GRB 080503: A very early blue kilonova and an adjacent non-thermal radiation component

Abstract

The temporal behavior of the very dim optical afterglow of GRB 080503 is at odds with the regular forward shock afterglow model and a sole kilonova component responsible for optical emission has been speculated in some literature. Here we analyze the optical afterglow data available in archive and construct time-resolved spectra. The significant detection by Keck-I in {\it G/R} bands at $t\sim 3$ day, which has not been reported before, as well as the simultaneous Gemini-North {\it r} band measurement, are in favor of a power-law spectrum that is well consistent with the optical to X-ray spectrum measured at $t\sim 4.5$ day. However, for $t\le 2$ day, the spectra are thermal-like and a straightforward interpretation is a kilonova emission from a neutron star merger, making it, possibly, the first detection of a very early kilonova signal at $t\sim 0.05$ day. A non-thermal nature of optical emission at late times ($t\sim 2$ day), anyhow, can not be ruled out because of the large uncertainty of the {\it g}-band data. We also propose to classify the neutron star merger induced optical transients, according to the temporal behaviors of the kilonova and the non-thermal afterglow emission, into four types. GRB 080503 would then represent the first observation of a sub-group of neutron star merger driven optical transients (i.e., Type IV) consisting of an early blue kilonova and an adjacent non-thermal afterglow radiation.

Accepted to ApJ. 15 pages, 4 figures, 5 tables

References in corpus (11)

• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• An Ordinary Short Gamma-Ray Burst with Extraordinary Implications: Fermi-GBM Detection of GRB 170817A
• Spectroscopic identification of r-process nucleosynthesis in a double neutron star merger
• Illuminating Gravitational Waves: A Concordant Picture of Photons from a Neutron Star Merger
• Optical emission from a kilonova following a gravitational-wave-detected neutron-star merger
• Kilonovae
• Kilonova Light Curves from the Disk Wind Outflows of Compact Object Mergers
• GRB 080503 late afterglow re-brightening: signature of a magnetar powered merger-nova
• Fallback Accretion onto a Newborn Magnetar: short GRBs with Extended Emission
• The photospheric radiation model for the prompt emission of Gamma-ray Bursts: Interpreting four observed correlations
• Calibration of photometry from the Gemini Multi-Object Spectrograph on Gemini North

Cited by in corpus (3)

• Multi-Peaked Non-Thermal Light Curves from Magnetar-Powered Gamma-Ray Bursts
• Comparison of the Origin of Short Gamma-Ray Bursts with or without Extended Emission
• Detection of Low-Redshift Excess in Supernova-Linked Gamma-Ray Bursts