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Large-scale Evolution of Seconds-long Relativistic Jets from Black Hole–Neutron Star Mergers
- Source :
- The Astrophysical Journal Letters, Vol 954, Iss 1, p L21 (2023)
- Publication Year :
- 2023
- Publisher :
- IOP Publishing, 2023.
-
Abstract
- We present the first numerical simulations that track the evolution of a black hole–neutron star (BH–NS) merger from premerger to r ≳ 10 ^11 cm. The disk that forms after a merger of mass ratio q = 2 ejects massive disk winds (3–5 × 10 ^−2 M _⊙ ). We introduce various postmerger magnetic configurations and find that initial poloidal fields lead to jet launching shortly after the merger. The jet maintains a constant power due to the constancy of the large-scale BH magnetic flux until the disk becomes magnetically arrested (MAD), where the jet power falls off as L _j ∼ t ^−2 . All jets inevitably exhibit either excessive luminosity due to rapid MAD activation when the accretion rate is high or excessive duration due to delayed MAD activation compared to typical short gamma-ray bursts (sGRBs). This provides a natural explanation for long sGRBs such as GRB 211211A but also raises a fundamental challenge to our understanding of jet formation in binary mergers. One possible implication is the necessity of higher binary mass ratios or moderate BH spins to launch typical sGRB jets. For postmerger disks with a toroidal magnetic field, dynamo processes delay jet launching such that the jets break out of the disk winds after several seconds. We show for the first time that sGRB jets with initial magnetization σ _0 > 100 retain significant magnetization ( σ ≫ 1) at r > 10 ^10 cm, emphasizing the importance of magnetic processes in the prompt emission. The jet–wind interaction leads to a power-law angular energy distribution by inflating an energetic cocoon whose emission is studied in a companion paper.
Details
- Language :
- English
- ISSN :
- 20418213 and 20418205
- Volume :
- 954
- Issue :
- 1
- Database :
- Directory of Open Access Journals
- Journal :
- The Astrophysical Journal Letters
- Publication Type :
- Academic Journal
- Accession number :
- edsdoj.fed61236d19496ebac054b27eaa86e5
- Document Type :
- article
- Full Text :
- https://doi.org/10.3847/2041-8213/aceeff