LOFAR Detection of 110–188 MHz Emission and Frequency-dependent Activity from FRB 20180916B

Abstract

The object FRB 20180916B is a well-studied repeating fast radio burst source. Its proximity (∼150 Mpc), along with detailed studies of the bursts, has revealed many clues about its nature, including a 16.3 day periodicity in its activity. Here we report on the detection of 18 bursts using LOFAR at 110-188 MHz, by far the lowest-frequency detections of any FRB to date. Some bursts are seen down to the lowest observed frequency of 110 MHz, suggesting that their spectra extend even lower. These observations provide an order-of-magnitude stronger constraint on the optical depth due to free-free absorption in the source's local environment. The absence of circular polarization and nearly flat polarization angle curves are consistent with burst properties seen at 300-1700 MHz. Compared with higher frequencies, the larger burst widths (∼40-160 ms at 150 MHz) and lower linear polarization fractions are likely due to scattering. We find ∼2-3 rad m −2 variations in the Faraday rotation measure that may be correlated with the activity cycle of the source. We compare the LOFAR burst arrival times to those of 38 previously published and 22 newly detected bursts from the uGMRT (200-450 MHz) and CHIME/ FRB (400-800 MHz). Simultaneous observations show five CHIME/FRB bursts when no emission is detected by LOFAR. We find that the burst activity is systematically delayed toward lower frequencies by about 3 days from 600 to 150 MHz. We discuss these results in the context of a model in which FRB 20180916B is an interacting binary system featuring a neutron star and high-mass stellar companion.

Periodic Fast Radio Bursts from Luminous X-ray Binaries

“…In previous scenarios attributing FRBs to NS activity in a binary, this periodicity was proposed to result from free-free absorption by the companion star wind (e.g., Lyutikov et al 2020). However, such a scenario predicts a narrower observing window at lower radio frequencies, in tension with observations of FRB 180916 (Pastor-Marazuela et al 2020;Pleunis et al 2021). By contrast, in the super-Eddington accretion scenario presented here, a more natural explanation arises from geometric beaming by the narrow clean funnel as the BH jet crosses the observer line of sight (Figure 1; see also Katz 2017).…”

“…If the accretion disk undergoes precession with a period P (Figure 1), then any ballistic ejection of material along the instantaneous jet direction will encounter the disk wind material from an earlier orientation of the disks by a radial scale no larger than: The Thomson column of this material encountered by an FRB emitted at smaller radii can be estimated as For    M M w E d d , time variability of this column could generate variations in DM ≈ 5 × 10 5 τ T pc cm −3 over the timescale P, distinct from that accumulated through the quiescent jet cavity (Equation ( 10)). If the accretion disk wind is magnetized, then propagation through it could generate a more significant local time-variable RM across the active phase (see inset of Figure 1), as observed in FRB 180916 (Pleunis et al 2021) Figure 7. The distributions of the projected physical offsets of ULX (solid green) and FRB (brown) sources from their respective host galactic centers are represented by the solid green and brown histograms, respectively.…”

“…Observations of the periodic repeater, FRB 180916, reveal that the burst activity window (duty cycle; see Equation (5)) is narrower, and peaks earlier in phase, at higher radio frequencies (Pastor-Marazuela et al 2020). Furthermore, the low-frequency bursts observed exhibit greater average fluences (Pastor-Marazuela et al 2020;Pleunis et al 2021). In the synchrotron maser scenario (Section 2.5), the frequency of the radio emission scales with the properties of the FRB-generating transient flare and the pre-existing quiescent jet as (Equation ( 14…”

Periodic activity from fast radio burst FRB180916 explained in the frame of the orbiting asteroid model

“…While this paper was under review new bursts were published in Pleunis et al (2021) (see also Pastor-Marazuela et al 2020). This additional data contains a new set of the CHIME/FRB data which we fully include in our analysis, and low frequency observations from LOFAR and uGMRT.…”

A Southern-Hemisphere all-sky radio transient monitor for SKA-Low prototype stations

“…20180916B discovered by Canadian Hydrogen Intensity Mapping Experiment (CHIME/FRB CHIME/FRB Collaboration et al 2018Collaboration et al , 2019 and recently detected by LOFAR at 110-188 MHz (Pleunis et al 2020;Pastor-Marazuela et al 2020) and Sardinia Radio Telescope (Pilia et al 2020) or FRB 20200125A discovered by Green Bank Telescope at 350 MHz (Parent et al 2020). Although the Northern Hemisphere systems cover some fractions of the southern sky, to date, no dedicated system capable of continuous monitoring of the entire Southern Hemisphere has existed.…”