GROND coverage of the main peak of Gamma-Ray Burst 130925A

Abstract

Prompt or early optical emission in gamma-ray bursts is notoriously difficult to measure, and observations of the dozen cases show a large variety of properties. Yet, such early emission promises to help us achieve a better understanding of the GRB emission process(es). We performed dedicated observations of the ultra-long duration (T90 about 7000 s) GRB 130925A in the optical/near-infrared with the 7-channel "Gamma-Ray Burst Optical and Near-infrared Detector" (GROND) at the 2.2m MPG/ESO telescope. We detect an optical/NIR flare with an amplitude of nearly 2 mag which is delayed with respect to the keV--MeV prompt emission by about 300--400 s. The decay time of this flare is shorter than the duration of the flare (500 s) or its delay. While we cannot offer a straightforward explanation, we discuss the implications of the flare properties and suggest ways toward understanding it.

9 pages, 9 figures, accepted for publ. in A&A

References in corpus (8)

• GROND - a 7-channel imager
• Quasi-blackbody component and radiative efficiency of the prompt emission of gamma-ray bursts
• A statistical study of gamma-ray burst afterglows measured by the Swift Ultra-violet Optical Telescope
• Energy input and response from prompt and early optical afterglow emission in gamma-ray bursts
• A hot cocoon in the ultralong GRB 130925A: hints of a PopIII-like progenitor in a low density wind environment
• Continuous optical monitoring during the prompt emission of GRB 060111B
• Prompt optical emission from residual collisions in GRB outflows
• A Unified Model of the Prompt Optical Emission of Gamma-Ray Bursts

Cited by in corpus (8)

• A Comparative Study of Long and Short GRBs. I. Overlapping Properties
• Dust in the wind: the role of recent mass loss in long gamma-ray bursts
• The ultra-long GRB 220627A at z=3.08
• Swift/UVOT: 18 Years of Long GRB Discoveries and Advances
• Possible correlations between the emission properties of short GRBs and their offsets from the host galaxies
• ALMA Host galaxy observation of the off-axis Gamma-Ray Burst XRF020903
• The Spectral Sharpness Angle of Gamma-ray Bursts
• Is Bremsstrahlung A Possible Mechanism to Explain the Thermal Feature in the GRB 130925A X-ray Afterglow?