# Cyclotron emission, absorption, and the two faces of X-ray pulsar A 0535+262

## TL;DR

This study analyzes a low-luminosity observation of X-ray pulsar A 0535+262, revealing two spectral components and providing new measurements of cyclotron line energy, challenging previous correlations with accretion rate.

## Contribution

It presents the first detection of cyclotron emission at very low luminosity and measures the cyclotron line energy at an unprecedented low luminosity level.

## Key findings

- Cyclotron line energy measured at 47.7 keV at low luminosity.
- No positive correlation between cyclotron energy and accretion rate.
- Identification of a second spectral component as cyclotron emission.

## Abstract

Deep NuSTAR observation of X-ray pulsar A 0535+262, performed at a very low luminosity of $\sim7\times10^{34}$ erg s$^{-1}$, revealed the presence of two spectral components. We argue that the high-energy component is associated with cyclotron emission from recombination of electrons collisionally excited to the upper Landau levels. The cyclotron line energy of $E_{\rm cyc}=47.7\pm0.8$ keV was measured at the luminosity of almost an order of magnitude lower than what was achieved before. The data firmly exclude a positive correlation of the cyclotron energy with the mass accretion rate in this source.