Characterization of the Repeating FRB 20220912A with the Allen Telescope Array (2312.07756v1)

Abstract: FRB 20220912A is a repeating Fast Radio Burst (FRB) that was discovered in Fall 2022 and remained highly active for several months. We report the detection of 35 FRBs from 541 hours of follow-up observations of this source using the recently refurbished Allen Telescope Array, covering 1344 MHz of bandwidth primarily centered at 1572 MHz. All 35 FRBs were detected in the lower half of the band with non-detections in the upper half and covered fluences from 4-431 Jy-ms (median$=$48.27 Jy-ms). We find consistency with previous repeater studies for a range of spectrotemporal features including: bursts with downward frequency drifting over time; a positive correlation between bandwidth and center frequency; and a decrease in sub-burst duration over time. We report an apparent decrease in the center frequency of observed bursts over the 2 months of the observing campaign (corresponding to a drop of $6.21\pm 0.76$ MHz per day). We predict a cut-off fluence for FRB 20220912A of $F_\textrm{max}\lesssim 10^4$ Jy-ms, for this source to be consistent with the all-sky rate, and find that FRB 20220912A significantly contributed to the all-sky FRB rate at a level of a few percent for fluences of $\sim$100 Jy-ms. Finally, we investigate characteristic timescales and sub-burst periodicities and find a) a median inter-subburst timescale of 5.82$\pm$1.16 ms in the multi-component bursts and b) no evidence of strict periodicity even in the most evenly-spaced multi-component burst in the sample. Our results demonstrate the importance of wideband observations of FRBs, and provide an important set of observational parameters against which to compare FRB progenitor and emission mechanism models.

• The paper provides a comprehensive analysis of FRB 20220912A using 541 hours of ATA observations that yielded 35 burst detections.
• The paper demonstrates the effective use of wide-band dual-tuning and advanced digital signal processing to uncover detailed spectrotemporal features.
• The paper reveals that the center frequency decreases by approximately 6.21 MHz per day, offering valuable constraints on progenitor models and environmental conditions.

Characterization of the Repeating FRB 20220912A with the Allen Telescope Array

This paper presents a comprehensive analysis of the repeating Fast Radio Burst (FRB) 20220912A observed using the Allen Telescope Array (ATA), including the instrumental configuration and data processing methods employed in the paper. The key findings provide insights into the characteristics and implications of FRB 20220912A within the broader context of FRB research.

Observational Campaign and Methodology

The research team conducted an extensive observing campaign lasting 541 hours, using the ATA's wide-band dual-tuning capabilities, primarily centered at 1572 MHz with 1344 MHz bandwidth. The campaign yielded 35 FRB detections, confined to the lower half of the frequency band, and exhibiting fluences ranging from 4 to 431 Jy-ms. The paper leverages the revised capabilities of the ATA's digital signal processing systems, enabling efficient FRB detection and characterization across 20-element beamformed outputs.

Spectrotemporal Features of FRB 20220912A

In its spectrotemporal analysis, the paper identifies several key characteristics of FRB 20220912A:

1. Downward Frequency Drifting: A common feature among repeater FRBs, this phenomenon was observed here as well, implying similar underlying emission mechanisms.
2. Correlation Between Bandwidth and Center Frequency: A statistically significant positive correlation was observed, which is essential for understanding the emission physics and propagation effects.
3. Time Evolution of Center Frequency: Notably, the center frequency of the bursts decreased by approximately 6.21 MHz per day over the campaign, suggesting temporal variability in the FRB's activity window within the ATA's frequency band.

Implications and Future Directions

The findings have theoretical implications for distinguishing between different progenitor models, including magnetospheric versus external shocks. The decrease in center frequency and consistent spectrotemporality are indicative of potential environmental changes or intrinsic emission mechanism evolution. The derived all-sky rate function suggests that the brightest bursts from repeaters like FRB 20220912A contribute significantly to the overall FRB rate, emphasizing their importance in constraining models.

Moreover, the apparent cutoff fluence of FRB 20220912A implies limitations in emission energy, influencing constraints on the density and magnetization of the progenitor environment. This paper underscores the necessity for ongoing wide-band and multi-frequency observations to further refine the understanding of FRB emission mechanisms and their host environments.

Conclusion

Ultimately, this paper exemplifies the utility of the ATA in exploring the diverse landscape of FRB phenomenology. By disentangling spectrotemporal properties across broad frequencies, researchers can enhance the interpretability of these enigmatic cosmic events. Continuing enhancements to observatory infrastructure, combined with innovative data analysis techniques, will propel future investigations, potentially unveiling novel emissions and advancing our astrophysical comprehension of FRBs.