FRB 20250316A
GCN Circular 39909
Malte Busmann, Jennifer Fabà, Daniel Gruen, Mathias Mucke, Xiaoxiong Zuo (LMU), Brendan O'Connor, and Antonella Palmese (CMU) report on behalf of a larger collaboration:
We observed the localization of FRB 20250316A (Ng et al., ATel #17081; Andrew et al., GCN 39886). With the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the g and i band on multiple nights. Observations started 2.53d after the FRB or 5.8h after the discovery of an uncataloged X-ray source EP J120944.2+585060 by Einstein Probe (GCN 39834).
| Time (UT) | t - t0 (d) | Band | Exposures | Depth (3 sigma, AB mag) | Depth Diff (3 sigma, AB mag) |
|---|---|---|---|---|---|
| 2025-03-18T21:14:03 | 2.53 | g | 10x 180 s | 24.3 | Used as Reference |
| 2025-03-18T21:14:03 | 2.53 | i | 10x 180 s | 23.7 | Used as Reference |
| 2025-03-22T20:05:28 | 6.48 | g | 16x 180 s | 21.9 | - |
| 2025-03-22T20:05:28 | 6.48 | i | 16x 180 s | 21.6 | - |
| 2025-03-23T23:11:05 | 7.61 | g | 15x 180 s | 24.4 | 23.5 |
| 2025-03-23T23:11:05 | 7.61 | i | 15x 180 s | 23.8 | 23.0 |
| 2025-03-28T03:33:48 | 11.79 | g | 10x 180 s | 23.0 | 22.9 |
| 2025-03-28T03:33:48 | 11.79 | i | 10x 180 s | 22.5 | 22.5 |
We performed difference imaging against templates from the LegacySurvey (g) and PS1 (i). We also used our first observation as a template and do not detect any excess flux at the FRB location in either case. This is consistent with the observations of Becerra et al. (ATel #17082, GCN 39843, 39853), Niino et al.(ATel #17084), Hashimoto (ATel #17095), Yang et al. (ATel #17101), Troja et al. (ATel #17109, GCN 39869), Dong et al. (ATel #17112), Aryan et al. (GCN 39839), Pereyra et al. (GCN 39858), Jiang et al. (GCN 39864), Gillanders et al. (GCN 39883), and Simha et al. (ATel #17116, GCN 39887).
The magnitudes are calibrated against the PS1 catalog and are not corrected for galactic extinction.
We thank Christoph Ries and Michael Schmidt from the Wendelstein Observatory staff for obtaining these observations.
GCN Circular 39887
S. Simha (U. Chicago-Northwestern), T. Eftekhari (Northwestern) report on behalf of the CHIME/FRB Collaboration:
The CHIME/FRB Collaboration reports on optical imaging and spectroscopy of the sub-arcsecond CHIME Outrigger localization (ATel #17114, GCN #39886) of the nearby, bright FRB 20250316A (ATel #17081). We obtained deep g-band observations starting at 24 March 2025 12:39:44 UT (PI: T. Eftekhari; 15 x 120-sec exposures) with the Gemini-North Multi-Object Spectrograph (GMOS-N) mounted on the 8-m Gemini North telescope at Maunakea, Hawai'i. Observations were taken in clear conditions with an average airmass of 1.6 and seeing of 0.8". We do not detect any strong, possible transient (point source) optical emission at the FRB location (1-sigma; ATel #17114) and measure a 3-sigma point-source limiting magnitude at this location of g > 23.8 mag (AB). However, we detect a clump of extended optical emission in the host galaxy, offset from the FRB localization region by ~1.2" (measured from the brightest pixel in the g-band image). At a distance to NGC 4141 of ~40 Mpc, the corresponding projected physical distance between the FRB and this clump is ~250 pc.
We also obtained long-slit optical spectroscopy with GMOS-N starting at 25 March 2025 10:41:44 (PI: T. Eftekhari; 8 x 900-sec exposures) at an airmass of ~1.33. We used a 1" slit width, the B480 grating, and the GG455 blocking filter at central wavelengths of 640 and 650 nm. The slit was oriented at a position angle of 10.6 degrees East of North to cover both the FRB localization region and the nearby extended optical emission. While we do not detect any transient spectral features or features at the FRB position, we detect strong nebular emission from the nearby optical clump, including H-beta, H-alpha, and [OIII] at a common redshift of z~0.0065, consistent with emission from a star-forming region within the host.
We thank Gemini Observatory staff, including Jennifer Andrews, for assistance with planning and executing the observations.
