Prompt Periodicity in the GRB 211211A Precursor: Black-hole or magnetar engine?

Lamb, GP, Baxter, T, Omand, CMB, Dimple, McGrath, Z, Turnbull, C, Burns, E, Hamidani, H, Mandel, I, Page, KL, Rosswog, S, Sarin, N, Blain, A, Datrier, L, Kobayashi, S, Levan, A, Starling, R, Gompertz, B, Habeeb, N, Nguyen, K et al (2025) Prompt Periodicity in the GRB 211211A Precursor: Black-hole or magnetar engine? Monthly Notices of the Royal Astronomical Society, 450 (3). ISSN 0035-8711

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Abstract

The merger origin long GRB 211211A was a class (re-)defining event. A precursor was identified with a ∼1 s separation from the main burst, as well as a claimed candidate quasi-periodic oscillation (QPO) with a frequency ∼20 Hz. Here, we explore the implications of the precursor, assuming the quasi-periodicity is real. The precursor variability timescale requires relativistic motion with a Lorentz factor Γ ≳ 80, and implies an engine driven jetted outflow. The declining amplitude of the consecutive pulses requires an episodic engine with an ‘on/off’ cycle consistent with the QPO. For a black-hole central engine, the QPO can have its origin in Lense-Thirring precession of the inner disk at ∼6 − 9 rg (gravitational radii) for a mass M• ≤ 4.5 M⊙, and ≲ 7 rg for M• > 4.5 M⊙ and dimensionless spin χ ∼ 0.3 − 0.9. Alternatively, at a disk density of ∼108 − 12 g cm−3, the required magnetic field strength for a QPO via magnetohydrodynamic effects will be on the order B ∼ 1012 − 14 G. If the central engine is a short lived magnetar or hypermassive neutron star, then a low-frequency QPO can be produced via instabilities within the disk at a radius of ∼20 − 70 km, for a disk density ∼109 − 12 g cm−3 and magnetic field ≳ 1013 − 14 G. The QPO cannot be coupled to the neutron star spin, as the co-rotation radius is beyond the scale of the disk. Neither engine can be ruled out – however, we favour an origin for the precursor candidate QPO as early jet-disk coupling for a neutron star – black hole merger remnant with mass M• > 4.5 M⊙.

Item Type:	Article
Uncontrolled Keywords:	5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press (OUP)
Date of acceptance:	29 May 2025
Date of first compliant Open Access:	13 June 2025
Date Deposited:	13 Jun 2025 13:08
Last Modified:	13 Jun 2025 13:15
DOI or ID number:	10.1093/mnras/staf892
URI:	https://researchonline.ljmu.ac.uk/id/eprint/26585

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