H.E.S.S. detection of very high-energy γ-ray emission from the quasar PKS 0736+017

• Verfasst von: Abdalla, Hassan [VerfasserIn]
• Verfasst von: Bernlöhr, Konrad [VerfasserIn]
• Verfasst von: Eisenacher Glawion, Dorit [VerfasserIn]
• Verfasst von: Hinton, James Anthony [VerfasserIn]
• Verfasst von: Hofmann, Werner [VerfasserIn]
• Verfasst von: Quirrenbach, Andreas [VerfasserIn]
• Verfasst von: Rieger, Frank M. [VerfasserIn]
• Verfasst von: Schwemmer, Stephanie [VerfasserIn]
• Verfasst von: Wagner, Stefan [VerfasserIn]
• Titel: H.E.S.S. detection of very high-energy γ-ray emission from the quasar PKS 0736+017
• Körperschaft: H.E.S.S. Collaboration [VerfasserIn]
• Verf.angabe: 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]
• E-Jahr: 2020
• Jahr: 28 January 2020
• Umfang: 11 S.
• Fussnoten: Gesehen am 13.02.2020
• Titel Quelle: Enthalten in: Astronomy and astrophysics
• Ort Quelle: Les Ulis : EDP Sciences, 1969
• Jahr Quelle: 2020
• Band/Heft Quelle: 633(2020) Artikel-Nummer A162, 11 Seiten
• ISSN Quelle: 1432-0746
• DOI: doi:10.1051/0004-6361/201935906
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1689964820

Abstract

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.