GCN Circular 39886
Shion Andrew (MIT) reports on behalf of the CHIME/FRB Collaboration:
We have derived a sub-arcsecond VLBI localization for FRB 20250316A (see ATel #17081, ATel #17086; this is the first such localization using the full CHIME/FRB Outriggers array. This consists of the CHIME core and the KKO Outrigger (Lanman et al. 2024) near Penticton, BC, and two additional Outrigger stations at Green Bank Observatory (GBO) and Hat Creek Radio Observatory (HCO). The position below is consistent with the ~10" position of the potential X-ray counterpart EP J120944.2+585060 detected by the Einstein Probe (ATel #17100) but is inconsistent with the 90% confidence interval reported from Swift/XRT observations (ATel #17109).
We derive our position by referencing delays on each of the three CHIME-Outrigger baselines to nearby in-beam International Celestial Reference Frame (ICRF) calibrators observed simultaneously with the FRB (Andrew et al. 2024). On all CHIME-Outrigger baselines, we phase reference our visibilities to the calibrator RFC J1204+5202 (https://astrogeo.org/sol/rfc/rfc_2024b/; Petrov & Kovalev 2025), located ~6 degrees away from the FRB.
Five additional in-beam ICRF calibrators were observed on all three baselines between CHIME and its Outriggers, which we use to derive a representative error budget for the FRB localization. The calibrators completely surround the FRB, spanning ~+/- 1 degree in hour angle and +50/-20 degrees in declination relative to CHIME zenith, while the FRB is located ~0.2 degrees east and ~10 degrees north of CHIME zenith. We check for imperfect calibrator selection and direction-dependent effects by 1) calibrating the target to all other usable calibrators, and 2) calibrating known calibrator positions to other calibrators, which maximizes on-sky angular separations. Both procedures give RMS delay errors no larger than 1 ns, 3 ns, and 6ns on the CHIME-KKO, CHIME-HCO and CHIME-GBO baselines, respectively. This yields the following 1-sigma (stat+sys) localization ellipse for the location of FRB 20250316A:
Right Ascension = 12h09m44.31s
Declination = +58d50m56.70s
a_err = 150 milliarcsec
b_err = 100 milliarcsec
theta = 2.4 degrees East of North
All coordinates are in the ICRF. We have included our one-sigma localization contour over the Epoch 1 r-band MMT image reported in ATel #17112. We note that to account for astrometric offsets due to optical-radio reference frame ties, we have inflated our localization errors in the plot by 150mas (added in quadrature).
The full four-station array is still being commissioned, and its astrometric performance will be fully characterized in an upcoming work. However, we note that the error from our bootstrapping procedure is consistent with our archival test localizations of over 200 ICRF calibrators and well-localized pulsars at similar target-calibrator separations and at cross-correlation signal-to-noise ratios lower than those in the dataset used here. Furthermore, the abundance of in-beam calibrators may enable additional improvements on the preliminary position quoted here. Follow-up observations are strongly encouraged to definitively establish whether EP J120944.2+585060 is spatially coincident with FRB 20250316A, and to characterize the nature of this potential X-ray counterpart.
Link to MMT Image https://storage.googleapis.com/chimefrb-dev.appspot.com/FRB20250316A/FRB20250316A_fulloutriggerarray_loc.png
GCN Circular 39883
J. H. Gillanders (Oxford), M. Huber, K. C. Chambers (IfA, Univ. Hawaii), S. J. Smartt, K. W. Smith, S. Srivastav (Oxford), M. Nicholl, D. Young, M. Fulton (QUB), T.-W. Chen (NCU, Taiwan) A. S. B. Schultz, T. de Boer, J. Fairlamb, G. Paek, C. C. Lin, T. Lowe, E. Magnier, P. Minguez, I. A. Smith, R. J. Wainscoat (IfA, Univ. Hawaii).
We observed the field of FRB 20250316A (Ng et al., ATel 17081) and EP J120944.2+585060 (Sun et al., ATel 17100, GCN 39834) using the Pan-STARRS telescope system (Chambers et al., 2016, arXiv e-prints, 1612.05560) on MJD 60757.42 (2025-03-23 10:04 UTC), ~7.06 days after the FRB detection (Ng et al., ATel 17081). The Pan-STARRS system consists of two 1.8m telescope units located at the summit of Haleakala on the Hawaiian island of Maui, employing an SDSS-like filter system denoted as grizy, and a broad w-filter, which is a composite of the gri-filters.
Our observation consisted of 6x150s exposures in i-band, and 3x150s in r-band. The images were processed with the Pan-STARRS pipeline, where they underwent astrometric and photometric calibration, and stacking (Magnier et al., 2020a, ApJS, 251, 3; Magnier et al., 2020b, ApJS, 251, 6; Waters et al., 2020, ApJS, 251, 4).
