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tokens: luminosity and thus accretion rate. For this purpose we used the results of our spectral analysis of the emission of the sources in a wide energy range, obtained during previous outbursts with the RXTE and INTEGRAL observatories ( Tsygankov et al. 2006 , 2007 ). It was found that the source flux in the 0.510 keV energy was 50% from the bolometric (i.e. flux in the 0.5100 keV energy range). Based on these results, in the subsequent calculations we used the coefficient 2 for the conversion of fluxes for both sources in the bright (accretion) state. In the propeller state, Swift /XRT energy coverage is sufficient to detect most of the emergent flux and no additional bolometric correction is needed. Indeed, this conclusion is valid both for the black body and power-law models due to the low temperatures ( keV) or steep photon indexes (). The bolometric correction may introduce additional uncertainty because of our ignorance of the broadband source spectrum at luminosities around the transition. We estimated this uncertainty at the level of 1020% and added it to the final uncertainty for the limiting luminosity. Taking all uncertainties into account, we estimate the bolometric limiting luminosities for the onset of the propeller regime at erg s and erg s for 4U 0115+63 and V 0332+53, respectively. Fig. 4 Observed correlation between a combination of the propeller limiting luminosity and the period, , and independently determined magnetic field strength for five pulsars and one accreting magnetar (M82 X-2) is shown with circles with error bars ( Tsygankov et al. 2016 ). The dashed and dash-dotted lines represent the theoretical dependence from Eq. ( 2 ), assuming NS standard parameters (, km) and and , respectively. The red star and open box indicate the positions of 4U 0115+63 and V 0332+53 obtained in this work, respectively. 4.2. “Propeller” effect The “propeller effect” ( Illarionov Sunyaev 1975 ) is caused by a substantial centrifugal barrier produced by the rotating magnetosphere of the neutron star. The matter stopped at the magnetospheric radius can only penetrate the magnetosphere if the velocity of the field lines is lower than the local Keplerian velocity. In other words, the matter will be accreted only in the case when the magnetospheric radius () is smaller than the corotation radius (). The magnetospheric radius depends on the mass accretion rate, and, therefore, one can estimate the limiting luminosity corresponding to the onset of the propeller regime by equating the corotation and magnetospheric radii (see e.g. Campana et al. 2002 ) where is the neutron star mass in units of 1.4 , is neutron star radius in units of cm, its rotational period in seconds, is the magnetic field strength in units of G, and is the mass accretion rate onto the neutron star. Factor relates the magnetospheric radius for disc accretion to the Alfvén radius calculated for spherical accretion and is usually assumed to be ( Ghosh Lamb 1978 ). Because the