Search for pulsed radio emission from SWIFT J174540.7-290015

ATel #8729; Yogesh Maan (NCRA-TIFR), Mayuresh Surnis (NCRA-TIFR), M. A. Krishnakumar (NCRA-TIFR), Bhal Chandra Joshi (NCRA-TIFR), P. K. Manoharan (NCRA-TIFR)
on 25 Feb 2016; 07:38 UT
Credential Certification: Bhal Chandra Joshi (bcj@ncra.tifr.res.in)

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To probe the possible magnetar nature of the transient X-ray source SWIFT J174540.7-290015 (ATEL #8649), we conducted radio observations at 1390 MHz and 327 MHz, using the Giant Meterwave Radio Telescope (GMRT) and the Ooty Radio Telescope (ORT), respectively, with the phase centre of the telescopes pointing at RA (J2000): 17 45 40.74 and Dec (J2000): -29 00 14.7 (ATEL #8649). The source was observed at the two frequencies for 2.7 and 3.5 hours respectively. SWIFT J174540.7-290015 was detected as a transient X-ray source on 6 February, 2016 (ATEL #8649). We observed the source using the ORT on 10 February, 2016 at 327 MHz with 4 ms sampling time and 1024 frequency channels across the 16 MHz bandwidth. Our search for any periodic or transient emission from the source in the DM range of 0--3000 pc/cc did not result in any significant detection. The 5-sigma flux density upper limits for the periodic and transient radio signals from the source at 327 MHz are 4.5 mJy and 15 Jy, respectively. For computing these limits, we have assumed 10% pulse duty cycle for the periodic signal, and a pulse-width of 10 ms for the transient signal.

Observations at 1390 MHz were conducted on 15 February, 2016, using 15 dishes of the GMRT in phased-array mode, with a time resolution of 0.12 ms and 512 channels across a bandwidth of 33 MHz (Director's discretionary time for the proposal ddtB210). Search for any periodic or transient signals in the DM range 0--3000 pc/cc from these data also did not result in any significant detection. Using these data, we constrain the 5-sigma periodic and transient flux densities of the source at 1390 MHz to 70 uJy and 0.2 Jy, respectively (assuming 10% pulse duty cycle and 10 ms pulse-width).

The X-ray spectrum of the source was equally well characterized by both a power-law and a blackbody model (ATEL #8649), but a power-law model alone seems to fit the 3-80 keV spectrum well (ATEL #8684). If the source is a magnetar, our radio observations suggests a "radio quiet" magnetar with high magnetic field (Rea et al. 2012). Our observations also do not rule out a transient accreting neutron star.

We thank the GMRT and the ORT staff members for making these observations possible. We are also thankful for a prompt allocation of Director's discretionary time for these observations.

Ref : Rea et al. 2012, ApJL, 748, L12