Marginal detection of radio pulsations from the magnetar SGR 1935+2154 with the Medicina Northern Cross
ATel #13783; M. Burgay, M. Pilia (INAF OA-Cagliari), G. Bernardi, G. Naldi, G. Pupillo, A. Magro (INAF IRA-BO), G. Setti, G. Bianchi (INAF IRA-BO, Uni-Bo), A. Possenti (INAF OA-Cagliari)
on 4 Jun 2020; 23:51 UT
Credential Certification: Marta Burgay (burgay@oa-cagliari.inaf.it)
Subjects: Radio, Neutron Star, Soft Gamma-ray Repeater, Pulsar, Fast Radio Burst, Magnetar
We report on a ~7-sigma detection of periodic radio pulsations from the currently active magnetar SGR 1935+2154 (ATel #13675; ATel #13678; ATel #13682; ATel #13685; ATel #13687) with the Medicina Northern Cross (MNC; Locatelli et al. 2020, MNRAS, 494, 1229). The MNC observes at 408 MHz with a 16 MHz bandwidth, a 781 kHz channel width and a 138 us sampling time. The detection was obtained on May 30, during the continuation of a still on-going observational campaign started on Apr 30 (ATel #13739), in which the source is monitored at transit for up to 1.5 hrs, almost daily.
The observations on the 30th started at UT 00:31:03 and finished at UT 02:01:01. Data were folded using the spin period measured from NuStar data (ATel #13720) and the dispersion measure (DM) of the FRB-like bursts detected on April 28th (Atel #13681, #13684). A search spanning +/- 1 ms around the nominal period (and +/- 200 pc/cm3 in DM) was carried out on the folded data, and resulted in a marginal detection of a periodic signal with period P = 3.24760(3) s, DM = 316(18) pc/cm3 and width of order 100 ms (see plot in the link below).
Given the system equivalent flux density of MNC, SEFD = 1020 Jy, this 7-sigma detection implies a flux density of ~4 mJy. No detections were obtained in any of the other observations, including those performed in the days before and after 30th May, with flux density upper limits between 3 and 6 mJy, depending on the duration of the observation. This points to the source experiencing a phase of intermittent emission of radio pulsations.
The period observed at MNC is about 0.3 ms longer than that measured by NuStar on May 2 2020 (ATel #13720) and would translate into an average Pdot = 1.2e-10 s/s, about an order of magnitude larger than that derived from the X-ray analysis of the 2014 outburst (Israel et al. 2016, MNRAS, 457, 3448). In fact, timing irregularities, including significant variations of the Pdot, are not uncommon in radio emitting magnetars (e.g. Camilo et al. 2016, ApJ, 820, 110; Archibald et al. 2018, ApJ, 869, 180A ).
Given the low significance, a comparison of the spin period from close-by high energy observations would be important to confirm the MNC radio detection.
Plot of the radio pulsed detection of SGR J1935+2154 at MNC
