# Investigating the nature of INTEGRAL Gamma-ray Bursts and sub-threshold triggers with Swift follow up

## TL;DR

This study investigates weak INTEGRAL triggers for gamma-ray bursts, confirming some as real GRBs through Swift follow-up, and compares their properties with Swift BAT GRBs, revealing similar low-fluence detection capabilities.

## Contribution

It demonstrates that real GRBs can be identified among INTEGRAL's weak triggers and compares their properties with Swift BAT GRBs, highlighting similar low-fluence detection levels.

## Key findings

- Six weak triggers classified as GRBs, including one discovered by the campaign.
- INTEGRAL and Swift detect similar low-fluence GRBs, with Swift being more sensitive to short, low-fluence events.
- Correlation between gamma-ray and X-ray properties supports previous findings.

## Abstract

We explore the potential of INTEGRAL to improve our understanding of the low fluence regime for explosive transients, such as GRBs. We probe the nature of the so-called "WEAK" INTEGRAL triggers, when the gamma-ray instruments record intensity spikes that are below the usual STRONG significance thresholds. In a targeted Swift follow-up campaign, we observed 15 WEAK triggers. We find six of these can be classified as GRBs. This includes GRB150305A, a GRB discovered from our campaign alone. We also identified a source coincident with one trigger, IGRW151019, as a candidate AGN. We show that real events such as GRBs exist within the IBAS WEAK trigger population. A comparison of the fluence distributions of the full INTEGRAL IBAS and Swift BAT GRB samples showed that the two are similar. We also find correlations between the prompt gamma-ray and X-ray properties of the two samples, supporting previous investigations. We find that both satellites reach similar, low fluence levels regularly, although Swift is more sensitive to short, low fluence GRBs.