Hunting Be X-ray binary outbursts in the Magellanic Clouds

Be/X-ray binaries (BeXRBs) are a major subclass of high-mass X-ray binaries (HMXBs) that accord the majority of accreting X-ray pulsar systems. These systems consist of a highly magnetised neutron star (NS), which accretes matter from a non super-giant Be type donor star. Since in order to form such systems a young stellar population is needed, their numbers within a galaxy is correlated with the recent star formation. BeXRBs are highly variable in the X-rays exhibiting moderate (LX~1036 erg/s or major outbursts (LX>1037 erg/s). The X-ray variability is attributed to their irregular/wobbly mass transfer mechanism, as accretion is fuelled by material ejected in the equatorial plane of the Be star, forming a decretion disk around it.

The Magellanic Clouds (MCs) offer a unique possibility to study the population of high-energy sources of a whole galaxy.  Their moderate and well measured distances of ~50 kpc for the Large Magellanic Cloud (LMC) and ~60 kpc for the Small Magellanic Cloud (SMC) as well as their low Galactic foreground absorption  (~6 x 1020 cm-2) makes them ideal targets for studying X-ray binary systems. Moreover Due to recent episodes of star formation ∼20-50 Myr ago, the MCs harbour a large population of high-mass X-ray binaries (HMXBs). The SMC Is know to host 64 HMXRB pulsars and about as many aditional candidates candidate systems ,  while the ~10 times larger LMC has only 19 confirmed HMXB pulsars and ~50 candidate systems. A study of the BeXRB populations in the MCs and other nearby Galaxies could provide a major step in the understanding of their link to the properties of the host galaxies, like the recent star formation and metallicity.  

During my PhD studies I have been working on the study of accreting NS in HMXB systems.
Hunting BeXRB ouburst...  that is how I would describe this quest. Given the transient nature of  BeXRBs, we need to be prepared to perform observation during their outburst in order to obtain quality data. For doing so, I have served as a principal investigator in multiple observational proposals with some of the biggest X-ray telescope of our era like XMM-Newton,  Swift,  Chandra, and NuSTAR. Dy collecting high quility X-ray data, and complimentary multi-wavelength observations we have improved our understanding of this fascinating systems. 

Image:  Walt Feimer, NASA/Goddard Space Flight Center (Corresponding video)

See refereed publications:

1) Multi-wavelength properties of IGR J05007-7047 (LXP 38.55) and identification as a Be X-ray binary pulsar in the LMC
2) Discovery of SXP 265, a Be/X-ray binary pulsar in the Wing of the Small Magellanic Cloud
3) Spectral and temporal properties of RX J0520.5-6932 (LXP 8.04) during a type-I outburst
4) Swift J053041.9-665426, a new Be/X-ray binary pulsar in the Large Magellanic Cloud
5) SXP 15.6: X-ray spectral and temporal properties of a newly discovered pulsar in the Small Magellanic Cloud
6) Identification of IGR J01217-7257 with the transient SMC pulsar XTE J0119-731 (SXP 2.16) using XMM-Newton
7) EXTraS discovery of two pulsators in the direction of the LMC: a Be/X-ray binary pulsar in the LMC and a candidate double-degenerate polar in the foreground