Detection of Bursts from FRB 121102 with the Effelsberg 100-m Radio Telescope at 5 GHz and the Role of Scintillation

TL;DR

This study reports the detection of three bursts from FRB 121102 at 5 GHz, analyzes their frequency structure and scintillation effects, and discusses how propagation phenomena influence burst detectability.

Contribution

First detection of FRB 121102 bursts at 5 GHz with analysis of scintillation effects and burst rate variability, highlighting the role of interstellar scintillation in burst detection.

Findings

Detected three bursts at 5 GHz with frequency structure.

Measured scintillation bandwidth consistent with Galactic ISM predictions.

Observed burst rate variability possibly due to scintillation boosting.

Abstract

FRB 121102, the only repeating fast radio burst (FRB) known to date, was discovered at 1.4 GHz and shortly after the discovery of its repeating nature, detected up to 2.4 GHz. Here we present three bursts detected with the 100-m Effelsberg radio telescope at 4.85 GHz. All three bursts exhibited frequency structure on broad and narrow frequency scales. Using an autocorrelation function analysis, we measured a characteristic bandwidth of the small-scale structure of 6.4$\pm$1.6 MHz, which is consistent with the diffractive scintillation bandwidth for this line of sight through the Galactic interstellar medium (ISM) predicted by the NE2001 model. These were the only detections in a campaign totaling 22 hours in 10 observing epochs spanning five months. The observed burst detection rate within this observation was inconsistent with a Poisson process with a constant average occurrence rate; three bursts arrived in the final 0.3 hr of a 2 hr observation on 2016 August 20. We therefore observed a change in the rate of detectable bursts during this observation, and we argue that boosting by diffractive interstellar scintillations may have played a role in the detectability. Understanding whether changes in the detection rate of bursts from FRB 121102 observed at other radio frequencies and epochs are also a product of propagation effects, such as scintillation boosting by the Galactic ISM or plasma lensing in the host galaxy, or an intrinsic property of the burst emission will require further observations.