GMRT non-detection of pulsed radio emission from EP J223759.5+531421 (EP260628c)

ATel #17872; Yogesh Maan (NCRA - TIFR), Pulak Mohapatra (NCRA - TIFR), Chandreyee Maitra (IUCAA), Joeri van Leeuwen (ASTRON), Banshi Lal (NCRA - TIFR), Yash Bhusare (NCRA - TIFR)
on 5 Jul 2026; 08:52 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Yogesh Maan (maan@astron.nl)

Tweet

A new magnetar candidate, EP260628c, was recently caught in an X-ray outburst by the Einstein Probe's Wide-field X-ray Telescope on June 28, 2026 (Yang et al., Atel #17859). A localization with 10'' precision was obtained using subsequent observations by the Follow-up X-ray Telescope and NuSTAR. Combined timing analysis refined an initial, tentative 3 second period into a coherent, double-peaked X-ray pulsation period of 5.995872(3) second. The slow spin period, a sudden X-ray outburst, and the X-ray spectral properties of EP260628c, now designated as EP J223759.5+531421, suggest the source to be a newly identified magnetar candidate (Rea et al., Atel #17870).

We observed EP J223759.5+531421 with the upgraded Giant Metrewave Radio Telescope (GMRT), utilizing 200 MHz of bandwidth centered at 650 MHz. The filterbank data were recorded with a sampling time of 0.16384 ms and 4096 channels across the bandwidth. Two separate scans were conducted on the target, with the start times UTC 2026-07-01T22:57:58 and UTC 2026-07-02T00:03:48, and integration times of 45 and 25 minutes, respectively. Following the excision of radio frequency interference (RFI) using RFIClean (Maan et al. 2021), we searched for any dispersed radio signals at and around the above reported period of 5.995872(3) seconds (ATel #17870) using the pulsar exploration and search toolkit (PRESTO; Ransom et al. 2002) and PSRCHIVE (Hotan et al. 2004), separately in the two scans. We also conducted a general search for any periodic radio signals using PRESTO, up to a maximum dispersion measure (DM) of 700 pc/cc (the YMW16 Galactic electron density model, Yao et al. 2017, suggests a maximum DM of 235 pc/cc along this line of sight). None of the above periodicity searches resulted in a genuine astrophysical signal, with a 10-sigma upper limit of 95 micro-Jy on the flux density, assuming a pulse-width 20% of the period. Our search for isolated, bright radio bursts also did not result in any genuine astrophysical bursts, however, we note that significant RFI contamination in some parts of the data might have affected this search. We place a 10-sigma upper limit of 100 mJy on any bright 10 ms wide pulse in our data.

The above non-detection of radio signals suggests the magnetar candidate EP J223759.5+531421 to be either radio quiet or extremely faint. It is also possible that the onset of observable radio emission has not happened yet. Continued sensitive radio observations will help in establishing the radio nature of this source.

We would like to thank the scheduling team and the observatory for the prompt scheduling of our observations. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research.

References:
(1) Maan, Y., van Leeuwen, J., and Vohl, D. 2021, A&A, 650, A80.
(2) Ransom, S. M., Eikenberry, S. S., and Middleditch, J. 2002, AJ, 124, 1788.
(3) Hotan, A. W., van Straten, W., and Manchester, R. N. 2004, PASA, 21, 302.
(4) Yao J. M., Manchester R. N. and Wang N. 2017, ApJ, 835, 29.