J/ApJ/859/8ivo://CDS.VizieR/J/ApJ/859/8doi:10.26093/cds/vizier.18590008CDSLiu X.Dittmann A.Shen Y.Jiang L.2019-06-06T05:03:11Z2019-05-14T11:18:14ZCDS support team

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

cds-question@unistra.frvisible-astronomysloan-photometryquasarsA small fraction of quasars show an unusually high nitrogen-to-carbon ratio (N/C) in their spectra. These "nitrogen-rich" (N-rich) quasars are a long-standing puzzle because their interstellar medium implies stellar populations with abnormally high metallicities. It has recently been proposed that N-rich quasars may result from tidal disruption events (TDEs) of stars by supermassive black holes. The rapid enhancement of nitrogen and the depletion of carbon due to the carbon-nitrogen-oxygen cycle in supersolar mass stars could naturally produce high N/C. However, the TDE hypothesis predicts that the N/C should change with time, which has never hitherto been observed. Here we report the discovery of the first N-rich quasar with rapid N/C variability that could be caused by a TDE. Two spectra separated by 1.7yrs (rest-frame) show that the NIII]{lambda}1750/CIII]{lambda}1909 intensity ratio decayed by ~86%+/-14% (1{sigma}). Optical (rest-frame UV) light-curve and X-ray observations are qualitatively consistent with the TDE hypothesis; though, the time baseline falls short of a definitive proof. Putting the single-object discovery into context, statistical analyses of the ~80 known N-rich quasars with high-quality archival spectra show evidence (at a 5{sigma} significance level) of a decrease in N/C on timescales of >1 year (rest-frame) and a constant level of ionization (indicated by the CIII]{lambda}1909/CIV{lambda}1549 intensity ratio). If confirmed, our results demonstrate the method of identifying TDE candidates in quasars via abundance ratio variability, opening a new window of TDE observations at high redshift (z>2) with upcoming large-scale time-domain spectroscopic surveys.2018ApJ...859....8Lhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/859/8CatalogResearchIsServedByTAP VizieR generic servicerelated-toIX/10 : ROSAT All-Sky Bright Source Catalogue (1RXS) (Voges+ 1999)VIII/59 : the FIRST Survey, version 1999Jul (White+ 1999)VII/252 : SDSS-DR5 quasar catalog (Schneider+, 2007)VII/260 : The SDSS-DR7 quasar catalog (Schneider+, 2010)J/ApJS/166/470 : SDSS-Spitzer type I QSOs IR photometry (Richards+, 2006)J/ApJ/658/815 : Radio loudness of active galactic nuclei (Sikora+, 2007)J/ApJ/685/773 : X-ray-UV relations in SDSS DR5 QSOs (Gibson+, 2008)J/ApJ/679/962 : Quasars with strong nitrogen emission lines (Jiang+, 2008)J/ApJ/696/870 : Catalina Real-time Transient Survey (CRTS) (Drake+, 2009)J/ApJ/699/800 : Mass functions of active black holes (Vestergaard+, 2009)J/ApJS/183/17 : The SDSS DR5/XMM-Newton quasar survey (Young+, 2009)J/ApJS/194/45 : QSO properties from SDSS-DR7 (Shen+, 2011)J/ApJ/753/125 : NIR spectroscopy follow-up of 60 SDSS-DR7 QSOs (Shen+, 2012)J/ApJ/793/38 : Palomar Transient Factory phot. observations (Arcavi+, 2014)J/MNRAS/463/3813 : ASASSN-15oi UBVI M2W1W2 light curves (Holoien+, 2016)J/MNRAS/455/2918 : Phot. & line luminosities for ASASSN-14li (Holoien+, 2016)J/ApJ/819/154 : SDSS-DR7 QSOs with X-ray and UV luminosities (Lusso+, 2016)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/859/8https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/859/8http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/859/8https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/859/8https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/859/8http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/859/8GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tap2.040811542443644e-19 6.090060298487514e-19OpticaldefaultJ/ApJ/859/8/table2Optical photometry from the literature for SDSS J120414.37+351800.5recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMJD[53108.2/56449.3] Modified Julian Datedtime.epochdoubleVmag[18/19.5]? CRTS V-band Vega magnitudemagphot.mag;em.opt.Vfloatnullablee_Vmag[0.1/0.4]? The 1{sigma} uncertainty in Vmagmagstat.error;phot.mag;em.opt.VfloatnullableRmag[18.7/19.8]? PTF R-band Vega magnitudemagphot.mag;em.opt.Rfloatnullablee_Rmag[0.04/0.3]? The 1{sigma} uncertainty in Rmagmagstat.error;phot.mag;em.opt.Rfloatnullableumag[19.34]? SDSS u-band AB magnitudemagphot.mag;em.opt.Ufloatnullablee_umag[0.03]? The 1{sigma} uncertainty in umagmagstat.error;phot.mag;em.opt.Ufloatnullablegmag[18.84]? SDSS g-band AB magnitudemagphot.mag;em.opt.Bfloatnullablee_gmag[0.01]? The 1{sigma} uncertainty in gmagmagstat.error;phot.mag;em.opt.Bfloatnullablermag[18.74]? SDSS r-band AB magnitudemagphot.mag;em.opt.Rfloatnullablee_rmag[0.01]? The 1{sigma} uncertainty in rmagmagstat.error;phot.mag;em.opt.Rfloatnullableimag[18.75]? SDSS i-band AB magnitudemagphot.mag;em.opt.Ifloatnullablee_imag[0.01]? The 1{sigma} uncertainty in imagmagstat.error;phot.mag;em.opt.Ifloatnullablezmag[18.48]? SDSS z-band AB magnitudemagphot.mag;em.opt.Ifloatnullablee_zmag[0.03]? The 1{sigma} uncertainty in zmagmagstat.error;phot.mag;em.opt.Ifloatnullable