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Register a new userEmpirically determined dilution factors of stripped-envelope, core-collapse SNe: Paper II - Using GRB-SNe to determine the Hubble Constant
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Zach Cano
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The aim of this work is to use gamma-ray burst supernovae (GRB-SNe) as cosmological probes to measure the Hubble constant, $H_0$, in the local Universe. In the context of the Expanding Photosphere Method (EPM), I use empirically derived dilution factors of a sample of nearby SNe Ic, which were derived in Paper I of a two-paper series, as a proxy for the dilution factors of GRB-SNe. It is seen that the dilution factors as a function of temperature in $VI$ display the least amount of scatter, relative to $BVI$ and $BV$. A power-law function is fit to the former, and is used to derive model dilution factors which are then used to derive EPM distances to GRB-SNe 1998bw and 2003lw: $36.7pm9.6$ and $372.2pm137.1$ Mpc, respectively. In linear Hubble diagrams in filters $BVR$, I determine the offset of the Hubble ridge line, and armed with the peak absolute magnitudes in these filters for the two aforementioned GRB-SNe, I find a (weighted average) Hubble constant of $bar{H_{0,rm w}} = 61.9pm12.3$ km s$^{-1}$ Mpc$^{-1}$ for GRB-SNe located at redshifts $zle0.1$. The 20% error is consistent with the value of $H_0$ calculated by Planck and SNe Ia within 1$sigma$. I tested the fitting method on five nearby SNe Ic, and found that their EPM distances varied by 18-50%, with smaller errors found for those SNe which had more numerous usable observations. For SN 2002ap, its EPM distance was overestimated by 18%, and if the distance to SN 1998bw was similarly over-estimated by the same amount, the resultant value of the Hubble constant is $H_0 = 72$ km s$^{-1}$ Mpc$^{-1}$, which perfectly matches that obtained using SNe Ia. [abridged]
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In this work, the empirically derived dilution/correct factors of a sample stripped-envelope, core-collapse supernovae (SE-SNe), including five SNe IIb, four SNe Ib, six SNe Ic and two relativistic broad-lined type Ic supernovae (SNe IcBL) are presented. The ultimate goal of this project is to derive model-free distances to the host galaxy of one or more gamma-ray burst supernova (GRB-SN), and to exploit their observed luminosity$-$decline relationship by employing them as cosmological probes. In the first part of a two-paper analysis, I present my method for deriving the dilution factors of the SE-SN sample, which were chosen on the basis that cosmological-model-independent distances exist to their host galaxies, and each has a sufficient dataset that allows for host-subtracted, dereddened rest-frame $BVI$ LCs to be constructed, and time-series spectra. A Planck function was fit to the data to derive the blackbody radius and blackbody temperature as a function of time, while the blueshifted velocity of either Si II $lambda$6355 or Fe II $lambda$5169 was used a proxy of the photospheric velocity, and hence photospheric radius. The ratio of these empirically derived radii was taken as the dilution/correct factor. I then compared the empirically derived dilution factors with synthetic values obtained from radiative transfer models calculated for SE-SNe arising from binary systems. It is seen that the empirical dilution factors of the SNe Ic and GRB-SNe, the latter which were derived based on luminosity distances calculated from their spectroscopic redshift, are very similar. It is found that the dilution factors of the two relativistic SN IcBL are very different to those of the GRB-SNe, meaning that these engine-driven events may arise from fundamentally different progenitor systems.
