A 50 s quasi-periodic oscillation in the early X-ray afterglow of GRB 220711B

TL;DR

This paper reports a 50-second quasi-periodic oscillation in the early X-ray afterglow of GRB 220711B, suggesting jet precession from a hyper-accreting black hole and proposing a new formation channel involving stellar mergers.

Contribution

It provides the first evidence of a low-frequency QPO in GRB afterglow, linking it to jet precession and proposing a novel progenitor scenario involving stellar mergers.

Findings

Detection of a 0.02 Hz QPO in early X-ray afterglow.

QPO likely caused by jet precession from a hyper-accreting black hole.

Proposes a new GRB formation channel involving stellar mergers.

Abstract

It is generally believed that long duration gamma-ray bursts (GRBs) originate from the core collapse of rapidly spinning massive stars and at least some of them are powered by hyper-accreting black holes. However, definite proofs about the progenitor and central engine of these GRBs have not been directly observed in the past. Here we report the existence of a Quasi-Periodic Oscillation (QPO) signature with periodic frequency $\sim$0.02 Hz in the early X-ray afterglow phase of GRB 220711B. Such a low-frequency QPO likely signals the precession of a relativistic jet launched from a GRB hyper-accreting black hole central engine. The energy injection signature from the \textbf{late} X-ray observations (from $5\times 10^2s\sim 1\times10^4s$) is consistent with the precession hypothesis. The prompt $\gamma$-ray light curve does not show any QPO signature, suggesting that the X-ray flaring emission in the early afterglow phase and prompt emission likely originate from different accretion processess, indicating that the progenitor stars of GRBs have a core-envelope structure with a stratified angular momentum distribution and the late-time accretion disk likely has a misalignment with respect to the rotation axis of the black hole. Such a misalignment is not expected in a canonical collapsar model. As a result, the QPO signature in GRB 220711B may reveal a new formation channel of long GRBs, possibly a stellar-merger-induced core collapse, with the orbital angular momentum of the binary misaligned with the spin axis of the collapsing star.