Please use this identifier to cite or link to this item:
http://hdl.handle.net/2445/172347
Title: | H.E.S.S. detection of very high-energy γ-ray emission from the quasar PKS 0736+017 |
Author: | H. E. S. S. Collaboration Cerruti, Matteo |
Keywords: | Raigs gamma Física de partícules Quàsars Gamma rays Particle physics Quasars |
Issue Date: | Jan-2020 |
Publisher: | EDP Sciences |
Abstract: | Context. Flat-spectrum radio-quasars (FSRQs) are rarely detected at very high energies (E ≥ 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. Aims. Following the detection of MeV-GeV γ-ray flaring activity from the FSRQ PKS 0736+017 (z = 0.189) with Fermi-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 γ-ray emission in the VHE band. Methods. H.E.S.S. ToO observations were carried out during the nights of February 18, 19, 21, and 24, 2015. Together with Fermi-LAT, the multi-wavelength coverage of the flare includes Swift observations in soft X-ray and optical-UV bands, and optical monitoring (photometry and spectro-polarimetry) by the Steward Observatory, and the ATOM, the KAIT, and the ASAS-SN telescopes. Results. VHE emission from PKS 0736+017 was detected with H.E.S.S. only during the night of February 19, 2015. Fermi-LAT data indicate the presence of a γ-ray flare, peaking at the time of the H.E.S.S. detection, with a flux doubling timescale of around six hours. The γ-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 γ-ray observations with H.E.S.S. and Fermi-LAT are used to put constraints on the location of the γ-ray emitting region during the flare: it is constrained to be just outside the radius of the broad-line region rBLR with a bulk Lorentz factor Γ ≃ 20, or at the level of the radius of the dusty torus rtorus with Γ ≃ 60. Conclusions. PKS 0736+017 is the seventh FSRQ known to emit VHE photons, and at z = 0.189 is the nearest so far. The location of the γ-ray emitting region during the flare can be tightly constrained thanks to opacity, variability, and collimation arguments. |
Note: | Reproducció del document publicat a: https://doi.org/10.1051/0004-6361/201935906 |
It is part of: | Astronomy & Astrophysics, 2020, vol. 633, p. A162 |
URI: | http://hdl.handle.net/2445/172347 |
Related resource: | https://doi.org/10.1051/0004-6361/201935906 |
ISSN: | 0004-6361 |
Appears in Collections: | Articles publicats en revistes (Institut de Ciències del Cosmos (ICCUB)) |
Files in This Item:
File | Description | Size | Format | |
---|---|---|---|---|
700512.pdf | 517.92 kB | Adobe PDF | View/Open |
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.