A Search for Prompt Very High Energy Emission from Satellite-detected Gamma-ray Bursts using Milagro

TL;DR

This study used the Milagro observatory to search for very high energy gamma-ray emission from satellite-detected GRBs, aiming to detect prompt or delayed signals and constrain theoretical models.

Contribution

First comprehensive search for VHE gamma-ray emission from GRBs detected by Swift using Milagro's wide field of view and continuous observation capabilities.

Findings

No significant VHE emission detected from the GRBs in the sample.

Established upper limits on VHE emission for the observed GRBs.

Provided constraints on GRB emission models based on non-detections.

Abstract

Gamma-ray bursts (GRBs) have been detected up to GeV energies and are predicted by many models to emit in the very high energy (VHE, > 100 GeV) regime too. Detection of such emission would allow us to constrain GRB models. Since its launch, in late 2004, the Swift satellite has been locating GRBs at a rate of approximately 100 per year. The rapid localization and follow-up in many wavelengths has revealed new and unexpected phenomena, such as delayed emission in the form of bright X-ray flares. The Milagro gamma-ray observatory is a wide field of view (2 sr) instrument employing a water Cherenkov detector to continuously ($>$ 90% duty cycle) observe the overhead sky in the 100 GeV to 100 TeV energy range. Over 100 GRBs are known to have been in the field of view of Milagro since January 2000, including 57 since the launch of Swift (through May 2007). We discuss the results of the searches for prompt emission from these bursts, as well as for delayed emission from the X-ray flares observed in some of the Swift bursts.