# The discovery of weak coherent pulsations in the ultraluminous X-ray source NGC 1313 X-2

## TL;DR

This paper reports the discovery of weak, sinusoidal X-ray pulsations from the ultraluminous X-ray source NGC 1313 X-2, providing evidence for a neutron star accretor and insights into its magnetic field and accretion processes.

## Contribution

First detection of weak pulsations in NGC 1313 X-2, supporting neutron star models for ULXs and suggesting strong winds or jets are involved in accretion.

## Key findings

- Pulsation period of ~1.5 seconds with 5% pulsed fraction.
- Detections unlikely due to false noise, confirmed by simulations.
- Implications for neutron star magnetic field and accretion history.

## Abstract

We report the detection of weak pulsations from the archetypal ultraluminous X-ray source (ULX) NGC 1313 X-2. Acceleration searches reveal sinusoidal pulsations in segments of two out of six new deep observations of this object, with a period of $\sim$ 1.5 s and a pulsed fraction of $\sim$ 5%. We use Monte Carlo simulations to demonstrate that the individual detections are unlikely to originate in false Poisson noise detections given their very close frequencies; their strong similarity to other pulsations detected from ULXs also argues they are real. The presence of a large bubble nebula surrounding NGC 1313 X-2 implies an age of order 1 Myr for the accreting phase of the ULX, which implies that the neutron star's magnetic field has not been suppressed over time by accreted material, nor has the neutron star collapsed into a black hole, despite an average energy output into the nebula two orders of magnitude above Eddington. This argues that most of the accreted material has been expelled over the lifetime of the ULX, favouring physical models including strong winds and/or jets for neutron star ULXs.