Περίληψη:
We present a toy model for radio emission in high-mass X-ray binaries
(HMXBs) with strongly magnetized neutron stars (NSs) where a
wind-collision region is formed by the NS outflow and the stellar wind
of the massive companion. Radio emission is expected from the
synchrotron radiation of shock-accelerated electrons and the free-free
emission of the stellar wind. We found that the predicted relation
between the GHz luminosity (L-R) and the accretion X-ray luminosity
(L-X) can be written as L-R alpha L-X(b) for most parameters. No
correlation with X-rays is expected (b = 0) when the thermal emission of
the stellar wind dominates in radio. We typically find a steep
correlation (b = 12/7) for sub-Eddington X-ray luminosities and a more
shallow one [b = 2(p - 1)/7] for super-Eddington X-ray luminosities,
where p is the power-law index of accelerated electrons. The maximum
predicted radio luminosity is independent of the NS properties, while it
depends on the stellar wind momentum, binary separation distance, and
the minimum electron Lorentz factor. Using a Bayesian approach, we
modelled the radio observations of SwiftJ0243.6+6124 that cover a wide
range of mass accretion rates. Our results support a shock origin for
the radio detections at sub-Eddington X-ray luminosities. However, no
physically meaningful parameters could be found for the super-Eddington
phase of the outburst, suggesting a different origin. Future
observations with more sensitive instruments might reveal a large number
of HMXBs with strongly magnetized NSs in radio, allowing the
determination of the slope in the L-R-L-X relation, and putting the
wind-collision scenario into test.
Συγγραφείς:
Chatzis, Margaritis
Petropoulou, Maria
Vasilopoulos, Georgios
