The Double-Burst Nature and Early Afterglow Evolution of Long GRB 110801A

Abstract

We present a comprehensive temporal and spectral analysis of the long-duration gamma-ray burst GRB 110801A, utilizing multi-band data from the Neil Gehrels Swift Observatory and ground-based telescopes. The $\gamma$-ray emission exhibits a distinct two-episode (``double-burst'') structure. Rapid follow-up observations in the optical and X-ray bands provide full coverage of the second burst. The optical light curve begins to rise approximately 135 s after the trigger, significantly preceding the second emission episode observed in X-rays and $\gamma$-rays at $\sim 320$ s. This chromatic behavior suggests different physical origins for the optical and high-energy emissions. Joint broadband spectral fitting (optical to $\gamma$-rays) during the second episode reveals that a two-component model, consisting of a power-law plus a Band function, provides a superior fit compared to single-component models. We interpret the power-law component as the afterglow of the first burst (dominating the optical band), while the Band component is attributed to the prompt emission of the second burst (dominating the high-energy bands). A physical synchrotron model is also found to be a viable candidate to explain the high-energy emission. Regarding the afterglow, the early optical light curve displays a sharp transition from a rise of $\sim t^{2.5}$ to $\sim t^{6.5}$, which is well-explained by a scenario involving both reverse shock (RS) and forward shock (FS) components. We constrain the key physical parameters of the burst, deriving an initial Lorentz factor ${\Gamma }_0\sim 60$, a jet half-opening angle ${\theta }_j\sim 0.09$, and an isotropic kinetic energy $E_{\mathrm{k},\mathrm{iso}}\sim 10^{54.8}$ erg.

16 pages, 12 figures

References in corpus (21)

• Multi-messenger Observations of a Binary Neutron Star Merger
• The Supernova -- Gamma-Ray Burst Connection
• An online repository of Swift/XRT light curves of GRBs
• GRB Radiative Efficiencies Derived from the Swift Data: GRBs vs. XRFs, Long vs. Short
• A Comprehensive Analysis of the Swift/XRT Data: II. Diverse Physical Origins of the Shallow Decay Segment
• Detection of a Thermal Spectral Component in the Prompt Emission of GRB 100724B
• Klein-Nishina Effects on Optically Thin Synchrotron and Synchrotron Self-Compton Spectrum
• Precursors in Swift Gamma Ray Bursts with redshift
• Synchrotron emission in small scale magnetic field as possible explanation for prompt emission spectra of gamma-ray bursts
• Internal Energy Dissipation of Gamma-Ray Bursts Observed with Swift: Precursors, Prompt Gamma-rays, Extended emission and Late X-ray Flares
• Photosphere emission in the X-Ray Flares of Swift Gamma-Ray Bursts and Implications for the Fireball Properties
• GRB jet structure and the jet break
• Afterglows from precursors in Gamma Ray Bursts. Application to the optical afterglow of GRB 091024
• GRB 170817A as a Refreshed Shock Afterglow viewed off-axis
• Gamma rays from a reverse shock with turbulent magnetic fields in GRB 180720B
• Evolution of the afterglow optical spectral shape of GRB 201015A in the first hour: evidence for dust destruction
• The Signature of Refreshed Shocks in the of Afterglow of GRB030329
• An optical-ultraviolet flare with absolute AB magnitude of -39.4 detected in GRB 220101A
• External Shock in a Multi-Bursting Gamma-ray Burst: Energy Injection Phase induced by the Later Launched Ejecta
• A comprehensive view of blackbody components in the X-ray spectra of GRBs
• A Method to Measure Photometries of Moderately-Saturated UVOT Sources