# All at once: transient pulsations, spin down and a glitch from the Pulsating Ultraluminous X-ray Source M82 X-2

## TL;DR

This paper reports the first detection of spin down and a glitch in the pulsating ultraluminous X-ray source M82 X-2, providing new insights into its timing behavior and challenging existing models.

## Contribution

It presents the first observation of spin down and a glitch in a PULX, refining orbital parameters and expanding understanding of PULX timing properties.

## Key findings

- Detected a spin down rate of 5x10^-11 Hz/s between 2014-2016
- Identified the first positive glitch in a PULX system
- Refined the orbital period of M82 X-2

## Abstract

M82 X-2 is the first pulsating ultraluminous X-ray source (PULX)to be identified. Since the discovery in 2014, NuSTAR has observed the M82 field 15 times throughout 2015 and 2016. In this paper, we report the results of pulsation searches in all these datasets, and find only one new detection. This new detection allows us to refine the orbital period of the source and measure an average spin down rate between 2014 and 2016 of 5x10^-11 Hz/s, which is in contrast to the strong spin up seen during the 2014 observations and represent the first detection of spin down in a PULX system. Thanks to the improved orbital solution allowed by this new detection, we are also able to detect pulsations in additional segments of the original 2014 dataset. We find a glitch superimposed on the very strong and variable spin-up already reported, the first positive glitch identified in a PULX system. We discuss the new findings in the context of current leading models for PULXs.