J/AJ/161/196ivo://CDS.VizieR/J/AJ/161/196doi:10.26093/cds/vizier.51610196CDSPena-herazo H.A.Massaro F.Gu M.Paggi A.Landoni M.D'abrusco R.,Ricci F.Masetti N.Chavushyan V.2022-12-14T08:35:23Z2021-07-15T13:31:50ZCDS support team

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

cds-question@unistra.frbl-lacertae-objectsquasarsactive-galactic-nucleiredshiftedvisible-astronomyThe extragalactic {gamma}-rays sky observed by the Fermi Large Area Telescope (LAT) is dominated by blazars. In the fourth release of the Fermi LAT Point Source Catalog (4FGL) are sources showing a multifrequency behavior similar to that of blazars but lacking an optical spectroscopic confirmation of their nature, known as blazar candidates of uncertain type (BCUs). We aim at confirming the blazar nature of BCUs and test if new optical spectroscopic observations can reveal spectral features, allowing us to get a redshift estimate for known BL Lac objects. We also aim to search for and discover changing-look blazars (i.e., blazars that show a different classification at different epochs). We carry out an extensive search for optical spectra available in the Large Sky Area Multi-object Fibre Spectroscopic Telescope (LAMOST) Data Release 5 (DR5) archive. We select sources out of the 4FGL catalog, the list of targets from our follow-up spectroscopic campaign of unidentified or unassociated {gamma}-ray sources, and the multifrequency catalog of blazars: the Roma-BZCAT. We select a total of 392 spectra. We also compare some of the LAMOST spectra with those available in the literature. We classify 20 BCUs confirming their blazar-like nature. Then we obtain 15 new redshift estimates for known blazars. We discover 26 transitional (i.e., changing-look) blazars that changed their classification. Finally, we are able to confirm the blazar-like nature of six BL Lac candidates. All remaining sources analyzed agree with previous classifications. BL Lac objects are certainly the most elusive type of blazars in the {gamma}-ray extragalactic sky.2021AJ....161..196Phttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/161/196CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toIX/32 : ROSAT Bright Survey (Fischer+, 1998-2000)VII/259 : 6dF galaxy survey final redshift release (Jones+, 2009)VII/274 : The Roma BZCAT - 5th edition (Massaro+, 2015)V/164 : LAMOST DR5 catalogs (Luo+, 2019)J/ApJ/707/L56 : VLBI and bright Fermi/LAT sources (Kovalev, 2009)J/ApJ/715/429 : First Fermi-LAT AGN catalog (1LAC) (Abdo+, 2010)J/ApJ/716/30 : SED of Fermi bright blazars (Abdo+, 2010)J/ApJS/188/405 : Fermi-LAT first source catalog (1FGL) (Abdo+, 2010)J/ApJ/748/49 : Optical spectroscopy of 1LAC broad-line blazars (Shaw+, 2012)J/ApJ/748/68 : WISE IR colors of gamma-ray blazars (D'Abrusco+, 2012)J/ApJ/752/61 : Blazars in unidentified gamma-ray sources (Massaro+, 2012)J/ApJ/753/83 : Associations to 1FGL sources (Ackermann+, 2012)J/ApJ/756/33 : X-ray sources near 2 bright gamma-ray sources (Cheung+, 2012)J/ApJS/199/31 : Fermi LAT second source catalog (2FGL) (Nolan+, 2012)J/ApJS/201/10 : SDSS quasar catalog with Swift observations (Wu+, 2012)J/AJ/146/120 : MOJAVE. X. Parsec-scale kinematics of AGNs (Lister+, 2013)J/ApJ/763/L36 : MgII and FeII flux of the blazar 3C454.3 (Leon-Tavares+, 2013)J/ApJ/764/135 : Spectroscopic redshifts of BL Lac objects (Shaw+, 2013)J/ApJ/779/133 : X-ray & radio fluxes unassociated 2FGL sources (Acero+, 2013)J/ApJS/206/12 : Blazars with gamma-ray counterparts. I. (D'Abrusco+, 2013)J/ApJS/206/13 : Blazars with gamma-ray counterparts. II. (Massaro+, 2013)J/ApJS/207/4 : Unidentified gamma-ray sources. III. Radio (Massaro+, 2013)J/ApJS/207/16 : BL Lac candidates for TeV observations (Massaro+, 2013)J/ApJS/208/25 : Swift X-ray observations of 1FGL sources (Takeuchi+, 2013)J/ApJS/209/9 : Unidentified gamma-ray sources. IV. X-ray (Paggi+, 2013)J/ApJS/209/10 : UGSs. V. kernel approach (Massaro+, 2013)J/MNRAS/432/1294 : Fermi unassociated sources ATCA observations (Petrov+, 2013)J/ApJ/780/73 : Redshifts of BL Lac objects from Fermi (Ajello+, 2014)J/ApJ/782/41 : 231 AGN candidates from the 2FGL catalog (Doert+, 2014)J/ApJS/215/14 : WISE cand. gamma-ray blazar radio sources (D'Abrusco+, 2014)J/A+A/579/A34 : 1WHSP: VHE gamma-ray blazar candidates (Arsioli+, 2015)J/ApJ/810/14 : Third catalog of LAT-detected AGNs (3LAC) (Ackermann+, 2015)J/ApJS/217/2 : Refined associations of Fermi/LAT sources (Massaro+, 2015)J/ApJS/217/4 : 2FGL sources observed between 5-9GHz (Schinzel+, 2015)J/ApJS/218/23 : Fermi LAT third source catalog (3FGL) (Acero+, 2015)J/A+A/588/A141 : The