The magnetar XTE J1810-197 remains in radio quiescence

ATel #18040; Marcus E. Lower (Swinburne), Jade Salisbury (Swinburne), Ryan M. Shannon (Swinburne), Fernando Camilo (SARAO), Paul Scholz (YorkU), George Younes (UMBC-CSST/NASA Goddard), John E. Reynolds (CSIRO) and John M. Sarkissian (CSIRO)
on 14 Sep 2026; 09:25 UT
Credential Certification: Marcus Lower (mlower@swin.edu.au)

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Following a reported X-ray burst from the direction of the magnetar XTE J1810-197 (PSR J1809-1943) by MAXI/GSC (ATel #18039), we triggered a search for renewed radio emission using the Ultra-Wideband Low (UWL; Hobbs et al. 2020) receiver system on Murriyang, the Parkes 64-m radio telescope. Our observation was taken under the P1102 non-a-priori assignable project in support of the P885 long-term radio magnetar monitoring program.

We observed XTE J1810-197 for 3329 seconds starting at UTC 2026-09-13-04:35:22. Simultaneous pulsar fold and search mode data were recorded using the Apollo backend, with 256 microsecond sampling and 3328 x 1 MHz width frequency channels spanning the full 704-4032 MHz bandwidth of the UWL. The data were coherently dispersed at the magnetar's nominal dispersion measure of 178 pc cm^-3.

No pulsed radio emission was detected at the 5.54 s spin period of XTE J1810-197 during our observation. We infer an approximate upper-limit of 20 microJy on the presence of any periodic emission, derived via the radiometer equation assuming a limiting S/N > 7 and a 10 percent pulse duty cycle.

We searched for single pulses from XTE J1810-197 by folding the search-mode data at the magnetar rotation period. Three pulse candidates with a frequency-averaged peak S/N > 6 were identified out of the 595 rotations that were recorded. However, all three candidates were confirmed by visual inspection to be the result of impulsive, zero-DM radio-frequency interference.

Our non-detection may indicate that the X-ray event detected by MAXI/GSC did not originate from XTE J1810-197. However, a delayed onset of radio emission (similar to 1E 1547.0-5408; Israel et al. 2021) cannot be ruled out. Follow-up high-energy observations to probe for an increase in the persistent X-ray flux of the magnetar are needed to confirm whether or not it has entered a new outburst state.

XTE J1810-197 is regularly monitored at radio wavelengths by the P885 program at an approximately 10 day observing cadence.

We thank Shi Dai and the ATNF staff for their prompt scheduling of the observation. Murriyang, CSIRO's Parkes radio telescope, is part of the Australia Telescope National Facility which is funded by the Australian Government for operation as a National Facility managed by CSIRO. We acknowledge the Wiradjuri people as the traditional owners of the Observatory site.

References: Hobbs et al. 2020, PASA, 37, e012; Israel et al. 2021, ApJ, 907, 7