# Evolution of the extended X-ray emission from the PSR B1259-63/LS 2883 binary in the 2014-2017 binary cycle

## TL;DR

This study tracks the evolution of extended X-ray emission from the binary system PSR B1259-63/LS 2883 over multiple years, revealing accelerated ejecta and synchrotron emission consistent with pulsar wind interactions.

## Contribution

First detailed multi-epoch X-ray observations of the extended emission in PSR B1259-63/LS 2883, showing acceleration and providing insights into pulsar wind interactions.

## Key findings

- The X-ray clump is accelerated to about 0.15c.
- The clump's X-ray emission is consistent with synchrotron radiation.
- Hubble observations set an upper limit on optical flux.

## Abstract

We have performed a series of Chandra X-ray Observatory observations of the gamma-ray binary LS 2883, which is comprised of a young pulsar (PSR B1259-63) orbiting a massive Be star with a period of 1236.7 days. The system was observed in 5 epochs, spanning a range from 352 to 1175 days after the periastron passage on 2014 May 4. The observations confirmed the recurrent nature of the high-speed ejecta that appear as an extended X-ray structure (clump) moving away from the binary. Compared to the results of the previous monitoring campaign (between the 2010 and 2014 periastron passages), this time we find evidence suggesting that the clump is accelerated to a projected velocity $ v_{\perp}\approx0.15c$ with an acceleration $a_{\perp}=47\pm2$ cm s$^{-2}$ (for uniformly accelerated motion), assuming that it was launched near periastron passage. The observed X-ray properties of the clump are consistent with synchrotron emission from pulsar wind particles accelerated at the interface between the pulsar wind and the clump. We have also performed contemporaneous observations with the {\sl Hubble Space Telescope}, which are used to set an upper limit on the optical flux of the extended emission.