SN 2017cfd: A Normal Type Ia Supernova Discovered Very Young

Abstract

The Type Ia supernova (SN Ia) 2017cfd in IC 0511 (redshift z = 0.01209 ± 0.00016) was discovered by the Lick Observatory Supernova Search 1.6 ± 0.7 d after the fitted first-light time (FFLT; 15.2 d before B-band maximum brightness). Photometric and spectroscopic follow-up observations show that SN 2017cfd is a typical, normal SN Ia with a peak luminosity M B ≈ −19.2±0.2 mag, ∆m 15 (B) = 1.16 mag, and reached a B-band maximum ∼16.8 d after the FFLT. We estimate there to be moderately strong host-galaxy extinction (A V = 0.39 ± 0.03 mag) based on MLCS2k2 fitting. The spectrum reveals a Si II λ6355 velocity of ∼ 11, 200 km s −1 at peak brightness. SN 2017cfd was discovered very young, with multiband data taken starting 2 d after the FFLT, making it a valuable complement to the currently small sample (fewer than a dozen) of SNe Ia with color data at such early times. We find that its intrinsic early-time (B − V ) 0 color evolution belongs to the "blue" population rather than to the distinct "red" population. Using the photometry, we constrain the companion star radius to be 2.5 R , thus ruling out a red-giant companion.

ZTF Early Observations of Type Ia Supernovae. III. Early-time Colors As a Test for Explosion Models and Multiple Populations

“…This conclusion is in contrast with the claim in Stritzinger et al (2018) although we note that B−V might be a better combination compared to g−r to test for the presence of multiple populations (see Section 3.1). Our findings are consistent with the B−V color evolution reported in (Han et al 2020, see their Figure 5), where there appears to be no gap between the red and blue class when adding six events to the sample of Stritzinger et al (2018). Surprisingly, Han et al (2020) claims the presence of two distinct classes, although we note that similarly to Stritzinger et al (2018) no analysis is provided to corroborate their conclusion.…”

“…However, contrary to previous claims in the literature (Stritzinger et al 2018), the slope distribution does not show any evidence for bimodality and it is consistent with being drawn from a single population. We note that our findings are based on a subsample of 34 normal SNeIa with at least three detections in the first 6 days since first light, a sample that is about twice (and not three times, see above) as large as the one in the literature after applying the same criteria (Stritzinger et al 2018;Han et al 2020).…”

“…) -E B V MW values from Table 3 of Yao et al (2019) are used for step (i) and (ii), while the full light curves 18 are fit using the program SNooPy 17 Here we count only events with the first color measurement within 5days from first light, i.e., a total of 19 SNe combining the sample of Stritzinger et al (2018) and Han et al (2020). The sample of Jiang et al (2018) reports discovery phases relative to maximum light rather than first light (see their Table 1).…”

“…Similar conclusions were drawn by Jiang et al (2018) when inspecting light curves of 23 relatively young SNeIa. Recently, Han et al (2020) added six events to the sample of Stritzinger et al (2018) and claimed to confirm the distinction between red and blue events (but see discussion in Section 5).…”

Distribution of Si II $λ$6355 Velocities of Type Ia Supernovae and Implications for Asymmetric Explosions

“…For example, in both the merger model (e.g., Pakmor et al 2012) and the head-on collision model (e.g., Kushnir et al 2013), the companion white dwarf is also destroyed. On the other hand, in some models the companion white dwarf could survive (e.g., Shen et al 2018). A few SNe Ia with earlytime observations have already ruled out a giant companion (e.g., Silverman et al 2012c;Zheng et al 2013;Goobar et al 2014;Cao et al 2015;Im et al 2015;Hosseinzadeh et al 2017;Holmbo et al 2019;Li et al 2019;Kawabata et al 2019;Han et al 2020), and for the extreme case of SN 2011fe, the companion was constrained to be a white dwarf (Nugent et al 2011;Bloom et al 2012), thus favoring the double-degenerate scenario. However, such early-time observations are still quite rare, and our understanding of the progenitor systems and explosion mechanisms remains substantially incomplete both theoretically and observationally (see a recent review by Jha et al 2019).…”