skip to main content


The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 11:00 PM ET on Friday, July 12 until 2:00 AM ET on Saturday, July 13 due to maintenance. We apologize for the inconvenience.

Title: Empirical Assessment of Aperiodic and Periodic Radio Bursts from Young Precessing Magnetars

We analyze the slow periodicities identified in burst sequences from FRB 121102 and FRB 180916 with periods of about 16 and 160 days, respectively, while also addressing the absence of any fast periodicity that might be associated with the spin of an underlying compact object. Both phenomena can be accounted for by a young, highly magnetized, precessing neutron star that emits beamed radiation with significant imposed phase jitter. Sporadic narrow-beam emission into an overall wide solid angle can account for the necessary phase jitter, but the slow periodicities with 25%–55% duty cycles constrain beam traversals to be significantly smaller. Instead, phase jitter may result from variable emission altitudes that yield large retardation and aberration delays. A detailed arrival time analysis for triaxial precession includes wobble of the radio beam and the likely larger, cyclical torque resulting from the changes in the spin–magnetic moment angle. These effects will confound identification of the fast periodicity in sparse data sets longer than about a quarter of a precession cycle unless fitted for and removed as with orbital fitting. Stochastic spin noise, likely to be much larger than in radio pulsars, may hinder detection of any fast periodicity in data spans longer than a few days. These decoherence effects will dissipate as sources of fast radio bursts age, so they may evolve into objects with properties similar to Galactic magnetars.

more » « less
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astrophysical Journal
Medium: X Size: Article No. 97
Article No. 97
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract We report the discovery of seven new Galactic pulsars with the Canadian Hydrogen Intensity Mapping Experiment’s Fast Radio Burst (CHIME/FRB) backend. These sources were first identified via single pulses in CHIME/FRB, then followed up with CHIME/Pulsar. Four sources appear to be rotating radio transients, pulsar-like sources with occasional single-pulse emission with an underlying periodicity. Of those four sources, three have detected periods ranging from 220 ms to 2.726 s. Three sources have more persistent but still intermittent emission and are likely intermittent or nulling pulsars. We have determined phase-coherent timing solutions for the latter two. These seven sources are the first discovery of previously unknown Galactic sources with CHIME/FRB and highlight the potential of fast radio burst detection instruments to search for intermittent Galactic radio sources. 
    more » « less

    We show that the 216.8 ± 0.1 ms periodicity reported for the fast radio burst (FRB) 20191221A is very constraining for burst models. The high accuracy of burst periodicity (better than one part in 103), and the 2 per cent duty cycle (ratio of burst duration and interburst interval), suggest a pulsar-like rotating beam model for the observed activity; the radio waves are produced along open field lines within ∼107 cm of the neutron star surface, and the beam periodically sweeps across the observer as the star spins. According to this picture, FRB 20191221A is a factor ∼1012 scaled up version of galactic pulsars with one major difference, whereas pulsars convert rotational kinetic energy to EM waves and the outbursts of 20191221A require conversion of magnetic energy to radiation.

    more » « less

    At least some fast radio bursts (FRBs) are produced by magnetars. Even though mounting observational evidence points towards a magnetospheric origin of FRB emission, the question of the location for FRB generation continues to be debated. One argument suggested against the magnetospheric origin of bright FRBs is that the radio waves associated with an FRB may lose most of their energy before escaping the magnetosphere because the cross-section for e± to scatter large-amplitude electromagnetic waves in the presence of a strong magnetic field is much larger than the Thompson cross-section. We have investigated this suggestion and find that FRB radiation travelling through the open field line region of a magnetar’s magnetosphere does not suffer much loss due to two previously ignored factors. First, the plasma in the outer magnetosphere ($r \gtrsim 10^9$ cm), where the losses are potentially most severe, is likely to be flowing outwards at a high Lorentz factor γp ≥ 103. Secondly, the angle between the wave vector and the magnetic field vector, θB, in the outer magnetosphere is likely of the order of 0.1 radian or smaller due in part to the intense FRB pulse that tilts open magnetic field lines so that they get aligned with the pulse propagation direction. Both these effects reduce the interaction between the FRB pulse and the plasma substantially. We find that a bright FRB with an isotropic luminosity $L_{\rm frb} \gtrsim 10^{42} \, {\rm erg \ s^{-1}}$ can escape the magnetosphere unscathed for a large section of the γp − θB parameter space, and therefore conclude that the generation of FRBs in magnetar magnetosphere passes this test.

    more » « less
  4. 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) ≈ 8.9Myr−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.

    more » « less
  5. Abstract

    We present the discovery of an as yet nonrepeating fast radio burst (FRB), FRB 20210117A, with the Australian Square Kilometre Array Pathfinder (ASKAP), as a part of the Commensal Real-time ASKAP Fast Transients Survey. The subarcsecond localization of the burst led to the identification of its host galaxy atz= 0.214(1). This redshift is much lower than what would be expected for a source dispersion measure (DM) of 729 pc cm−3, given typical contributions from the intergalactic medium and the host galaxy. Optical observations reveal the host to be a dwarf galaxy with little ongoing star formation—very different to the dwarf host galaxies of the known repeating FRBs 20121102A and 20190520B. We find an excess DM contribution from the host and attribute it to the FRB’s local environment. We do not find any radio emission from the FRB site or host galaxy. The low magnetized environment and the lack of a persistent radio source indicate that the FRB source is older than those found in other dwarf host galaxies, establishing the diversity of FRB sources in dwarf galaxy environments. We find our observations to be fully consistent with the “hypernebula” model, where the FRB is powered by an accretion jet from a hyperaccreting black hole. Finally, our high time resolution analysis reveals burst characteristics similar to those seen in repeating FRBs. We encourage follow-up observations of FRB 20210117A to establish any repeating nature.

    more » « less