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Abstract We present the localization and host galaxy of FRB 20190208A, a repeating source of fast radio bursts (FRBs) discovered using CHIME/FRB. As part of the Pinpointing REpeating ChIme Sources with EVN dishes repeater localization program on the European VLBI Network (EVN), we monitored FRB 20190208A for 65.6 hr at ∼1.4 GHz and detected a single burst, which led to its very long baseline interferometry localization with 260 mas uncertainty (2σ). Follow-up optical observations with the MMT Observatory (i≳ 25.7 mag (AB)) found no visible host at the FRB position. Subsequent deeper observations with the Gran Telescopio Canarias, however, revealed an extremely faint galaxy (r= 27.32 ± 0.16 mag), very likely (99.95%) associated with FRB 20190208A. Given the dispersion measure of the FRB (∼580 pc cm−3), even the most conservative redshift estimate ( ) implies that this is the lowest-luminosity FRB host to date (≲108L⊙), even less luminous than the dwarf host of FRB 20121102A. We investigate how localization precision and the depth of optical imaging affect host association and discuss the implications of such a low-luminosity dwarf galaxy. Unlike the other repeaters with low-luminosity hosts, FRB 20190208A has a modest Faraday rotation measure of a few tens of rad m−2, and EVN plus Very Large Array observations reveal no associated compact persistent radio source. We also monitored FRB 20190208A for 40.4 hr over 2 yr as part of the Extragalactic Coherent Light from Astrophysical Transients repeating FRB monitoring campaign on the Nançay Radio Telescope and detected one burst. Our results demonstrate that, in some cases, the robust association of an FRB with a host galaxy will require both high localization precision and deep optical follow-up.
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The unseen host galaxy and high dispersion measure of a precisely localized fast radio burst suggests a high-redshift origin
ABSTRACT FRB 20210912A is a fast radio burst (FRB), detected and localized to subarcsecond precision by the Australian Square Kilometre Array Pathfinder. No host galaxy has been identified for this burst despite the high precision of its localization and deep optical and infrared follow-up, to 5σ limits of R = 26.7 mag and Ks = 24.9 mag with the Very Large Telescope. The combination of precise radio localization and deep optical imaging has almost always resulted in the secure identification of a host galaxy, and this is the first case in which the line of sight is not obscured by the Galactic disc. The dispersion measure of this burst, DMFRB = 1233.696 ± 0.006 pc cm−3, allows for a large source redshift of z > 1 according to the Macquart relation. It could thus be that the host galaxy is consistent with the known population of FRB hosts, but is too distant to detect in our observations (z > 0.7 for a host like that of the first repeating FRB source, FRB 20121102A); that it is more nearby with a significant excess in DMhost, and thus dimmer than any known FRB host; or, least likely, that the FRB is truly hostless. We consider each possibility, making use of the population of known FRB hosts to frame each scenario. The fact of the missing host has ramifications for the FRB field: even with high-precision localization and deep follow-up, some FRB hosts may be difficult to detect, with more distant hosts being the less likely to be found. This has implications for FRB cosmology, in which high-redshift detections are valuable.
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- PAR ID:
- 10442056
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 525
- Issue:
- 1
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 994-1007
- Size(s):
- p. 994-1007
- Sponsoring Org:
- National Science Foundation
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