* Astronomy

Title: The hydrogen-poor superluminous supernova iPTF13ajg and its host galaxy in absorption and emission
Author: Paul M. Vreeswijk, Sandra Savaglio, Avishay Gal-Yam, Annalisa De Cia, Robert M. Quimby, Mark Sullivan, S. Bradley Cenko, Daniel A. Perley, Alexei V. Filippenko, Kelsey I. Clubb, Francesco Taddia, Jesper Sollerman, Giorgos Leloudas, Iair Arcavi, Adam Rubin, Mansi M. Kasliwal, Yi Cao, Ofer Yaron, David Tal, Eran O. Ofek, John Capone, Alexander S. Kutyrev, Vicki Toy, Peter E. Nugent, Russ Laher, Jason Surace, Shrinivas R. Kulkarni

We present imaging and spectroscopy of a hydrogen-poor superluminous supernova (SLSN) discovered by the intermediate Palomar Transient Factory: iPTF13ajg. At a redshift of z=0.7403, derived from narrow absorption lines, iPTF13ajg peaked at an absolute magnitude M(u,AB)=-22.5, one of the most luminous supernovae to date. The uBgRiz light curves, obtained with the P48, P60, NOT, DCT, and Keck telescopes, and the nine-epoch spectral sequence secured with the Keck and the VLT (covering 3 rest-frame months), are tied together photometrically to provide an estimate of the flux evolution as a function of time and wavelength. The observed bolometric peak luminosity of iPTF13ajg is 3.2x10^44 erg/s, while the estimated total radiated energy is 1.3x10^51 erg. We detect narrow absorption lines of Mg I, Mg II, and Fe II, associated with the cold interstellar medium in the host galaxy, at two different epochs with X-shooter at the VLT. From Voigt-profile fitting, we derive the column densities log N(Mg I)=11.94±0.06, log N(Mg II)=14.7±0.3, and log N(Fe II)=14.25±0.10. These column densities, as well as the Mg I and Mg II equivalent widths of a sample of hydrogen-poor SLSNe taken from the literature, are at the low end of those derived for gamma-ray bursts (GRBs), whose progenitors are also thought to be massive stars. This suggests that the environments of SLSNe and GRBs are different. From the nondetection of Fe II fine-structure absorption lines, we derive a strict lower limit on the distance between the supernova and the narrow-line absorbing gas of 50 pc. No host-galaxy emission lines are detected, leading to an upper limit on the unobscured star-formation rate of SFR([OII])<0.07 Msun/yr. Late-time imaging shows the host galaxy of iPTF13ajg to be faint, with g(AB)~27.0 and R(AB)>=26.0 mag, which roughly corresponds to M(B,Vega) >~ -17.7 mag.

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