Interpreting the X-ray afterglows of gamma-ray bursts with radiative losses and millisecond magnetars

• Published in: Monthly notices of the Royal Astronomical Society Vol. 499; no. 4; pp. 5986 - 5992
• Main Authors: Sarin, Nikhil, Lasky, Paul D, Ashton, Gregory
• Format: Journal Article
• Language: English
• Published: Oxford University Press 01.12.2020
• Subjects: gamma-ray burst: general; gamma-ray bursts
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/staa3090

ABSTRACT The spin-down energy of millisecond magnetars has been invoked to explain X-ray afterglow observations of a significant fraction of short and long gamma-ray bursts. Here, we extend models previously introduced in the literature, incorporating radiative losses with the spin-down of a magnetar central engine through an arbitrary braking index. Combining this with a model for the tail of the prompt emission, we show that our model can better explain the data than millisecond-magnetar models without radiative losses or those that invoke spin-down solely through vacuum dipole radiation. We find that our model predicts a subset of X-ray flares seen in some gamma-ray bursts. We can further explain the diversity of X-ray plateaus by altering the radiative efficiency and measure the braking index of newly born millisecond magnetars. We measure the braking index of GRB061121 as $n=4.85^{+0.11}_{-0.15}$ suggesting the millisecond-magnetar born in this gamma-ray burst spins down predominantly through gravitational-wave emission.