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A statistical study of the optical spectral variability in gamma-ray blazars

A statistical study of the optical spectral variability in gamma-ray blazars
A statistical study of the optical spectral variability in gamma-ray blazars
Blazars optical emission is generally dominated by relativistic jets, although the host galaxy, accretion disk and broad line region (BLR) may also contribute significantly. Disentangling their contributions has been challenging for years due to the dominance of the jet. To quantify the contributions to the spectral variability, we use the statistical technique for dimensionality reduction Non-Negative Matrix Factorization on a spectroscopic data set of 26 훾-ray blazars. This technique allows to model large numbers of spectra in terms of a reduced number of components. We use a priori knowledge to obtain components associated to meaningful physical processes. The sources are classified according to their optical spectrum as host-galaxy dominated BL Lac objects (BL Lacs), BL Lacs, or Flat Spectrum Radio Quasars (FSRQs). Host-galaxy sources show less variability, as expected, and bluer-when-brighter trends, as the other BL Lacs. For FSRQs, more complicated colour-flux behaviours are observed: redder-when-brighter for low states saturating above a certain level and, in some cases, turning to bluer-when-brighter. We are able to reproduce the variability observed during 10 years using only 2 to 4 components, depending on the type. The simplest scenario corresponds to host-galaxy blazars, whose spectra are reconstructed using the stellar population and a power law for the jet. BL Lac spectra are reproduced using from 2 to 4 power laws. Different components can be associated to acceleration/cooling processes taking place in the jet. The reconstruction of FSRQs also incorporates a QSO-like component to account for the BLR, plus a very steep power law, associated to the accretion disk
0035-8711
Castro Segura, Noel
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Otero-Santos, J.
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Acosta-Pulido, J. A.
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Becerra González, J.
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Luashvili, A.
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González Martín, O.
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Raiteri, C.M.
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Carnerero, M.I.
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Castro Segura, Noel
0dee6349-38d9-4a0e-b389-df77063638d5
Otero-Santos, J.
6ddaf13a-4068-42d1-8a32-77139e6e62f6
Acosta-Pulido, J. A.
d9c92523-3167-4c2b-9a0c-ca6e2076c904
Becerra González, J.
9e39b57e-d42b-43d6-aefa-14bed6517c0b
Luashvili, A.
74e00231-cfa7-4d47-8a0b-bfb69a07b373
González Martín, O.
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Raiteri, C.M.
f448ade6-c324-4040-8e97-0da994508f73
Carnerero, M.I.
a3fa1487-2fe0-44a8-b38a-866504020d3d

Castro Segura, Noel, Otero-Santos, J., Acosta-Pulido, J. A., Becerra González, J., Luashvili, A., González Martín, O., Raiteri, C.M. and Carnerero, M.I. (2022) A statistical study of the optical spectral variability in gamma-ray blazars. Monthly Notices of the Royal Astronomical Society. (In Press)

Record type: Article

Abstract

Blazars optical emission is generally dominated by relativistic jets, although the host galaxy, accretion disk and broad line region (BLR) may also contribute significantly. Disentangling their contributions has been challenging for years due to the dominance of the jet. To quantify the contributions to the spectral variability, we use the statistical technique for dimensionality reduction Non-Negative Matrix Factorization on a spectroscopic data set of 26 훾-ray blazars. This technique allows to model large numbers of spectra in terms of a reduced number of components. We use a priori knowledge to obtain components associated to meaningful physical processes. The sources are classified according to their optical spectrum as host-galaxy dominated BL Lac objects (BL Lacs), BL Lacs, or Flat Spectrum Radio Quasars (FSRQs). Host-galaxy sources show less variability, as expected, and bluer-when-brighter trends, as the other BL Lacs. For FSRQs, more complicated colour-flux behaviours are observed: redder-when-brighter for low states saturating above a certain level and, in some cases, turning to bluer-when-brighter. We are able to reproduce the variability observed during 10 years using only 2 to 4 components, depending on the type. The simplest scenario corresponds to host-galaxy blazars, whose spectra are reconstructed using the stellar population and a power law for the jet. BL Lac spectra are reproduced using from 2 to 4 power laws. Different components can be associated to acceleration/cooling processes taking place in the jet. The reconstruction of FSRQs also incorporates a QSO-like component to account for the BLR, plus a very steep power law, associated to the accretion disk

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2202.08851 - Accepted Manuscript
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Accepted/In Press date: 17 February 2022
Additional Information: arXiv:2202.08851

Identifiers

Local EPrints ID: 456836
URI: http://eprints.soton.ac.uk/id/eprint/456836
ISSN: 0035-8711
PURE UUID: fb55189a-82f4-48cb-bf4f-4f1b9fe0a0ba

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Date deposited: 12 May 2022 16:48
Last modified: 12 May 2022 16:48

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Contributors

Author: Noel Castro Segura
Author: J. Otero-Santos
Author: J. A. Acosta-Pulido
Author: J. Becerra González
Author: A. Luashvili
Author: O. González Martín
Author: C.M. Raiteri
Author: M.I. Carnerero

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