Abstract
We report on the discovery of FRB 20200120E, a repeating fast radio burst (FRB) with a low dispersion measure (DM) detected by the Canadian Hydrogen Intensity Mapping Experiment FRB project. ...The source DM of 87.82 pc cm
−3
is the lowest recorded from an FRB to date, yet it is significantly higher than the maximum expected from the Milky Way interstellar medium in this direction (∼50 pc cm
−3
). We have detected three bursts and one candidate burst from the source over the period 2020 January–November. The baseband voltage data for the event on 2020 January 20 enabled a sky localization of the source to within ≃14 arcmin
2
(90% confidence). The FRB localization is close to M81, a spiral galaxy at a distance of 3.6 Mpc. The FRB appears on the outskirts of M81 (projected offset ∼20 kpc) but well inside its extended H
i
and thick disks. We empirically estimate the probability of a chance coincidence with M81 to be <10
−2
. However, we cannot reject a Milky Way halo origin for the FRB. Within the FRB localization region, we find several interesting cataloged M81 sources and a radio point source detected in the Very Large Array Sky Survey. We search for prompt X-ray counterparts in Swift Burst Alert Telescope and Fermi/GBM data, and, for two of the FRB 20200120E bursts, we rule out coincident SGR 1806−20-like X-ray bursts. Due to the proximity of FRB 20200120E, future follow-up for prompt multiwavelength counterparts and subarcsecond localization could be constraining of proposed FRB models.
We report on the detection of seven bursts from the periodically active, repeating fast radio burst (FRB) source FRB 180916.J0158+65 in the 300-400 MHz frequency range with the Green Bank Telescope ...(GBT). Emission in multiple bursts is visible down to the bottom of the GBT band, suggesting that the cutoff frequency (if it exists) for FRB emission is lower than 300 MHz. Observations were conducted during predicted periods of activity of the source, and had simultaneous coverage with the Low Frequency Array (LOFAR) and the FRB backend on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. We find that one of the GBT-detected bursts has potentially associated emission in the CHIME band (400-800 MHz) but we detect no bursts in the LOFAR band (110-190 MHz), placing a limit of on the spectral index of broadband emission from the source. We also find that emission from the source is severely band-limited with burst bandwidths as low as ∼40 MHz. In addition, we place the strictest constraint on observable scattering of the source, <1.7 ms at 350 MHz, suggesting that the circumburst environment does not have strong scattering properties. Additionally, knowing that the circumburst environment is optically thin to free-free absorption at 300 MHz, we find evidence against the association of a hyper-compact H ii region or a young supernova remnant (age <50 yr) with the source.
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.
We report on simultaneous radio and X-ray observations of the repeating fast radio burst source FRB 180916.J0158+65 using the Canadian Hydrogen Intensity Mapping Experiment (CHIME), Effelsberg, and ...Deep Space Network (DSS-14 and DSS-63) radio telescopes and the Chandra X-ray Observatory. During 33 ks of Chandra observations, we detect no radio bursts in overlapping Effelsberg or Deep Space Network observations and a single burst during CHIME/FRB source transits. We detect no X-ray events in excess of the background during the Chandra observations. These non-detections imply a 5 limit of <5 × 10−10 erg cm−2 for the 0.5-10 keV fluence of prompt emission at the time of the radio burst and 1.3 × 10−9 erg cm−2 at any time during the Chandra observations. Given the host-galaxy redshift of FRB 180916.J0158+65 (z ∼ 0.034), these correspond to energy limits of <1.6 × 1045 erg and <4 × 1045 erg, respectively. We also place a 5 limit of <8 × 10−15 erg s−1 cm−2 on the 0.5-10 keV absorbed flux of a persistent source at the location of FRB 180916.J0158+65. This corresponds to a luminosity limit of <2 × 1040 erg s−1. Using an archival set of radio bursts from FRB 180916.J0158+65, we search for prompt gamma-ray emission in Fermi/GBM data but find no significant gamma-ray bursts, thereby placing a limit of 9 × 10−9 erg cm−2 on the 10-100 keV fluence. We also search Fermi/LAT data for periodic modulation of the gamma-ray brightness at the 16.35 days period of radio burst activity and detect no significant modulation. We compare these deep limits to the predictions of various fast radio burst models, but conclude that similar X-ray constraints on a closer fast radio burst source would be needed to strongly constrain theory.
