Red and Reddened: Ultraviolet through Near-infrared Observations of Type Ia Supernova 2017erp
Abstract
We present space-based ultraviolet/optical photometry and spectroscopy with the Swift Ultra-Violet/Optical Telescope and Hubble Space Telescope (HST), respectively, along with ground-based optical photometry and spectroscopy and near-infrared spectroscopy of supernova SN 2017erp. The optical light curves and spectra are consistent with a normal SN Ia. Compared to previous photometric samples in the near-ultraviolet (NUV), SN 2017erp has UV colors that are redder than NUV-blue SNe Ia corrected to similar optical colors. The chromatic difference between SNe 2011fe and 2017erp is dominated by the intrinsic differences in the UV rather than the expected dust reddening. This chromatic difference is similar to the SALT2 color law, derived from rest-frame ultraviolet photometry of higher redshift SNe Ia. Differentiating between intrinsic UV diversity and dust reddening can have important consequences for determining cosmological distances with rest-frame ultraviolet photometry. This ultraviolet spectroscopic series is the first from HST of a normal, albeit reddened, NUV-red SN Ia and is important for analyzing SNe Ia with intrinsically redder NUV colors. We show model comparisons suggesting that metallicity could be the physical difference between NUV-blue and NUV-red SNe Ia, with emission peaks from reverse fluorescence near 3000 Å implying a factor of ∼10 higher metallicity in the upper layers of SN 2017erp compared to SN 2011fe. Metallicity estimates are very model dependent, however, and there are multiple effects in the UV. Further models and UV spectra of SNe Ia are needed to explore the diversity of SNe Ia, which show seemingly independent differences in the near-UV peaks and mid-UV flux levels.
Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #14665.- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2019
- DOI:
- 10.3847/1538-4357/ab1a3f
- arXiv:
- arXiv:1808.04729
- Bibcode:
- 2019ApJ...877..152B
- Keywords:
-
- dust;
- extinction;
- supernovae: general;
- supernovae: individual: SN2017erp;
- SN2011fe;
- SN2011by;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- submitted to AAS journals v2 author list updated. SN2017erp data available at https://github.com/pbrown801/SN2017erp v3 arxiv author list metadata updated