Radio properties of the magnetar near Sagittarius A* from observations with the Australia Telescope Compact Array

Abstract We have carried out observations of the newly discovered magnetar in the direction of Sagittarius A* using the Australia Telescope Compact Array (ATCA) in four frequency bands from 4.5 to 20 GHz. Radio pulsations are clearly detected at all frequencies. We measure the pulsar's dispersion measure to be 1650 ± 50 cm−3 pc, the highest of any of the known pulsars. Once Faraday rotation has been taken into account, the pulse profile is more than 80 per cent linearly polarized at all frequencies and has a small degree (5 per cent) of circular polarization. The rotation measure of −67000 ± 500 rad m−2 is the largest (in magnitude) ever measured for a pulsar but still a factor of 8 smaller than Sgr A* itself. The combination of the dispersion and rotation measures implies an integrated magnetic field strength of −50 μG along the line of sight. The flux density appears to have increased by about a factor of 2 between observations made 30 d apart. This object therefore joins the small class of radio emitting magnetars.

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