| 1. |
- Aharonian, F., et al.
(author)
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TeV flaring activity of the AGN PKS 0625-354 in November 2018
- 2024
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 683
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Journal article (peer-reviewed)abstract
- Most gamma-ray detected active galactic nuclei are blazars with one of their relativistic jets pointing towards the Earth. Only a few objects belong to the class of radio galaxies or misaligned blazars. Here, we investigate the nature of the object PKS 0625-354, its gamma-ray flux and spectral variability and its broad-band spectral emission with observations from H.E.S.S., Fermi-LAT, Swift-XRT, and UVOT taken in November 2018. The H.E.S.S. light curve above 200 GeV shows an outburst in the first night of observations followed by a declining flux with a halving time scale of 5.9 h. The gamma gamma-opacity constrains the upper limit of the angle between the jet and the line of sight to similar to 10 degrees. The broad-band spectral energy distribution shows two humps and can be well fitted with a single-zone synchrotron self Compton emission model. We conclude that PKS 0625-354, as an object showing clear features of both blazars and radio galaxies, can be classified as an intermediate active galactic nuclei. Multi-wavelength studies of such intermediate objects exhibiting features of both blazars and radio galaxies are sparse but crucial for the understanding of the broad-band emission of gamma-ray detected active galactic nuclei in general.
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| 2. |
- Aharonian, F., et al.
(author)
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Unveiling extended gamma-ray emission around HESS J1813-178
- 2024
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 686
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Journal article (peer-reviewed)abstract
- Context. HESS J1813-178 is a very-high-energy gamma-ray source spatially coincident with the young and energetic pulsar PSR J1813-1749 and thought to be associated with its pulsar wind nebula (PWN). Recently, evidence for extended high-energy emission in the vicinity of the pulsar has been revealed in the Fermi Large Area Telescope (LAT) data. This motivates revisiting the HESS J1813-178 region, taking advantage of improved analysis methods and an extended dataset. Aims. Using data taken by the High Energy Stereoscopic System (H.E.S.S.) experiment and the Fermi-LAT, we aim to describe the gamma-ray emission in the region with a consistent model, to provide insights into its origin. Methods. We performed a likelihood-based analysis on 32 hours of H.E.S.S. data and 12 yr of Fermi-LAT data and we fitted a spectromorphological model to the combined datasets. These results allowed us to develop a physical model for the origin of the observed.-ray emission in the region. Results. In addition to the compact very-high-energy gamma-ray emission centred on the pulsar, we find a significant yet previously undetected component along the Galactic plane. With Fermi-LAT data, we confirm extended high-energy emission consistent with the position and elongation of the extended emission observed with H.E.S.S. These results establish a consistent description of the emission in the region from GeV energies to several tens of TeV. Conclusions. This study suggests that HESS J1813-178 is associated with a gamma-ray PWN powered by PSR J1813-1749. A possible origin of the extended emission component is inverse Compton emission from electrons and positrons that have escaped the confines of the pulsar and form a halo around the PWN.
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