Low frequency observations of magnetar Swift J1555.2-5402 with the uGMRT

ATel #14799; Shubham Singh (NCRA-TIFR), Jayanta Roy (NCRA-TIFR)
on 19 Jul 2021; 13:35 UT
Credential Certification: Jayanta Roy (jroy@ncra.tifr.res.in)

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A new magnetar Swift J1555.2-5402, was discovered by Swift/BAT on 3rd June (Palmer et al. GCN #30120). Further observations with Swift and NICER found a rotation period of 3.861 seconds for this new source ( ATel #14674). A slow down rate of 6.0E-11 s/s for this magnetar was reported by Israel et al. (ATel # 14679). Magnetic field strength inferred from this slow down rate is 5E14 G. Earlier radio follow up with NASA DSN radio dish centred at 2.3 GHz and 8.4 GHz (ATel #14678) and Parkes UWL over 0.7 to 4 GHz (ATel #14680) reported non-detection limits for pulsations and bursts. We report results from a search of pulsation and burst with the uGMRT in band-4 (550-750 MHz). We observed the source on 16th June (16:54:39-17:52:39 UT for 58 mins) and 30th June (15:53:54-17:09:54 UT for 76 mins). The band-4 filterbank was with 4096 channels over 200 MHz band-width sampled at 81.92 micro-second time-resolution. Since the uGMRT can not observe sky below -54 degrees declination, the beam centre was off from the phase centre (set to the source coordinates 15h55m08.56s, -54d03m38.7s). Thus the offset of magnetar location from the pointing centre was varying during the scan from ~0.7-times of HPBW (~36' at 650 MHz) to ~1.8-times of HPBW. We searched for radio pulsations and bursts over a DM range of 0 to 2000 pc cm^-3. We used Fast Folding Algorithm (FFA, V. Morello et al. (2020)) for periodicity search and AstroAccelerate (Adamek and Armour 2020) for single pulse search. We did not find any radio emission, either pulsation or burst above a SNR of 5. We used detection of a nearby known pulsar J1602-5100 to calibrate the gain of the phased array beam. The corresponding 5-sigma upper limit of flux density for pulsation is 0.2 mJy (assuming 10% duty-cycle) and for burst is 0.9 Jy ms. We thank the staff of the GMRT who have made these observations possible. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research.