The colours of BL Lac objects: a new approach to their classification

Massaro, E.; Nesci, R.; Piranomonte, S.

doi:10.1111/j.1365-2966.2012.20782.x

Cited by 38 publications

(43 citation statements)

References 56 publications

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“…Three out of four sources are extragalactic, while WISE J122859.87+104032.8 has a clear WD optical spectrum, making it the only WD contaminant of the BZB region in the mid-IR color-color diagram. Moreover WISE J122859.87+104032.8 has a negative value of the u − r a situation that never occurs for the known BZBs (Massaro et al 2012c;Massaro et al 2014b). WISE J172633.50+530300.3 also shows a featureless optical spectrum with a peculiar continuum shape; this could be due to the presence of a nearby source clearly visible in the SDSS image but not in the WISE one.…”

Section: Bzbs Wds and Welqs At Mid-ir Wavelengthsmentioning

confidence: 98%

RADIO-WEAK BL LAC OBJECTS IN THEFERMIERA

Massaro

Marchesini

D’Abrusco

et al. 2017

ApJ

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The existence of "radio weak BL Lac objects" (RWBLs) has been an open question, still unsolved, since the discovery that quasars could be radio-quiet or radio-loud. Recently several groups identified RWBL candidates, mostly found while searching for low energy counterparts of the unidentified/unassociated gamma-ray sources listed in the Fermi catalogs. Confirming RWBLs is a challenging task since they could be confused with white dwarfs or weak emission line quasars when there are not sufficient data to precisely draw their broad band spectral energy distribution and their classification is mainly based on a featureless optical spectra. Motivated by the recent discovery that Fermi BL Lacs appear to have very peculiar mid-IR emission, we show that it is possible to distinguish between WDs, WELQs and BL Lacs using the [3.4]-[4.6]-[12]µm color-color plot built using the WISE magnitudes when the optical spectrum is available. On the basis of this analysis, we identify WISE J064459.38+603131 and WISE J141046.00+740511.2 as the first two genuine RWBLs, both potentially associated with Fermi sources. Finally, to strengthen our identification of these objects as true RWBLs, we present multifrequency observations for these two candidates to show that their spectral behavior is indeed consistent with those of the BL Lac population.

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Section: Bzbs Wds and Welqs At Mid-ir Wavelengthsmentioning

confidence: 98%

RADIO-WEAK BL LAC OBJECTS IN THEFERMIERA

Massaro

Marchesini

D’Abrusco

et al. 2017

ApJ

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“…However, these two sources appear to have an optical spectrum dominated by the emission of their host elliptical galaxies instead of by nonthermal continuum arising from their jet. To establish whether the optical emission is dominated by the host galaxy or by the jet emission, we adopted the same criterion as defined by Massaro et al (2012d) based on the calcium break (Ca, H, and K) contrast adapted to the SDSS optical colors. We considered the optical spectrum dominated by nonthermal emission if the flux emitted at frequencies above the Ca, H, and K was higher than the one radiated below.…”

Section: Roma-bzcat Sources With Uncertain Nature or Unknown Redshiftsmentioning

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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“…In a series of papers, Massaro et al (2011Massaro et al ( , 2012, D'Abrusco et al (2012) show that most blazars occupy a specific region of the IR colour-colour diagram, which they termed the blazar strip. In Paper I, we extended the blazar strip in the WISE colour-colour diagram to include all the Sedentary Survey blazars and called it the Sedentary WISE colour domain (SWCD).…”

Section: Introductionmentioning

confidence: 99%

2WHSP: A multi-frequency selected catalogue of high energy and very high energyγ-ray blazars and blazar candidates

Chang

Arsioli

Giommi

et al. 2017

A&A

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Aims. High synchrotron peaked blazars (HSPs) dominate the γ-ray sky at energies higher than a few GeV; however, only a few hundred blazars of this type have been cataloged so far. In this paper we present the 2WHSP sample, the largest and most complete list of HSP blazars available to date, which is an expansion of the 1WHSP catalogue of γ-ray source candidates off the Galactic plane. Methods. We cross-matched a number of multi-wavelength surveys (in the radio, infrared and X-ray bands) and applied selection criteria based on the radio to IR and IR to X-ray spectral slopes. To ensure the selection of genuine HSPs, we examined the SED of each candidate and estimated the peak frequency of its synchrotron emission (ν peak ) using the ASDC SED tool, including only sources with ν peak > 10 15 Hz (equivalent to ν peak > 4 eV). Results. We have assembled the largest and most complete catalogue of HSP blazars to date, which includes 1691 sources. A number of population properties, such as infrared colours, synchrotron peak, redshift distributions, and γ-ray spectral properties have been used to characterise the sample and maximize completeness. We also derived the radio log N-log S distribution. This catalogue has already been used to provide seeds to discover new very high energy objects within Fermi-LAT data and to look for the counterparts of neutrino and ultra high energy cosmic ray sources, showing its potential for the identification of promising high-energy γ-ray sources and multi-messenger targets.

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The colours of BL Lac objects: a new approach to their classification

Cited by 38 publications

References 56 publications

RADIO-WEAK BL LAC OBJECTS IN THEFERMIERA

RADIO-WEAK BL LAC OBJECTS IN THEFERMIERA

Optical spectroscopic observations ofγ-ray blazar candidates

2WHSP: A multi-frequency selected catalogue of high energy and very high energyγ-ray blazars and blazar candidates

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