2024ApJ...974..221F

We present our optical observations and multiwavelength analysis of the GRB 200613A detected by the Fermi satellite. Time-resolved spectral analysis of the prompt gamma-ray emission was conducted utilizing the Bayesian block method to determine statistically optimal time bins. Based on the Bayesian Information Criterion, the data generally favor the Band+blackbody (BB) model. We speculate that the main Band component comes from the Blandford-Znajek mechanism, while the additional BB component comes from the neutrino annihilation process. The BB component becomes significant for a low-spin, high-accretion-rate black hole central engine, as evidenced by our model comparison with the data. The afterglow light curve exhibits typical power-law decay, and its behavior can be explained by the collision between the ejecta and the constant interstellar medium. Model fitting yields the following parameters: ${E}_{K,{\rm{iso}}}=({2.04}_{-1.50}^{+11.8})\times {10}^{53}$ erg, ${{\rm{\Gamma }}}_{0}={354}_{-217}^{+578}$, $p={2.09}_{-0.03}^{+0.02}$, ${n}_{18}=({2.04}_{-1.87}^{+9.71})\times {10}^{2}$ cm^–3, ${\theta }_{j}={24.0}_{-5.54}^{+6.50}$ degree, ${\epsilon }_{e}={1.66}_{-1.39}^{+4.09})\times {10}^{-1}$ and ${\epsilon }_{B}=({7.76}_{-5.9}^{+48.5})\times {10}^{-6}$. In addition, we employed the public Python package Prospector to perform a spectral energy distribution modeling of the host galaxy. The results suggest that the host galaxy is a massive galaxy ($\mathrm{log}({M}_{* }/{M}_{\odot })={11.75}_{-0.09}^{+0.10}$) with a moderate star formation rate (${\rm{SFR}}={22.58}_{-7.22}^{+13.63}{M}_{\odot }$ yr^–1). This SFR is consistent with the SFR of ∼34.2M_⊙ yr^–1 derived from the [O II] emission line in the observed spectrum.