MWA view of Fermi blazars (Giroletti+, 2016)J/ApJS/222/5 : The second Fermi-LAT >50GeV catalog (2FHL) (Ackermann+, 2016)J/ApJS/224/26 : Spectral energy distributions Roma BZCAT blazars (Mao+, 2016)J/ApJS/226/20 : X-ray, opt. & radio SEDs of Fermi blazars (Fan+, 2016)J/ApJ/838/139 : Radio follow-up on 3FGL unassociated sources (Schinzel+, 2017)J/MNRAS/470/1291 : Classifying 3FGL with ANN (Salvetti+, 2017)J/ApJ/861/130 : BL Lac objects GTC low resolution spectroscopy (Landoni+,2018)J/A+A/631/A150 : Softly X-raying the gamma-ray sky I. (Marchesini+, 2019)J/ApJ/887/18 : Classific. of X-ray counterparts of 3FGL sources (Kaur+, 2019)J/ApJS/242/4 : Two new catalogs of blazar candidates (D'Abrusco+, 2019)J/A+A/643/A103 : Fermi-LATi sources low-energy counterparts (Pena-Herazo+,2020)J/ApJS/247/33 : The Fermi LAT fourth source catalog (4FGL) (Abdollahi+, 2020)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/161/196https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/161/196http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/161/196https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/161/196https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/161/196http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/161/196GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/AJ/161/196/table1 (Classification results)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/161/196/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/161/196/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/161/196/table1?GETtext/xml+votable180.050000true1.33420835.40297220.0055555555555555566/29 49 532 615 730-731 851 1120 2066 2098 2100 2107 2228 2249 2255 2273 2280 2295 2439 2441 2484 2564 2601 2610 2616 2621 2628 2650 2671 4160 4312 4405 4543 4550 4601 4695-4696 4748 4795 4865 4918 4940 4960 4963-4964 4968 4992 5009 5033 5072 5098 5119 5139 5154 5163 5191-5192 5200-5201 5212 5270 5284 5303 5306 5311 5352-5353 5364 5371 5491 5510 5516 5522-5523 5536 5546 5552-5553 5567 5574 5584 5592 5637 5645 5676 5723 5767 5792 5801 5804 5814 5817 5821 5836 5864 5867 5870 5918 5985 5990 6004 6014-6015 6018 6067 6096 6104 6200 6244 6252 6348 6361-6362 6406 6409 6465 6477 6483 6496 6498-6499 6501 6504 6507 6515 6519 6534 6548-6549 6619 6623 6646-6647 6754 6815 7176 7192 7212 7222 7261 7265 7315-7316 7346 7354 7426 8321 8374 8615 8699 8741 8751 8759 8762 8805 8858 8868 8915 8943 8955 9003 9060 9075 9104 9123 9136 9151 9159 9164 9168 9196 9244 9284 9311 9321 9327 9353 9369 9372 9383 9402 9472 9497 9501 9546 9637 9655 9669 9676 9705 9723 10061 10148 10152 10157 10250 10319 10337 10401 10409 10426 10440 10512 10519 10522 10524 10526 10550 10561 10571-10572 10650 10706 10715 10756 10780 10798 10810 10815 10848 10932 10949 10969 10996 11027 11035 11094 11118 11124 11126 11143 11153 11212 11267 11290 11334 11429 11444 11490 13586 13650 13692 13705 13796 17657 17732 17785 17791 17820 18005 18035 18096 18110 18158 18183-18184 18190 18210 18214 18253 18343 18812 18868 18871 18902 19056 19085 19144 19200 19217 19246 19271 19281 19332 19344 19436 19483 19499 19566 19593 19609 19616 19618 19629 19872 19907 20005 20049 20072 20099 20141 20195 20290 20438 20468 22501 23222 23261 23901 24027 25937 25948 25983 26035 26073 26203 26244 26248 26254 26274 26278 26283 26292 26297 26310 26390 26470 26483 26539 26550 26571 26595-26596 26614 26946 26975 27003 27021 27034 27036 27063 27080 27082 27095 27212 27217 27219 27243 27290 27324 27423 27573 27612 27711 27750 27796-27798 27846 27851 27905 27945 28002 28037 28066 28083 28138-28139 28167 28208 28210 28270 28315 28318 28342-28343 28383 28432 28471 28492 28495 28517 28532 28539 28561 28583 28589 28616 28618 31407 31430 31656 32497 32511 32641 45044https://cdsarc.cds.unistra.fr/viz-bin/moc/J/AJ/161/196?format=asciiOpticaldefaultJ/AJ/161/196/table1Classification resultsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintCatOriginal sample catalog (1)src.sample;meta.tablecharNameSource namemeta.id;meta.maincharClass1Class in the sample catalog (2)src.classcharz1[0.01/3.41]? Redshift in the sample catalogsrc.redshiftdoublenullableLAMOSTLAMOST designated namemeta.id.crosscharClass2Class identified thanks to our analysis (2)src.classcharz2[0.01/3.43]? Redshift measurement thanks to our analysissrc.redshiftfloatnullableSDSSspec?True/false flag indicating an available SDSS spectrum (204 false, 188 true)meta.codecharSimbadSimbad column added by the CDSmeta.ref.urlchar_RAPositions from LAMOST names (right ascension part)degpos.eq.ra;meta.main_DEPositions from LAMOST names (declination part)degpos.eq.dec;meta.main