The Second Plateau in X-ray Afterglow Providing Additional Evidence for Rapidly Spinning Magnetars as the GRB Central Engine

Abstract

Evidence for the central engine of gamma-ray bursts (GRBs) has been collected in the Neil Gehrels \emph{Swift} data. For instance, some GRBs show an internal X-ray plateau followed by very steep decay, which is difficult to be interpreted within the framework of a black hole (BH) central engine, but are consistent within a rapidly spinning magnetar engine picture. The very steep decay at the end of the plateau suggests a sudden cessation of the central engine, which is explained as the collapse of a supra-massive magnetar into a black hole when it spins down. Here we propose that some additional evidence, such as a second X-ray plateau feature would show up, if the fall-back accretion could activate the newborn BH and sufficient energy could be transferred from the newborn BH to the GRB blast wave. With a systematic data analysis for all long GRBs, we find three candidates in \emph{Swift} sample, i.e., GRBs 070802, 090111, and 120213A, whose X-ray afterglow light curves contain two plateaus, with the first one being an internal plateau. We find that in a fairly loose and reasonable parameter space, the second X-ray plateau data for all 3 GRBs could be well interpreted with our proposed model. Future observations are likely to discover more similar events, which could offer more information of the properties of the magnetar as well as the newborn BH.

accepted for publication by ApJ

References in corpus (14)

• An online repository of Swift/XRT light curves of GRBs
• X-Ray Flares from Postmerger Millisecond Pulsars
• A Comprehensive Analysis of the Swift/XRT Data: II. Diverse Physical Origins of the Shallow Decay Segment
• The Millisecond Magnetar Central Engine in short GRBs
• Fallback and Black Hole Production in Massive Stars
• Mass Fall-back and Accretion in the Central Engine of Gamma-Ray Bursts
• Hyper-accreting black hole as GRB central engine. I: Baryon loading in GRB jets
• Properties of Gamma-Ray Burst Progenitor Stars
• Giant X-ray Bump in GRB 121027A: Evidence for Fall-back Disk Accretion
• Hyperaccreting Black Hole as Gamma-Ray Burst Central Engine. II. Temporal evolution of central engine parameters during Prompt and Afterglow Phases
• Hyperaccreting Neutron-Star Disks and Neutrino Annihilation
• Black hole hyperaccretion inflow-outflow model. I. long and ultra-long gamma-ray bursts
• Signature of a New-Born Black Hole from the Collapse of a Supra-massive Millisecond Magnetar
• Constraints on Gamma-ray Burst Inner Engines in a Blandford-Znajek Framework

Cited by in corpus (7)

• Science objectives of the Einstein Probe mission
• Closure relations during the plateau emission of Swift GRBs and the fundamental plane
• Identifying Black Hole Central Engines in Gamma-Ray Bursts
• Giant X-ray and optical Bump in GRBs: evidence for fall-back accretion model
• GRB 171205A: Hypernova and Newborn Neutron Star
• A Possible kilonova powered by magnetic wind from a newborn black hole
• The evolution effects of radius and moment of inertia for rapidly rotating neutron stars