FRB 20250316A: X-ray Flux Upper Limits with NICER and Simultaneous Radio Observations with CHIME/Pulsar
ATel #17117; Aaron B. Pearlman (McGill University; Trottier Space Institute at McGill University) on behalf of the CHIME/FRB Collaboration, and Keith C. Gendreau (NASA GSFC), Zaven Arzoumanian (NASA GSFC), Elizabeth C. Ferrara (University of Maryland; CRESST II; NASA GSFC), Joheen Chakraborty (MIT), Teruaki Enoto (Kyoto University; RIKEN), Tolga Guver (Istanbul University), Chin-Ping Hu (NCUE)
on 28 Mar 2025; 16:39 UT
Credential Certification: Aaron Pearlman (aaron.b.pearlman@physics.mcgill.ca)
Subjects: Radio, X-ray, Transient, Fast Radio Burst
FRB 20250316A is a bright fast radio burst (FRB) discovered by the CHIME/FRB Collaboration (ATel #17081) and associated with the nearby galaxy NGC 4141, located at a distance of ~40 Mpc. Using the full CHIME/FRB Outriggers VLBI array, the FRB source was localized with sub-arcsecond precision (ATels #17086, #17114, #17115) to a region near a clump of extended optical emission (ATel #17116, GCN #39887). Observations with the Einstein Probe (EP) Follow-up X-ray Telescope (FXT) revealed a potentially variable X-ray source (ATel #17100) spatially coincident with FRB 20250316A (ATels #17100, #17114, #17115).
We performed six target-of-opportunity (ToO) X-ray observations of FRB 20250316A using NICER, starting at 2025-03-18 00:44:27 UTC and ending on 2025-03-21 00:26:58 UTC, with a total exposure of 6.7 ks. We report 3σ upper limits on the persistent 0.5-10 keV X-ray flux (Fx) of FRB 20250316A, assuming a fiducial absorbed power-law spectral model with a hydrogen column density of NH = 1.43 × 1020 cm-2 and a photon index of Γ = 2 (see Pearlman et al. 2025 for details).
Observation Mid-Time (UTC) | 3σ Persistent X-ray Flux Upper Limit (erg cm-2 s-1):
2025-03-18 00:53:49 | Fx < 4 × 10-13
2025-03-18 08:33:33 | Fx < 1 × 10-12
2025-03-19 00:12:49 | Fx < 5 × 10-13
2025-03-19 07:53:49 | Fx < 3 × 10-12
2025-03-20 08:25:23 | Fx < 4 × 10-13
2025-03-21 00:13:11 | Fx < 7 × 10-14
These NICER X-ray flux upper limits are consistent with previous X-ray flux measurements of EP J120944.2+585060 obtained from EP/FXT and Swift/XRT observations (ATels #17100, #17101, #17109). Our deepest NICER X-ray flux upper limit corresponds to a 3σ upper limit of Lx < 1040 erg s-1 on the persistent X-ray luminosity of FRB 20250316A in the 0.5-10 keV energy range, using a distance of 40 Mpc to FRB 20250316A (ATel #17081).
We also carried out a search for X-ray bursts in the NICER data, with widths between 100 ns and 100 s, using a Bayesian Blocks algorithm (Scargle 1998; Pearlman et al. 2025). No astrophysical X-ray bursts were detected with a statistical significance above 3σ.
Additionally, we performed a search for X-ray pulsations between 0.1 and 1000 Hz in the NICER data using the Rayleigh (Z12) statistic (Buccheri et al. 1983). We also conducted a PRESTO-based acceleration search with zmax = ± 200 Fourier bins (Ransom et al. 2002). These periodicity searches were conducted in the 0.5-2.0, 2.0-10.0, and 0.5-10.0 keV energy ranges using all of our NICER observations, as well as data from individual exposures. In each case, no significant evidence of X-ray pulsations was found above a 3σ detection threshold.
NICER observations on 2025-03-18 and 2025-03-20 were scheduled during high time resolution follow-up radio observations of FRB 20250316A with CHIME/Pulsar (The CHIME/Pulsar Collaboration et al. 2021). We performed a coherent search for radio bursts with widths between 40.96 μs and 13 ms (see Pearlman et al. 2025 for details). No radio bursts were detected above a signal-to-noise ratio of 7 in the 400-800 MHz band during these CHIME/Pulsar observations.
These NICER observations were performed under an approved NICER General Observer Cycle 7 ToO program focused on X-ray observations of nearby FRB sources (PI: A. B. Pearlman). NICER will continue to observe FRB 20250316A.
NICER is a 0.2-12 keV X-ray telescope operating on the International Space Station. NICER is a non-imaging telescope with a field of view of ~30 arcmin2. The NICER mission and portions of the NICER science team activities are funded by NASA.
