A burst storm from the repeating FRB 20200120E in an M81 globular cluster

TL;DR

This study reports a burst storm from the nearby repeating FRB 20200120E in an M81 globular cluster, revealing unique activity patterns, energy distribution, and stability in dispersion measure, with implications for understanding FRB origins.

Contribution

It presents the first detailed observation of a burst storm from FRB 20200120E, highlighting its distinct burst rate, energy distribution, wait-time characteristics, and stable dispersion measure, contrasting with other known repeaters.

Findings

53 bursts occurred within 40 minutes during the storm

The energy distribution follows a power-law with index 2.39

The wait-time distribution is bi-modal with peaks at ~1 s and ~24 ms

Abstract

The repeating fast radio burst (FRB) source FRB 20200120E is exceptional because of its proximity and association with a globular cluster. Here we report $60$ bursts detected with the Effelsberg telescope at 1.4 GHz. We observe large variations in the burst rate, and report the first FRB 20200120E `burst storm', where the source suddenly became active and 53 bursts (fluence $\geq 0.04$ Jy ms) occurred within only 40 minutes. We find no strict periodicity in the burst arrival times, nor any evidence for periodicity in the source's activity between observations. The burst storm shows a steep energy distribution (power-law index $\alpha = 2.39\pm0.12$) and a bi-modal wait-time distribution, with log-normal means of 0.94$^{+0.07}_{-0.06}$ s and 23.61$^{+3.06}_{-2.71}$ s. We attribute these wait-time distribution peaks to a characteristic event timescale and pseudo-Poisson burst rate, respectively. The secondary wait-time peak at $\sim1$ s is $\sim50\times$ longer than the $\sim24$ ms timescale seen for both FRB 20121102A and FRB 20201124A -- potentially indicating a larger emission region, or slower burst propagation. FRB 20200120E shows order-of-magnitude lower burst durations and luminosities compared with FRB 20121102A and FRB 20201124A. Lastly, in contrast to FRB 20121102A, which has observed dispersion measure (DM) variations of $\Delta{\rm DM} >1$ pc cm$^{-3}$ on month-to-year timescales, we determine that FRB 20200120E's DM has remained stable ($\Delta{\rm DM} <0.15$ pc cm$^{-3}$) over $>10$ months. Overall, the observational characteristics of FRB 20200120E deviate quantitatively from other active repeaters, but it is unclear whether it is qualitatively a different type of source.