A new class of X-ray Pulsars ?

Abstract

While the distribution of spin periods of High Mass X-ray Binaries (HMXBs) spans more than four orders of magnitude (69ms - 25min), the few known X-ray pulsars accreting from very low mass companions (<1 Msun) have very similar periods between 5.4 and 8.7s . These pulsars display also several other similarities and they are probably members of a subclass of Low Mass X-ray Binaries (LMXBs) with similar magnetic field (a few 10^11 G), companion stars and, possibly, evolutionary histories. If they are rotating at, or close to, the equilibrium period, their properties are consistent with luminosities of the order of a few 10^35 erg/s. These pulsars might represent the closest members of a subclass of LMXBs characterized by lower luminosities, higher magnetic fields and smaller ages than non-pulsating LMXBs.

12 pages (figures included), latex style included, HIGHLIGHTS OF EUROPEAN ASTRONOMY, Proc. 4th European and 39th Italian Astron. Soc. Meetings (Catania, Italy), M. Rodono' and S. Catalano (eds.), Mem.S.A.It., 1996 (in press)