HUNTING FOR TREASURES AMONG THE<i>FERMI</i>UNASSOCIATED SOURCES: A MULTIWAVELENGTH APPROACH

Acero, Fabio; Donato, D.; Ojha, R.; Stevens, J.; Edwards, P. G.; Ferrara, E. C.; Blanchard, J.; Lovell, J. E. J.; Thompson, D. J.

doi:10.1088/0004-637x/779/2/133

Cited by 49 publications

(55 citation statements)

References 34 publications

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“…Although the Fermi-LAT observatory is greatly improving it by the continuous signal addition over the years, the task remains challenging, if we consider that one third of the 3FGL lastly-released source catalog are still unassociated to counterparts in other frequency band. Preliminary searches of these unassociated/unidentified gamma-ray sources (henceforth UGS) by various authors (Mirabal et al 2012;Massaro et al 2012;D'Abrusco et al 2013;Acero et al 2013a;Doert & Errando 2014;Landi et al 2015;Paiano et al 2017a) found clear indications that the large majority of them are AGNs of the blazar class.…”

Section: Introductionmentioning

confidence: 99%

Optical Spectroscopic Survey of a Sample of Unidentified Fermi Objects

Paiano

Falomo

Franceschini

et al. 2017

ApJ

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We present optical spectroscopy secured at the 10m Gran Telescopio Canarias of the counterparts of 20 extragalactic γ-ray sources detected by the Fermi satellite. The observations allow us to investigate the nature of these sources and to determine their redshift. We find that all optical counterparts have a spectrum that is consistent with a BL Lac object nature. We are able to determine the redshift for 11 objects and set spectroscopic redshift limits for five targets. Only for four sources the optical spectrum is found featureless. In the latter cases we can set lower limits on the redshift based on the assumption that they are hosted by a typical massive elliptical galaxy whose spectrum is diluted by the non thermal continuum. The observations allow us to unveil the nature of these gamma-ray sources and provide a sanity check of a tool to discover the counterparts of γ-ray emitters/blazars based on their multiwavelength emission.

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Section: Introductionmentioning

confidence: 99%

Optical Spectroscopic Survey of a Sample of Unidentified Fermi Objects

Paiano

Falomo

Franceschini

et al. 2017

ApJ

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“…Other attempts have been made with non-parametric techniques, such as kernel density estimators, using additional information obtained in radio (Massaro et al 2013a,c) or X-rays (Paggi et al 2013), to identify potential blazar counterparts for a few tens of unassociated sources in the 2FGL catalogue. Finally, one can deal with unassociated sources individually, this is done in the study of Acero et al (2013) for a limited sample of sources, by combining multiwavelength observations and analysing the spectral energy distributions of the sources.…”

Section: Introductionmentioning

confidence: 99%

Research and characterisation of blazar candidates among theFermi/LAT 3FGL catalogue using multivariate classifications

Lefaucheur

Pita

2017

A&A

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Context. In the recently published 3FGL catalogue, the Fermi/LAT collaboration reports the detection of γ-ray emission from 3034 sources obtained after four years of observations. The nature of 1010 of those sources is unknown, whereas 2023 have wellidentified counterparts in other wavelengths. Most of the associated sources are labelled as blazars (1717/2023), but the BL Lac or FSRQ nature of 573 of these blazars is still undetermined. Aims. The aim of this study was two-fold. First, to significantly increase the number of blazar candidates from a search among the large number of Fermi/LAT 3FGL unassociated sources (case A). Second, to determine the BL Lac or FSRQ nature of the blazar candidates, including those determined as such in this work and the blazar candidates of uncertain type (BCU) that are already present in the 3FGL catalogue (case B). Methods. For this purpose, multivariate classifiers -boosted decision trees and multilayer perceptron neural networks -were trained using samples of labelled sources with no caution flag from the 3FGL catalogue and carefully chosen discriminant parameters. The decisions of the classifiers were combined in order to obtain a high level of source identification along with well controlled numbers of expected false associations. Specifically for case A, dedicated classifications were generated for high (|b| > 10• ) and low (|b| ≤ 10 • ) galactic latitude sources; in addition, the application of classifiers to samples of sources with caution flag was considered separately, and specific performance metrics were estimated. Results. We obtained a sample of 595 blazar candidates (high and low galactic latitude) among the unassociated sources of the 3FGL catalogue. We also obtained a sample of 509 BL Lacs and 295 FSRQs from the blazar candidates cited above and the BCUs of the 3FGL catalogue. The number of expected false associations is given for different samples of candidates. It is, in particular, notably low (∼9/425) for the sample of high-latitude blazar candidates from case A.

