Carnegie Supernova Project-II: The Near-infrared Spectroscopy Program
We present the H-band wavelength region of 37 postmaximum light near-infrared spectra of three normal, nine transitional, and four subluminous type Ia supernovae (SNe Ia), extending from +5 days to +20 days relative to the epoch of B-band maximum. We introduce a new observable, the blue-edge velocity, v edge, of the prominent Fe/Co/Ni-peak H-band emission feature, which is quantitatively measured. The v edge parameter is found to decrease over subtype ranging from around ‑14,000 km s‑1 for normal SNe Ia, to ‑10,000 km s‑1 for transitional SNe Ia, down to ‑5000 km s‑1 for the subluminous SNe Ia. Furthermore, inspection of the +10 ± 3 days spectra indicates that v edge is correlated with the color-stretch parameter, s BV , and hence with peak luminosity. These results follow the previous findings that brighter SNe Ia tend to have 56Ni located at higher velocities as compared to subluminous objects. As v edge is a model-independent parameter, we propose it can be used in combination with traditional observational diagnostics to provide a new avenue to robustly distinguish between leading SNe Ia explosion models. This Letter includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.
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Publication Date:
NSF-PAR ID:
10093381
Journal Name:
Publications of the Astronomical Society of the Pacific
Volume:
131
Issue:
995
Page Range or eLocation-ID:
1
ISSN:
0004-6280
Spectropolarimetry enables us to measure the geometry and chemical structure of the ejecta in supernova explosions, which is fundamental for the understanding of their explosion mechanism(s) and progenitor systems. We collected archival data of 35 Type Ia supernovae (SNe Ia), observed with Focal Reducer and Low-Dispersion Spectrograph (FORS) on the Very Large Telescope at 127 epochs in total. We examined the polarization of the Si ii λ6355 Å line ($p_{\rm Si\, \small {II}}$) as a function of time, which is seen to peak at a range of various polarization degrees and epochs relative to maximum brightness. We reproduced the $\Delta m_{15}\!-\!p_{\rm Si\, \small {II}}$ relationship identified in a previous study, and show that subluminous and transitional objects display polarization values below the $\Delta m_{15}\!-\!p_{\rm Si\, \small {II}}$ relationship for normal SNe Ia. We found a statistically significant linear relationship between the polarization of the Si ii λ6355 Å line before maximum brightness and the Si ii line velocity and suggest that this, along with the $\Delta m_{15}\!-\!p_{\rm Si\, \small {II}}$ relationship, may be explained in the context of a delayed-detonation model. In contrast, we compared our observations to numerical predictions in the $\Delta m_{15}\!-\!v_{\rm Si\, \small {II}}$ plane and found a dichotomy in the polarization propertiesmore »