Discovery of the z = 0.869 Superluminous Supernova DES14X2byo

ATel #6635; M. L. Graham, W. Zheng, A. V. Filippenko (University of California, Berkeley); P. Challis, R. Kirshner, J. Parrent (Harvard-Smithsonian Center for Astrophysics); F. J. Castander, R. Casas (ICE, IEEC/CSIC, Barcelona); D. Garcia-Alvarez (SA) and D. Perez-Valladares (GTC operations, IAC); R. Miquel (IFAE, Barcelona); R. C. Smith (NOAO/CTIO); M. Schubnell (University of Michigan); R. Kessler, D. Scolnic (University of Chicago); R. A. Covarrubias (University of Illinois / NCSA); R. C. Wolf, J. A. Fischer, J.-L. Fischer, L. Gladney, M. March, M. Sako (University of Pennsylvania); P. J. Brown, K. Krisciunas, N. Suntzeff (Texas A&M University); C. D'Andrea, R. Nichol, A. Papadopoulos (University of Portsmouth); M. Smith, M. Sullivan (University of Southampton); R. Maartens (University of the Western Cape); R. Gupta, E. Kovacs, S. Kuhlmann, H. Spinka (Argonne National Laboratory); E. Ahn, D. A. Finley, J. Frieman, J. Marriner, W. Wester (Fermilab); G. Aldering, A. G. Kim, R. C. Thomas (Lawrence Berkeley National Laboratory); K. Barbary, J. S. Bloom, D. Goldstein, P. Nugent, S. Perlmutter (Lawrence Berkeley National Laboratory + University of California, Berkeley); R. J. Foley (University of Illinois); S. Desai, K. Paech (Ludwig Maximilians University, Munich)
on 29 Oct 2014; 00:29 UT
Credential Certification: Chris D'Andrea (chris.dandrea@port.ac.uk)

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We report the spectroscopic classification of of DES14X2byo as a type I superluminous supernova (SLSN-I), discovered by the Dark Energy Survey (ATel #4668). DES14X2byo is located at R.A. = 02:23:46.93, Decl. = -06:08:12.3, and was discovered on 22 September 2014 at r = 23.4 mag. No host galaxy is visible in DES template imaging, which is complete to r = 24.0 mag. We obtained spectra with the OSIRIS spectrograph (wavelength range 490-940 nm) on the Gran Telescopio CANARIAS (GTC), the Blue Channel Spectrograph (330-850 nm) on the MMT, and LRIS (340-1025 nm) on Keck I on 17 October, 22 October, and 23 October, respectively. All three spectra are similar to each other and to near-maximum spectra of several SLSNe I at z = 0.86, consistent with narrow Mg II 2800 absorption clearly detected at z = 0.869. We presume that this redshift is the redshift of the SN. In the LRIS spectrum, we also detect narrow Fe II 2600 absorption and [O II] 3727 emission at the SN redshift and a second Mg II system at z = 0.851.

DES14X2byo is near maximum brightness (r=21.4 on 25 October), and further observations are encouraged.