AP Librae: The Extended Jet as the Source of VHE Emission?

Zacharias, M.; Wagner, S. J.

doi:10.3390/galaxies4040063

Cited by 5 publications

(12 citation statements)

References 12 publications

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“…They attributed this to the gross non-simultaneity of the Fermi-LAT and X-ray observations (∼ 7 years) and the possible presence of an X-ray jet. However Sanchez et al (2015) confirmed these findings with quasi-simultaneous X-ray and Fermi /LAT observations (see also Zacharias & Wagner 2016).…”

Section: Introductionsupporting

confidence: 60%

“…Our aim in this study is to explain the very broad second component in AP Librae and in particular to test the clear predictions of the models invoking IC/CMB in the kpcscale jet for the TeV emission (e.g. Zacharias & Wagner 2016). These models predict a high level of infrared synchrotron emission from the jet, provided by the same electrons required to explain the TeV emission.…”

Section: Introductionmentioning

confidence: 98%

“…Subsequently several efforts were made to move beyond a simple SSC model for the VHE emission. Both Zacharias & Wagner (2016) and Sanchez et al (2015) suggested that inverse Compton scattering off cosmic microwave background photons in the extended jet (the IC/CMB mechanism, first proposed by Tavecchio et al 2000, for another source) could explain the high-energy Fermi/LAT and H.E.S.S. emission, although the synchrotron spextrum of the large-scale jet was severely unconstrained in these works.…”

Section: Introductionmentioning

confidence: 99%

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Circumnuclear Dust in AP Librae and the source of its VHE emission

Roychowdhury,

Meyer,

Georganopoulos

et al. 2021

Preprint

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The broad high-energy spectral component in blazars is usually attributed to various inverse Compton scattering processes in the relativistic jet, but has not been clearly identified in most cases due to degeneracies in physical models. AP Librae, a low-synchrotron-peaking BL Lac object (LBL) detected in 2015 by H.E.S.S. at very high energies (VHE; > 0.5 TeV), has an extremely broad high-energy spectrum, covering ∼ 9 decades in energy. Standard synchrotron self-Compton models generally fail to reproduce the VHE emission, which has led to the suggestion that it might arise not from the blazar core, but on kiloparsec scales from inverse Compton scattering of cosmic microwave background (CMB) photons by a still-relativistic jet (IC/CMB). IC/CMB models for the TeV emission of AP Librae in prior works have implied a high level of infrared emission from the kpc-scale jet. With newly obtained Hubble Space Telescope imaging, we obtain a deep upper limit on the kpc-scale jet emission at 1.6 µm, well below the expected level. High-resolution ALMA imaging in bands 3-9 reveals a residual dust disk signature after core subtraction, with a clearly thermal spectrum, and an extent (∼500 pc) which matches with a non-jet residual emission seen after PSF subtraction in our 1.6 µm HST imaging. We find that the unusually broad GeV and VHE emission in AP Librae can be reproduced through the combined IC scattering of photons from the CMB and the dust disk, respectively, by electrons in both the blazar core and sub-kpc jet.

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Section: Introductionsupporting

confidence: 60%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Circumnuclear Dust in AP Librae and the source of its VHE emission

Roychowdhury,

Meyer,

Georganopoulos

et al. 2021

Preprint

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“…From our highresolution VLA, ALMA, and HST imaging campaign we have been able to more accurately sample the synchrotron spectrum of the X-ray emitting jet (red data points and upper limit with phenomenological power-law+exponential cutoff model as a blue dashed curve). The infrared upper limit (in red) in particular rules out the IC/CMB model of [35], shown as cyan curves. In addition, a fit to the orange ALMA data points (orange-dashed) has been indicated, which is a blackbody at temperature 25 K, having typical size ∼ 100 pc.…”

Section: Figurementioning

confidence: 99%

“…Several efforts have been made to move beyond a simple SSC model and explain the TeV emission. Both [35] and [30] suggested that inverse Compton scattering off cosmic microwave background photons in the extended jet (the IC/CMB mechanism) could explain the high-energy LAT and H.E.S.S. emission, although the synchrotron emission of the large-scale jet was severely under-constrained in these works.…”

Section: Introductionmentioning

confidence: 99%

What is the origin of the very high energy (VHE) emission from AP Librae?

Roychowdhury¹,

Meyer²,

Georganopoulos³

et al. 2021

Proceedings of 37th International Cosmic Ray Conference — PoS(ICRC2021)

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The high-energy spectral component in blazars is usually attributed to various inverse Compton scattering processes in the relativistic jet, but has not been clearly identified in most cases due to degeneracies in physical models. AP Librae, a low-synchrotron-peaking BL Lac object (LBL) detected in 2015 by H.E.S.S. at TeV energies, has an extremely broad high-energy spectrum, covering ∼ 9 decades in energy. Standard synchrotron self-Compton models generally fail to reproduce the VHE emission, which has lead to the suggestion that it might arise not from the blazar core, but on kilo-parsec scales from inverse-Compton scattering of cosmic microwave background (CMB) photons by a still-relativistic jet. Such a model makes specific predictions for the level of infrared emission from the kpc-scale jet which we can now rule out with newly obtained Hubble imaging. Sub-mm ALMA imaging has also revealed the presence of a ∼ 500 pc quasi-thermal circumnuclear disk, which is the first detection of a torus in a BL Lac. We find that the VHE emission can be reproduced through inverse-Compton scattering of torus photons by electrons in the sub-kpc jet. This explanation could be further evaluated with deep and high dynamic range imaging in the sub-mm and far infrared and continued monitoring of the source at TeV energies to test for variability.

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A multiwavelength view of BL Lacs neutrino candidates

Righi

Tavecchio

Pacciani

2018

Monthly Notices of the Royal Astronomical Society

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The discovery of high-energy astrophysical neutrinos by IceCube kicked off a new line of research to identify the electromagnetic counterparts producing these neutrinos. Among the extragalactic sources, Blazars are promising candidate neutrino emitters. Their structure, with a relativistic jet pointing to the Earth, offers a natural accelerator of particles and for this reason a perfect birthplace of high energy neutrinos. A good characterisation of the spectral energy distribution of Blazars can improve the understanding of their physical composition and the emission processes involved. Starting from our previous works, we select those BL Lac in spatial correlation with IceCube events. We obtain a sample of 7 sources and we start an observational campaign to have a better characterisation of the synchrotron peak. During our analysis a new source, namely TXS0506+056, has been added because of its position inside the angular uncertainty of a muon track event detected by IceCube. TXS0506+056, was in a high-state during the neutrino event and we will consider it as benchmark to check the properties of the other sources of the sample during the related neutrino detection. We obtain a better characterisation of the SED for the sources of our sample. A prospective extreme Blazar, a very peculiar low synchrotron peak (LSP) source with a large separation of the two peaks and a twin of TXS0506+056 come up. We also provide the γ-ray light curve to check the trend of the sources around the neutrino detection but no clear patterns are in common among the sources.

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AP Librae: The Extended Jet as the Source of VHE Emission?

Cited by 5 publications

References 12 publications

Circumnuclear Dust in AP Librae and the source of its VHE emission

Circumnuclear Dust in AP Librae and the source of its VHE emission

What is the origin of the very high energy (VHE) emission from AP Librae?

A multiwavelength view of BL Lacs neutrino candidates

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