A. Furniss
The Firm Redshift Lower Limit of the Most Distant TeV-detected Blazar PKS 1424+240
Furniss, A.; Williams, D.A.; Danforth, C.; Fumagalli, M.; Prochaska, J.X.; Primack, J.; Urry, C.M.; Stocke, J.; Filippenko, A.V.; Neely, W.
Authors
D.A. Williams
C. Danforth
Professor Michele Fumagalli michele.fumagalli@durham.ac.uk
Academic Visitor
J.X. Prochaska
J. Primack
C.M. Urry
J. Stocke
A.V. Filippenko
W. Neely
Abstract
We present the redshift lower limit of z ≥ 0.6035 for the very high energy (VHE; E ≥ 100 GeV) emitting blazar PKS 1424+240 (PG 1424+240). This limit is inferred from Lyβ and Lyγ absorption observed in the far-ultraviolet spectra from the Hubble Space Telescope/Cosmic Origins Spectrograph. No VHE-detected blazar has shown solid spectroscopic evidence of being more distant. At this distance, VHE observations by VERITAS are shown to sample historically large gamma-ray opacity values at 500 GeV, extending beyond τ = 4 for low-level models of the extragalactic background light (EBL) and beyond τ = 5 for high levels. The majority of the z = 0.6035 absorption-corrected VHE spectrum appears to exhibit a lower flux than an extrapolation of the contemporaneous Large Area Telescope power-law fit beyond 100 GeV. However, the highest energy VERITAS point is the only point showing agreement with this extrapolation, possibly implying the overestimation of the gamma-ray opacity or the onset of an unexpected VHE spectral feature. A curved log parabola is favored when fitting the full range of gamma-ray data (0.5-500 GeV). While fitting the absorption-corrected VHE data alone results in a harder differential power law than that from the full range, the indices derived using three EBL models are consistent with the physically motivated limit set by Fermi acceleration processes.
Citation
Furniss, A., Williams, D., Danforth, C., Fumagalli, M., Prochaska, J., Primack, J., …Neely, W. (2013). The Firm Redshift Lower Limit of the Most Distant TeV-detected Blazar PKS 1424+240. Astrophysical Journal Letters, 768(2), Article L31. https://doi.org/10.1088/2041-8205/768/2/l31
Journal Article Type | Article |
---|---|
Publication Date | May 10, 2013 |
Deposit Date | Apr 6, 2014 |
Publicly Available Date | Jun 30, 2014 |
Journal | Astrophysical Journal Letters |
Print ISSN | 2041-8205 |
Electronic ISSN | 2041-8213 |
Publisher | American Astronomical Society |
Peer Reviewed | Peer Reviewed |
Volume | 768 |
Issue | 2 |
Article Number | L31 |
DOI | https://doi.org/10.1088/2041-8205/768/2/l31 |
Keywords | BL Lacertae objects: individual (PKS 1424+240 (PG 1424+240)), Diffuse radiation, Galaxies: active, Intergalactic medium, Ultraviolet: general. |
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Copyright Statement
© 2013. The American Astronomical Society. All rights reserved.
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