We report on the discovery and analysis of bursts from nine new repeating fast radio burst (FRB) sources found using the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. These ...sources span a dispersion measure (DM) range of 195-1380 pc cm−3. We detect two bursts from three of the new sources, three bursts from four of the new sources, four bursts from one new source, and five bursts from one new source. We determine sky coordinates of all sources with uncertainties of ∼10′. We detect Faraday rotation measures (RMs) for two sources, with values −20(1) and −499.8(7) rad m−2, that are substantially lower than the RM derived from bursts emitted by FRB 121102. We find that the DM distribution of our events, combined with the nine other repeaters discovered by CHIME/FRB, is indistinguishable from that of thus far non-repeating CHIME/FRB events. However, as previously reported, the burst widths appear statistically significantly larger than the thus far non-repeating CHIME/FRB events, further supporting the notion of inherently different emission mechanisms and/or local environments. These results are consistent with previous work, though are now derived from 18 repeating sources discovered by CHIME/FRB during its first year of operation. We identify candidate galaxies that may contain FRB 190303.J1353+48 (DM = 222.4 pc cm−3).
We report on the discovery of eight repeating fast radio burst (FRB) sources found using the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. These sources span a dispersion measure ...(DM) range of 103.5-1281 pc cm−3. They display varying degrees of activity: six sources were detected twice, another three times, and one 10 times. These eight repeating FRBs likely represent the bright and/or high-rate end of a distribution of infrequently repeating sources. For all sources, we determine sky coordinates with uncertainties of ∼10′. FRB 180916.J0158+65 has a burst-averaged DM = 349.2 0.3 pc cm−3 and a low DM excess over the modeled Galactic maximum (as low as ∼20 pc cm−3); this source also has a Faraday rotation measure (RM) of −114.6 0.6 rad m−2, which is much lower than the RM measured for FRB 121102. FRB 181030.J1054+73 has the lowest DM for a repeater, 103.5 0.3 pc cm−3, with a DM excess of ∼70 pc cm−3. Both sources are interesting targets for multi-wavelength follow-up due to their apparent proximity. The DM distribution of our repeater sample is statistically indistinguishable from that of the first 12 CHIME/FRB sources that have not yet repeated. We find, with 4 significance, that repeater bursts are generally wider than those of CHIME/FRB bursts that have not repeated, suggesting different emission mechanisms. Many of our repeater events show complex morphologies that are reminiscent of the first two discovered repeating FRBs. The repetitive behavior of these sources will enable interferometric localizations and subsequent host galaxy identifications.
Abstract
Fast radio burst (FRB) source FRB 20180916B exhibits a 16.33-day periodicity in its burst activity. It is as of yet unclear what proposed mechanism produces the activity, but polarization ...information is a key diagnostic. Here we report on the polarization properties of 44 bursts from FRB 20180916B detected between 2018 December and 2021 December by CHIME/FRB, the FRB project on the Canadian Hydrogen Intensity Mapping Experiment. In contrast to previous observations, we find significant variations in the Faraday rotation measure (RM) of FRB 20180916B. Over the 9-month period 2021 April and 2021 December we observe an apparent secular increase in RM of ∼50 rad m
−2
(a fractional change of over 40%) that is accompanied by a possible drift of the emitting band to lower frequencies. This interval displays very little variation in the dispersion measure (ΔDM ≲ 0.8 pc cm
−3
), which indicates that the observed RM evolution is likely produced from coherent changes in the Faraday-active medium’s magnetic field. Burst-to-burst RM variations appear unrelated to the activity cycle phase. The degree of linear polarization of our burst sample (≳80%) is consistent with the negligible depolarization expected for this source in the 400–800 MHz bandpass of CHIME. FRB 20180916B joins other repeating FRBs in displaying substantial RM evolution. This is consistent with the notion that repeater progenitors may be associated with young stellar populations by their preferential occupation of dynamic magnetized environments commonly found in supernova remnants, in pulsar wind nebulae, or near high-mass stellar companions.