SPS Seminar - The emerging class of ultra-long gamma-ray bursts: GRB 121027A

When:  Thursday 5^th March at 14.30 (coffee available from 14.00)

Where:  Robert Hooke Seminar Room

Speaker:  Rhaana Starling – University of Leicester

Hosted by:  Beatriz Mingo & John Bray

Abstract:

Gamma-ray bursts (GRBs) are transient astrophysical events that signal the death of a massive star, or the merger of two compact objects. Typical GRBs begin with one or more flares at gamma-ray energies and transition to a steady decline in brightness, an afterglow, at lower energies and both of these emission episodes likely originate in a relativistic outflow from the central engine.

A new class of transient, the ultralong gamma-ray bursts (ULGRBs), was proposed following the Swift satellite detection throughout 2010-2013 of three new transients active for thousands of seconds at gamma-ray energies and with afterglows as luminous as typical GRBs.

The puzzle of either sustaining the injection of energy into the jet, or reactivating the central engine, has occupied the field since the observations of bursts with precursors, X-ray plateau phases and late-time X-ray flares. Ultralong GRBs bring new information to this problem.

Ideas to generate such long-lasting emission include the collapse of a larger progenitor star than those thought responsible for classical long GRBs, while other studies looked at mechanisms that could combine with a classical GRB scenario such as late-time energy injection from fall-back material.

The definition of a ULGRB must currently be restricted to its initial gamma-ray and subsequent early X-ray characteristics. New facilities such as SVOM and THESEUS will have lower energy triggering capability, bringing more examples and potentially revealing the extent of the ultralong population. Wide-field monitoring and prompt optical and radio observations will plug gaps in the spectral coverage, required to understand energy generation mechanisms and constrain the progenitors.

Here I will present multiwavelength data of GRB 121027A, in the context of ultralong-duration GRB origins.