THE FIRM REDSHIFT LOWER LIMIT OF THE MOST DISTANT TeV-DETECTED BLAZAR PKS 1424+240

Journal Article · Fri May 10 04:00:00 EDT 2013 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/768/2/L31· OSTI ID:22130671

Furniss, A.; Williams, D. A.; Primack, J. ^[1]; Danforth, C.; Stocke, J. ^[2]; Fumagalli, M. ^[3]; Prochaska, J. X. ^[4]; Urry, C. M. ^[5]; Filippenko, A. V. ^[6]; Neely, W. ^[7]

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1. Santa Cruz Institute of Particle Physics, and Department of Physics, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States)
2. CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, 389-UCB, Boulder, CO 80309 (United States)
3. Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
4. Department of Astronomy and Astrophysics, UCO/Lick Observatory, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)
5. Department of Astronomy, Yale University, New Haven, CT 06520-8120 (United States)
6. Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States)
7. NF/Observatory, Silver City, NM 88041 (United States)

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 Ly{beta} and Ly{gamma} 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 {tau} = 4 for low-level models of the extragalactic background light (EBL) and beyond {tau} = 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.

• OSTI ID: 22130671
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 768; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION
ACCELERATION
BL LACERTAE OBJECTS
EXTRAPOLATION
FAR ULTRAVIOLET RADIATION
GALAXIES
GAMMA RADIATION
OPACITY
PARABOLAS
RED SHIFT
SPACE
SPECTRA
TELESCOPES
TEV RANGE