Letter to the Editor

Timing diagrams and correlations in gamma-ray bursts signal jets from accretion into black holes

Department of Experimental Physics, University College Dublin, Dublin 4, Ireland

Corresponding author: S. McBreen, smcbreen@bermuda.ucd.ie

Received: 22 October 2001
Accepted: 10 December 2001

Abstract

The temporal properties of a sample of 498 bright gamma-ray bursts (GRBs) with durations between 0.05 s and 674 s were analysed. The large range in duration (T₉₀) is accompanied by a similarly large range in the median values of the pulse timing properties including rise time, fall time, FWHM and separation between the pulses. Four timing diagrams relating these pulse properties to T₉₀ are presented and show the power law relationships between the median values of the 4 pulse timing properties and T₉₀, but also that the power laws depend in a consistent manner on the number of pulses per GRB. The timing diagrams are caused by the correlated properties of the pulses in the burst and can be explained by a combination of factors including the Doppler boost factor Γ, a viewing effect caused by a jet and different progenitors. GRBs with similar values of T₉₀ have a wide range in the number of pulses. GRBs with the large number of short and spectrally hard pulses may occur either from a homogeneous jet with a higher average value of Γ or close to the axis of an inhomogeneous jet with higher values of Γ near the rotation axis. The less luminous GRBs with fewer pulses may originate further from the axis of the inhomogeneous jet. The pulses in GRBs have six distinctive statistical properties including correlations between time intervals, correlations between pulse amplitudes, an anticorrelation between pulse amplitudes and time intervals, and a link to intermittency in GRS 1915+105. The timing diagrams and correlated pulses suggest that GRBs are powered by accretion processes signalling jets from the formation of black holes.