H.E.S.S. detection of very high-energy γ-ray emission from the quasar PKS 0736+017
Flat-spectrum radio-quasars (FSRQs) are rarely detected at very high energies (<i>E<i/> ≥ 100 GeV) due to their low-frequency-peaked spectral energy distributions. At present, only six FSRQs are known to emit very high-energy (VHE) photons, representing only 7% of the VHE extragalactic c...
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| Main Authors: | , , , , , , , , |
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| Corporate Author: | |
| Format: | Article (Journal) |
| Language: | English |
| Published: |
28 January 2020
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| In: |
Astronomy and astrophysics
Year: 2020, Volume: 633, Pages: A162 |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/201935906 |
| Online Access: | Verlag, Volltext: https://doi.org/10.1051/0004-6361/201935906 Verlag: https://www.aanda.org/articles/aa/abs/2020/01/aa35906-19/aa35906-19.html 
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| Author Notes: | H.E.S.S. Collaboration: H. Abdalla, K. Bernlöhr, D. Glawion, J.A. Hinton, W. Hofmann, A. Quirrenbach, F. Rieger, S. Schwemmer, S.J. Wagner [und weitere] |
| Summary: | Flat-spectrum radio-quasars (FSRQs) are rarely detected at very high energies (<i>E<i/> ≥ 100 GeV) due to their low-frequency-peaked spectral energy distributions. At present, only six FSRQs are known to emit very high-energy (VHE) photons, representing only 7% of the VHE extragalactic catalog, which is largely dominated by high-frequency-peaked BL Lacertae objects.<i>Aims.<i/> Following the detection of MeV-GeV <i>γ<i/>-ray flaring activity from the FSRQ PKS 0736+017 (<i>z<i/> = 0.189) with <i>Fermi<i/>-LAT, the H.E.S.S. array of Cherenkov telescopes triggered target-of-opportunity (ToO) observations on February 18, 2015, with the goal of studying the <i>γ<i/>-ray emission in the VHE band.<i>Methods.<i/> H.E.S.S. ToO observations were carried out during the nights of February 18, 19, 21, and 24, 2015. Together with <i>Fermi<i/>-LAT, the multi-wavelength coverage of the flare includes <i>Swift<i/> observations in soft X-ray and optical-UV bands, and optical monitoring (photometry and spectro-polarimetry) by the <i>Steward<i/> Observatory, and the ATOM, the KAIT, and the ASAS-SN telescopes.<i>Results.<i/> VHE emission from PKS 0736+017 was detected with H.E.S.S. only during the night of February 19, 2015. <i>Fermi<i/>-LAT data indicate the presence of a <i>γ<i/>-ray flare, peaking at the time of the H.E.S.S. detection, with a flux doubling timescale of around six hours. The <i>γ<i/>-ray flare was accompanied by at least a 1 mag brightening of the non-thermal optical continuum. No simultaneous observations at longer wavelengths are available for the night of the H.E.S.S. detection. The <i>γ<i/>-ray observations with H.E.S.S. and <i>Fermi<i/>-LAT are used to put constraints on the location of the <i>γ<i/>-ray emitting region during the flare: it is constrained to be just outside the radius of the broad-line region <i>r<i/><sub><i>B<i/><i>L<i/><i>R<i/><sub/> with a bulk Lorentz factor Γ ≃ 20, or at the level of the radius of the dusty torus <i>r<i/><sub>torus<sub/> with Γ ≃ 60.<i>Conclusions.<i/> PKS 0736+017 is the seventh FSRQ known to emit VHE photons, and at <i>z<i/> = 0.189 is the nearest so far. The location of the <i>γ<i/>-ray emitting region during the flare can be tightly constrained thanks to opacity, variability, and collimation arguments. |
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| Item Description: | Gesehen am 13.02.2020 |
| Physical Description: | Online Resource |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/201935906 |