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On the redshift of the very high energy blazar 3C 66A.

Furniss, A. and Fumagalli, M. and Danforth, C. and Williams, D.A. and Prochaska, J.X. (2013) 'On the redshift of the very high energy blazar 3C 66A.', Astrophysical journal., 766 (1). p. 35.


As a bright gamma-ray source, 3C 66A is of great interest to the high-energy astrophysics community, having a potential for placing cosmological constraints on models for the extragalactic background light (EBL) and the processes which contribute to this photon field. No firm spectroscopic redshift measurement has been possible for this blazar due to a lack of intrinsic emission and absorption features in optical spectra. We present new far-ultraviolet spectra from the Hubble Space Telescope/Cosmic Origins Spectrograph (HST/COS) of the BL Lac object 3C 66A covering the wavelength range 1132-1800 Å. The data show a smooth continuum with intergalactic medium absorption features which can be used to place a firm lower limit on the blazar redshift of z ≥ 0.3347. An upper limit is set by statistically treating the non-detection of additional absorbers beyond z = 0.3347, indicating a redshift of less than 0.41 at 99% confidence and ruling out z ≥ 0.444 at 99.9% confidence. We conclude by showing how the redshift limits derived from the COS spectra remove the potential for this gamma-ray emitting blazar to place an upper limit on the flux of the EBL using high energy data from a flare in 2009 October.

Item Type:Article
Keywords:BL Lacertae objects: individual (3C 66A), Diffuse radiation, Intergalactic medium, Ultraviolet: general.
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Publisher statement:© 2013. The American Astronomical Society. All rights reserved.
Date accepted:No date available
Date deposited:30 June 2014
Date of first online publication:March 2013
Date first made open access:No date available

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