A1 Vertaisarvioitu alkuperäisartikkeli tieteellisessä lehdessä
A significant hardening and rising shape detected in the MeV/GeV νFν spectrum from the recently discovered very-high-energy blazar S4 0954+65 during the bright optical flare in 2015 February
Tekijät: Yasuyuki T. TANAKA, Josefa BECERRA GONZALEZ, Ryosuke ITOH,Justin D. FINKE, Yoshiyuki INOUE, Roopesh OJHA,, Bryce CARPENTER, Elina LINDFORS, Felicia KRAUSS, Rachele DESIANTE, Kensei SHIKI, Yasushi FUKAZAWA, Francesco LONGO, Julie E. MCENERY,Sara BUSON, Kari NILSSON, Vandad FALLAH RAMAZANI, Riho REINTHAL,Leo TAKALO, Tapio PURSIMO, and Walter BOSCHIN
Kustantaja: Oxford University Press
Julkaisuvuosi: 2016
Journal: Publications- Astronomical Society of Japan
Artikkelin numero: 51
Vuosikerta: 68
Numero: 4
Sivujen määrä: 10
ISSN: 0004-6264
DOI: https://doi.org/10.1093/pasj/psw049
Rinnakkaistallenteen osoite: https://arxiv.org/abs/1604.05427
We report on Fermi Large Area Telescope (LAT) and multi-wavelength
results on the recently discovered very-high-energy (VHE, E > 100
GeV) blazar S4 0954+65 (z = 0.368) during an exceptionally bright
optical flare in 2015 February. During the time period (2015 February
13/14, or MJD 57067) when the MAGIC telescope detected VHE γ-ray
emission from the source, the Fermi-LAT data indicated a significant
spectral hardening at GeV energies, with a power-law photon index of 1.8
± 0.1-compared with the 3FGL (The Fermi LAT 4-Year Point Source
Catalog) value (averaged over four years of observation) of 2.34
± 0.04. In contrast, Swift X-Ray Telescope data showed a
softening of the X-ray spectrum, with a photon index of 1.72 ±
0.08 (compared with 1.38 ± 0.03 averaged during the flare from
MJD 57066 to 57077), possibly indicating a modest contribution of
synchrotron photons by the highest-energy electrons superposed on the
inverse Compton component. Fitting of the quasi-simultaneous (<1 d)
broad-band spectrum with a one-zone synchrotron plus inverse-Compton
model revealed that GeV/TeV emission could be produced by
inverse-Compton scattering of external photons from the dust torus. We
emphasize that a flaring blazar showing high flux of ≳1.0 ×
10-6 photons cm-2 s-1 (E > 100 MeV)
and a hard spectral index of ΓGeV < 2.0 detected by
Fermi-LAT on daily timescales is a promising target for TeV follow-up by
ground-based Cherenkov telescopes to discover high-redshift blazars,
investigate their temporal variability and spectral features in the VHE
band, and also constrain the intensity of the extragalactic background
light.
