The X-ray quiescence of Swift J195509.6+261406 (GRB 070610): an optical bursting X-ray binary?

TL;DR

This study used Chandra X-ray observations to analyze the quiescent state of Swift J195509.6+261406, suggesting it is likely a low-mass X-ray binary with a black hole or neutron star, rather than a magnetar.

Contribution

The paper provides the first stringent upper limits on the quiescent X-ray emission of Swift J195509.6+261406, challenging the magnetar hypothesis and proposing a binary system with a low-mass companion as the most plausible nature.

Findings

Upper limits on quiescent X-ray emission exclude typical magnetar scenario.

Data supports a low-mass X-ray binary with a short orbital period.

Optical flares are consistent with a binary system hosting a compact object.

Abstract

We report on a 63ks Chandra observation of the X-ray transient Swift J195509.6+261406 discovered as the afterglow of what was first believed to be a long duration Gamma-Ray Burst (GRB 070610). The outburst of this source was characterized by unique optical flares on timescales of second or less, morphologically similar to the short X-ray bursts usually observed from magnetars. Our Chandra observation was performed ~2 years after the discovery of the optical and X-ray flaring activity of this source, catching it in its quiescent state. We derive stringent upper limits on the quiescent emission of Swif J195509.6+261406 which argues against the possibility of this object being a typical magnetar. Our limits show that the most viable interpretation on the nature of this peculiar bursting source, is a binary system hosting a black hole or a neutron star with a low mass companion star (< 0.12 M_{\odot}), and with an orbital period smaller than a few hours.