Outstanding X-ray emission from the stellar radio pulsar CU Virginis

TL;DR

This paper reports on the unusually strong and hard X-ray emission from the star CU Virginis, suggesting a persistent magnetospheric or auroral origin beyond standard stellar models.

Contribution

It provides detailed X-ray spectral analysis of CU Virginis, revealing persistent, hard X-ray emission that challenges existing explanations and proposes magnetospheric or auroral mechanisms.

Findings

X-ray luminosity of 3 x 10^28 erg/s with a very hard spectrum

Spectral modeling indicates hot plasma at about 25 MK or nonthermal components

X-ray emission remains steady over six years, suggesting a persistent source

Abstract

We present X-ray observations of CU Vir performed with XMM-Newton and Chandra. With Lx = 3 x 10^28 erg/s the source is moderately X-ray bright, but its spectrum is extremely hard compared to other Ap stars. Spectral modelling requires multi-component models with predominant hot plasma at temperatures of about Tx = 25 MK or, alternatively, a nonthermal spectral component. The Chandra observations was performed six years later than the one by XMM-Newton, yet the source has similar X-ray flux and spectrum, suggesting a steady and persistent X-ray emission. To explain its full X-ray properties, a generating mechanism beyond standard explanations like the presence of a low-mass companion or magnetically confined wind-shocks is required. Magnetospheric activity might be present or, as proposed for fast rotating strongly magnetic Bp stars, the X-ray emission of CU Vir is predominantly auroral in nature.