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
In this paper, 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. Finally, we emphasize that a flaring blazar showing high flux of ≳1.0 × 10-6 photons cm-2s-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.
- Research Organization:
- Hiroshima Univ., Higashihiroshima (Japan); NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
- Sponsoring Organization:
- USDOE; National Aeronautics and Space Administration (NASA); Japan Society for the Promotion of Science (JSPS) (Japan)
- Contributing Organization:
- Fermi LAT Collaboration
- Grant/Contract Number:
- NNH12ZDA001N; NNH13ZDA001N-FERMI; 15K17652
- OSTI ID:
- 1355691
- Journal Information:
- Publications of the Astronomical Society of Japan, Vol. 68, Issue 4; ISSN 0004-6264
- Country of Publication:
- United States
- Language:
- English
Web of Science
Detection of the blazar S4 0954+65 at very-high-energy with the MAGIC telescopes during an exceptionally high optical state
|
journal | September 2018 |
High-energy neutrino flux from individual blazar flares
|
journal | September 2019 |
Detection of the blazar S4 0954+65 at very-high-energy with the MAGIC telescopes during an exceptionally high optical state
|
text | January 2018 |
| High energy neutrino flux from individual blazar flares | text | January 2019 |
Similar Records
PKS 1502+106: A new and distant gamma-ray blazar in outburst discovered by the Fermi Large Area Telescope
PKS 1502+106: A NEW AND DISTANT GAMMA-RAY BLAZAR IN OUTBURST DISCOVERED BY THE FERMI LARGE AREA TELESCOPE