J/ApJS/207/4 Unidentified γ-ray sources. III. Radio (Massaro+, 2013)
Unveiling the nature of the unidentified γ-ray sources.
III. Gamma-ray blazar-like counterparts at low radio frequencies.
Massaro F., D'Abrusco R., Giroletti M., Paggi A., Masetti N., Tosti G.,
Nori M., Funk S.
<Astrophys. J. Suppl. Ser., 207, 4 (2013)>
=2013ApJS..207....4M 2013ApJS..207....4M
ADC_Keywords: Photometry, infrared ; Radio sources ; Gamma rays ;
Active gal. nuclei
Keywords: BL Lacertae objects: general - galaxies: active -
gamma rays: galaxies - gamma rays: general - quasars: general -
radiation mechanisms: non-thermal - radio continuum: galaxies
Abstract:
About one-third of the γ-ray sources listed in the second Fermi
Large Area Telescope catalog (2FGL) have no firmly established
counterpart at lower energies and so are classified as unidentified
γ-ray sources (UGSs). Here, we propose a new approach to find
candidate counterparts for the UGSs based on the 325 MHz radio survey
performed with the Westerbork Synthesis Radio Telescope in the
northern hemisphere. First, we investigate the low-frequency radio
properties of blazars, the largest known population of γ-ray
sources; then we search for sources with similar radio properties
combining the information derived from the Westerbork Northern Sky
Survey (WENSS, Rengelink et al. 1997, Cat. J/A+AS/124/259; superseded
by Cat. VIII/62) with those of the NRAO Very Large Array Sky Survey
(NVSS, Condon et al. 1998, Cat. VIII/65). We present a list of
candidate counterparts for 32 UGSs with at least one counterpart in
the WENSS. We also performed an extensive research in the literature
to look for infrared and optical counterparts of the γ-ray
blazar candidates selected using the low-frequency radio observations
to confirm their nature. On the basis of our multifrequency research,
we identify 23 new γ-ray blazar candidates out of the 32 UGSs
investigated. Comparison with previous results on the UGSs is also
presented. Finally, we speculate on the advantages of using
low-frequency radio observations to associate UGSs and to search for
γ-ray pulsar candidates.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 114 58 Unidentified γ-ray sources (32 unique 2FGL)
--------------------------------------------------------------------------------
See also:
II/311 : WISE All-Sky Data Release (Cutri+ 2012)
VIII/62 : The Westerbork Northern Sky Survey (Leiden, 1998)
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
J/ApJS/206/17 : New gamma-ray blazar candidates in the 3PBC (Maselli+, 2013)
J/ApJS/206/13 : Unidentified gamma-ray sources. Paper II. (Massaro+, 2013)
J/ApJS/206/12 : Unidentified gamma-ray sources. Paper I. (D'Abrusco+, 2013)
J/ApJS/199/31 : Fermi LAT second source catalog (2FGL) (Nolan+, 2012)
J/ApJ/744/177 : VLBA 5GHz observations of Fermi/LAT AGN (Linford+, 2012)
J/ApJ/743/171 : The 2LAC catalog (Ackermann+, 2011)
J/ApJ/726/16 : γ-ray loud blazars (Linford+, 2011)
J/ApJ/709/1407 : SED of the Fermi blazars (Li+, 2010)
J/ApJS/175/97 : CGRaBS: γ-ray blazar candidates survey (Healey+, 2008)
J/ApJ/626/95 : Gamma-ray blazar candidates (Sowards-Emmerd+, 2005)
J/ApJ/609/564 : Blazar counterparts for 3EG sources (Sowards-Emmerd+, 2004)
J/ApJ/590/109 : Gamma-ray blazar in northern sky (Sowards-Emmerd+, 2003)
J/A+A/379/755 : Radio data of X- and gamma-ray loud blazars (Venturi+, 2001)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- 2FGL 2FGL name (JHHMM.m+DDMM)
14- 15 A2 --- --- [WN]
17- 27 A11 --- WN WENSS name (HHMM.m+DDMM)
29 A1 --- f_WN [AB*] Flag on WENSS name (1)
31- 34 A4 --- --- [NVSS]
36- 49 A14 --- NVSS NVSS name (JHHMMSS+DDMMSS)
51- 55 F5.2 --- alpha [-0.1,2.1] Radio spectral index α
between 1400 and 325MHz
(S(ν)∝ν-α)
57- 61 F5.2 mag [3.4/4.6] [-0.61,1.15]? WISE [3.4]-[4.6] color index
63- 66 F4.2 mag e_[3.4/4.6] [0.03,0.43]? [3.4/4.6] 1σ error
68 A1 --- l_[4.6/12] Limit flag on [4.6/12]
70- 73 F4.2 mag [4.6/12] [0.93,4.73]? WISE [4.6]-[12] color index
75- 78 F4.2 mag e_[4.6/12] [0.04,0.5]? [4.6/12] 1σ error
80 A1 --- l_[12/22] Limit flag on [12/22]
82- 85 F4.2 mag [12/22] [1.76,4.54]? WISE [12]-[22] color index
87- 90 F4.2 mag e_[12/22] [0.11,0.61]? [12/22] 1σ error
92-108 A17 --- Notes Note(s) (2)
110-114 F5.3 --- z ? Redshift
--------------------------------------------------------------------------------
Note (1): The capital letter indicates a γ-ray blazar candidate
of type A (-1.00<α<0.55) or type B (0.55<α<0.65),
respectively (α is the spectral index between 1400 and 325MHz).
We found 22 γ-ray blazar candidates, 14 of type A and 8 of type
B, out of the 32 unidentified γ-ray sources (UGSs) selected with
at least a WENSS radio source as a candidate counterpart. See Section
3 for details. The source WN 1514.8+3701 (flagged with an "*") can be
considered to be a blazar-like source on the basis of the
multifrequency investigation (see Section 5 for more details) even if
its α1400325 spectral index is not in agreement with the
type A and type B candidates.
Note (2): Note as follows:
N = NVSS (VIII/65)
F = FIRST (VIII/90)
M = 2MASS (II/246)
w = WISE (II/311)
s = SDSS dr9 (V/139)
QSO = quasar
v = variable in WISE bands (var_flag>5 in at least one band;
see Cutri et al. 2012, Cat. II/311, for additional details);
rv = variable in the radio bands at 1.4GHz.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
References:
D'Abrusco et al. Paper I. 2013ApJS..206...12D 2013ApJS..206...12D Cat. J/ApJS/206/12
Massaro et al. Paper II. 2013ApJS..206...13M 2013ApJS..206...13M Cat. J/ApJS/206/13
(End) Emmanuelle Perret [CDS] 08-Aug-2013