Upper limit on the optical fluence of FRB 180916.J0158+65
ATel #13493; Luca Zampieri (INAF-Astronomical Observatory of Padova), Aleksandr Burtovoi, Michele Fiori, Giampiero Naletto, Paolo Ochner (University of Padova), Massimo Turatto (INAF-Astronomical Observatory of Padova), Luciano Nicastro, Eliana Palazzi (INAF-OAS Bologna), Maura Pilia, Andrea Possenti (INAF-Astronomical Observatory of Cagliari), Piergiorgio Casella (INAF-Astronomical Observatory of Rome), Nanda Rea (Institute of Space Sciences ICE-CSIC, IEEC, Barcelona)
on 17 Feb 2020; 16:20 UT
Credential Certification: Luca Zampieri (luca.zampieri@oapd.inaf.it)
Subjects: Optical, Fast Radio Burst
FRB 180916.J0158+65 is a fast radio burst (FRB) source, showing repeating burst activity (The CHIME/FRB Collaboration 2019, ApJ Letters, 885, L24). It has been recently localized with high accuracy and associated to a star-forming region in a nearby (redshift 0.0337 +/- 0.0002) massive spiral galaxy (Marcote et al. 2020, Nature, 577, 190). Very recently, a 16.35 +/- 0.18 day periodicity in the arrival times of the radio bursts has been reported (The CHIME/FRB Collaboration 2020, Nature, in press). This allows dedicated searches for bursts at other wavelengths during time intervals of possible radio activity (ATel #13446, #13462).
We observed the area of the sky centered at the position of FRB 180916.J0158+65 (RA=01 58 00.75017, Dec=+65 43 00.3152; J2000) with the fiber-fed fast optical photon counter IFI+IQUEYE (Naletto et al. 2009, A&A, 508, 531; Zampieri et al. 2019, Contrib. Astron. Obs. Skalnate' Pleso 49, 85), mounted at the 1.2 m Galileo telescope in Asiago. The source was observed on Feb 4, 5 and 7, 2020. The field of view of the instrument is a circular region with a diameter of 12.5 arcsec. Simultaneous monitoring observations of the field were carried out also with the 67/92 Schmidt telescope, equipped with a 4096x4096 CCD camera that covers a field of view of 1 square degree. The observations were performed within the framework of a joint radio+optical observing campaign of FRB 180916.J0158+65, during an expected maximum of the radio burst activity (ATel #13492). The log of the observations is reported in the table below.
Instrument | Date | Exposure/Filter
67/92 Schmidt | Feb 4 18:47:00-22:09:00 | Sequence of 2 m acquisitions - no filter
IFI+Iqueye | Feb 4 19:53:57-21:26:12 | 5.5 ks - no filter
IFI+Iqueye | Feb 5 18:25:01-19:55:01 | 5.4 ks - no filter
IFI+Iqueye | Feb 5 19:57:07-20:57:07 | 3.6 ks - no filter
IFI+Iqueye | Feb 5 22:45:02-23:15:02 | 1.8 ks - no filter
IFI+Iqueye | Feb 7 17:56:43-19:56:43 | 7.2 ks - no filter
67/92 Schmidt | Feb 7 18:16:52-23:07:35 | Sequence of 5 m acquisitions - filter i sloan
IFI+Iqueye | Feb 7 21:20:38-22:50:38 | 5.4 ks - no filter
The average IFI+Iqueye count rate at the position of FRB 180916.J0158+65 was between 2400 and 3800 counts/s. Two other observations of 3.6 ks duration, centered at different positions and not containing any field stars (off-source), were performed on Feb 5 21:31:50-22:31:50 and Feb 7 20:04:03-21:04:03. The average rate at these positions was 2800 and 3200 counts/s, respectively. The 67/92 Schmidt CCD readout time is between a few seconds and 10 s.
We performed a blind search for any significant increase in the optical count rate on 1-ms binned light curves of the IFI+IQUEYE observations (not background subtracted). We do not detect any significant peak above 3 sigma in both the on-source and off-source observations (assuming a Poisson distribution and accounting for the total number of trials/bins in each observation). The 3 sigma upper limit is 18-22 counts/bin (the average rate is 2.4-3.8 counts/bin), corresponding to an instantaneous (1 ms) magnitude V~11 and a fluence ~0.151 Jy ms.
Standard data reduction was applied to the simultaneous Schmidt images. No source was detected in any of the images down to the limiting magnitude (i~19.5, fluence ~5.0/12.6 Jy ms for a 2/5 m exposure), which is consistent with the upper limit inferred from the non-detection with IFI+IQUEYE.