uGMRT Detection of Polarised Bursts from LPT J1634+44

ATel #17562; Chahat Dudeja (NCRA-TIFR), Suryarao Bethapudi (Bonn, Germany), Kshitij Bane (NCRA-TIFR), Abhinav Narayan (IIT-Indore), Sridhar Gajendran (NCRA-TIFR), Jayanta Roy (NCRA-TIFR), Sanjay Kudale (NCRA-TIFR), Narendranath Patra (IIT-Indore)
on 26 Dec 2025; 16:47 UT
Credential Certification: Jayanta Roy (jroy@ncra.tifr.res.in)

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We report the first detection of a long-period radio transient, LPT J1634+44 (Bloot et al. 2025, A&A, 699, A341; Dong et al. 2025, ApJ, 988, L29), using SPOTLIGHT (https://spotlight.ncra.tifr.res.in/), the uGMRT commensal transient search survey. ATels (#17434 and #17440) from CHIME and Effelsberg reported activity from J1634+44. Therefore, we carried out observations with uGMRT. In Band-4 (550-750 MHz), we detected three bursts at MJDs 61021.163594768, 61021.182956071, and 61025.12661678. We recorded full polarisation data during observation of MJD 61021, which allowed for polarisation calibration, RM measurement and RM correction for two of the three detected bursts (see the plot at the link below). The bursts show a strong circular polarisation fraction, with Stokes V contributing a significant fraction of Stokes I throughout the pulse profile, agreeing with Dong et al. (2025, ApJ, 988, L29). We noted this is the first polarisation measurement of an LPT with the uGMRT. The flux densities of the detected bursts are around 0.2-11 Jy. The observation of MJD 61025 was conducted in Phased-Array Spectral Voltage (PASV) mode, which allows for high time resolution coherently dedispersed analysis. This analysis reveals clear microstructure within the burst down to timescales of ~100 microseconds. In parallel with these targeted observations, we are running a project called "LIGHT" to search for long-period radio transients in GMRT archival data using image-based search methods. We applied the same "LIGHT" image-based pipeline to SPOTLIGHT 1-second visibility data and detected this source through a fast imaging search, making it the first LPT identified with the SPOTLIGHT system. The 1-second images containing the pulse (with a width of ~6 seconds), overlaid on the high-time-resolution data resolving pulse micro-structure, are shown in the plot at the link below. We thank the GMRT operations team for scheduling and supporting these observations. The GMRT is operated by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research.

The plots of de-dispersed, polarisation calibrated, RM-corrected dynamic spectra, frequency-averaged total, linear and circular polarised time series of the bursts of MJD 61021; micro-structures of MJD 61025 overlaid with pulse from low-resolution imaging data from SPOTLIGHT can be found here