J/A+A/708/A220 BASALT faint blazar candidates (Casadei+, 2026)
A new sample of faint Blazar cAndidates with Strong opticAl variabiLiTy
(BASALT).
Casadei S., Raiteri C.M., Carnerero M.I., Capetti A., Massaro F.
<Astron. Astrophys. 708, A220 (2026)>
=2026A&A...708A.220C 2026A&A...708A.220C (SIMBAD/NED BibCode)
ADC_Keywords: BL Lac objects ; Galaxies, radio ; Photometry, infrared ; Optical
Keywords: catalogs - surveys - galaxies: active - BL Lacertae objects: general
Abstract:
We present a sample of blazar candidates from the Very Large Array Sky
Survey (VLASS) catalog, with cross-referencing to optical and infrared
data from the Panoramic Survey Telescope & Rapid Response System
(Pan-STARRS) and the Wide-Field Infrared Survey Explorer (WISE),
respectively. We focus on compact radio sources and employ a
multistage selection process to minimize contamination from non-blazar
sources. We considered constraints derived from the radio-optical
spectral index and from the infrared and optical colors. We identified
the variable objects through an optical variability analysis of
Pan-STARRS light curves using two reference samples of stars. We
further selected sources whose variability exceeds the level observed
in quasars. This led to the selection of 3467 candidates with
blazar-like properties and strong optical variability. Only 45% is
available in other blazar candidate catalogs, with the remainder
representing new identifications. In particular, we unveil a large
population of faint sources, down to r∼20.5. The blazar nature
of a subsample of these sources is confirmed by available spectra. Our
work offers new insights into the blazar population and serves as a
foundation for future variability studies, especially in view of the
upcoming Legacy Survey of Space and Time at the Vera C. Rubin
Observatory, which will reach even fainter sources.
Description:
Full version of Table A.1 from the paper, including multiwavelength
properties of faint blazar candidates selected through strong optical
variability (BASALT sample).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 299 3467 BASALT sample
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Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 12 E12.6 mag Medianmag Median synthetic magnitude
14- 25 E12.6 mag MAD Median absolute deviation (1)
27- 57 A31 --- CompName VLASS component name
59- 73 F15.11 deg RAdeg Right Ascension (VLASS) (J2000) (2)
75- 89 F15.11 deg DEdeg Declination (VLASS) (J2000) (2)
91-102 E12.6 deg e_RAdeg Uncertainty on RAdeg
104-115 E12.6 deg e_DEdeg Uncertainty on DEdeg
117-128 E12.6 mJy Ftot Integrated radio flux density
130-141 E12.6 mJy e_Ftot Uncertainty on total flux
143-154 E12.6 mJy Fpeak Peak radio flux density
156-167 E12.6 mJy e_Fpeak Uncertainty on peak flux
169-180 E12.6 arcsec Maj Major axis
182-193 E12.6 arcsec e_Maj Uncertainty on major axis
195-201 F7.5 --- Citoh Compactness factor (Citoh)
203-209 F7.4 mag gmag Pan-STARRS PSF g magnitude (3)
211-218 F8.6 mag e_gmag ?=- Uncertainty on gmag
220-226 F7.4 mag gKmag ?=- Pan-STARRS Kron g magnitude (3)
228-235 F8.6 mag e_gKmag ?=- Uncertainty on gKmag
237-243 F7.4 mag rmag Pan-STARRS PSF r magnitude (3)
245-252 F8.6 mag e_rmag ?=- Uncertainty on rmag
254-260 F7.4 mag rKmag ?=- Pan-STARRS Kron r magnitude (3)
262-269 F8.6 mag e_rKmag ?=- Uncertainty on rKmag
271-279 F9.6 --- alfaRO Radio-to-optical spectral index
281-289 F9.6 mag W1mag WISE W1 magnitude
291-299 F9.6 mag W2mag WISE W2 magnitude
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Note (1): MAD is used as a variability indicator.
Note (2): VLASS: Very Large Arra
Note (3): Pan-STARRS magnitudes include PSF and Kron measurements.
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Acknowledgements:
Samantha Casadei, samantha.casadei(at)unito.it
License: CC-BY-4.0 [see https://spdx.org/licenses/]
(End) Samantha Casadei [UniTo, Italia], Patricia Vannier [CDS] 25-Mar-2026