# Swift, XMM-Newton, and NuSTAR observations of PSR J2032+4127/MT91 213

## TL;DR

This paper presents multi-instrument X-ray and optical observations of the gamma-ray binary PSR J2032+4127/MT91 213, revealing variable X-ray activity and environmental interactions that inform predictions of its 2017 periastron outburst.

## Contribution

It provides new observational insights into the variability and environment of PSR J2032+4127, aiding understanding of its behavior during periastron.

## Key findings

- X-ray brightness increased by a factor of ~10 since 2013
- Detected multiple X-ray flares with a slowly increasing baseline
- Flares associated with denser environment and softer spectra during flaring state

## Abstract

We report our recent Swift, NuSTAR, and XMM-Newton X-ray and Lijiang optical observations on PSR J2032+4127/MT91 213, the gamma-ray binary candidate with a period of 45-50 years. The coming periastron of the system was predicted to be in November 2017, around which high-energy flares from keV to TeV are expected. Recent studies with Chandra and Swift X-ray observations taken in 2015/16 showed that its X-ray emission has been brighter by a factors of ~10 than that before 2013, probably revealing some on-going activities between the pulsar wind and the stellar wind. Our new Swift/XRT lightcurve shows no strong evidence of a single vigorous brightening trend, but rather several strong X-ray flares on weekly to monthly timescales with a slowly brightening baseline, namely the low state. The NuSTAR and XMM-Newton observations taken during the flaring and the low states, respectively, show a denser environment and a softer power-law index during the flaring state, implying that the pulsar wind interacted with stronger stellar winds of the companion to produce the flares. These precursors would be crucial in studying the predicted giant outburst from this extreme gamma-ray binary during the periastron passage in late 2017.