# Super-Eddington accretion onto the Galactic ultraluminous X-ray pulsar Swift J0243.6+6124

## TL;DR

This study analyzes the spectral behavior of the first Galactic ultraluminous X-ray pulsar Swift J0243.6+6124 during its 2017-2018 outburst, revealing super-Eddington accretion features, wind formation, and spectral component changes.

## Contribution

It provides the first detailed spectral analysis of a Galactic ULX pulsar during super-Eddington accretion, highlighting the presence of optically-thick outflows and wind signatures.

## Key findings

- Super-Eddington accretion powers massive winds.
- Blackbody components saturate at the neutron star's Eddington luminosity.
- Iron line becomes more significant and blueshifted at high accretion rates.

## Abstract

We report on the spectral behavior of the first Galactic ultraluminous X-ray pulsar Swift J0243.6+6124 with NuSTAR observations during its 2017-2018 outburst. At sub-Eddington levels, the source spectrum is characterized by three emission components, respectively from the accretion column, the hot spot, and a broad iron line emission region. When the source is above the Eddington limit, the hot spot temperature increases and the spectrum features two more blackbody components. One blackbody component has a radius of 10-20 km and is likely originated from the top of the accretion column. The other one saturates at a blackbody luminosity of (1 - 2)*10^38 erg/s, coincident with the Eddington limit of a neutron star. This is well consistent with the scenario that super-Eddington accretion onto compact objects will power optically-thick outflows and indicates an accretion rate 60-80 times the critical value. This suggests that super-Eddington accretion onto magnetized systems can also power massive winds. At super-Eddington levels, the iron line becomes more significant and blueshifted, and is argued to be associated with the ultrafast wind in the central funnel or jets. This source, if located in external galaxies, will appear like other ultraluminous pulsars.