Fig. 2: Early-time radio light curves and spectral index evolution of GRB 221009A.
From: Precise measurements of self-absorbed rising reverse shock emission from gamma-ray burst 221009A
Top: our first observation of GRB 221009A with the AMI-LA, separated into eight frequency channels and the flux density derived in 15 min time intervals as well the 3 and 5 GHz light curves from the ATA. Bottom: the two-point spectral index \({\alpha }_{{\nu }_{1}}^{{\nu }_{2}}\) (\({F}_{\nu }\propto {\nu }^{{\alpha }_{{\nu }_{1}}^{{\nu }_{2}}}\), where ν1 and ν2 are the lower and upper frequencies used to calculate the two-point spectral index, respectively) measured between the highest and lowest of the eight AMI-LA quick-look frequency channels and the two ATA bands. Clear evolution can be seen throughout the observations, with the spectral index initially consistent with optically thick synchrotron emission (α ≈ 2.5) and flattening with time. This is indicative of a break frequency (probably the self-absorption break) beginning to move into the AMI-LA observing band and then through the ATA observing bands. We mark the location of α = 2.5 and α = 0 with dashed horizontal lines to aid the reader. Error bars represent 1σ uncertainties.
