Detection of radio pulsations from the direction of the NuSTAR 3.76 second X-ray pulsar at 8.35 GHz

ATel #5040; Ralph Eatough (Max-Planck-Institut fuer Radioastronomie: MPIfR), Ramesh Karuppusamy (MPIfR), Michael Kramer (MPIfR), Bernd Klein (MPIfR), David Champion (MPIfR), Alex Kraus (MPIfR), Evan Keane (Jodrell Bank Centre for Astrophysics: JBCA), Cees Bassa (JBCA), Andrew Lyne (JBCA), Patrick Lazarus (MPIfR), Joris Verbiest (MPIfR), Paulo Freire (MPIfR), Andreas Brunthaler (MPIfR), Heino Falcke (ASTRON, Nijmegen)
on 2 May 2013; 21:48 UT
Credential Certification: Evan Keane (ekean@jb.man.ac.uk)

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As part of continued efforts to detect radio pulsations from the 3.76-second X-ray pulsar discovered with the NuSTAR telescope (ATels #5020, #5027, #5033, #5035), we have performed a ~2.5 hour observation with the Max Planck Institute for Radio Astronomy (MPIfR) Effelsberg radio telescope at a central frequency of 8.35 GHz. This observation was performed at these observing frequencies to mitigate the expected strong scattering of radio waves in the Galactic Centre region (scattering time ~ freq.^-4).

Using a secondary focus cryogenically cooled receiver (system temperature ~22 K) we recorded summed polarisations for 128 spectral channels, across a bandwidth of 500 MHz, and with a data sampling interval of ~65 microseconds. Observations started on 2013-05-02 at 01:11:20 UTC on the updated source position provided in ATel #5032.

We have detected a narrow (duty cycle ~ 2%) bright (signal-to-noise ratio ~140) pulse with a spin period matching the NuSTAR discovery period (see link to pulsar diagnostic plot generated with the psrchive software package: http://psrchive.sourceforge.net/ ). Assuming typical contributions to the system temperature from spillover, we estimate the flux density at 8.35 GHz to be ~0.2 mJy. Note, this signal is not seen in two 30 minute off-source observations at the same telescope elevation.

Compared with the previously reported detections at lower frequencies (Atel #5035), the duty cycle of the pulse is markedly smaller, and in addition, we do not observe any changes in the spin period over the 2.5 hr observation. We also note that the dispersion measure appears to be high (DM~4000 pc cm^-3) however the small dispersive delays at this frequency result in large uncertainties. Such a large dispersion measure would plausibly place this source at the Galactic Centre. We continue to work on constraining this further.

We note that without a multi-beam receiver (where multiple sky positions are recorded simultaneously) we cannot yet conclusively rule out the possibility that the signal reported here is caused by terrestrial RFI in the primary telescope beam, however, we find the evidence of this source's authenticity to be compelling.

Diagnostic plot: www.mpifr-bonn.mpg.de/staff/reatough/public/pdmp-cand.pdf

Diagnostic Plot