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Spectroscopic redshift of the gamma-ray Blazar B2 1215+30 from Lyα emission.

Furniss, A. and Worseck, G. and Fumagalli, M. and Johnson, C. A. and Williams, D. A. and Pontrelli, P. and Prochaska, J. X. (2019) 'Spectroscopic redshift of the gamma-ray Blazar B2 1215+30 from Lyα emission.', Astronomical journal., 157 (2). p. 41.


We report on Cosmic Origin Spectrograph observations of the gamma-ray bright blazar B2 1215+30, collected in 2015 November. These observations allow for the confirmation of the source redshift from the detection of a Lyα emission feature at λ ~ 1374 Å. The emission feature places the source at a redshift of z = 0.1305 ± 0.003, confirming the source's ground-based spectral measurement. The gamma-ray emission of the source is discussed in the context of the source distance, required for the accurate reconstruction of the intrinsic gamma-ray emission taking the absorption by the extragalactic background light into account. The source distance is found to be low enough that the previously reported detection of an exceptional flaring event from B2 1215+30 in 2014 cannot be used to investigate opacity-specific spectral and variability characteristics introduced by possible ultra-high-energy cosmic-ray propagation.

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Publisher statement:Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Date accepted:18 November 2018
Date deposited:23 January 2019
Date of first online publication:07 January 2019
Date first made open access:23 January 2019

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