Far-UV HST Spectroscopy of an Unusual Hydrogen-poor Superluminous Supernova: SN2017egm Academic Article uri icon

abstract

  • Abstract SN2017egm is the closest (z=0.03) H-poor superluminous supernova (SLSN-I) detected to date, and a rare example of an SLSN-I in a massive, metal-rich galaxy. We present the HST UV and optical spectra covering 10005500 , taken at +3 day relative to the peak. Our data reveal two absorption systems at redshifts matching the host galaxy NGC 3191 (z=0.0307) and its companion galaxy (z=0.0299) 73 apart. Weakly damped Ly absorption lines are detected at these two redshifts, with H i column densities of (3.00.8)1019 and (3.70.9)1019 cm2, respectively. This is an order of magnitude smaller than the H i column densities in the disks of nearby galaxies (>1010 M ) and suggests that SN2017egm is on the near side of NGC 3191 and has a low host extinction (E(BV)0.007). Using unsaturated metal absorption lines, we find that the host of SN2017egm probably has a solar or higher metallicity and is unlikely to be a dwarf companion to NGC 3191. Comparison of early-time UV spectra of SN2017egm, Gaia16apd, iPTF13ajg, and PTF12dam finds that the continuum at >2800 is well fit by a blackbody, whereas the continuum at <2800 is considerably below the model. The degree of UV suppression varies from source to source, with the 14002800 continuum flux ratio of 1.5 for Gaia16apd and 0.4 for iPTF13ajg. This cannot be explained by the differences in magnetar power or blackbody temperature. Finally, the UV spectra reveal a common set of seven broad absorption features and their equivalent widths are similar (within a factor of 2) among the four events.

published proceedings

  • ASTROPHYSICAL JOURNAL

altmetric score

  • 0.25

author list (cited authors)

  • Yan, L., Perley, D. A., De Cia, A., Quimby, R., Lunnan, R., Rubin, K., & Brown, P. J.

citation count

  • 31

complete list of authors

  • Yan, Lin||Perley, DA||De Cia, A||Quimby, R||Lunnan, R||Rubin, Kate HR||Brown, PJ

publication date

  • May 2018