SXP 1062, a young Be X-ray binary pulsar with long spin period; Implications for the neutron star birth spin

Astronomy and Astrophysics (Impact Factor: 5.08). 12/2011; DOI: 10.1051/0004-6361/201118369
Source: arXiv

ABSTRACT (shortened) The 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, 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 SXP 1062 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 1062 s shows a very high average
spin-down rate of 0.26 s 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 10 ms 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 0.5 s 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.

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