4.6.1. General Properties and Milti-Wavelength Observations

The duration is estimated as *T*<sup>90</sup> = 48 ± 16 s in the 15–350 keV band by Swift-BAT [220] and around 29.9 s in the 50–300 keV band by Fermi-GBM. The light curve shows a multiple

peak structure with a main peak around 20 s after the trigger time. The time-averaged GBM spectrum in the first 50 s is best fit by a Band function with *E<sup>p</sup>* = 326 ± 7 keV, *α* = −1.06 ± 0.01 and *β<sup>T</sup>* = −2.25 ± 0.03. The isotropic equivalent energy *Eγ*,*iso* in the 10–1000 keV band is (4.71 <sup>±</sup> 0.16) <sup>×</sup> <sup>10</sup><sup>53</sup> erg, as calculated from the fluence measured by Fermi-GBM.

Fermi-LAT observed the GRB starting from around 3500 s and up to 5500 s. No significant emission was reported [221]. Swift-XRT began the observation at *t* = 2966.8 s due to an observational constrain. A fading source was detected following a broken power-law behavior with decay indices of 1.97+0.10 <sup>−</sup>0.09 and 1.07+0.15 <sup>−</sup>0.10 and a break at 9078 s [222]. Optical observations were also performed by several instruments. The *r*-band light curve made along with VLT data point [223] and inferred data from FRAM-ORM [224] show a power-law decay in flux with the index equal to 1. The Liverpool Telescope observations, performed around 177 s after the trigger time, seems to be around the peak of the optical afterglow [225]. The HAWC observatory followed-up the event but no significant detection was identified in the TeV band [226]. Redshift estimation of *z* = 1.1 was performed by the ESO VLT [227].
