The propeller effect should cut off accretion in fast-spinning neutron star high mass X-ray binaries ( HMXBs ) at low mass transfer rates .
However , accretion continues in some HMXBs at L _ { \textsl { x } } < 10 ^ { 34 } erg s ^ { -1 } , as evidenced by continuing pulsations .
Indications of spectral softening in systems in the propeller regime suggest that some HMXBs are undergoing fundamental changes in their accretion regime .
A 39 ks XMM-Newton observation of the transient HMXB V0332+53 found it at a very low X-ray luminosity ( L _ { \textsl { x } } \sim 4 \times 10 ^ { 32 } erg s { { } ^ { -1 } } ) .
A power-law spectral fit requires an unusually soft spectral index ( 4.4 ^ { +0.9 } _ { -0.6 } ) , while a magnetized neutron star atmosphere model , with temperature Log T _ { \text { eff } } 6.7 \pm 0.2 K and inferred emitting radius of \sim 0.2 - 0.3 km , gives a good fit .
We suggest that the quiescent X-ray emission from V0332+53 is mainly from a hot spot on the surface of the neutron star .
We could not detect pulsations from V0332+53 , due to the low count rate .
Due to the high N _ { H } , thermal emission from the rest of the neutron star could be only weakly constrained , to Log T _ { \text { eff } } < 6.14 ^ { +0.05 } _ { -6.14 } K , or < 3 \times 10 ^ { 33 } erg s { { } ^ { -1 } } .