* Astronomy

Blobrana · L

RE: 1E161348-5055

Blobrana · L

Title: On the origin of the 6.67 hr period pulsar 1E 161348-5055
Authors: N. R. Ikhsanov, V. Yu. Kim, N. G. Beskrovnaya, L. A. Pustil'nik

The point X-ray source 1E 161348-5055 is observed to display pulsations with the period 6.67 hr and |\dot{P}| < 1.6x10^{-9} s/s. The source is associated with the supernova remnant RCW 103 and is widely believed to be a ~2000 yr young neutron star. Observations give no evidence for the neutron star to be a member of a binary system. Nevertheless, it resembles an accretion-powered pulsar with the magnetospheric radius ~3000 km and the mass-accretion rate ~10^{14} g/s. This situation could be described in terms of accretion from a (residual) fossil disk established from the material falling back towards the star after its birth. However, current fall-back accretion scenarios encounter major difficulties explaining an extremely long spin period of the young neutron star. We show that the problems can be avoided if the accreting material is magnetized. The star in this case is surrounded by a fossil magnetic slab in which the material is confined by the magnetic field of the accretion flow itself. We find that the surface magnetic field of the neutron star within this scenario is ~ 10^{12} G and that a presence of ~10^{-7} solar masses magnetic slab would be sufficient to explain the origin and current state of the pulsar.

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Blobrana · L

Title: 1E161348-5055 in the Supernova Remnant RCW 103: A Magnetar in a Young Low Mass Binary System?
Authors: Fabio Pizzolato, Monica Colpi, Andrea De Luca, Sandro Mereghetti, Andrea Tiengo

We suggest that the unique X-ray source 1E161348-5055 at the centre of the supernova remnant RCW 103 consists of a neutron star in close orbit with a low mass main sequence star. The time signature of 6.67 hr is interpreted as the neutron star's spin period. This requires the neutron star to be endowed with a high surface magnetic field of~10^15 G. Magnetic or/and material (propeller) torques are able to spin rapidly the young neutron star down to an asymptotic, equilibrium spin period in close synchronism with the orbital period, similarly to what happens in the Polar Cataclysmic Variables. 1E161348-5055 could be the first case of a magnetar born in a young low mass binary system.

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Blobrana · L

Embedded in the heart of a supernova remnant 10,000 light-years away is a stellar object the likes of which astronomers have never seen before in our galaxy.

At first glance, the object looks like a densely packed stellar corpse known as a neutron star surrounded by a bubble of ejected stellar material, exactly what would be expected in the wake of a supernova explosion.
However, a closer 24.5-hour examination with the European Space Agency's XMM Newton X-ray satellite reveals that the energetic X-ray emissions of the blue, point-like object cycles every 6.7 hours-tens of thousands of times longer than expected for a freshly created neutron star.
It is behaviour that's more commonly seen in neutron stars that have been around for several million years, researchers say.

"The behaviour we see is especially puzzling in view of its young age, less than 2,000 years. For years we have had a sense that the object is different, but we never knew how different until now" - Andrea De Luca, Istituto Nazionale di Astrofisica (INAF) in Milan, study leader.

The finding is detailed in the July 7 issue of the journal Science.

Called 1E161348-5055, or 1E for short, the object is embedded almost in the exact centre of RCW103, a supernova remnant located 10,000 light-years away in the constellation Norma. Astronomers think that 1E and RCW103 were both born in the same catastrophic event.
Like other neutron stars, which form when a star at least eight times more massive than the Sun runs out of fuel and explodes as a supernova, 1E is estimated to be only about 12.5 miles (20 km) across.

One explanation for the neutron star's strange behaviour is that it might be a magnetar, an exotic subclass of highly magnetized neutron stars. Of the dozen or so magnetars that are known, however, most usually spin several times per minute-much faster than 1E.
This explanation might still work, however, if the magnetar is surrounded by a debris disk that is helping to slow down the neutron star's spin. This scenario has never been observed before and would mark the discovery of a novel stage in neutron star evolution if confirmed.

Another explanation, scientists say, is that 1E is part of a binary system with a normal, low-mass star with only half the mass, or less, of our Sun.
Such X-ray binary systems are known, but they usually involve systems that are millions of times older than 1E.

Despite the many speculations, the short answer is that scientists simply don't yet know how to explain 1E's strange behaviour.

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