The featureless and non-variable optical spectral energy distribution of AXP 4U 0142+61

DOI: 
10.1093/mnrasl/slw024
Publication date: 
01/05/2016
Main author: 
Muñoz-Darias, T.
IAA authors: 
de Ugarte Postigo, A.
Authors: 
Muñoz-Darias, T.;de Ugarte Postigo, A.;Casares, J.
Journal: 
Monthly Notices of the Royal Astronomical Society
Publication type: 
Article
Volume: 
458
Pages: 
L114-L117
Abstract: 
We present GTC-10.4 m spectroscopy and multiband photometry of the faint (r ̃ 26) optical counterpart of the anomalous X-ray pulsar 4U 0142+61. The 5000-9000 Å spectrum - the first obtained for a magnetar - is featureless, allowing us to set an equivalent width upper limit EW 〈 25 Å to the presence of emission lines in the H α region. Multiband photometry in the g, r, i, z Sloan Digital Sky Survey (SDSS) bands obtained at different epochs over 12 yr shows no significant variability from minutes-to-years time-scales. The photometry has been calibrated, for the first time, against the SDSS itself, resulting in solid upper limits to variability ranging from ̃0.2 mag in i (over 12 yr) to 0.05 mag in z (over 1.5 yr). The shape of the optical + near-infrared (literature values) spectral energy distribution is not well constrained due to the high extinction along the line of sight. Using a Markov Chain Monte Carlo analysis, we find that it can be described by a power law with a spectral index β = -0.7 ± 0.5 and E(B - V) = 1.5 ± 0.4. We also discuss on the implications of adding hard X-ray flux values from literature to the spectral fitting.
Database: 
ADS
SCOPUS
WOK
SCOPUS
URL: 
https://ui.adsabs.harvard.edu/#abs/2016MNRAS.458L.114M/abstract
ADS Bibcode: 
2016MNRAS.458L.114M
Keywords: 
stars: magnetars;stars: neutron;pulsars: individual: 4U 0142+61;Astrophysics - High Energy Astrophysical Phenomena;Astrophysics - Solar and Stellar Astrophysics