Narrow, kiloJansky FRB detected by the DSA-110

ATel #17420; Pranav Sanghavi (Center for Astrophysics | Harvard & Smithsonian), Liam Connor (Center for Astrophysics | Harvard & Smithsonian), Vikram Ravi (California Institute of Technology) on behalf of the Deep Synoptic Array-110 (DSA-110) collaboration
on 26 Sep 2025; 00:27 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Pranav Sanghavi (pranav.sanghavi@cfa.harvard.edu)

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The Deep Synoptic Array (DSA-110) is a radio interferometer at the Owens Valley Radio Observatory (OVRO). The array consists of 96 4.65-m dishes automatically steerable in elevation, observing on the meridian. It conducts a real-time FRB search over a 187.5 MHz bandwidth centered at 1405 MHz by forming 512 coherent, fan-shaped search beams. For this observation, 81 core antennas and 12 outriggers were online.

On 2025 September 24 at 2025-09-24T04:08:23.8272 UTC, the DSA-110 real-time system detected FRB 20250924A, a bright, apparent non-repeater. The burst was initially detected with the modest signal-to-noise ratio (S/N) of 19, but on closer inspection, the pulse was found to be so bright that it saturated the bit-depth of the synthesized search-beam data. After forming a beam at the correct position and without RFI excision, the S/N was found to be ~2000. FRB 20250924A was bright enough to be detected in all individual 4.65 m antennas with S/N ~ 20. The peak flux density was 1.9 kJy in the leading 60 microsecond sub-pulse. The fluence integrated over the multicomponent FRB is 185 Jy ms. The event had an optimal dispersion measure of 405.25 pc/cm^3.

Using the saved voltage data, we performed an interferometric localization of the burst. The burst was localized at RA, Dec = (20h31m06.38s, +53d50m56.4s; J2000). Localizations for the full DSA-110 array are being commissioned, but initial checks suggest an arcsecond-level localization precision for this event. The Galactic line-of-sight dispersion measure in this direction is ~155 pc/cm^3 (from the NE2001 model), suggesting the event is extragalactic.

The NE2001 DM value results in an extragalactic DM of roughly 200-230 pc/cm^3, depending on assumptions about the Milky Way's halo contribution. For an extragalactic DM of ~215 pc/cm^3, the redshift is expected to be less than 0.21 with 90% confidence. This assumes the P(DMex | z) distribution from Connor et al. (2025). At the median redshift of z=0.10 from P(DMex | z), the energy released by FRB 20250924A is nearly 5e31 erg/Hz.

Multi-wavelength follow-up observations are encouraged as are deep radio follow-up observations to search for repeat bursts.

The incoherent beam dynamic spectrum of FRB 20250924A