Long-term evolution, X-ray outburst and optical/infrared emission of SGR 0501+4516

TL;DR

This paper models the long-term evolution and X-ray/optical emission of SGR 0501+4516 using a fallback disc framework, explaining its current state and emission properties based on neutron star and disc parameters.

Contribution

It demonstrates that the observed properties of SGR 0501+4516 can be explained by a fallback disc model with specific initial conditions and magnetic field, extending previous models to this source.

Findings

X-ray luminosity and period match model predictions

Optical/IR emission aligns with irradiated fallback disc

Source remains in accretion phase for 2-5 x 10^5 years

Abstract

We have analyzed the long-term evolution and the X-ray outburst light curve of SGR 0501+4516 in the frame of the fallback disc model. We have shown that the X-ray luminosity, period and period derivative of this typical soft gamma repeater can be achieved by a neutron star with a large range of initial disc masses provided that the source has a magnetic dipole field of ~ 1.4 x 10^{12} G on the pole of the star. At present, the star is accreting matter from the disc, which has an age ~ 3 x 10^4 yr, and will remain in the accretion phase until t ~ 2 - 5 x 10^5 yr depending on the initial disc mass. With its current rotational rate, this source is not expected to give pulsed radio emission even if the accretion on to the star is hindered by some mechanism. The X-ray enhancement light curve of SGR 0501+4516 can be accounted for by the same model applied earlier to the X-ray enhancement light curves of other anomalous X-ray pulsars/soft gamma repeaters with the same basic disc parameters. We have further shown that the optical/IR data of SGR 0501+4516 is in good agreement with the emission from an irradiated fallback disc with the properties consistent with our long-term evolution model.