Optical spectroscopy of blazars for the Cherenkov Telescope Array – II

Kasai, E.; Goldoni, P.; Pita, S.; Williams, D. A.; Max-Moerbeck, W.; Hervet, O.; Cotter, Garret; Backes, Michael; Boisson, C.; González, J. Becerra; Almeida, U. Barres de; D’Ammando, F.; Ramazani, Vandad Fallah; Lindfors, E.

doi:10.1093/mnras/stac3167

Cited by 10 publications

(3 citation statements)

References 95 publications

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“…However, from the analysis of the GTC acquisition image, we are not able to detect the host galaxy (𝑀 (𝑅) > −22.6). A spectrum of the source was published by Kasai et al (2023) after we performed our observation and our redshift is compatible with theirs. 4FGL J2030.5+2235: This 𝛾-ray source is unassociated in the 4FGL-DR3 catalogue.…”

Section: Fgl J20309+1935supporting

confidence: 81%

The spectra of IceCube Neutrino (SIN) candidate sources -- III. Optical spectroscopy and source characterization of the full sample

Paiano¹,

Falomo²,

Treves³

et al. 2023

Preprint

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A correlation between astrophysical high-energy neutrinos and blazars has been suggested by various authors. In particular, a likely association between IceCube events and intermediate and high-energy peaked BL Lac objects has led to a sample of 47 objects having a high probability of being neutrino sources. In the first paper of this series we reported optical spectroscopy of 17 objects, which together with data taken from the literature covered 80 per cent of the sample. Here we present spectroscopy obtained at large aperture telescopes of a further 17 objects (plus four additional targets), which completes the sample coverage. For twelve objects we are able to determine the redshift (0.07 < 𝑧 < 1.6), while for the others we set a lower limit on it, based on either the robust detection of intervening absorption systems or on an estimation derived from the absence of spectral signatures of the host galaxy. With these new data we expand and reinforce the main results of our previous papers, namely the fact that in terms of their broad-band properties our sources appear to be indistinguishable from the rest of the blazar population and the relatively large (> 34 per cent and possibly as high as 80 per cent) fraction of masquerading BL Lac objects, for which the low equivalent width of the emission lines is due to the brightness of the boosted continuum, rather than being an intrinsic property, in our sample.

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Section: Fgl J20309+1935supporting

confidence: 81%

The spectra of IceCube Neutrino (SIN) candidate sources -- III. Optical spectroscopy and source characterization of the full sample

Paiano¹,

Falomo²,

Treves³

et al. 2023

Preprint

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“…Goldoni et al (2021) presented spectra for 19 sources, eleven of which had their redshifts determined successfully. Kasai et al (2023) presented spectra for 33 sources (including 13 spectra for eight sources that were of lower quality and featureless). Fourteen of the sources had their redshifts determined successfully.…”

Section: Selected Resultsmentioning

confidence: 99%

“…Table 1 provides a list of some of the spectroscopic instruments and telescopes used by the task force. In the last column of the table are the combined total numbers of sources observed by each telescope, published in the first two papers by the task force (Goldoni et al 2021;Kasai et al 2023) and are to be published in the upcoming third paper.…”

Section: The Cta Redshift Task Force and Its Objectivesmentioning

confidence: 99%

Redshift determination of blazars for the Cherenkov Telescope Array

Kasai,

Goldoni,

Pita

et al. 2021

Proc. IAU

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Blazars are the most numerous type of observed high-energy gamma-ray emitters. However, their emission mechanisms and population properties are still not well-understood. Crucial to this understanding are their cosmological redshifts, which are often not easy to obtain. This presents a great challenge to the next-generation ground-based observatory for very-high-energy gamma rays, the Cherenkov Telescope Array (CTA), which aims to detect a large number of distant blazars to study their intrinsic emission properties and to place tight constraints on the extragalactic background light density, amongst others. The successful investigation of these subjects needs a precise redshift determination. Motivated by these challenges, the CTA redshift task force initiated more than 3 years ago a spectroscopic observing program using some of the largest optical and infrared telescopes to measure the redshifts of a large fraction of blazars that are likely to be detected with CTA. In this proceedings, we give an overview of the CTA redshift task force, discuss some of the difficulties associated with measuring the redshifts of blazars and present our sample selection and observing strategies. We end the proceedings with reporting selected results from the program, the on-going collaborative efforts and our plans for the future.

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Optical spectroscopy of blazars for the Cherenkov Telescope Array – III

D’Ammando,

Goldoni,

Max-Moerbeck

et al. 2024

A&A

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Blazars, which include BL Lacs and flat-spectrum radio quasars (FSRQs), represent the brightest persistent extragalactic sources in the high-energy (HE; 10 MeV -- 100 GeV) and very-high-energy (VHE; $E$ $>$ 100 GeV) gamma -ray sky. Due to their almost featureless optical/UV spectra, it is challenging to measure the redshifts of BL Lacs. As a result, about 50<!PCT!> of gamma -ray BL Lacs lack a firm measurement of this property, which is fundamental for population studies, indirect estimates of the extragalactic background light (EBL), and fundamental physics probes (e.g. searches for Lorentz-invariance violation or axion-like particles). This paper is the third in a series of papers aimed at determining the redshift of a sample of blazars selected as prime targets for future observations with the next generation, ground-based VHE gamma -ray astronomy observatory, Cherenkov Telescope Array Observatory (CTAO). The accurate determination of the redshift of these objects is an important aid in source selection and planning of future CTAO observations. Promising targets were selected following a sample selection obtained with Monte Carlo simulations of CTAO observations. The selected targets were expected to be detectable with CTAO in observations of 30 hours or less. We performed deep spectroscopic observations of 41 of these blazars using the Keck II, Lick, SALT, GTC, and ESO/VLT telescopes. We carefully searched for spectral lines in the spectra and whenever features of the host galaxy were detected, we attempted to model the properties of the host galaxy. The magnitudes of the targets at the time of the observations were also compared to their long-term light curves. Spectra from 24 objects display spectral features or a high signal-to-noise ratio (S/N). From these, 12 spectroscopic redshifts were determined, ranging from 0.2223 to 0.7018. Furthermore, 1 tentative redshift (0.6622) and 2 redshift lower limits at $z$ > 0.6185 and $z$ > 0.6347 were obtained. The other 9 BL Lacs showed featureless spectra, despite the high S/N (geq 100) observations. Our comparisons with long-term optical light curves tentatively suggest that redshift measurements are more straightforward during an optical low state of the active galactic nucleus (AGN). Overall, we have determined 37 redshifts and 6 spectroscopic lower limits as part of our programme thus far.

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Optical spectroscopy of blazars for the Cherenkov Telescope Array – II

Cited by 10 publications

References 95 publications

The spectra of IceCube Neutrino (SIN) candidate sources -- III. Optical spectroscopy and source characterization of the full sample

The spectra of IceCube Neutrino (SIN) candidate sources -- III. Optical spectroscopy and source characterization of the full sample

Redshift determination of blazars for the Cherenkov Telescope Array

Optical spectroscopy of blazars for the Cherenkov Telescope Array – III

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