An extreme magneto-ionic environment associated with the fast radio burst source FRB 121102

Abstract

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...

Radiation forces constrain the FRB mechanism

“…Luo et al 2018;Ravi 2019) -or 3x10 42 erg s −1 (bottom three panels), which is roughly the median luminosity for the bursts of the repeater FRB 121102 (e.g. Michilli et al 2018;Hessels et al 2019). We do not impose a prior on this luminosity as it is dependent on the details of the maser process whereas the focus of this paper is to provide general constraints that should apply to all maser mechanisms operating in shocks.…”

“…And the lower three panels of Figure 3 show results for radio luminosity of 3x10 42 erg s −1 which is the median luminosity for bursts of the repeater FRB 121102 (e.g. Michilli et al 2018;Hessels et al 2019). The observed luminosity is used for the calculation of particle acceleration upstream of the shock front, and for no other aspect of the maser mechanism.…”

“…Fast radio bursts (FRBs) are milli-second-duration bright (flux density ∼ Jansky) transient events observed between 400 MHz and 7 GHz frequencies (Amiri et al 2019a(Amiri et al , 2019bRavi 2019aRavi , 2019bRavi et al 2019;Oslowski et al 2019;Kocz et al 2019;Bannister et al 2019;Gajjar et al 2018;Michilli et al 2018;Farah et al 2018;Shannon et al 2018;Bannister et al 2017;Law et al 2017;Chatterjee et al 2017;Marcote et al 2017;Tendulkar et al 2017;Spitler et al 2016;Petroff et al 2016;Spitler et al 2014; Thornton et al 2013;Lorimer et al 2007). Numerous mechanisms have been suggested for the generation of the coherent radio emission of FRBs, eg.…”

FRB coherent emission from decay of Alfvén waves

“…It is firmly established that at least a few milli-second duration, very bright, radio signals that have been detected between about 400 MHz and 7 GHz (known as Fast Radio Bursts or FRBs) are coming from a distance of about a Gpc or more, eg. Lorimer et al 2007; Thornton et al 2013;Spitler et al 2014;Petroff et al 2016;Bannister et al 2017;Law et al 2017;Chatterjee et al 2017;Marcote et al 2017;Tendulkar et al 2017;Gajjar et al 2018;Michilli et al 2018;Farah et al 2018;Shannon et al 2018;Oslowski et al 2019;Kocz et al 2019;Bannister et al 2019;CHIME Collaboration 2019a and2019b;Ravi 2019aRavi , 2019bRavi et al 2019. Many mechanisms have been suggested for the generation of high luminosity coherent radio waves from Fast Radio Bursts (FRBs), eg. Katz (2014Katz ( , 2016, Murase et al (2016;, Kumar et al (2017), Metzger et al (2017), Zhang (2017), Beloborodov (2017), Cordes (2017), Ghisellini & Locatelli (2018), Lu & Kumar (2018), Metzger et al (2019), Thompson (2019), Wang & Lai (2019), ; for a recent review see Katz (2018).…”

The Remnant of Neutron Star-White Dwarf Merger and the Repeating Fast Radio Bursts

“…Only one of the repeating FRBs, namely FRB 121102, has been localized with a star forming host galaxy to at redshift of 0.193 ( [18] and references therein). Detailed follow-up observations show that the source is highly magnetized [19], likely in an environment of a magnetar [20][21][22]. The repeating pulses of FRB 121102 show complex frequency and time structure [23].…”