Flares from Galactic centre pulsars: a new class of X-ray transients?

Abstract

Despite intensive searches, the only pulsar within 0.1 pc of the central black hole in our Galaxy, Sgr A*, is a radio-loud magnetar. Since magnetars are rare among the Galactic neutron star population, and a large number of massive stars are already known in this region, the Galactic centre (GC) should harbor a large number of neutron stars. Population syntheses suggest several thousand neutron stars may be present in the GC. Many of these could be highly energetic millisecond pulsars which are also proposed to be responsible for the GC gamma-ray excess. We propose that the presence of a neutron star within 0.03~pc from Sgr~A* can be revealed by the shock interactions with the disk around the central black hole. As we demonstrate, these interactions result in observable transient non-thermal X-ray and gamma-ray emission over timescales of months, provided that the spin down luminosity of the neutron star is L_{sd}~10^{35} erg/s. Current limits on the population of normal and millisecond pulsars in the GC region suggest that a number of such pulsars are present with such luminosities.