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“…To achieve this goal, we developed several procedures based on the blazar properties, such as 1) the use of their peculiar IR colors (Massaro et al 2013a,b), discovered thanks to the all-sky survey of the Wide-Field Infrared Survey Explorer (WISE; Wright et al 2010); 2) the flat shape of their radio spectra maintained even at MHz frequencies (Massaro et al 2012b;Nori et al 2014); or 3) combining radio observations with the IR colors (Massaro et al 2012c). In addition, multifrequency analyses based on A&A 575, A124 (2015) X-ray follow-up observations (e.g., Mirabal & Halpern 2009;Paggi et al 2013;Takeuchi et al 2013;Stroh et al 2013;Acero et al 2013) and radio campaigns (e.g., Petrov et al 2013) were also used to complete our search. However, all the proposed methods, even if coupled with X-ray observations, cannot guarantee that the selected candidates are indeed blazars and that the selection procedures are not contaminated by different source classes with blazar-like properties (e.g., Stern & Assef 2013).…”

Section: Introductionmentioning

confidence: 99%

Optical spectroscopic observations ofγ-ray blazar candidates

Massaro

Landoni

D’Abrusco

et al. 2015

A&A

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Context. We recently started a systematic search of low-energy counterparts of the unidentified γ-ray sources (UGSs) listed in the Fermi-Large Area Telescope (LAT) First Source Catalog (1FGL) and the Fermi-LAT 2-Year Source Catalog (2FGL). Aims. The main goal of our investigation is to find active galaxies belonging to the blazar class that lie within the positional uncertainty region of the UGSs and thus could be their potential low-energy counterparts. Methods. To achieve our aims, we first adopted several procedures based on the peculiar observational properties of blazars in the radio and in the IR. Then we carried out a follow-up spectroscopic campaign in the optical band to verify the nature of the candidates selected as potential counterparts of the UGSs. Here we present the results of the observations carried out in 2013 in the northern hemisphere at Kitt Peak National Observatory (KPNO). Optical spectroscopy is crucial to confirm the nature of the sources and can be used to estimate their redshifts; it will also allow us to test the robustness of our methods when the whole campaign is completed. Results. Here we present the optical spectroscopic observations of 39 sources. Within our sample we found that 6 sources are blazars, candidates to be low-energy counterparts of the UGSs listed in the 2FGL. We confirm that an additional 8 sources, previously classified as active galaxies of uncertain type and associated in the 2FGL, are also all BL Lac objects. Moreover, we also present 20 new spectra for known blazars listed in the Multi-frequency Catalogue of Blazars as having an uncertain redshift and/or being classified as BL Lac candidates. Conclusions. We conclude that our methods for selecting γ-ray blazar candidates allows us to discover new blazars and increase the list of potential low-energy counterparts for the Fermi UGSs.

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HUNTING FOR TREASURES AMONG THEFERMIUNASSOCIATED SOURCES: A MULTIWAVELENGTH APPROACH

Cited by 49 publications

References 34 publications

Optical Spectroscopic Survey of a Sample of Unidentified Fermi Objects

Optical Spectroscopic Survey of a Sample of Unidentified Fermi Objects

Research and characterisation of blazar candidates among theFermi/LAT 3FGL catalogue using multivariate classifications

Optical spectroscopic observations ofγ-ray blazar candidates

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