From these stacked target images, which cover the entire localisation region of FRB 20250316A (Leung et al., ATel 17086) and the EP-FXT error region of EP J120944.2+585060 (Sun et al., ATel 17100, GCN 39834), we do not detect any new optical sources down to 5-sigma limiting AB magnitudes of r~23.5 and i~23.5.
These non-detections are consistent with previously reported observations by Becerra et al., ATel 17082, GCN 39853; Niino et al., ATel 17084; Hashimoto ATel 17095; Yang et al., ATel 17101;
Troja et al., ATel 17109, GCN 39869; Dong et al., ATel 17112; Aryan et al., GCN 39839; Pereyra et al., GCN 39858; Jiang et al., GCN 39864.
GCN Circular 39839
A. Aryan, T.-W. Chen (both NCU), S. Yang (HNAS), C.-C. Ngeow, Y. J. Yang, Y.-H. Lee, A. Sankar. K, W.-J. Hou, H.-Y. Hsiao (all NCU), A. K. H. Kong (NTHU), T. Hashimoto, V.V. Vignesh, M. Mohanraj, T.-C. Yang (all NCHU), T. Goto (NTHU), C.-H. Niu (CCNU), S. C.-C. Ho (ANU), E. Kilerci-Eser (Sabanci U.), Y.-H. Zhu (NAOC), D. Li (Tsinghua U.), Y. Niino (U. Tokyo), S. Yamasaki (NCHU), Y.-A. Chen (NTHU), J.-S. Zhang (CAS), P. Wang (CAS), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), M.-H. Lee, Y.-C. Pan, C.-H. Lai, C.-S. Lin, H.-C. Lin, J.-K. Guo (all NCU), L. L. Fan, Z. N. Wang, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report:
We observed the field of the fast radio burst 20250316A (Ng et al., ATel#17081; Leung et al., ATel#17086) using the 1m LOT and 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al. 2024, arXiv:2406.09270). A candidate associate X-ray source was detected by the EP mission (Sun et al., GCN 39834). The first LOT epoch of observations in the r band started at 11:30 UT on the 22nd of March 2025 (MJD = 60756.479), ~6.12 days after the CHIME detection (3.84 days after the EP X-ray source), while the first SLT epoch of observations in the z band started at 12:57 UT on the 22nd of March 2025 (MJD = 60756.540), ~7.18 days after the CHIME detection (3.90 days after the EP X-ray source).
We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. In the stacked frames, we do not detect any potential uncataloged optical afterglow counterpart candidate within the updated localization provided by Leung et al. (ATel#17086). Moreover, we used the Kinder pipeline (Yang et al. 2021, A&A, 646, A22) to subtract the stacked images using the templates from Pan-STARRS1 (Chambers et al. 2016 arXiv:1612.05560). We also utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction utilizing the "sfft" (Hu, 2022, ApJ, 936, 157) and "hotpants" (Becker A., 2015, ascl.soft. ascl:1504.004) algorithms. We found no evidence of any prominent optical afterglow counterpart candidate in the difference images as well.
We further employed AutoPhOT to perform PSF photometry on the combined frames. The details of the observation and 3-sigma upper limits (in the AB system) were as follows:
Telescope | Filter | MJD (start) | t-t_CHIME (d) | t-t_EP (d) | Exposure (s) | Magnitude | Average Seeing | MedianAirmass
LOT | r | 60756.479 | 6.12 | 3.84 | 300 * 12 | >22.31 | 1".4 | 1.59
LOT | g | 60756.501 | 6.14 | 3.86 | 300 * 6 | >22.32 | 1".3 | 1.66
LOT | i | 60756.529 | 6.17 | 3.89 | 300 * 12 | >22.40 | 1".2 | 1.40
SLT | z | 60756.540 | 7.18 | 3.90 | 300 * 31 | >20.51 | 1".4 | 1.30
The non-detection of optical afterglow counterpart candidate is consistent with previous reports by Becerra et al. (ATel#17082), Niino et al. (ATel#17083), and our previous observations reported in Hashimoto et al. (Atel#17095). t_CHIME is the discovery time of CHIME FRB 20250316A, and t_EP is detection time of the corresponding EP X-ray source EP J120944.2+585060.
The presented upper limits were calibrated using the field stars from the Pan-STARRS1 catalog and were not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_g = 0.07 mag, A_r = 0.05, A_i = 0.03 mag, and A_z = 0.02 mag, respectively, in the direction of the burst (Schlafly & Finkbeiner 2011).
