Fermi LARGE AREA TELESCOPE DETECTION OF TWO VERY-HIGH-ENERGY (E > 100 GeV) γ-RAY PHOTONS FROM THE z = 1.1 BLAZAR PKS 0426–380
Abstract
We report the Fermi Large Area Telescope (LAT) detection of two very-high-energy (VHE, E > 100 GeV) γ-ray photons from the directional vicinity of the distant (redshift, z = 1.1) blazar PKS 0426–380. The null hypothesis that both the 134 and 122 GeV photons originate from unrelated sources can be rejected at the 5.5σ confidence level. We therefore claim that at least one of the two VHE photons is securely associated with PKS 0426–380, making it the most distant VHE emitter known to date. The results are in agreement with recent Fermi-LAT constraints on the extragalactic background light (EBL) intensity, which imply a z ≅ 1 horizon for ≅ 100 GeV photons. The LAT detection of the two VHE γ-rays coincided roughly with flaring states of the source, although we did not find an exact correspondence between the VHE photon arrival times and the flux maxima at lower γ-ray energies. Modeling the γ-ray continuum of PKS 0426–380 with daily bins revealed a significant spectral hardening around the time of the first VHE event detection (LAT photon index Γ ≅ 1.4) but on the other hand no pronounced spectral changes near the detection time of the second one. This combination impliesmore »
- Authors:
-
- Hiroshima Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan)
- Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352 (United States)
- W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States)
- Institute of Space and Astronautical Science, JAXA, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan)
- Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450 (United States)
- Praxis Inc., Alexandria, VA 22303 (United States)
- Center for Earth Observing and Space Research, College of Science, George Mason University, Fairfax, VA 22030 (United States)
- Department of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan)
- Max-Planck-Institut für Physik, D-80805 München (Germany)
- Publication Date:
- OSTI Identifier:
- 22215389
- Resource Type:
- Journal Article
- Journal Name:
- Astrophysical Journal Letters
- Additional Journal Information:
- Journal Volume: 777; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; DETECTION; FLARING; GALAXIES; GAMMA RADIATION; GEV RANGE; HYPOTHESIS; PHOTONS; RED SHIFT; SPECTRAL HARDENING; TELESCOPES
Citation Formats
Tanaka, Y. T., Mizuno, T., Cheung, C. C., Dermer, C. D., Inoue, Y., Stawarz, Ł., Ajello, M., Wood, D. L., Chekhtman, A., Fukazawa, Y., Ohno, M., Paneque, D., and Thompson, D. J., E-mail: ytanaka@hep01.hepl.hiroshima-u.ac.jp. Fermi LARGE AREA TELESCOPE DETECTION OF TWO VERY-HIGH-ENERGY (E > 100 GeV) γ-RAY PHOTONS FROM THE z = 1.1 BLAZAR PKS 0426–380. United States: N. p., 2013.
Web. doi:10.1088/2041-8205/777/1/L18.
Tanaka, Y. T., Mizuno, T., Cheung, C. C., Dermer, C. D., Inoue, Y., Stawarz, Ł., Ajello, M., Wood, D. L., Chekhtman, A., Fukazawa, Y., Ohno, M., Paneque, D., & Thompson, D. J., E-mail: ytanaka@hep01.hepl.hiroshima-u.ac.jp. Fermi LARGE AREA TELESCOPE DETECTION OF TWO VERY-HIGH-ENERGY (E > 100 GeV) γ-RAY PHOTONS FROM THE z = 1.1 BLAZAR PKS 0426–380. United States. https://doi.org/10.1088/2041-8205/777/1/L18
Tanaka, Y. T., Mizuno, T., Cheung, C. C., Dermer, C. D., Inoue, Y., Stawarz, Ł., Ajello, M., Wood, D. L., Chekhtman, A., Fukazawa, Y., Ohno, M., Paneque, D., and Thompson, D. J., E-mail: ytanaka@hep01.hepl.hiroshima-u.ac.jp. 2013.
"Fermi LARGE AREA TELESCOPE DETECTION OF TWO VERY-HIGH-ENERGY (E > 100 GeV) γ-RAY PHOTONS FROM THE z = 1.1 BLAZAR PKS 0426–380". United States. https://doi.org/10.1088/2041-8205/777/1/L18.
@article{osti_22215389,
title = {Fermi LARGE AREA TELESCOPE DETECTION OF TWO VERY-HIGH-ENERGY (E > 100 GeV) γ-RAY PHOTONS FROM THE z = 1.1 BLAZAR PKS 0426–380},
author = {Tanaka, Y. T. and Mizuno, T. and Cheung, C. C. and Dermer, C. D. and Inoue, Y. and Stawarz, Ł. and Ajello, M. and Wood, D. L. and Chekhtman, A. and Fukazawa, Y. and Ohno, M. and Paneque, D. and Thompson, D. J., E-mail: ytanaka@hep01.hepl.hiroshima-u.ac.jp},
abstractNote = {We report the Fermi Large Area Telescope (LAT) detection of two very-high-energy (VHE, E > 100 GeV) γ-ray photons from the directional vicinity of the distant (redshift, z = 1.1) blazar PKS 0426–380. The null hypothesis that both the 134 and 122 GeV photons originate from unrelated sources can be rejected at the 5.5σ confidence level. We therefore claim that at least one of the two VHE photons is securely associated with PKS 0426–380, making it the most distant VHE emitter known to date. The results are in agreement with recent Fermi-LAT constraints on the extragalactic background light (EBL) intensity, which imply a z ≅ 1 horizon for ≅ 100 GeV photons. The LAT detection of the two VHE γ-rays coincided roughly with flaring states of the source, although we did not find an exact correspondence between the VHE photon arrival times and the flux maxima at lower γ-ray energies. Modeling the γ-ray continuum of PKS 0426–380 with daily bins revealed a significant spectral hardening around the time of the first VHE event detection (LAT photon index Γ ≅ 1.4) but on the other hand no pronounced spectral changes near the detection time of the second one. This combination implies a rather complex variability pattern of the source in γ-rays during the flaring epochs. An additional flat component is possibly present above several tens of GeV in the EBL-corrected Fermi-LAT spectrum accumulated over the ∼8 month high state.},
doi = {10.1088/2041-8205/777/1/L18},
url = {https://www.osti.gov/biblio/22215389},
journal = {Astrophysical Journal Letters},
issn = {2041-8205},
number = 1,
volume = 777,
place = {United States},
year = {Fri Nov 01 00:00:00 EDT 2013},
month = {Fri Nov 01 00:00:00 EDT 2013}
}
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