J/ApJ/870/13ivo://CDS.VizieR/J/ApJ/870/13doi:10.26093/cds/vizier.18700013CDSShappee B.J.Holoien T.W.-S.Drout M.R.Auchettl K.Stritzinger M.D.,Kochanek C.S.Stanek K.Z.Shaya E.Narayan G. (The ASAS-SN)Brown J.S.,Bose S.Bersier D.Brimacombe J.Chen P.Dong S.Holmbo S.Katz B.,Munoz J.A.Mutel R.L.Post R.S.Prieto J.L.Shields J.Tallon D.,Thompson T.A.Vallely P.J.Villanueva S. (The ATLAS)Denneau L.,Flewelling H.Heinze A.N.Smith K.W.Stalder B.Tonry J.L.Weiland H.,Barclay T.Barentsen G.Cody A.M.Dotson J.Foerster F.Garnavich P.,Gully-Santiago M.Hedges C.Howell S.Kasen D.Margheim S.Mushotzky R.,Rest A.Tucker B.E.Villar A.Zenteno A. (The Kepler Spacecraft Team),Beerman G.Bjella R.Castillo G.Coughlin J.Elsaesser B.Flynn S.,Gangopadhyay R.Griest K.Hanley M.Kampmeier J.Kloetzel R.Kohnert L.,Labonde C.Larsen R.Larson K.A.McCalmont-Everton K.M.McGinn C.,Migliorini L.Moffatt J.Muszynski M.Nystrom V.Osborne D.Packard M.,Peterson C.A.Redick M.Reedy L.H.Ross S.E.Spencer B.Steward K.,Van Cleve J.E.Vinicius de Miranda Cardoso J.Weschler T.,Wheaton A. (The Pan-STARRS)Bulger J.Chambers K.C.Flewelling H.A.,Huber M.E.Lowe T.B.Magnier E.A.Schultz A.S.B.Waters C.Z.Willman M.,Baron E.Chen Z.Derkacy J.M.Huang F.Li L.Li W.Li X.Mo J.,Rui L.Sai H.Wang L.Wang L.Wang X.Xiang D.Zhang J.Zhang J.,Zhang K.Zhang T.Zhang X.Zhao X.Brown P.J.Hermes J.J.Nordin J.,Points S.Sodor A.Strampelli G.M.Zenteno A.2020-10-07T12:50:35Z2020-07-24T13:52:39ZCDS support team

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

cds-question@unistra.frphotometryvisible-astronomysupernovaeOn 2018 February 4.41, the All-Sky Automated Survey for SuperNovae (ASAS-SN) discovered ASASSN-18bt in the K2 Campaign 16 field. With a redshift of z=0.01098 and a peak apparent magnitude of B_max_=14.31, ASASSN-18bt is the nearest and brightest Supernovae Ia type (SNe Ia) yet observed by the Kepler spacecraft. Here we present the discovery of ASASSN-18bt, the K2 light curve, and prediscovery data from ASAS-SN and the Asteroid Terrestrial-impact Last Alert System. The K2 early-time light curve has an unprecedented 30-minute cadence and photometric precision for an SN Ia light curve, and it unambiguously shows a ~4 day nearly linear phase followed by a steeper rise. Thus, ASASSN-18bt joins a growing list of SNe Ia whose early light curves are not well described by a single power law. We show that a double-power-law model fits the data reasonably well, hinting that two physical processes must be responsible for the observed rise. However, we find that current models of the interaction with a nondegenerate companion predict an abrupt rise and cannot adequately explain the initial, slower linear phase. Instead, we find that existing published models with shallow ^56^Ni are able to span the observed behavior and, with tuning, may be able to reproduce the ASASSN-18bt light curve. Regardless, more theoretical work is needed to satisfactorily model this and other early-time SNe Ia light curves. Finally, we use Swift X-ray nondetections to constrain the presence of circumstellar material (CSM) at much larger distances and lower densities than possible with the optical light curve. For a constant-density CSM, these nondetections constrain {rho}<4.5x10^5^cm^-3^ at a radius of 4x10^15^cm from the progenitor star. Assuming a wind-like environment, we place mass loss limits of dM/dt<8x10^-6^M{sun}/yr for {nu}_w_=100km/s, ruling out some symbiotic progenitor systems. This work highlights the power of well-sampled early-time data and the need for immediate multiband, high-cadence follow-up for progress in understanding SNe Ia.2019ApJ...870...13Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/870/13CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/870/13https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/870/13http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/870/13https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/870/13https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/870/13http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/870/13GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticaldefaultJ/ApJ/870/13/table1Photometric observationsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJDJulian date of the observation; JD-2450000dtime.epochdoubleBandMagnitude band of observation (K2, V, g, o) (1)instr.bandpass;obscharl_magLimit flag on magnitudemeta.code.errorcharmag[14.2/21.2] Apparent magnitudemagphot.magfloate_mag[0.001/0.8]? Error on magmagstat.error;phot.magfloatnullableTelTelescope identifier (ASAS-SN, ATLAS, K2)meta.id;instr.telchar