The Emission Mechanism of Gamma-Ray Bursts: Identification via Optical-IR Slope Measurements

TL;DR

This paper proposes an observational method using a fast-slewing, multi-channel telescope to measure optical-IR slopes in gamma-ray bursts, aiming to verify emission models and explore GRB environments.

Contribution

It introduces a new experimental setup with high-time resolution optical-IR measurements to test synchrotron emission models of GRBs.

Findings

Expected to measure 3-8 GRBs per year.

Will verify or falsify the 2EPLS synchrotron model.

Potential to study dust evaporation around GRBs.

Abstract

There is no consensus on the emission mechanism of $\gamma$-ray bursts (GRBs). A synchrotron model can produce $\gamma$-ray spectra with the empirical Band function form, from a piece-wise two-power-law electron energy distribution (2EPLS). This model predicts that for the same $\gamma$-ray spectrum, optical emission can be very different in $f_{\nu}$ log slope, and in flux relative to $\gamma$-rays,depending on model parameter values. The model only allows a small set of $f_{\nu}$ log slopes in the optical -thereby allowing a clear path to verification or falsification. Measurements of prompt GRB emission in the optical thus far give no useful information about the spectral shape within the band, and therefore cannot be used to evaluate such predictions. We describe an experiment that responds to GRB alerts with a fast-slewing telescope, with 3+ simultaneous, high-time resolution cameras. Three channels measure two slopes in order to evaluate the model. We propose cross-correlation of $\gamma$ and OIR light curves to verify that GRB are single-component dominated, or to quantify additional contributions. Previous CCD measurements have limited-time resolution due to read noise. Electron-multiplied CCDS (EMCCDs) can be used to greatly reduce read noise allowing exposure times of a few hundred ms. Our Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) utilizes a 70 cm telescope that can point in $\le$ 8 s, with 3 optical channels. The NUTTelA-TAO is expected to measure 3-8 GRB/yr, and verify/refute the 2EPLS model with just a few bright GRBs. A space-based experiment with an IR channel would make improved measurements of the self-absorption frequency and physical conditions within the GRB jet. Additional science includes detection of dust evaporation due to GRBs, a tool to study progenitor environment dust.