Bibcode
Muñoz-Darias, T.; de Ugarte Postigo, A.; Casares, J.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society: Letters, Volume 458, Issue 1, p.L114-L117
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5
2016
Citations
5
Refereed citations
4
Description
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.