# The X-ray Pulsar 2A 1822-371 as a Super Eddington source

## TL;DR

This study suggests that the X-ray pulsar 2A 1822-371 is a mildly super-Eddington source with a stable spin-up, challenging previous models and indicating it could evolve into a millisecond pulsar soon.

## Contribution

The paper proposes a new model for 2A 1822-371 involving a thin accretion outflow and a super-Eddington transfer rate, revising previous assumptions about its corona and geometry.

## Key findings

- No thick corona needed in the model
- System is likely a mildly super-Eddington source
- Stable spin-up observed over 13 years

## Abstract

The low mass X-ray binary 2A 1822-371 is an eclipsing system with an accretion disc corona and with an orbital period of 5.57 hr. The primary is an 0.59 s X-ray pulsar with a proposed strong magnetic field of 10^10-10^12 G. In this paper we study the spin evolution of the pulsar and constrain the geometry of the system. We find that, contrary to previous claims, a thick corona is not required, and that the system characteristics could be best explained by a thin accretion outflow due to a super-Eddington mass transfer rate and a geometrically thick inner accretion flow. The orbital, spectral and timing observations can be reconciled in this scenario under the assumption that the mass transfer proceeds on a thermal timescale which would make 2A 1822-371, a mildly super-Eddington source viewed at high inclination angles. The timing analysis on 13 years of RXTE data show a remarkably stable spin-up that implies that 2A 1822-371, might quickly turn into a millisecond pulsar in the next few thousand years.