GCN Circular 39834
H. Sun, H. Q. Cheng, D. Y. Li, H. Y. Liu, C. C. Jin, Z. X. Ling, W. D. Zhang, Y. Liu (NAO, CAS), B. Zhang (UNLV), D. F. Hu, Y. Li, J. J. Geng, X. F. Wu (PMO, CAS), J. W. Hu, H. W. Pan, C. Zhang, L. Chen, S. Q. Jiang, Y. J. Song, T. Zhao (NAO, CAS), Y. Chen, C. K. Li, J. Guan, S. M. Jia, H. S. Zhao, J. Zhang, M. Y. Ge, W. W. Cui, H. Feng, W. Li, C. Z. Liu, F. J. Lu, L. M. Song, J. Wang, J. J. Xu, D. W. Han, S. N. Zhang, X. F. Zhao, Q. C. Zhao, Z. H. Yang, Q. C. Shui (IHEP, CAS), Q. C. Liu (THU), L. Piro (INAF), V. Burwitz, P. Friedrich, N. Meidinger, K. Nandra, A. Rau (MPE), J.-U. Ness, A. Santovincenzo (ESA), Nanda Rea (ICE-CSIC), P. O'Brien (Univ. of Leicester), B. Cordier (CEA), W. Yuan (NAO, CAS) report on behalf of the Einstein Probe team:
We observed the field of the bright fast radio burst FRB 20250316A (Ng, ATel #17081) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. A total of four observations were conducted. In the first observation, which began at 2025-03-17T16:57:29 with an exposure time of 2.9 ks, no X-ray sources were detected within 3 arcmin of the CHIME position. In the second observation, starting at 2025-03-18T15:23:50 with also 2.9 ks exposure, FXT detected a weak, uncatalogued X-ray source, designated as EP J120944.2+585060. The position of this source is consistent with the refined localization provided by CHIME (Leung, ATel #17086). The unabsorbed X-ray flux is 3.4 x 10^-14 erg/cm2/s in the 0.5 - 10 keV band.
In the third observation starting at 2025-03-21T05:50:01 with an exposure of 5.8 ks, the X-ray source was clearly detected at a flux consistent with the previous level. The refined source position is RA = 182.4341 deg, Dec = 58.8499 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). This position remains consistent with the CHIME localization, suggestive of EP J120944.2+585060 being likely associated with the source of FRB 20250316A. Preliminary analysis of the forth observation, taken 11 hours after the third one, shows a marginal trend of decrease of the source flux, though the the telemetry data received is not complete yet. Further analysis is ongoing. A Chandra DDT observation has been requested.
If EP J120944.2+585060 is indeed associated with FRB 20250316A and located near the candidate host galaxy NGC 4141, which has a redshift of 0.0067 (Connor, ATel #17091), the inferred X-ray luminosity is approximately 3 x 10^39 erg/s in the 0.5 - 10 keV band during the EP observations.
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES.
GCN Circular 39787
Jin-Peng Zhang, Yan-Qiu Zhang, Wang-Chen Xue, Shao-Lin Xiong, Yue Wang (IHEP) and Ce Cai (HEBNU) report on behalf of the Insight-HXMT team:
At the event time 2025-03-16T08:33:50.842 UTC (T0) of FRB 20250316A (Ng et al., ATel 17081; Leung et al., ATel 17086), Insight-HXMT/HE was observing normally and monitored the full location error region of FRB 20250316A.
The routine blind search of Insight-HXMT/HE data found no burst candidate around the time of FRB 20250316A. Thus, we implemented a targeted search [1] from T0 - 100 s to T0 + 5 s, and identified no candidate above 3 sigma.
Considering three typical spectral models (i.e. soft, normal and hard Band functions), three timescales and the FRB localization (RA = 182.476 deg, Dec = +58.8494 deg (J2000)), the 3 sigma upper limits of the gamma-ray transient energy flux (10 keV-1 MeV, in units of 10^-7 erg/s/cm^2) are reported below:
Timescale (s) Soft Normal Hard
0.1 7.17 7.48 3.27
1 2.26 2.36 1.03
10 0.72 0.75 0.33
With the distance of 40.8 Mpc from NGC 4141, the probable host galaxy of this FRB, we further calculate the following upper limits of the gamma-ray transient intrinsic isotropic luminosity (1 keV-10 MeV, in units of 10^47 erg/s):
Timescale (s) Soft Normal Hard
0.1 1.43 1.49 0.65
1 0.45 0.47 0.21
10 0.14 0.15 0.07
We note that the above results are preliminary. Refined results will be reported.
Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://hxmten.ihep.ac.cn/.
[1] C. Cai et al. MNRAS, 508, 3910–3920 (2021) https://doi.org/10.1093/mnras/stab2760