Long term monitoring of FRB~20121102 with the Nançay Radio Telescope and multi-wavelength campaigns including INTEGRAL

TL;DR

This study conducts a coordinated, multi-wavelength campaign to search for high-energy (hard X-ray/soft gamma-ray) and optical counterparts to FRB 20121102, a highly active repeating source with a well-characterized host. Utilizing INTEGRAL for gamma rays, the Nançay Radio Telescope and Arecibo for radio bursts, and optical facilities at OHP, the team executes both a focused 2017 run and a triggering 2019 follow-up, complemented by an extensive 2016–2020 long-term radio monitoring. The 2019 campaign yields no contemporaneous high-energy detections but places stringent upper limits on gamma-ray emission ($F_{25-400\ ext{keV}}^{ ext{lim}}\le 2.7\times10^{-7}$ erg cm$^{-2}$) and persistent high-energy emission ($F_{25-100\ ext{keV}}^{ ext{lim}}\le 3.8\times10^{-11}$ erg cm$^{-2}$), and reports 131 additional FRB bursts from NRT, refining the periodic active window to $154\pm2$ days. The results support magnetar-based progenitor scenarios while highlighting the possible roles of beaming and environment in suppressing detectable high-energy counterparts. Overall, the work demonstrates the power of simultaneous, multi-wavelength campaigns to constrain FRB energetics and guide theoretical models.

Abstract

The origin(s) of Fast Radio Bursts (FRBs), mysterious radio bursts coming from extragalactic distances, remains unknown. Multi-wavelength observations are arguably the only way to answer this question unambiguously. We attempt to detect hard X-ray/soft gamma-ray counterparts to one of the most active FRB sources, FRB20121102, as well as improve understanding of burst properties in radio through a long-term monitoring campaign using the Nançay Radio Telescope (NRT). Multi-wavelength campaigns involving the International Gamma-ray Astrophysics Laboratory (INTEGRAL) satellite, the Nançay Radio Observatory, the optical telescopes at the Observatoire de Haute Provence as well as Arecibo were conducted between 2017 and 2019. In 2017, the telescopes were scheduled to observe simultaneously between Sept 24-29. We specifically used the Fast Response Enhanced CCDs for the optical observations to ensure a high time resolution. In 2019, we changed the strategy to instead conduct ToO observations on INTEGRAL and other available facilities upon positive detection triggers from the NRT. In the 2017 campaign, FRB20121102 was not in its burst activity window. We obtain a 5-sigma optical flux limit of 12 mJy ms using the GASP and a 3-sigma limit from OHP T120cm R-band image of R=22.2 mag of any potential persistent emission not associated to radio bursts. In the 2019 campaign, we have simultaneous INTEGRAL data with 11 radio bursts from the NRT and Arecibo. We obtain a 5-sigma upper limit of 2.7e-7 erg/cm2 in the 25-400 keV energy range for contemporary radio and high energy bursts, and a 5-sigma upper limit of 3.8e-11 erg/cm2 for permanent emission in the 25-100 keV energy range. In addition, we report on the regular observations from NRT between 2016-2020, which accounts for 119 additional radio bursts from FRB20121102. We present an updated fit of the periodic active window of 154+/-2 days.

Figures (10)

• Figure 1: INTEGRAL image at the sky position of FRB 20121102 taken during revolution 1867 at 25--100 keV. The gray-scale bar gives the sources significance over the field of view. Only the Crab pulsar is clearly detected at more than 50 sigmas.
• Figure 2: GASP observation of FRB 20121102 from the 2017 campaign. The plot, from the night of September 27th, shows the flux in each 0.9-ms frame. In total, there were $\approx$ 13.7 million frames. Shown are the EMCCD counts (left y axis) from the FRB region in each frame (left y-axis) and the flux in mJy ms (right y axis). Also shown is the 5 $\sigma$ upper limit. From 13.7 million frames, we expected to observe 4.1 frames with a flux above 5 $\sigma$. The fact that we see 5 frames above 5 $\sigma$ implies no significant enhancement is detected.
• Figure 3: GASP observations of the Crab pulsar taken during the 2017 campaign. The plot shows a 1 hour observation starting at 2017:09:29 02::20:01. The red line shows the linear polarisation and the black line is the optical light curve referenced to the Jodrell Bank ephemeris, 1993MNRAS.265.1003L and http://www.jb.man.ac.uk/ pulsar/crab.html. The linear polarisation in the off-pulse region, from phase 0.7-0.9, is 37 $\pm$ 5 % consistent with other measurements, see (e.g.) 2009MNRAS.397..103S
• Figure 4: A 1.5$\times$ 1.5 sub-section of our R-band stacked image obtained in the field of FRB 20121102 with the T120cm telescope at Observatoire de Haute-Provence. The expected location of FRB 20121102 is indicated with the empty black circle at the center. North is to the top and East is to the left.
• Figure 5: The time windows of the telescope facilities that participated in the 2019 campaign. Each radio burst detected is shown as a vertical black tick.