X-ray Observations by Swift of the Repeating FRB 180916.J0158+65

ATel #13462; M. Tavani (INAF/IAPS & Univ. Roma Tor Vergata), F. Verrecchia (INAF/OAR & ASI/SSDC), C. Casentini (INAF/IAPS), M. Perri (INAF/OAR & ASI/SSDC), A. Ursi (INAF/IAPS), C. Pittori, F. Lucarelli (INAF/OAR & ASI/SSDC), A. Bulgarelli (INAF/OAS-Bo), M. Pilia, A. Corongiu (INAF/OA-Cagliari), G. Bernardi, G. Naldi, G. Pupillo (INAF/IRA), on behalf of a large Collaboration.
on 8 Feb 2020; 21:27 UT
Credential Certification: Francesco Verrecchia (francesco.verrecchia@asdc.asi.it)

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We report the preliminary results of the Swift XRT and UVOT instrument observations of the repeating Fast Radio Burst source FRB180916.J0158+65 (J2000 R.A., Dec.= 29.500, 65.733 deg) during a 6-day interval of possible radio bursting activity (Amiri et al. 2020, arXiv: 2001.10275v1).

Swift X-ray observations are part of a multiwavelength campaign that includes gamma-ray observations by AGILE and radio observations by the Sardinia Radio Telescope and by the Northern Cross radio telescope in Medicina.

We observed the location of FRB180916.J0158+65 daily from Feb. 3rd to Feb. 8th, 2020 obtaining XRT data in Photon Counting (PC) mode.

A preliminary analysis indicates that no X-ray source was significantly detected in any observation. Considering the Galactic HI column density value in the source direction (N_H = 7.1 x 10^21 cm^-2, Kalberla et al. 2005, A&A, 440, 775) and assuming a single power-law spectrum of photon index 2, we obtain the following 3-sigma upper limits (ULs) for each individual observations in the range 0.3-10 keV:

 
+---------------------------------+ 
| Day of | Effective | X-ray U.L. | 
| Feb.   | Exposure  | (x 10^-13  | 
|        |    (s)    | erg/cm^2/s)| 
+---------------------------------+ 
|  3rd   |  1677.0   |    3.3     | 
|  4th   |  1966.0   |    2.4     | 
|  5th   |  1304.0   |    3.5     | 
|  6th   |  2006.0   |    2.3     | 
|  7th   |  2016.0   |    2.7     | 
|  8th   |  1264.0   |    3.4     | 
+--------+-----------+------------+ 

Combining all the observations we obtain an overall 3-sigma upper limit: 1.06 x 10^-3 counts/s (for a total effective exposure of 10232 s) that corresponds to a flux UL: 5.5 x 10^-14 erg/cm^2/s. Assuming a source distance of 150 Mpc, this flux upper limit implies an isotropic-equivalent average X-ray luminosity less than 1.5 x 10^41 erg/s.

Additional analysis of Swift data is in progress.

The Swift mission is part of NASA's medium explorer (MIDEX) program, led by NASA with participation of Italy and the UK. We thank the Swift Team for making these observations possible, in particular B. Cenko and B. Sbarufatti (Swift Observatory Duty Scientist).