FRB 20121102A is active again with significantly smaller DM as revealed by FAST
ATel #15619; Pei Wang(NAOC), Yongkun Zhang(NAOC), Weiwei Zhu(NAOC), Bing Zhang(UNLV), Di Li(NAOC), Junshuo Zhang(NAOC), Jinhuang Cao(NAOC), Yi Feng(Zhejiang Lab), Jinlin Han(NAOC), Kejia Lee(PKU&NAOC), Yuan-Pei Yang(YNU), Chenhui Niu(NAOC), Jiarui Niu(NAOC), Weiyang Wang(PKU), Chenchen Miao(NAOC), Rui Luo(CSIRO), Ye Li(PMO), Bojun Wang(PKU), Fayin Wang(NJU), Xuefeng Wu(PMO), Heng Xu(PKU), Jinchen Jiang(PKU), Jiangwei Xu(PKU), Yunpeng Men(PKU), Dejiang Zhou(NAOC), Jumei Yao(NAOC), Wenfei Yu(SHAO), Chunfeng Zhang(PKU), Songbo Zhang(PMO)
on 19 Sep 2022; 04:09 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Pei Wang (wangpei@nao.cas.cn)
Subjects: Radio, Request for Observations, Transient, Fast Radio Burst
FAST has been monitoring FRB 20121102A for 0.5 to 1 hour daily to weekly since February of 2022, with the central beam of the FAST 19-beams L-band Array pointing to RA = 05h31m58.70s, DEC = +33d08m52.5s (Chatterjee et al. 2017; Marcote et al. 2017), taking pulsar-searching data with a 49.152 microsecond sampling and 4096 frequency channels in between 1.0 GHz and 1.5 GHz. Following non-detections until August 1st, 2022 (between UTC 2022-08- 01 03:59:00 and UTC 2022-08-01 04:29:00), FAST detected at least 300 bursts from FRB 20121102A with a peak burst rate of 200/hr and estimated fluence between 0.03 and 0.3 Jy ms from the following dates: (UTC) 16th Aug., 21st Aug., 3rd Sep., 7th Sep. and 10-17th Sep., suggesting that this repeater is likely in another active episode. This recent activation of FRB 20121102A is generally consistent with the proposed periodicity of Rajwade et al. (2020) and Cruces et al. (2020), even though in several previous projected active windows no burst was detected by FAST. By combining the bursts collected in Raiwade et al. (2020) and Cruces et al. (2020) and the newly detected by FAST in 2019 and 2022, the projected turn-off date is around 17th Oct. - 1st Dec. 2022. If the source is continuously on after the projected turning-off time, it suggests that the putative period of the source becomes less robust or has evolution.
The optimal dispersion measure (DM) of the bursts is constrained to 552.5 +/- 0.9 pc cm-3 which is measured using the method in Seymour et al. (2019), from MJD 59806 till now. This indicates that the DM of FRB 20121102A has decreased by about 10 pc cm-3 (i.e. 2%) compared to earlier detections in Li et al. (2020), suggesting a previously unseen temporal DM variation over 10 years. We encourage more follow-up monitoring efforts with multi-band facilities.
FAST is a Chinese national mega-science facility, built and operated by the National Astronomical Observatories, Chinese Academy of Sciences (NAOC). We appreciate all the members in the FAST FRB key science project collaboration for their support and assistance during the observations.
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