摘要：Aims. We present the results of the monitoring programmes performed with
the Swift/XRT telescope and aimed specifically to detect an abrupt
decrease of the observed flux associated with a transition to the propeller regime in two
well-known X-ray pulsars 4U 0115+63 and V 0332+53.
Methods. Both sources form binary systems with Be optical companions and
undergo so-called giant outbursts every 3−4 years. The current observational campaigns were performed with the
Swift/XRT telescope in the soft X-ray band (0.5−10 keV) during the declining phases of the
outbursts exhibited by both sources in 2015.
Results. The transitions to the propeller regime were detected at the
threshold luminosities of (1.4 ± 0.4) ×
1036 erg s-1 and (2.0 ±
0.4) × 1036 erg s-1 for 4U 0115+63 and V 0332+53, respectively. Spectra of
the sources are shown to be significantly softer during the low state. In both sources,
the accretion at rates close to the aforementioned threshold values briefly resumes during
the periastron passage following the transition into the propeller regime. The strength of
the dipole component of the magnetic field required to inhibit the accretion agrees well
with estimates based on the position of the cyclotron lines in their spectra, thus
excluding presence of a strong multipole component of the magnetic field in the vicinity
of the neutron star.
