Fast radio bursts (FRBs) are millisecond-duration, extragalactic radio flashes of unknown physical origin [1][2][3] . FRB 121102, the only known repeating FRB source [4][5][6] , has been localized to a star-forming region in a dwarf galaxy 7-9 at redshift z = 0.193, and is spatially coincident with a compact, persistent radio source 7,10 . The origin of the bursts, the nature of the persistent source, and the properties of the local environment are still debated. Here we present bursts that show ∼100% linearly polarized emission at a very high and variable Faraday rotation measure in the source frame: RM src = +1.46 × 10 5 rad m −2 and +1.33 × 10 5 rad m −2 at epochs separated by 7 months, in addition to narrow ( 30 µs) temporal structure. The large and variable rotation measure demonstrates that FRB 121102 is in an extreme and dynamic magneto-ionic environment, while the short burst durations argue for a neutron star origin. Such large rotation measures have, until now, only been observed 11,12 in the vicinities of massive black holes (M BH 10 4 M ). Indeed, the properties of the persistent radio source are compatible with those of a low-luminosity, accreting massive black hole 10 . The bursts may thus come from a neutron star in such an environment. However, the observed properties may also be explainable in other models, such as a highly magnetized wind nebula 13 or supernova remnant 14 surrounding a young neutron star. 2Using the 305-m William E. Gordon Telescope at the Arecibo Observatory, we detected 16 bursts from FRB 121102 at radio frequencies from 4.1 − 4.9 GHz (Table 1). The data recorder provided complete polarization parameters with 10.24-µs time resolution. See Methods and Extended Data Figs. 1-6 for observation and analysis details.The 4.5-GHz bursts have typical widths 1 ms, which are narrower than the 2 to 9-ms bursts previously detected at lower frequencies 5,15 . In some cases they show multiple components and structure close to the sampling time of the data. Burst #6 is particularly striking, with a width of 30 µs, which constrains the size of the emitting region to 10 km, modulo geometric and relativistic effects. Evolution in burst morphology with frequency complicates the determination 5 of dispersion measure (DM = d 0 n e (l) dl), but aligning the narrow component in Burst #6 results in DM= 559.7 ± 0.1 pc cm −3 , which is consistent 4,5,15,16 with other bursts detected since 2012, and suggests that any bona fide dispersion measure variations are at the 1% level.After correcting for Faraday rotation, and accounting for ∼2% depolarization from the finite channel widths, the bursts are consistently ∼100% linearly polarized (Fig. 1). The polarization angles PA = PA ∞ + θ (where PA ∞ is a reference angle at infinite frequency, θ = RMλ 2 is the rotation angle of the electric field vector and λ is the observing wavelength) are flat across the observed frequency range and burst envelopes (∆PA 5 • ms −1 ). This could mean that the burst durations reflect the timescale of the emission process and n...

FRB 121102 is the only known repeating fast radio burst source. Here we analyze a wide-frequency-range (1 − 8 GHz) sample of high-signal-to-noise, coherently dedispersed bursts detected using the Arecibo and Green Bank telescopes. These bursts reveal complex time-frequency structures that include sub-bursts with finite bandwidths. The frequency-dependent burst structure complicates the determination of a dispersion measure (DM); we argue that it is appropriate to use a DM metric that maximizes frequency-averaged pulse structure, as opposed to peak signal-to-noise, and find DM = 560.57 ± 0.07 pc cm −3 at MJD 57644. After correcting for dispersive delay, we find that the sub-bursts have characteristic frequencies that typically drift lower at later times in the total burst envelope. In the 1.1 − 1.7 GHz band, the ∼ 0.5 − 1-ms sub-bursts have typical bandwidths ranging from 100 − 400 MHz, and a characteristic drift rate of ∼ 200 MHz/ms towards lower frequencies. At higher radio frequencies, the sub-burst bandwidths and drift rate are larger, on average. While these features could be intrinsic to the burst emission mechanism, they could also be imparted by propagation effects in the medium local to the source. Comparison of the burst DMs with previous values in the literature suggests an increase of ∆DM ∼ 1 − 3 pc cm −3 in 4 years, though this could be a stochastic variation as opposed to a secular trend. This implies changes in the local medium or an additional source of frequency-dependent delay. Overall, the results are consistent with previously proposed scenarios in which FRB 121102 is embedded in a dense nebula.

No abstract

We present 41 bursts from the first repeating fast radio burst discovered (FRB 121102). A deep search has allowed us to probe unprecedentedly low burst energies during two consecutive observations (separated by one day) using the Arecibo telescope at 1.4 GHz. The bursts are generally detected in less than a third of the 580-MHz observing bandwidth, demonstrating that narrowband FRB signals may be more common than previously thought. We show that the bursts are likely faint versions of previously reported multi-component bursts. There is a striking lack of bursts detected below 1.35 GHz and simultaneous VLA observations at 3 GHz did not detect any of the 41 bursts, but did detect one that was not seen with Arecibo, suggesting preferred radio emission frequencies that vary with epoch. A power law approximation of the cumulative distribution of burst energies yields an index −1.8 ± 0.3 that is much steeper than the previously reported value of ∼ −0.7. The discrepancy may be evidence for a more complex energy distribution. We place constraints on the possibility that the associated persistent radio source is generated by the emission of many faint bursts (∼ 700 ms −1 ). We do not see a connection between burst fluence and wait time. The distribution of wait times follows a log-normal distribution centered around ∼ 200 s; however, some bursts have wait times below 1 s and as short as 26 ms, which is consistent with previous reports of a bimodal distribution. We caution against exclusively integrating over the full observing band during FRB searches, because this can lower signal-to-noise.

