Investigating the nature of the INTEGRAL gamma-ray bursts and sub-threshold triggers with Swift follow-up
journal contributionposted on 23.08.2017, 14:01 by A. B. Higgins, Rhaana Leigh Catherine Starling, D. Götz, S. Mereghetti, K. Wiersema, T. Maccarone, J. P. Osborne, N. R. Tanvir, P. T. O'Brien, A. J. Bird, A. Rowlinson, N. Gehrels
We explore the potential of the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) to improve our understanding of the low-fluence regime for explosive transients, such as Gamma-ray Bursts (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 GRB 150305A, a GRB discovered from our campaign alone. We also identified a source coincident with one trigger, IGRW151019, as a candidate active galactic nucleus.We show that real events such as GRBs exist within the INTEGRAL Burst Alert System (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.