High-frequency observations of the radio magnetar XTE J1810-197

ATel #12285; Gregory Desvignes (MPIfR, Bonn), Ralph Eatough (MPIfR, Bonn), Michael Kramer (MPIfR, Bonn), Ramesh Karuppusamy (MPIfR, Bonn), Alex Kraus (MPIfR, Bonn), Andrew Lyne (University of Manchester), Lina Levin (University of Manchester), Ben Stappers (University of Manchester), Mitch Mickaliger (University of Manchester)
on 11 Dec 2018; 23:06 UT
Credential Certification: Evan Keane (ekean@jb.man.ac.uk)

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Following a report of bright radio flaring of the magnetar XTE J1809-197 detected with the 76-m Lovell telescope at Jodrell Bank (Atel #12284), observations of this neutron star were conducted with the 100-m Effelsberg radio telescope of the Max Planck Institute for Radio Astronomy. Two consecutive observations, each lasting about 20 minutes and utilizing receivers operating at 4.74 GHz and 8.35 GHz with 500 MHz bandwidth, were initiated on December 11th 2018, 13h17 UTC (MJD 58463.5).

The data were folded in real-time using a rotational period as predicted by the Jodrell Bank observations (Atel #12284). Highly significant detections have been made at each frequency with measured average flux densities of 22.5+/-0.2 mJy at 4.74 GHz and 14.9+/-0.2 mJy at 8.35 GHz, giving a spectral index of -0.7. Evidence for bright single pulse emission is present throughout each of the 20-min integrations.

The average pulse profiles have changed morphology since earlier observations at similar frequencies, and no longer exhibit signs of interpulse emission (Lazaridis et al. 2008). Some frequency evolution in profile shape is observed in this data. Consistent with other radio magnetars, the pulse profiles are nearly 100% linearly polarised (e.g. ATel #5064) and exhibit about 10 per cent circular polarisation. The polarisation angle of the linear polarisation show a clear swing at each frequency.

Continued radio monitoring has started and higher frequency observations are scheduled.

References:
Lazaridis, K., Jessner, A., Kramer, M., et al., Radio spectrum of the AXP J1810-197 and of its profile components (2008), MNRAS, 390, 839.

The detection plots at 4.74 GHz and 8.35 GHz can be found at:
Pulse profile at 4.74 GHz
Pulse profile at 8.35 GHz