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ABSTRACT Among more than 1000 known fast radio bursts (FRBs), only five sources – FRBs 20121102A, 20190520B, 20201124A, 20240114A, and 20190417A – have confirmed associations with persistent radio sources. The observed quasi-steady emission is consistent with synchrotron radiation from a composite of magnetar wind nebula and supernova (SN) ejecta. Using a phenomenological model that incorporates simplified treatments of the nebular dynamics and particle acceleration, we compute the synchrotron flux by solving kinetic equations for energized electrons, accounting for electromagnetic cascades of electron–positron pairs interacting with nebular photons. Within the framework of our model, the rotation-powered scenario requires a young neutron star (NS) with age $$t_{\rm age}\approx 20\, {\rm yr}$$, dipolar magnetic field $$B_{\rm dip}\approx (3{\!-\!}5)\times 10^{12}\, {\rm G}$$ and initial spin period $$P_i\approx 1.5{\!-\!}3\, {\rm ms}$$ in an ultra-stripped SN progenitor to account for emissions from FRBs 20121102A and 20190520B. In contrast, FRB 20201124A requires $$t_{\rm age}\approx 10\, {\rm yr}$$, $$B_{\rm dip}\approx 5.5\times 10^{13}\, {\rm G}$$, and $$P_i\approx 10\, {\rm ms}$$ in a conventional core-collapse SN progenitor. For the magnetar-flare-powered model, NS aged $$t_{\rm age} \approx 25\, /40\, {\rm yr}$$ in a USSN progenitor and $$t_{\rm age} \approx 12.5\, {\rm yr}$$ in a CCSN progenitor explains the observed flux for FRB 20121102A/20190520B and FRB 20201124A, respectively. Finally, we estimate a minimum NS age $$t_{\rm age,min} \sim 1{\!-\!}3\, {\rm yr}$$ based on the near-source plasma contribution to observed DM, and $$t_{\rm age,min} \sim 6.5{\!-\!}10\, {\rm yr}$$ from the absence of radio signal attenuation.
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Mapping Obscured Star Formation in the Host Galaxy of FRB 20201124A
Abstract We present high-resolution 1.5–6 GHz Karl G. Jansky Very Large Array and Hubble Space Telescope (HST) optical and infrared observations of the extremely active repeating fast radio burst (FRB) FRB 20201124A and its barred spiral host galaxy. We constrain the location and morphology of star formation in the host and search for a persistent radio source (PRS) coincident with FRB 20201124A. We resolve the morphology of the radio emission across all frequency bands and measure a star formation rate (SFR) ≈ 8.9M⊙yr−1, approximately ≈2.5–6 times larger than optically inferred SFRs, demonstrating dust-obscured star formation throughout the host. Compared to a sample of all known FRB hosts with radio emission, the host of FRB 20201124A has the most significantly obscured star formation. While HST observations show the FRB to be offset from the bar or spiral arms, the radio emission extends to the FRB location. We propose that the FRB progenitor could have formed in situ (e.g., a magnetar born from a massive star explosion). It is still plausible, although less likely, that the progenitor of FRB 20201124A migrated from the central bar of the host. We further place a limit on the luminosity of a putative PRS at the FRB position ofL6.0GHz≲ 1.8 ×1027erg s−1Hz−1, among the deepest PRS luminosity limits to date. However, this limit is still broadly consistent with both magnetar nebulae and hypernebulae models assuming a constant energy injection rate of the magnetar and an age of ≳105yr in each model, respectively.
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- PAR ID:
- 10523585
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Astrophysical Journal
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 961
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 44
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.3847/1538-4357/ad0cbd
