A deep search for pulsar wind nebulae using pulsar gating

Using the Australia Telescope Compact Array (ATCA) we have imaged the fields around five promising pulsar candidates to search for radio pulsar wind nebulae (PWNe). We have used the ATCA in its pulsar gating mode; this enables an image to be formed containing only off-pulse visibilities, thereby dramatically improving the sensitivity to any underlying PWN. Data from the Molonglo Observatory Synthesis Telescope were also used to provide sensitivity on larger spatial scales. This survey found a faint new PWN around PSR B0906-49; here we report on non-detections of PWNe towards PSRs B1046-58, B1055-52, B1610-50 and J1105-6107. Our radio observations of the field around PSR B1055-52 argue against previous claims of an extended X-ray and radio PWNe associated with the pulsar. If these pulsars power unseen, compact radio PWN, upper limits on the radio flux indicate that less than 1e-6 of their spin-down energy is used to power this emission. Alternatively PSR B1046-58 and PSR B1610-50 may have relativistic winds similar to other young pulsars and the unseen PWN is resolved and fainter than our surface brightness sensitivity threshold. We can then determine upper limits on the local ISM density of 2.2e-3 cm^-3 and 1e-2 cm^-3, respectively. Furthermore we constrain the spatial velocities of these pulsars to be less than ~450 km/s and thus rule out the association of PSR B1610-50 with SNR G332.4+00.1 (Kes 32). Strong limits on the ratio of unpulsed to pulsed emission are also determined for three pulsars.Comment: 10 pages, 5 figures, MNRAS in pres

Radio continuum and polarization study of SNR G57.2+0.8 associated with magnetar SGR1935+2154

We present a radio continuum and linear polarization study of the Galactic supernova remnant G57.2+0.8, which may host the recently discovered magnetar SGR1935+2154. The radio SNR shows the typical radio continuum spectrum of a mature supernova remnant with a spectral index of $\alpha = -0.55 \pm 0.02$ and moderate polarized intensity. Magnetic field vectors indicate a tangential magnetic field, expected for an evolved SNR, in one part of the SNR and a radial magnetic field in the other. The latter can be explained by an overlapping arc-like feature, perhaps a pulsar wind nebula, emanating from the magnetar. The presence of a pulsar wind nebula is supported by the low average braking index of 1.2, we extrapolated for the magnetar, and the detection of diffuse X-ray emission around it. We found a distance of 12.5 kpc for the SNR, which identifies G57.2+0.8 as a resident of the Outer spiral arm of the Milky Way. The SNR has a radius of about 20 pc and could be as old as 41,000 years. The SNR has already entered the radiative or pressure-driven snowplow phase of its evolution. We compared independently determined characteristics like age and distance for both, the SNR and SGR1935+2154, and conclude that they are physically related.Comment: accepted by The Astrophysical Journal, 16 pages, 10 figure