The Hubble constant ($H_0$) tension between Type Ia Supernovae (SNe Ia) and Planck measurements ranges from 4 to 6 $sigma$. To investigate this tension, we estimate $H_{0}$ in the $Lambda$CDM and $w_{0}w_{a}$CDM models by dividing the Pantheon sample, the largest compilation of SNe Ia, into 3, 4, 20 and 40 bins. We fit the extracted $H_{0}$ values with a function mimicking the redshift evolution: $g(z)={H_0}(z)=tilde{H}_0/(1+z)^alpha$, where $alpha$ indicates an evolutionary parameter and $tilde{H}_0=H_0$ at $z=0$. We set the absolute magnitude of SNe Ia so that $H_0=73.5,, textrm{km s}^{-1},textrm{Mpc}^{-1}$, and we fix fiducial values for $Omega_{0m}^{Lambda CDM}=0.298$ and $Omega_{0m}^{w_{0}w_{a}CDM}=0.308$. We find that $H_0$ evolves with redshift, showing a slowly decreasing trend, with $alpha$ coefficients consistent with zero only from 1.2 to 2.0 $sigma$. Although the $alpha$ coefficients are compatible with 0 in 3 $sigma$, this however may affect cosmological results. We measure locally a variation of $H_0(z=0)-H_0(z=1)=0.4, textrm{km s}^{-1},textrm{Mpc}^{-1}$ in 3 and 4 bins. Extrapolating ${H_0}(z)$ to $z=1100$, the redshift of the last scattering surface, we obtain values of $H_0$ compatible in 1 $sigma$ with Planck measurements independently of cosmological models and number of bins we investigated. Thus, we have reduced the $H_0$ tension from $54%$ to $72%$ for the $Lambda$CDM and $w_{0}w_{a}$CDM models, respectively. If the decreasing trend of $H_0(z)$ is real, it could be due to astrophysical selection effects or to modified gravity.
We review recent UV observations of core-collapse supernovae (SNe) with the Swift Ultra-violet/Optical Telescope (UVOT) during its first two years. Rest-frame UV photometry is useful for differentiating SN types by exploiting the UV-optical spectral shape and more subtle UV features. This is useful for the real-time classification of local and high-redshift SNe using only photometry. Two remarkable SNe Ib/c were observed with UVOT -- SN2006jc was a UV bright SN Ib. Swift observations of GRB060218/SN2006aj began shortly after the explosion and show a UV-bright peak followed by a UV-faint SN bump. UV observations are also useful for constraining the temperature and ionization structure of SNe IIP. Rest-frame UV observations of all types are important for understanding the extinction, temperature, and bolometric luminosity of SNe and to interpret the observations of high redshift SNe observed at optical wavelengths.
In the current era of time-domain astronomy, it is increasingly important to have rigorous, data driven models for classifying transients, including supernovae. We present the first application of Principal Component Analysis to the spectra of stripped-envelope core-collapse supernovae. We use one of the largest compiled optical datasets of stripped-envelope supernovae, containing 160 SNe and 1551 spectra. We find that the first 5 principal components capture 79% of the variance of our spectral sample, which contains the main families of stripped supernovae: Ib, IIb, Ic and broad-lined Ic. We develop a quantitative, data-driven classification method using a support vector machine, and explore stripped-envelope supernovae classification as a function of phase relative to V-band maximum light. Our classification method naturally identifies transition supernovae and supernovae with contested labels, which we discuss in detail. We find that the stripped-envelope supernovae types are most distinguishable in the later phase ranges of $10pm5$ days and $15pm5$ days relative to V-band maximum, and we discuss the implications of our findings for current and future surveys such as ZTF and LSST.
We present 645 optical spectra of 73 supernovae (SNe) of Types IIb, Ib, Ic, and broad-lined Ic. All of these types are attributed to the core collapse of massive stars, with varying degrees of intact H and He envelopes before explosion. The SNe in our sample have a mean redshift <cz> = 4200 km/s. Most of these spectra were gathered at the Harvard-Smithsonian Center for Astrophysics (CfA) between 2004 and 2009. For 53 SNe, these are the first published spectra. The data coverage range from mere identification (1-3 spectra) for a few SNe to extensive series of observations (10-30 spectra) that trace the spectral evolution for others, with an average of 9 spectra per SN. For 44 SNe of the 73 SNe presented here, we have well-determined dates of maximum light to determine the phase of each spectrum. Our sample constitutes the most extensive spectral library of stripped-envelope SNe to date. We provide very early coverage (as early as 30 days before V-band max) for photospheric spectra, as well as late-time nebular coverage when the innermost regions of the SNe are visible (as late as 2 years after explosion, while for SN1993J, we have data as late as 11.6 years). This data set has homogeneous observations and reductions that allow us to study the spectroscopic diversity of these classes of stripped SNe and to compare these to SNe associated with gamma-ray bursts. We undertake these matters in follow-up papers.
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