J/ApJS/206/12 Blazars with γ-ray counterparts. I. (D'Abrusco+, 2013)
Unveiling the nature of unidentified γ-ray sources.
I. A new method for the association of γ-ray blazars.
D'Abrusco R., Massaro F., Paggi A., Masetti N., Tosti G., Giroletti M.,
Smith H.A.
<Astrophys. J. Suppl. Ser., 206, 12 (2013)>
=2013ApJS..206...12D 2013ApJS..206...12D
ADC_Keywords: BL Lac objects ; Photometry, infrared ; Redshifts ; QSOs ;
Gamma rays ; Cross identifications
Keywords: BL Lacertae objects: general - catalogs - galaxies: active -
gamma rays: general - infrared: general -
radiation mechanisms: non-thermal
Abstract:
We present a new method for identifying blazar candidates by examining
the locus, i.e., the region occupied by the Fermi γ-ray blazars
in the three-dimensional color space defined by the WISE infrared
colors. This method is a refinement of our previous approach that made
use of the two-dimensional projection of the distribution of WISE
γ-ray-emitting blazars (the Strip) in the three WISE color-color
planes. In this paper, we define the three-dimensional locus by means
of a principal component analysis of the color distribution of a large
sample of blazars composed of all the ROMA-BZCAT sources with
counterparts in the WISE All-Sky Catalog associated with γ-ray
sources in the second Fermi-LAT catalog (2FGL; the WISE Fermi blazars
sample, WFB). Our new procedure yields a total completeness of
ctot∼81% and a total efficiency of etot∼97%. We also obtain local
estimates of the efficiency and completeness as functions of the WISE
colors and galactic coordinates of the candidate blazars. The catalog
of all WISE candidate blazars associated with the WFB sample is also
presented, complemented by archival multi-frequency information for
the alternative associations. Finally, we apply the new association
procedure to all γ-ray blazars in the 2FGL and provide a catalog
containing all the γ-ray candidate blazars selected according to
our procedure.
Description:
The starting sample used in our analysis is the one presented in the
ROMA-BZCAT v4.1 (Massaro et al. 2009, Cat. J/A+A/495/691), released
in 2012 August, the most comprehensive blazar catalog existing in the
literature with 3149 bona fide blazars and blazar candidates.
We note that the coordinates reported in the ROMA-BZCAT are
non-uniform. The astrometric accuracy can be as low as ∼5",
corresponding to the uncertainty of the NRAO Very Large Array Sky
Survey (NVSS) for sources with radio fluxes close to the survey limit
(Condon et al. 1998, Cat. VIII/65). For this reason, we have developed
a method to perform the positional association between the ROMA-BZCAT
blazars and their WISE counterparts. We found 3032 out of 3149 (i.e.,
96.3% of the ROMA-BZCAT) blazars with an IR counterpart within 3.3" in
the WISE All-Sky data archive. Of these 3032 blazars, 1172 are BZBs
(BL Lac objects), including 919 BL Lac objects and 253 BL Lac
candidates, 1642 are BZQs (flat spectrum radio quasar), and 218 are
BZUs (blazar of uncertain type).
Among the 3032 selected blazars, only 673 have a counterpart in the
γ-rays according to the 2FGL and to the CLEAN sample presented
in the second Fermi-LAT catalog of AGNs (2LAC; Ackermann et al.
2011ApJ...743..171A 2011ApJ...743..171A). The sample of γ-ray-emitting blazars in
the ROMA-BZCAT catalog was derived excluding the BZU sources from our
sample of γ-ray-loud blazars. For this reason, the final WISE
Fermi Blazar Sample (WFB) sample includes only 610 WISE sources out of
673 WISE counterparts.
The sample of γ-ray blazars associated with the 2FGL contains
752 γ-ray sources, excluding all sources with any analysis flag.
We excluded from this list the 610 blazars already contained in the
WFB sample for a final number of 142 2FGL sources. These γ-ray
sources constitute the 2FGL Fermi blazar sample (hereinafter 2FB). The
2FB sample has been investigated with our association procedure
following the same approach used for the WFB sample.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table6.dat 118 10 *First 10 candidate blazars associated with WFB
sources that do not correspond to the WISE
counterparts of the associations in the 2FGL cat
table7.dat 120 10 *First 10 candidate blazars associated with
2FB sources
table8.dat 118 610 WISE Fermi blazar sample (WFB)
table9.dat 120 76 Fermi 2FGL blazar sample (2FB)
--------------------------------------------------------------------------------
Note on table6.dat: Table 6 shows some basic information for the first 10
candidate blazars associated with the WFB sample but representing alternative
associations of the γ-ray sources in the WFB sample (i.e., different
WISE sources from the counterparts identified for the WFB sample with the
positional method described in Section 2.2).
Note on table7.dat: The complete list of 2FB associations can be found in
Table 9 but with slightly differences in magnitudes.
