TITLE:   GCN CIRCULAR
NUMBER:  32973
SUBJECT: GRB 221009A：DAMPE observed a 34.7 GeV photon at 1.36 hour after the GBM trigger
DATE:    22/11/23 01:26:16 GMT
FROM:    Kai-Kai Duan at Purple Mountain Observatory  <duankk@pmo.ac.cn>

Kai-Kai Duan (Purple Mountain Observatory), Zun-Lei Xu (PMO), Zhao-Qiang Shen (PMO), Wei Jiang (PMO), Lu-Yao Jiang (PMO), Dong-Ya Guo (Institute of High Energy Physics), Wen-Xi Peng (IHEP), Fabio Gargano (Istituto Nazionale di Fisica Nucleare) and Xiang Li (PMO), report on behalf of the DAMPE collaboration: 

We report the observation of GRB 221009A with DAMPE, which has been reported by Swift (Kennea et al. GCN #32635, Krimm et al. GCN #32688), Fermi-GBM (Veres et al. GCN #32636, Lesage et al. GCN #32642), Fermi-LAT (Bissaldi et al. GCN #32637, Pillera et al. GCN #32658, Xia et al. GCN #32748), LHAASO (Huang et al. GCN #32677) and so on. 

Though the GRB is about 90 deg from the boresight of DAMPE at the moment of Fermi-GBM trigger (out of the normal FOV), the Unbiased-Trigger counts of DAMPE increased significantly from 227 to 233 seconds after the Fermi-GBM trigger. We believe that about 21 out of 35 events during the 6-second timespan were from the GRB, and the highest deposit energy is 2.4 GeV for these events.  

The FOV of DAMPE began to cover the GRB position about one hour later, and it observed a 34.7 GeV (RA = 289.93 deg, DEC = 19.96 deg) photon at 1.58 deg (with the 95% containment of the PSF as ~ 2 deg) from the swift localization of this GRB (RA = 288.265 deg, Dec = 19.774 deg, from Dichiara et al. GCN #32632) 4896 seconds after the Fermi-GBM trigger. The p-value of this photon emitted from background is 0.0003, corresponding to 3.6-sigma significance locally. During the past 6-year observation, DAMPE observed only one photon with energy above 30 GeV within 2 deg around this GRB position. 

At 9.37 and 16.26 days after the Fermi-GBM trigger, DAMPE observed 8.33 GeV (RA = 287.82 deg, DEC = 20.35 deg) and 10.74 GeV (RA = 287.48 deg, DEC = 19.88 deg) photons around 0.71 deg and 0.75 deg from the LAT localization of GRB 221009A. The local significance of these two photons are 3.10 and 3.22 sigma, respectively. The 95% containment of the PSF above 10 GeV is about 2 deg.  

The detailed data analysis is still on going. 

DAMPE is a satellite for dark matter detection indirectly, cosmic-ray physics and gamma-ray astronomy by detection of the high-energy electrons, cosmic rays and gamma rays.

[Editor's note: Reformatted at the request of the submitter.]