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Detection by Sardinia Radio Telescope of radio pulses at 7 GHz from the Magnetar PSR J1745-2900 in the Galactic center region

ATel #5053; Marco Buttu (INAF-Osservatorio Astronomico di Cagliari), Nichi D'Amico (INAF-OAC), Elise Egron (INAF-OAC), Maria Noemi Iacolina (INAF-OAC), Pasqualino Marongiu (INAF-OAC), Carlo Migoni (INAF-OAC), Alberto Pellizzoni (INAF-OAC), Sergio Poppi (INAF-OAC), Andrea Possenti (INAF-OAC), Alessio Trois (INAF-OAC), Gian Paolo Vargiu (INAF-OAC), on behalf of the Sardinia Radio Telescope Science Validation Team and the Commissioning Team
on 7 May 2013; 19:19 UT
Credential Certification: Marta Burgay (burgay@oa-cagliari.inaf.it)

Subjects: Radio, Neutron Star, Soft Gamma-ray Repeater, Pulsar

Referred to by ATel #: 5058, 5070, 5074, 5076, 5095, 5222

During the Sardinia Radio Telescope (SRT) science verification phase, we observed PSR J1745-2900, firstly detected as an X-ray flare from Sgr A* by Swift and then identified as a 3.76 s X-ray magnetar with NuSTAR telescope (ATels #5006, #5020, #5027, #5032, #5033, #5035), at a central frequency of 7.30 GHz. We used a Beam Wave Guide focus cryogenically cooled receiver (system temperature ~25 K). We recorded total power polarizations across a bandwidth of 730 MHz, with a data sampling interval of 40ms. Observations started on 2013-05-06 at 03:49:31 UTC on the source position provided in ATel #5032 and lasted for about 2 hours.

We have first detected a narrow (duty cycle ~ 2%) bright (signal-to-noise ratio ~14) pulsed signal with a spin period P=3.7635(1)s, matching the most recent X-ray detection (Atel #5046), superimposed on a low frequency interfering sinusoidal signal. By carefully removing the baseline on the total power raw data, we easily filtered out the interfering signal, which resulted in the firm detection of the pulsar signal. No such signal was present in an integration performed with the same setup, when looking 2 degrees away the magnetar position.

We note that the observed pulse width over the full band puts a limit on the dispersion measure DM < 4000 pc cm^-3. The availability of the pulsar backend will soon allow us to better define the actual DM.

Comparing the signal in the off-source and on-source pointing, and assuming the parameters of the antenna+receiver system, as derived during the technical commissioning of SRT, the estimated flux density at 7.3 GHz is about 0.1 mJy.

This is the first detection of the source at the 7 GHz band. Complementing the detections at Effelsberg radio telescope at 8 GHz (ATels #5040, #5043) and 5 GHz (ATel #5043), this observation conclusively rules out the possibility that those detections were caused by terrestrial RFI in the primary telescope beam and confirm the association of the radio signal to the magnetar seen in the X-ray band.

The detection plots can be found here.