Detection of a gamma-ray flare in the direction of FRB20240114A

ATel #16630; Yi Xing, Wenfei Yu (Shanghai Astronomical Observatory)
on 25 May 2024; 06:45 UT
Credential Certification: Wenfei Yu (wenfei@shao.ac.cn)

Tweet

The repeating fast radio burst FRB 20240114A (ATel #16420) has shown extreme radio burst activity since its discovery (ATel #16432; #16505; #16565; #16620). We had performed a search for gamma-ray emission potentially associated with the active repeating FRB with the Fermi LAT data at the precise position determined with the EVN (Atel #16542). Two episodes of enhanced gamma-ray emission have been identified in MJD 60330 - 60340 and MJD 60370 - 60385 (ATel #16594).

We have performed the same analysis with recent Fermi LAT data. In the 5-day averaged light curves extracted from photons (> 100 MeV) in a sky region centered at the FRB position with the contaminant angle of the LAT Point Spread Function (PSF), we have identified an additional episode of enhanced gamma-ray emission during the period MJD 60425 - 60430 (2024 April 25 - 30). The gamma-ray flux reached a similar flux level as in the previous active episodes. This confirms the variable nature of the underlying gamma-ray source.

To investigate sources responsible for the enhanced gamma-ray emission, we generated the 0.1 - 500 GeV Fermi LAT TS map during this episode. Although the TS values are not significant, the TS map helped us identify sources of gamma-ray emission in the FRB field of view and possibly make flux comparisons. We found two nearby Fermi catalog sources 4FGL J2136.2 + 0032 (more than 4 degrees away from the FRB) and 4FGL J2122.5+0345 (second nearest to the FRB, less than about two degrees away from the FRB) as well as a likely new gamma-ray component centered at the coordinates RA = 321.962 degrees and DEC = 4.13973 degrees with a 1 sigma radius of 0.5 degrees, which is consistent with the FRB position. The contribution from the Fermi catalog source 4FGL J2123.6+0535, which is the nearest to the FRB, is insignificant. The gamma-ray flux at the FRB position is estimated as 6.1E-8 photons/cm^2/s with the likelihood method.

We also found a gamma-ray flare in the form of triplets during an interval of only 15.7 seconds. The leading photon has an energy of 1.01 GeV, which arrived at MJD 60429.8434228366 with recorded coordinates of RA = 322.2002 degrees and DEC = 4.212177 degrees. We further extract photon series in a sky region centered at a specific position which has equal angular distance, d, to the two nearest Fermi catalog sources 4FGL J2123.6+0535 and 4FGL J2122.5+0345 and to FRB 20240114A, to avoid photon selection bias, with a radius of the energy dependent PSF plus d. We identified a fourth photon at 138 MeV which arrived in the triplet interval, at about 6 degrees away from the FRB position. The quadruplets show a GeV photon lead, with the relative time stamps of 0.0, 10.7, 11.6, 15.7 seconds and photon energies of 1.01 GeV, 138 MeV, 116 MeV and 141 MeV, respectively. The quadruplets correspond to a significant 15-second timing signal, as the daily averaged photon count is around 30 per day with typical daily exposure times of a few hours. Since the PSF of the LAT for photons at 1 GeV has a much smaller size than those 100 - 200 MeV photons, the GeV photon dominates the estimates of the position of the flare. We found the position of the GeV photon is much closer to the FRB, in favor of an association of the gamma-ray flare with FRB20240114A.

We encourage archival analysis of multi-wavelength observations during the episodes and the flare, and the continuation of monitoring observations of the FRB. The Fermi LAT 5-day averaged light curve, the TS map, and the position of the GeV photon are shown below (http://202.127.29.4/wenfei/ATEL_FRB20240114A_LAT_2nd.html).

We thank the Fermi Science Support Center (FSSC) for providing public data.