NuSTAR Analysis of the 2024 Periastron Passage of TeV Binary PSR B1259-63

TL;DR

This paper reports NuSTAR X-ray observations of the TeV binary PSR B1259-63 during its 2024 periastron passage, revealing the most energetic spectrum around 27 days post-periastron and discussing flux variability and spectral hardening.

Contribution

It provides new NuSTAR observational data during the 2024 periastron, highlighting spectral changes and variability in the X-ray emission of PSR B1259-63.

Findings

Spectral photon index $\Gamma$ = 1.5 around 27 days post-periastron

Detection of variable, short-term X-ray emission episodes

Spectral hardening correlated with flux variability

Abstract

PSR B1259-63 is a well studied TeV binary, with an energetic pulsar in orbit around a Be star. Using NuSTAR observations during the 2024 passage of the pulsar through the circumstellar disk, we find the spectrum to be the most energetic ($\Gamma$ = 1.5) around 27 days after periastron, during the first of two variable, short-term emission episodes of a contemporaneous GeV flare. We discuss the variability in the X-ray flux and the hardening of the spectrum with time, and in the context of previous observations and what that means for the competing energy loss and acceleration timescales.