# A possible origin of the Galactic Center magnetar SGR 1745-2900

## TL;DR

This paper proposes that the Galactic Center magnetar SGR 1745-2900 may originate from accreting neutron stars in intermediate-mass X-ray binaries, which undergo magnetic field amplification and dynamical interactions in dense stellar environments.

## Contribution

It introduces a model linking IMXBs with neutron star magnetic field amplification to the formation of GC magnetars and millisecond pulsars, highlighting the role of stellar encounters.

## Key findings

- Magnetic fields can be amplified within 1 Myr in accreting NSs with elastic crusts.
- Dynamical encounters in the GC can produce single NSs from NS binaries.
- The model explains the origin of the GC magnetar SGR 1745-2900.

## Abstract

Since a large population of massive O/B stars and putative neutron stars (NSs) located in the vicinity of the Galactic center (GC), intermediate-mass X-ray binaries (IMXBs) constituted by a NS and a B-type star probably exist here. We investigate the evolutions of accreting NSs in IMXBs (similar to M82 X-2) with a $\sim5.2M_\odot$ companion, and orbit period $\simeq2.53$ day. By adopting an mildly super-Eddington rate $\dot{M}=6\times10^{-8}M_\odot~{\rm yr}^{-1}$ for the early Case B Roche-lobe overflow (RLOF) accretion, we find only in accreting NSs with quite elastic crusts (slippage factor $s=0.05$), the toroidal magnetic fields can be amplified within 1 Myrs, which is assumed to be the longest duration of the RLOF. These IMXBs will evolve into NS+white dwarf (WD) binaries if they are dynamical stable. However, before the formation of NS+WD binaries, the high stellar density in the GC will probably lead to frequent encounters between the NS+evolved star binaries (in post-early Case B mass transfer phase) and NSs or exchange encounters with other stars, which may produce single NSs. These NSs will evolve into magnetars when the amplified poloidal magnetic fields diffuse out to the NS surfaces. Consequently, our results provide a possible explanation for the origin of the GC magnetar SGR 1745-2900. Moreover, the accreting NSs with $s>0.05$ will evolve into millisecond pulsars (MSPs). Therefore, our model reveals the GC magnetars and MSPs could both originate from the special kind of IMXBs.