exploiting *Swift*'s capabilities in a systematic study of SFXTs and classical
supergiant X-ray binaries (SGXBs) since 2007.
The unique combination of sensitivity and scheduling flexibility of *Swift*/XRT
allowed us to perform an efficient long-term monitoring of 16 including both SFXTs and classical SGXBs.
We followed source activity across more than 4 orders of magnitude in X-ray luminosity and sampled the light curves on timescales spanning from hours to years.
Our measurements of dynamic ranges, duty cycles as a function of luminosity, and of
luminosity distributions show systematic differences that
help discriminate between different models of SFXTs/SGXBs, while our outburst follow-ups
provide a steady advancement in the comprehension of the SFXT phenomenon.
In particular, the observations of the SFXT prototype IGR J17544-2619
on 2014 October 10, when the source reached a peak luminosity of $3\times10^{38}$ erg s$^{-1}$,
challenged, for the first time, the maximum theoretical luminosity achievable
by a wind-fed neutron star high mass X-ray binary. We propose that this giant outburst was due to the formation of a
transient accretion disc around the compact object.
Primary author
Patrizia Romano
(INAF)
Co-authors
David Burrows
(The Pennsylvania State University)
Enrico Bozzo
(ISDC)
Hans Krimm
(NASA Goddard Space Flight Center)
Jamie A. Kennea
(The Pennsylvania State University)
Lorenzo Ducci
(University of Tuebingen)
Neil Gehrels
(NASA Goddard Space Flight Center)
Paolo Esposito
(National Institute for Astrophysics - INAF)
Phil Evans
(University of Leicester)
Scott Barthelmy
(NASA Goddard Space Flight Center)
Stefano Vercellone
(INAF)
