TY  - JOUR
A1  - Bozzo, Enrico
A1  - Oskinova, Lida
A1  - Lobel, A.
A1  - Hamann, Wolf-Rainer
T1  - The super-orbital modulation of supergiant high-mass X-ray binaries
JF  - Astronomy and astrophysics : an international weekly journal
N2  - The long-term X-ray light curves of classical supergiant X-ray binaries and supergiant fast X-ray transients show relatively similar super-orbital modulations, which are still lacking a sound interpretation. We propose that these modulations are related to the presence of corotating interaction regions (CIRs) known to thread the winds of OB supergiants. To test this hypothesis, we couple the outcomes of three-dimensional (3D) hydrodynamic models for the formation of CIRs in stellar winds with a simplified recipe for the accretion onto a neutron star. The results show that the synthetic X-ray light curves are indeed modulated by the presence of the CIRs. The exact period and amplitude of these modulations depend on a number of parameters governing the hydrodynamic wind models and on the binary orbital configuration. To compare our model predictions with the observations, we apply the 3D wind structure previously shown to well explain the appearance of discrete absorption components in the UV time series of a prototypical B0.5I-type supergiant. Using the orbital parameters of IGRJ 16493-4348, which has the same B0.5I donor spectral type, the period and modulations in the simulated X-ray light curve are similar to the observed ones, thus providing support to our scenario. We propose that the presence of CIRs in donor star winds should be considered in future theoretical and simulation efforts of wind-fed X-ray binaries.
KW  - X-rays: stars
KW  - X-rays: binaries
KW  - gamma rays: stars
KW  - stars: massive
KW  - stars: neutron
Y1  - 2017
U6  - https://doi.org/10.1051/0004-6361/201731930
SN  - 1432-0746
VL  - 606
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Postnov, K.
A1  - Oskinova, Lida
A1  - Torrejon, J. M.
T1  - A propelling neutron star in the enigmatic Be-star gamma Cassiopeia
JF  - Monthly notices of the Royal Astronomical Society
N2  - gamma Cassiopeia (gamma Cas), is known to be a binary system consisting of a Be-type star and a low-mass (M similar to 1M(circle dot)) companion of unknown nature orbiting in the Be-disc plane. Here, we apply the quasi-spherical accretion theory on to a compact magnetized star and show that if the low-mass companion of gamma Cas is a fast spinning neutron star, the key observational signatures of. Cas are remarkably well reproduced. Direct accretion on to this fast rotating neutron star is impeded by the propeller mechanism. In this case, around the neutron star magnetosphere a hot shell is formed which emits thermal X-rays in qualitative and quantitative agreement with observed properties of the X-ray emission from gamma Cas. We suggest that gamma Cas and its analogues constitute a new subclass of Be-type X-ray binaries hosting rapidly rotating neutron stars formed in supernova explosions with small kicks. The subsequent evolutionary stage of gamma Cas and its analogues should be the X Per-type binaries comprising low-luminosity slowly rotating X-ray pulsars. The model explains the enigmatic X-ray emission from gamma Cas, and also establishes evolutionary connections between various types of rotating magnetized neutron stars in Be-binaries.
KW  - stars: emission-line, Be
KW  - stars: neutron
Y1  - 2017
U6  - https://doi.org/10.1093/mnrasl/slw223
SN  - 0035-8711
SN  - 1365-2966
VL  - 465
IS  - 1
SP  - L119
EP  - L123
PB  - Oxford Univ. Press
CY  - Oxford
ER  -