X-ray spectral properties of the pulsar EXO 2030+375 during an outburst

Abstract

We present the results of the spectral analysis carried out of the X-ray pulsar EXO 2030+375. The observations were made using the Rossi X-ray Timing Explorer (RXTE) satellite. Our study concentrates on the X-ray characteristics of this source at lower luminosities (Lx < 5 x1036 erg s-1) than have previously been observed and in the energy range 2.7-30 keV. The PCA X-ray continuum spectra can be represented by a model containing two components: a power law with an exponential cut-off at higher energies and a blackbody. The power-law component accounts for the high-energy part of the continuum whereas the blackbody component describes the part of the spectrum below ∼ 10 keV. The radius of the X-ray emission surface is found to be ∼ 1 km, which agrees with the size of the neutron star polar caps. Our results are compared with higher-luminosity studies and are seen to agree with trends observed in these previous findings. We also show the first hard X-ray spectrum (17-65 keV) of EXO 2030+375. A possible spectral feature at ∼ 36 keV is tentatively ascribed to a cyclotron absorption line.