Astronomy and Astrophysics, volume 537, L1-1 (2012/1-1)
SXP 1062, a young Be X-ray binary pulsar with long spin period. Implications for the neutron star birth spin.
HABERL F., STURM R., FILIPOVIC M.D., PIETSCH W. and CRAWFORD E.J.
Abstract (from CDS):
The Small Magellanic Cloud (SMC) is ideally suited to investigating the recent star formation history from X-ray source population studies. It harbours a large number of Be/X-ray binaries (Be stars with an accreting neutron star as companion), and the supernova remnants can be easily resolved with imaging X-ray instruments. We search for new supernova remnants in the SMC and in particular for composite remnants with a central X-ray source. We study the morphology of newly found candidate supernova remnants using radio, optical and X-ray images and investigate their X-ray spectra. Here we report on the discovery of the new supernova remnant around the recently discovered Be/X-ray binary pulsar CXOJ012745.97-733256.5 = SXP1062 in radio and X-ray images. The Be/X-ray binary system is found near the centre of the supernova remnant, which is located at the outer edge of the eastern wing of the SMC. The remnant is oxygen-rich, indicating that it developed from a type Ib event. From XMM-Newton observations we find that the neutron star with a spin period of 1062s (the second longest known in the SMC) shows a very high average spin-down rate of 0.26s per day over the observing period of 18-days. From the currently accepted models, our estimated age of around 10000-25000-years for the supernova remnant is not long enough to spin down the neutron star from a few 10ms to its current value. Assuming an upper limit of 25000-years for the age of the neutron star and the extreme case that the neutron star was spun down by the accretion torque that we have measured during the XMM-Newton observations since its birth, a lower limit of 0.5s for the birth spin period is inferred. For more realistic, smaller long-term average accretion torques our results suggest that the neutron star was born with a correspondingly longer spin period. This implies that neutron stars in Be/X-ray binaries with long spin periods can be much younger than currently anticipated.