We present results of the coordinated observing campaign that made the first subarcsecond localization of a Fast Radio Burst, FRB 121102. During this campaign, we made the first simultaneous detection of an FRB burst by multiple telescopes: the VLA at 3 GHz and the Arecibo Observatory at 1.4 GHz. Of the nine bursts detected by the Very Large Array at 3 GHz, four had simultaneous observing coverage at other observatories. We use multi-observatory constraints and modeling of bursts seen only at 3 GHz to confirm earlier results showing that burst spectra are not well modeled by a power law. We find that burst spectra are characterized by a ∼ 500 MHz envelope and apparent radio energy as high as 10 40 erg. We measure significant changes in the apparent dispersion between bursts that can be attributed to frequency-dependent profiles or some other intrinsic burst structure that adds a systematic error to the estimate of DM by up to 1%. We use FRB 121102 as a prototype of the FRB class to estimate a volumetric birth rate of FRB sources R FRB ≈ 5 × 10 −5 /N r Mpc −3 yr −1 , where N r is the number of bursts per source over its lifetime. This rate is broadly consistent with models of FRBs from young pulsars or magnetars born in superluminous supernovae or long gamma-ray bursts, if the typical FRB repeats on the order of thousands of times during its lifetime.

We undertook coordinated campaigns with the Green Bank, Effelsberg, and Arecibo radio telescopes during Chandra X-ray Observatory and XMM-Newton observations of the repeating fast radio burst FRB 121102 to search for simultaneous radio and X-ray bursts. We find 12 radio bursts from FRB 121102 during 70 ks total of X-ray observations. We detect no X-ray photons at the times of radio bursts from FRB 121102 and further detect no X-ray bursts above the measured background at any time. We place a 5σ upper limit of 3 × 10 −11 erg cm −2 on the 0.5-10 keV fluence for X-ray bursts at the time of radio bursts for durations < 700 ms, which corresponds to a burst energy of 4 × 10 45 erg at the measured distance of FRB 121102. We also place limits on the 0.5-10 keV fluence of 5 × 10 −10 erg cm −2 and 1 × 10 −9 erg cm −2 for bursts emitted at any time during the XMM-Newton and Chandra observations, respectively, assuming a typical X-ray burst duration of 5 ms. We analyze data from the Fermi Gamma-ray Space Telescope Gamma-ray Burst Monitor and place a 5σ upper limit on the 10-100 keV fluence of 4 × 10 −9 erg cm −2 (5 × 10 47 erg at the distance of FRB 121102) for gamma-ray bursts at the time of radio bursts. We also present a deep search for a persistent X-ray source using all of the X-ray observations taken to date and place a 5σ upper limit on the 0.5-10 keV flux of 4 × 10 −15 erg s −1 cm −2 (3 × 10 41 erg s −1 at the distance of FRB 121102). We discuss these non-detections in the context of the host environment of FRB 121102 and of possible sources of fast radio bursts in general.

The repeating fast radio burst source FRB 121102 has been shown to have an exceptionally high and variable Faraday rotation measure (RM), which must be imparted within its host galaxy, likely by or within its local environment. In the redshifted (z = 0.193) source reference frame, the RM decreased from 1.46 × 105 rad m−2 to 1.33 × 105 rad m−2 between 2017 January and August, showing day-timescale variations of ∼200 rad m−2. Here we present 16 FRB 121102 RMs from burst detections with the Arecibo 305 m radio telescope, the Effelsberg 100 m, and the Karl G. Jansky Very Large Array, providing a record of FRB 121102’s RM over a 2.5 yr time span. Our observations show a decreasing trend in RM, although the trend is not linear, dropping by an average of 15% year−1 and is ∼ 9.7 × 104 rad m−2 at the most recent epoch of 2019 August. Erratic, short-term RM variations of ∼103 rad m−2 week−1 were also observed between MJDs 58215–58247. A decades-old neutron star embedded within a still-compact supernova remnant or a neutron star near a massive black hole and its accretion torus have been proposed to explain the high RMs. We compare the observed RMs to theoretical models describing the RM evolution for FRBs originating within a supernova remnant. FRB 121102’s age is unknown, and we find that the models agree for source ages of ∼6–17 yr at the time of the first available RM measurements in 2017. We also draw comparisons to the decreasing RM of the Galactic center magnetar, PSR J1745−2900.

Magnetars are a promising candidate for the origin of Fast Radio Bursts (FRBs). The detection of an extremely luminous radio burst from the Galactic magnetar SGR J1935+2154 on 2020 April 28 added credence to this hypothesis. We report on simultaneous and non-simultaneous observing campaigns using the Arecibo, Effelsberg, LOFAR, MeerKAT, MK2 and Northern Cross radio telescopes and the MeerLICHT optical telescope in the days and months after the April 28 event. We did not detect any significant single radio pulses down to fluence limits between 25 mJy ms and 18 Jy ms. Some observing epochs overlapped with times when X-ray bursts were detected. Radio images made on four days using the MeerKAT telescope revealed no point-like persistent or transient emission at the location of the magnetar. No transient or persistent optical emission was detected over seven days. Using the multi-colour MeerLICHT images combined with relations between DM, NH and reddening we constrain the distance to SGR J1935+2154, to be between 1.5 and 6.5 kpc. The upper limit is consistent with some other distance indicators and suggests that the April 28 burst is closer to two orders of magnitude less energetic than the least energetic FRBs. The lack of single-pulse radio detections shows that the single pulses detected over a range of fluences are either rare, or highly clustered, or both. It may also indicate that the magnetar lies somewhere between being radio-quiet and radio-loud in terms of its ability to produce radio emission efficiently.