THE DISCOVERY OF THE MOST DISTANT KNOWN TYPE Ia SUPERNOVA AT REDSHIFT 1.914

We present the discovery of a Type Ia supernova (SN) at redshift $z = 1.914$\nfrom the CANDELS multi-cycle treasury program on the \\textit{Hubble Space\nTelescope (HST)}. This SN was discovered in the infrared using the Wide-Field\nCamera 3, and it is the highest-redshift Type Ia SN yet observed. We classify\nthis object as a SN\\,Ia by comparing its light curve and spectrum with those of\na large sample of Type Ia and core-collapse supernovae (SNe). Its apparent\nmagnitude is consistent with that expected from the $\\Lambda$CDM concordance\ncosmology. We discuss the use of spectral evidence for classification of $z >\n1.5$ SNe\\,Ia using {\\it HST} grism simulations, finding that spectral data\nalone can frequently rule out SNe\\,II, but distinguishing between SNe\\,Ia and\nSNe\\,Ib/c can require prohibitively long exposures. In such cases, a\nquantitative analysis of the light curve may be necessary for classification.\nOur photometric and spectroscopic classification methods can aid the\ndetermination of SN rates and cosmological parameters from the full\nhigh-redshift CANDELS SN sample.\n