NuSTAR Hard X-ray Observation of the Gamma-ray Binary Candidate HESS J1832-093

TL;DR

This study uses NuSTAR to observe the gamma-ray binary candidate HESS J1832-093, revealing non-thermal X-ray emission consistent with a non-accreting pulsar wind shock, and provides insights into its long-term flux and potential supernova remnant interactions.

Contribution

First hard X-ray detection of HESS J1832-093 with NuSTAR, supporting a non-accreting pulsar wind scenario and analyzing long-term flux variability and nearby sources.

Findings

Non-thermal X-ray emission detected up to ~30 keV.

Long-term X-ray flux increased by ~50%.

No pulsar period or binary modulation detected.

Abstract

We present a hard X-ray observation of the TeV gamma-ray binary candidate HESS J1832-093 coincident with supernova remnant (SNR) G22.7-0.2 using the Nuclear Spectroscopic Telescope Array (NuSTAR). Non-thermal X-ray emission from XMMU J183245-0921539, the X-ray source associated with HESS J1832-093, is detected up to ~30 keV and is well-described by an absorbed power-law model with the best-fit photon index $\Gamma = 1.5\pm0.1$. A re-analysis of archival Chandra and XMM-Newton data finds that the long-term X-ray flux increase of XMMU J183245-0921539 is $50^{+40}_{-20}$% (90% C.L.), much less than previously reported. A search for a pulsar spin period or binary orbit modulation yields no significant signal to a pulse fraction limit of fp < 19% in the range 4 ms < P < 40 ks. No red noise is detected in the FFT power spectrum to suggest active accretion from a binary system. While further evidence is required, we argue that the X-ray and gamma-ray properties of XMMU J183245-0921539 are most consistent with a non-accreting binary generating synchrotron X- rays from particle acceleration in the shock formed as a result of the pulsar and stellar wind collision. We also report on three nearby hard X-ray sources, one of which may be associated with diffuse emission from a fast-moving supernova fragment interacting with a dense molecular cloud.