GCN Circular 35175

M. Rigoselli, D. P. Pacholski, S. Mereghetti, R. Salvaterra (INAF, IASF-Milano) and S. Campana (INAF, OAB) on behalf of a larger collaboration report:

XMM-Newton carried out a target of opportunity observation  of GRB 231115A (Mereghetti et al., GCN 35037
Not found
 
 
; Fermi GBM Team, GCN 35035
Not found
 
 
) which is likely a magnetar giant flare in the M82 galaxy (D’Avanzo et al., GCN 35036
Not found
 
 
; Burns, GCN 35038
Not found
 
 
) and was also detected by Glowbug (Cheung et al., GCN 35045
Not found
 
 
), Insight-HXMT (Xue et al., GCN 35060
Not found
 
 
), Konus-Wind (Frederiks et al. GCN 35062
Not found
 
 
) and Swift/BAT (Ronchini et al., GCN 35065
Not found
 
 
).

The burst location was observed with the EPIC instrument on 2023-11-16 from 08:27 UT  to 21:19 UT (To+16.8 hr to To+29.7 hr).  A large fraction of the ~46 ks long observation was affected by high background, resulting in cleaned exposure times of 8.4 ks for the pn camera and 19.0 and 23.6 ks for the MOS1 and MOS2 cameras, respectively.

Comparison of  images in various energy ranges with those of the  EPIC observations of M82 in 2021 and 2022, does not reveal any new source inside the INTEGRAL IBAS error circle  (2 arcmin radius, Mereghetti et al., GCN 35037
Not found
 
 
). 

For about 50% of the error region, we derived a 3 sigma count rate upper limit of 0.004 pn cts/s in the 2-10 keV energy range. For an absorbed power law spectrum with photon index 2 and N_H=6.5E20 cm-2 this corresponds to about 3E-14 erg/cm2/s (2-10 keV). 

Diffuse X-ray emission from the central part of M82 affects the error region, resulting in limits higher than 0.01 pn cts/s (2-10 keV) in less than 20% of the error region.

The lack of detection of an X-ray afterglow associated to GRB 231115A in the XMM-Newton observation 16.8 hours after the trigger provides further evidence that the burst is likely a magnetar giant flare in the M82 galaxy.