We report on an 63ks Chandra observation of the X-ray transient SwiftJ195509.6+261406 discovered as the afterglow of what was first believed to be a long-duration gamma-ray burst (GRB070610). 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 SwiftJ195509.6+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) and with an orbital period smaller than a few hours. © 2011. The American Astronomical Society. All rights reserved.
- stars: magnetic field
- X-rays: stars