Upper limits on the pulsed radio emission of SGR 1935+2154 from the Ooty Radio Telescope and the Giant Meterwave Radio Telescope

ATel #6376; M. P. Surnis(NCRA-TIFR), M. A. Krishnakumar(NCRA-TIFR), Y. Maan(NCRA-TIFR),B. C. Joshi(NCRA-TIFR), P. K. Manoharan(NCRA-TIFR)
on 7 Aug 2014; 20:09 UT
Credential Certification: Bhal Chandra Joshi (bcj@ncra.tifr.res.in)

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We observed SGR 1935+2154 soon after its reported detection by SWIFT (GCN 16520; GCN 16522, ATEL #6299), using the Ooty Radio Telescope (ORT) and the Giant Meterwave Radio Telescope (GMRT), at 326.5 and 610.0 MHz respectively, at the position indicated in the initial XRT detection (ATEL #6299). We used the time allocated to us under Director's Discretionary Time. Pulsating X-ray emission with a period of 3.24998 s was recently reported with Chandra 75 Ks observations on July 28, 2014 (ATEL #6370). The source was observed with the ORT on July 9 and 14, 2014 (MJD 56847 and 56852 at 17:35:00 and 20:28:00 UTC respectively) at 326.5 MHz with 16 MHz band-pass. The two observations, lasting 4 and 3 hours respectively, were carried out with 1 ms sampling time and with 1024 channels across the band-pass. Both the data sets were incoherently dedispersed to 2240 trial DMs ranging from 0 - 1500 pc cm^-3 followed by a harmonic and single pulse search. No significant pulsation was detected. Subsequently, we also folded the data at the period reported in ATEL #6370 and did not detect any significant pulsation. We estimate an upper limit (8 standard deviation) on pulsed flux density of 0.4 mJy for an assumed 10 % duty cycle for the average emission at 326 MHz. Observations for about 2 hours were carried out using the GMRT at 20:00:05 UTC on July 14, 2014 (DDT B134), with 610 MHz receiver of 33.33333 MHz band-pass. The GMRT was used in a phased array of 15 antenna as well as an incoherent array including the remaining antennas. The data were recorded with 512 channels across the band-pass with 61 us sampling time. The data were incoherently dedispersed to 2240 trial DMs ranging from 0 - 1500 pc cm^-3 followed by a harmonic and single pulse search. No significant pulsation was detected. Subsequently, we also folded the data at the period reported in ATEL #6370 and did not detect any significant pulsation. We obtain a limit (8 standard deviation) of 0.2 mJy for an assumed 10 % duty cycle for the average emission at 610 MHz. At the GMRT, simultaneous imaging observations, at 610 MHz, were also carried out. No significant radio source is detected in the preliminary image at the position of the source, although a diffuse source, 7' West of the SGR position, is seen, which may be associated with SNR G57.2+0.8. We thank the GMRT and the ORT team for making these observations possible and allocating time.