An extragalactic gamma-ray binary formed in supernova 2022jli

TL;DR

The study identifies SN 2022jli as hosting a likely extragalactic gamma-ray binary formed in a core-collapse supernova, with a robust $P \approx 12.5$ day orbital period detected in Fermi-LAT data. Using aperture photometry, Lomb-Scargle analysis, and phase-resolved spectroscopy, the authors show phase-confined, jet-related gamma-ray emission consistent with a NS or stellar-mass BH primary in a high-mass companion binary. A jet-counter-jet model with plausible geometry reproduces the folded gamma-ray light curve, supporting a microquasar–like scenario and suggesting ultraluminous gamma-ray emission at extragalactic distance. These results provide a rare external example of high-energy binary formation in a supernova environment, offering insights into the origins and evolution of similar systems in the Milky Way and beyond.

Abstract

On May 5 2022, a type Ic supernova (SN) explosion SN~2022jli was discovered. This SN showed additional optical emissions, which were found to exhibit 12.4-day periodic undulations and concordant periodic velocity shifts. These key features likely indicate a compact object in a binary system was formed. A faint $γ$-ray source was also detected at the position of the SN and upon checking the $γ$-ray photons' arrival times, it was revealed that the same 12.4-day periodicity was likely present. Here we report our detailed analysis results for the $γ$-ray source. Not only was the $γ$-ray emission detectable for $\sim$1.5\,years since the discovery time, but a strong modulation at period 12.5\,day was also clearly determined. Considering the newly formed compact object to be a neutron star or a stellar-mass black hole, the putative binary, having an orbital period of 12.5\,day, is likely the first extragalactic high-energy system detected. The system may serve as a valuable example for the formation of many such binaries observed in the Milky Way and nearby galaxies.

Figures (3)

• Figure 1: Left: LSP power spectrum of Gsrc obtained from the LAT data from May 5 2022 to May 10 2023. A periodic signal near 12.4 day is clearly visible. Right: LSP power spectrum of Gsrc in a frequency window of from 1/14.0 to 1/11.0 day$^{-1}$. A Gaussian fit (blue dashed line) was used to determine the period and its uncertainty $P = 12.54\pm 0.18$ day (marked by the pink region). In both panels, the 12.4-day value is marked with a purple dashed line.
• Figure 2: Left: folded $\gamma$-ray light curve ( top) and ZTF optical light curves ( bottom). A model fit, consisting of a jet plus a counter-jet with the jets' height being 1.6$\times 10^{12}$ cm (see ref. dch10 for details), to the $\gamma$-ray light curve is shown (red solid line). Right: spectra obtained from the data in Ph$_3$ (blue) and Ph$_{1-4}$ (orange), where the phase ranges are marked blue and orange respectively in the left top panel. For comparison, the spectrum from the data in the whole detectable time period (i.e., from May 5 2022 to Oct. 27 2023) is also shown. The PL fits to the spectra are respectively plotted as the blue dashed line, orange dash-dotted line, and black solid line.
• Figure 3: Left: 90-day binned light curve (black data points) of Gsrc in 0.1--500 GeV from $T_0$ to Jul. 7 2025. The TS values of the data points are indicated by the red histogram. After $\sim$MJD 60244, the source was undetected. A smooth light curve (green data points), with each 90-day time bin shifted by 5 day forward, is also shown for comparison. The end of the optical light curves of SN 2022jli in ref. che+24 is marked by the orange dash-dotted line and the date of May 10 2023 (MJD 60074) is marked by the red dashed line. Right: power peak values of the $\sim$12.5-day signal, obtained from LSP analysis of AP light curves of different lengths (all starting from $T_0$ with a 30-day time step). The maximum value is 17.8 (marked by the red dashed line), when the AP light curve is from $T_0$ to May 10 2023.