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Far-UV HST Spectroscopy of an Unusual Hydrogen-poor Superluminous Supernova: SN2017egm

Yan, Lin and Perley, D. A. and De Cia, A. and Quimby, R. and Lunnan, R. and Rubin, Kate H. R. and Brown, P. J. (2018) Far-UV HST Spectroscopy of an Unusual Hydrogen-poor Superluminous Supernova: SN2017egm. Astrophysical Journal, 858 (2). Art. No. 91. ISSN 1538-4357. doi:10.3847/1538-4357/aabad5.

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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 1000–5500 Å, 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 Lyα absorption lines are detected at these two redshifts, with H I column densities of (3.0 ± 0.8) × 10^(19) and (3.7 ± 0.9) × 10^(19) cm^(−2), respectively. This is an order of magnitude smaller than the H I column densities in the disks of nearby galaxies (>10^(10) M⊙) and suggests that SN2017egm is on the near side of NGC 3191 and has a low host extinction (E(B − V) ~ 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 λ > 2800 Å is well fit by a blackbody, whereas the continuum at λ < 2800 Å is considerably below the model. The degree of UV suppression varies from source to source, with the 1400–2800 Å 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Yan, Lin0000-0003-1710-9339
Perley, D. A.0000-0001-8472-1996
De Cia, A.0000-0003-2082-1626
Quimby, R.0000-0001-9171-5236
Lunnan, R.0000-0001-9454-4639
Rubin, Kate H. R.0000-0001-6248-1864
Additional Information:© 2018 The American Astronomical Society. Received 2017 October 31; revised 2018 March 8; accepted 2018 March 24; published 2018 May 10. We acknowledge many useful discussions with Matt Nicholl at Harvard and Janet Chen at Max-Planck-Institut für Extraterrestrische Physik, in Germany on the measurements of gas-phase metallicities in NGC 3191 and the companion galaxy. We thank Nadia Blagorodnova for providing example python emcee scripts for our spectral fitting. We also thank Nick Scoville at Caltech for discussions on the H i column density distribution of nearby galaxies. Facility: HST. - Software: Python, Astropy.
Subject Keywords:supernovae: individual (SN2017egm, PTF12dam, iPTF13ajg, Gaia16apd)
Issue or Number:2
Record Number:CaltechAUTHORS:20180510-110312990
Persistent URL:
Official Citation:Lin Yan et al 2018 ApJ 858 91
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86334
Deposited By: Tony Diaz
Deposited On:10 May 2018 20:55
Last Modified:15 Nov 2021 20:37

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