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arXiv · 2302.08170

Evidence for non-thermal X-ray emission from the double WR colliding-wind binary Apep

S. del Palacio·F. García·M. De Becker·D. Altamirano·V. Bosch-Ramon·P. Benaglia·B. Marcote·G. E. Romero
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Abstract

Context: Massive colliding-wind binaries (CWBs) can be non-thermal sources. The emission produced in their wind-collision region (WCR) encodes information of both the shocks properties and the relativistic electrons accelerated in them. The recently discovered system Apep, a unique massive system hosting two Wolf-Rayet stars, is the most powerful synchrotron radio emitter among the known CWBs, being an exciting candidate to investigate the non-thermal processes associated with stellar wind shocks. Aims: We intend to break the degeneracy between the relativistic particle population and the magnetic field strength in the WCR of Apep by probing its hard X-ray spectrum, where inverse-Compton (IC) emission is expected to dominate. Methods: We observe Apep with NuSTAR for 60 ks and combine this with a re-analysis of a deep archival XMM-Newton observation to better constrain the X-ray spectrum. We use a non-thermal emission model to derive physical parameters from the results. Results: We detect hard X-ray emission consistent with a power-law component. This is compatible with IC emission produced in the WCR for a magnetic field of 100-160 mG and a fraction of ~1.5e-4 of the total wind kinetic power being converted into relativistic electron acceleration. Conclusions: This is the first time that the non-thermal emission from a CWB is detected both in radio and high energies. This allows us to derive the most robust constraints of the particle acceleration efficiency and magnetic field intensity in a CWB so far, reducing the typical uncertainty of a few orders of magnitude to just within a factor of two. This constitutes an important step forward in our characterisation of the physical properties of CWBs.

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S. del Palacio, F. García, M. De Becker, D. Altamirano, V. Bosch-Ramon, P. Benaglia, B. Marcote, G. E. Romero. 2023-02-16. Evidence for non-thermal X-ray emission from the double WR colliding-wind binary Apep. https://doi.org/10.1051/0004-6361/202245505

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