J/ApJS/207/4ivo://CDS.VizieR/J/ApJS/207/4doi:10.26093/cds/vizier.22070004CDSMassaro F.D'Abrusco R.Giroletti M.Paggi A.Masetti N.Tosti G.,Nori M.Funk S.2017-10-09T13:34:16Z2013-09-24T16:53:56ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frinfrared-photometryradio-sourcesgamma-ray-astronomyactive-galactic-nucleiAbout one-third of the {gamma}-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 {gamma}-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 {gamma}-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 J/A+AS/124/259; superseded by Cat.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 {gamma}-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 {gamma}-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 {gamma}-ray pulsar candidates.2013ApJS..207....4Mhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJS/207/4CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toII/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 : {gamma}-ray loud blazars (Linford+, 2011)J/ApJ/709/1407 : SED of the Fermi blazars (Li+, 2010)J/ApJS/175/97 : CGRaBS: {gamma}-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)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJS/207/4https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJS/207/4http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJS/207/4https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJS/207/4https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJS/207/4http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJS/207/4GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJS/207/4/table2 (Unidentified {gamma}-ray sources (32 unique 2FGL))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJS/207/4/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJS/207/4/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJS/207/4/table2?GETtext/xml+votable180.050000true0.6862.340.0055555555555555566/2754 3054 3099 3130 3338 3465 3871 4088 5352 6062 6292 7131 7405 7767 7936 9175 9821 9855 10096 11290 11457 12207 12277 13278 13279 15400 15468 15677 15783 24566 32628 32739https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJS/207/4?format=asciiInfraredRadioGamma-raydefaultJ/ApJS/207/4/table2Unidentified {gamma}-ray sources (32 unique 2FGL)l_[4.6/12]Limit flag on [4.6/12]meta.code.errorchar2FGL2FGL name (JHHMM.m+DDMM)meta.id.assoccharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintWNWENSS name (HHMM.m+DDMM)meta.idcharf_WN[AB*] Flag on WENSS name (1)meta.codecharNVSSNVSS name (JHHMMSS+DDMMSS)meta.id;meta.maincharalpha[-0.1,2.1] Radio spectral index {alpha} between 1400 and 325MHz (S({nu}){prop.to}{nu}^-{alpha}^)spect.index;em.radio.200-400MHzfloat[3.4/4.6][-0.61,1.15]? WISE [3.4]-[4.6] color indexmagphot.color;em.IR;em.IRfloatnullablee_[3.4/4.6][0.03,0.43]? [3.4/4.6] 1{sigma} errormagstat.errorfloatnullable[4.6/12][0.93,4.73]? WISE [4.6]-[12] color indexmagphot.color;em.IR;em.IRfloatnullablee_[4.6/12][0.04,0.5]? [4.6/12] 1{sigma} errormagstat.errorfloatnullablel_[12/22]Limit flag on [12/22]meta.code.errorchar[12/22][1.76,4.54]? WISE [12]-[22] color indexmagphot.color;em.IR;em.IRfloatnullablee_[12/22][0.11,0.61]? [12/22] 1{sigma} errormagstat.errorfloatnullableNotesNote(s) (2)meta.notecharz? Redshiftsrc.redshiftfloatnullableSimbadSimbad column added by the CDSmeta.ref.urlcharNEDSimbad column added by the CDSmeta.ref.urlchar_RAPositions from 2FGL catalog (J/ApJS/199/31) (right ascension part)degpos.eq.ra;meta.main_DEPositions from 2FGL catalog (J/ApJS/199/31) (declination part)degpos.eq.dec;meta.main