--------------------------------------------------------------------------------
See also:
II/311 : WISE All-Sky Data Release (Cutri+ 2012)
J/A+A/495/691 : Multifrequency catalog of blazars Roma-BZCAT (Massaro+, 2009)
J/ApJS/206/17 : New gamma-ray blazar candidates in the 3PBC (Maselli+, 2013)
J/ApJS/206/13 : Unidentified gamma-ray sources. II. (Massaro+, 2013)
J/ApJS/199/31 : Fermi LAT second source catalog (2FGL) (Nolan+, 2012)
J/A+A/541/A160 : X+gamma-ray observations of selected blazars (Giommi+, 2012)
J/A+A/538/A26 : BL Lac objects beyond z=1.3 (Rau+, 2012)
J/ApJ/743/171 : The 2LAC catalog (Ackermann+, 2011)
J/ApJ/732/116 : IR spectra of γ-ray bright blazars (Malmrose+, 2011)
J/ApJ/722/520 : Gamma-ray light curves of Fermi blazars (Abdo+, 2010)
J/ApJ/716/30 : SED of Fermi bright blazars (Abdo+, 2010)
J/ApJ/709/1407 : SED of the Fermi blazars (Li+, 2010)
J/ApJ/700/597 : FERMI LAT detected blazars (Abdo+, 2009)
Byte-by-byte Description of file: table[6789].dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- --- [2FGL]
5- 16 A12 --- 2FGL 2FGL name of the γ-ray source
associated (JHHMM.m+DDMM)
18- 36 A19 --- WISE WISE name of the candidate blazar
(JHHMMSS.ss+DDMMSS.s)
38- 67 A30 --- OName Alternative name in the litterature
(ROMA-BZCAT name for table 8)
69- 72 F4.2 mag [3.4/4.6] WISE 3.4-3.6 um color index (c1)
74- 77 F4.2 mag e_[3.4/4.6] 3.4-3.6 color index uncertainty
79- 82 F4.2 mag [4.6/12] WISE 4.6-12 um color index (c2)
84- 87 F4.2 mag e_[4.6/12] 4.6-12 color index uncertainty
89- 92 F4.2 mag [12/22] WISE 12-22 um color index (c3)
94- 97 F4.2 mag e_[12/22] 12-22 color index uncertainty
99-101 A3 --- Type Classification of the candidate blazar
according to our method (BZB=BL Lac object,
BZQ=Flat Spectrum Radio Quasar)
103 A1 --- Class [ABC] Class of the candidate blazar
according to our method (1)
105-109 A5 --- Notes Notes about available associations (2)
111-115 F5.3 --- z [0.02/3.11]? Redshift of the source
116 A1 --- u_z [?] Uncertainty flag on redshift
118 I1 --- Nbr ? Number of WISE sources in the background
region (3)
120 A1 --- Flag Reassociation flag (4)
--------------------------------------------------------------------------------
Note (1): The classes are sorted according to decreasing probability of the
WISE source being compatible with the model of the WFB locus: class A
sources are considered the most probable candidate blazars for the
high-energy source, while class B and class C sources are less
compatible with the WFB locus but are still deemed candidate blazars.
In more detail, class A candidate blazars have score S≤S90%, class
B candidate blazars have score S60%≤S≤S90%, and class C
candidate blazars have score S30%≤S≤S60% for each region. The
other sources considered outliers are discarded.
Note (2): Note about the available multi-wavelength information of the WISE
source, if already observed and/or classified:
M = 2MASS,
X = ROSAT;
s = SDSS DR8,
N = NVSS,
v = variable in WISE (var_flag>5 in at least one WISE filter)
Note (3): Number of WISE sources in the background region (BR) of the
γ-ray source selected as candidate blazars with class equal to
or higher than the class of the best candidate blazar selected in the
search radius of the high-energy source. The background region is the
annulus between r and r.sqrt(2) centered on the high-energy source and
r its search radius. See section 4.2.
Note (4): Flag indicating whether our association corresponds to the
association provided in the 2FGL catalog ("y"), or otherwise ("n").
--------------------------------------------------------------------------------
History:
From electronic version of the journal
References:
Massaro et al. Paper II. 2013ApJS..206...13M 2013ApJS..206...13M Cat. J/ApJ/206/13
Massaro et al. Paper III. 2013ApJS..207....4M 2013ApJS..207....4M Cat. J/ApJS/207/4
γ-ray-emitting blazars have infrared colors that distinguish them
from other galactic and extragalactic sources in the three-dimensional IR
color space:
Massaro et al. 2011bzc3.book.....M 2011bzc3.book.....M See Cat. J/A+A/495/691
D'Abrusco et al. 2012ApJ...748...68D 2012ApJ...748...68D
We used these results to develop an association method able to identity
IR-selected blazar candidates as low-energy counterparts of a γ-ray
source:
Massaro et al. 2012ApJ...750..138M 2012ApJ...750..138M
Massaro et al. 2012ApJ...752...61M 2012ApJ...752...61M
(End) Emmanuelle Perret [CDS] 24-Jun-2013