paper

Spectroscopic classification, variability and SED of the Fermi-detected CSS 3C 286: the radio-loudest NLS1 galaxy?

arXiv:2012.01785 · doi:10.1093/mnras/staa3708

Abstract

3C 286 is a well-known calibrator source in radio astronomy. It is also one of very few compact steep-spectrum sources (CSS) detected in -rays. Here, we perform a detailed spectroscopic and variability analysis and present the first quasi-simultaneous optical to X-ray spectral energy distribution in order to reveal physical mechanisms which dominate its emission at different wavelengths, and arrive at a reliable optical source classification. The first main result of our study reveals several pitfalls when applying simple broad- or narrow-line Seyfert 1 (BLS1 or NLS1) classification criteria which only look at the [OIII]-H complex. [OIII] and H can be dominated by the same outflow components, in which case FWHM(H) is no reliable classification criterion, and extinction by intrinsic or intervening material can make the highest-velocity H component undetectable. After careful combination of all information from UV-optical spectra along with multi-wavelength data, we confirm that 3C 286 can be classified as NLS1 galaxy, with line properties and SMBH mass (of order 10 M and accreting near the Eddington limit) close to the BLS1 regime, making it an important borderline object. The quasi-simultaneous SED taken with shows a sharp rise in the optical-UV, implying the presence of a strong accretion-disk component with EUV excess, consistent with emission-line diagnostics. Finally, we report the discovery of X-ray variability of 3C 286, plausibly dominated by jet emission, and variable by at least a factor . This result suggests to exercise caution when using 3C 286 as radio calibrator in high-resolution radio VLBI observations.

10 pages, 4 figures, MNRAS accepted

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