Does the Gamma-Ray Binary LS I + 61°303 Harbor a Magnetar?

• Published in: The Astrophysical journal Vol. 940; no. 2; pp. 128 - 138
• Main Authors: Suvorov, Arthur G., Glampedakis, Kostas
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.12.2022; IOP Publishing
• Subjects: Accretion; Astrophysics; Deceleration; Deposition; Evolution; Field strength; Gamma emission; Gamma rays; Magnetars; Magnetic dipoles; Magnetic fields; Neutron stars; Outbursts; Pulsars; Spin dynamics; Torque; X ray binaries; X ray stars
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac9b48

Abstract The high-mass X-ray binary LS I + 61°303 is also cataloged as a gamma-ray binary as a result of frequent outbursts at TeV photon energies. The system has released two soft-gamma flares in the past, suggesting a magnetar interpretation for the compact primary. This inference has recently gained significant traction following the discovery of transient radio pulses, detected in some orbital phases from the system, as the measured rotation and tentative spin-down rates imply a polar magnetic field strength of B p ≳ 10 14 G if the star is decelerating via magnetic dipole braking. In this paper, we scrutinize magnetic field estimates for the primary in LS I + 61°303 by analyzing the compatibility of available data with the system’s accretion dynamics, spin evolution, age limits, gamma-ray emissions, and radio pulsar activation. We find that the neutron star’s age and spin evolution are theoretically difficult to reconcile unless a strong propeller torque is in operation. This torque could be responsible for the bulk of even the maximum allowed spin-down, potentially weakening the inferred magnetic field by more than an order of magnitude.