Rotation Measure Evolution of the Repeating Fast Radio Burst Source FRB 121102

Abstract

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.

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

“…Of the new uGMRT bursts, G5 (Figures 6 and 7) has the most intriguing spectrotemporal properties, showing substructures that do not completely match the typical "sad trombone" downward-drift features seen from repeaters (e.g., Hessels et al 2019). A similar morphology has been observed in some bursts from FRB 20121102A (Caleb et al 2020;Hilmarsson et al 2021) and FRB 20180916B (Chawla et al 2020). However, it is unclear whether these represent drifting subbursts within a single burst envelope or a closely spaced set of separate bursts peaking at different frequencies and then each individually drifting downward in frequency.…”

The periodic origin of fast radio bursts

“…The first repeating FRB, FRB 121102 (Spitler et al 2016), was found to be in an extreme magnetized environment (Michilli et al 2018), which was revealed by the very high rotation measure (RM∼ 10 5 rad m −2 ). The RM decreases by ∼ 34% in 2.6 yr (Hilmarsson et al 2021). The high and rapidly variable RM can be well understood in the magnetar nebula model (Margalit & Metzger 2018;Katz 2021b).…”

The physics of fast radio bursts

“…The repeaters like FRB 121102 and FRB 180916 are nearly 100% linearly polarized and have a flat PA curve (i.e., PA does not vary obviously with time) [12,47,[65][66][67]. Note that the RM of FRB 121102 is the highest among all FRBs (∼ 10 5 rad/m 2 ) and is decreasing with time [65,68]. The non-repeaters like FRB 181112 and FRB 190102 are usually partial linearly or circularly polarized and their PAs vary significantly with time (named "PA swing") [58,69].…”