Flares from a candidate Galactic magnetar suggest a missing link to dim isolated neutron stars
Hanlon, L.; McBreen, B.; Bremer, M.; Klose, S.; Pandey, S. B.; Kann, D. A.; Pérez-Ramírez, D.; Markoff, S. B.; Guerrero, M. A.; Kraus, A.; Gorosabel, J.; Sánchez-Fernández, C.; Castro-Tirado, A. J.; Jelínek, M.; de Ugarte Postigo, A.; Sonbas, E.; Shahbaz, T.; Sluse, D.; Schulze, S.; Hudec, R.; Ferrero, P.; Winters, J. M.; Leon, S.; Aceituno, F. J.; French, J.; Melady, G.; Wilson, A. C.; Trushkin, S. A.; Fatkhullin, T. A.; Guziy, S.; Sokolov, V. V.; Sabau-Graziati, L.; Kubánek, P.; Durant, M.; Nuernberger, D.; Leventis, K.; Cunniffe, R.; Vítek, S.; González-Pérez, J. M.; Pavlenko, L.; Bursov, N. N.; Nizhelskij, N. A.
Spain, Russia, Germany, Switzerland, France, Chile, Ireland, Netherlands, United States, Czech Republic, Ukraine, India, Turkey
Abstract
Magnetars are young neutron stars with very strong magnetic fields of the order of 1014-1015G. They are detected in our Galaxy either as soft γ-ray repeaters or anomalous X-ray pulsars. Soft γ-ray repeaters are a rare type of γ-ray transient sources that are occasionally detected as bursters in the high-energy sky. No optical counterpart to the γ-ray flares or the quiescent source has yet been identified. Here we report multi-wavelength observations of a puzzling source, SWIFT J195509+261406. We detected more than 40 flaring episodes in the optical band over a time span of three days, and a faint infrared flare 11days later, after which the source returned to quiescence. Our radio observations confirm a Galactic nature and establish a lower distance limit of ~3.7kpc. We suggest that SWIFT J195509+261406 could be an isolated magnetar whose bursting activity has been detected at optical wavelengths, and for which the long-term X-ray emission is short-lived. In this case, a new manifestation of magnetar activity has been recorded and we can consider SWIFT J195509+261406 to be a link between the `persistent' soft γ-ray repeaters/anomalous X-ray pulsars and dim isolated neutron stars.