Publication Date:
2016-01-22
Description:
We report the results of a spectral and timing analysis of the poorly studied transient X-ray pulsar 2S 1553–542 using data collected with the NuSTAR and Chandra observatories and the Fermi /GBM instrument during an outburst in 2015. The properties of the source at high energies (〉30 keV) are studied for the first time and the sky position has been essentially improved. The source broad-band spectrum has a quite complicated shape and can be reasonably described by a composite model with two continuum components – a blackbody emission with the temperature about 1 keV at low energies and a power law with an exponential cut-off at high energies. Additionally, an absorption feature at ~23.5 keV is discovered both in phase-averaged and phase-resolved spectra and interpreted as the cyclotron resonance scattering feature corresponding to the magnetic field strength of the neutron star B ~ 3 x 10 12 G. Based on the Fermi /GBM data, the orbital parameters of the system were substantially improved, which allowed us to determine the spin period of the neutron star P = 9.27880(3) s and a local spin-up $\dot{P} \simeq -7.5 \times 10^{-10}$ s s –1 due to the mass accretion during the NuSTAR observations. Assuming accretion from the disc and using standard torque models, we estimated the distance to the system as d = 20 ± 4 kpc.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
