We report the early discovery of the optical afterglow of gamma-ray burst ( GRB ) 140801A in the 137 deg ^ { 2 } 3- \sigma error-box of the Fermi Gamma-ray Burst Monitor ( GBM ) .
MASTER is the only observatory that automatically react to all Fermi alerts .
GRB 140801A is one of the few GRBs whose optical counterpart was discovered solely from its GBM localization .
The optical afterglow of GRB 140801A was found by MASTER Global Robotic Net 53 sec after receiving the alert , making it the fastest optical detection of a GRB from a GBM error-box .
Spectroscopy obtained with the 10.4-m Gran Telescopio Canarias and the 6-m BTA of SAO RAS reveals a redshift of z = 1.32 .
We performed optical and near-infrared photometry of GRB 140801A using different telescopes with apertures ranging from 0.4-m to 10.4-m. GRB 140801A is a typical burst in many ways .
The rest-frame bolometric isotropic energy release and peak energy of the burst is E _ { \mathrm { iso } } = 5.54 _ { -0.24 } ^ { +0.26 } \times 10 ^ { 52 } erg and E _ { \mathrm { p,rest } } \simeq 280 keV , respectively , which is consistent with the Amati relation .
The absence of a jet break in the optical light curve provides a lower limit on the half-opening angle of the jet \theta = 6.1 deg .
The observed E _ { \mathrm { peak } } is consistent with the limit derived from the Ghirlanda relation .
The joint Fermi GBM and Konus- Wind analysis shows that GRB 140801A could belong to the class of intermediate duration .
The rapid detection of the optical counterpart of GRB 140801A is especially important regarding the upcoming experiments with large coordinate error-box areas .