Intense radio flare from the magnetar XTE J1810-197

ATel #12284; Andrew Lyne (University of Manchester), Lina Levin (University of Manchester), Ben Stappers (University of Manchester), Mitch Mickaliger (University of Manchester), Gregory Desvignes (MPIfR, Bonn), Michael Kramer (MPIfR, Bonn)
on 11 Dec 2018; 10:30 UT
Credential Certification: Lina Levin (Lina.Preston@manchester.ac.uk)

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The magnetar XTE J1810-197, discovered following an X-ray outburst in 2003 (Ibrahim et al. 2004), was the first magnetar to have detected radio pulsations (Camilo et al. 2006). The onset of the radio emission appeared to be connected with the X-ray outburst. As the X-ray flux decayed over time (Bernardini et al. 2011), so did the radio flux until late 2008, when the source was no longer visible at radio frequencies (Camilo et al. 2016).

We are regularly monitoring XTE J1810-197 with the 76-m Lovell Telescope at Jodrell Bank Observatory. After 10 years in this quiescent state, intense radio emission from XTE J1810-197 was observed to have resumed on 2018 December 8 (MJD 58460.6), with a signal to noise ratio of over 400 in a 30-minute observation with a 384-MHz wide band centered at 1532 MHz. The spin-period measured over the two days following the re-detection observation (P = 5.5414391(1) s on MJD 58461.5) is somewhat smaller than value (P = 5.541463 s) obtained from a 460-day extrapolation of the ephemeris derived from XMM-Newton, Chandra and NICER data (Pintore et al. 2018). The pulse shape is not dissimilar to shapes observed during some phases of the previous outburst at the same frequency.

Our last non-detection of the source was observed on 2018 October 26 (MJD 58417), with the Lovell Telescope. XTE J1810-197 was also monitored at higher frequencies with the 100-m Effelsberg Radio Telescope since early 2018, using the new C-X band receiver (4-8 GHz). The latest observation was collected on September 10 (MJD 58371) and no detection was made. Additional observations are now planned. We find no reports of increased X-ray emission of the source, although X-ray observations are currently restricted by the proximity of the source's line of sight to the Sun. We continue to monitor the emission from XTE J1810-197 in its newly re-activated phase and we encourage observation at X-ray energies and at other radio frequencies.