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

被引:21
作者
Tanaka, Y. T. [1 ]
Cheung, C. C. [2 ]
Inoue, Y. [3 ,4 ]
Stawarz, L. [5 ,6 ]
Ajello, M. [7 ]
Dermer, C. D. [2 ]
Wood, D. L. [8 ]
Chekhtman, A. [9 ]
Fukazawa, Y. [10 ]
Mizuno, T. [1 ]
Ohno, M. [10 ]
Paneque, D. [4 ,11 ]
Thompson, D. J. [12 ]
机构
[1] Hiroshima Univ, Hiroshima Astrophys Sci Ctr, Hiroshima 7398526, Japan
[2] Naval Res Lab, Div Space Sci, Washington, DC 20375 USA
[3] Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA
[4] Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA
[5] JAXA, Inst Space & Astronaut Sci, Chuo Ku, Sagamihara, Kanagawa 2525210, Japan
[6] Jagiellonian Univ, Astron Observ, PL-30244 Krakow, Poland
[7] Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA
[8] Praxis Inc, Alexandria, VA 22303 USA
[9] George Mason Univ, Coll Sci, Ctr Earth Observing & Space Res, Fairfax, VA 22030 USA
[10] Hiroshima Univ, Dept Phys Sci, Hiroshima 7398526, Japan
[11] Max Planck Inst Phys & Astrophys, D-80805 Munich, Germany
[12] NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA
关键词
acceleration of particles; galaxies: active; galaxies: jets; gamma rays: galaxies; quasars: individual (PKS 0426-380); radiation mechanisms: non-thermal; EXTRAGALACTIC BACKGROUND LIGHT; ACTIVE GALACTIC NUCLEI; BL LACERTAE OBJECTS; HOST GALAXIES; EMISSION; QUASAR; DISCOVERY; EVOLUTION; UNIVERSE; CATALOG;
D O I
10.1088/2041-8205/777/1/L18
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We report the Fermi Large Area Telescope (LAT) detection of two very-high-energy (VHE, E > 100 GeV) gamma-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 5.5s 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 similar or equal to 1 horizon for similar or equal to 100 GeV photons. The LAT detection of the two VHE gamma-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 gamma-ray energies. Modeling the gamma-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 Gamma similar or equal to 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 gamma-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 similar to 8 month high state.
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