A Reconciliation between the Consumer Price Index and the Personal Consumption Expenditures Price Index

The Bureau of Labor Statistics (BLS) prepares the Consumer Price Index for All Urban Consumers (CPI-U), and the Bureau of Economic Analysis prepares the Personal Consumption Expenditures (PCE) chain-type price index. Both indexes measure the prices paid by consumers for goods and services. Because the two indexes are based on different underlying concepts, they are constructed differently, and tend to behave differently over time. From the first quarter of 2002 through the second quarter of 2007, the CPI-U increased 0.4 percentage point per year faster than the PCE price index. This paper details and quantifies the differences in growth rates between the CPI-U and the PCE price index; it provides a quarterly reconciliation of growth rates for the 2002:Q1- 2007:Q2 time period. There are several factors that explain the differences in growth rates between the CPI and the PCE price index. First, the indexes are based on difference index-number formulas. The CPI-U is based on a Laspeyres index; the PCE price index is based on a Fisher-Ideal index. Second, the relative weights assigned to the detailed item prices in each index are different because they are based on different data sources. The weights used in the CPIU are based on a household survey, while the weights used in the PCE price index are based on business surveys. Third, there are scope differences between the two indexes— that is, there are items in the CPI-U that are out-of-scope of the PCE price index, and there are items in the PCE price index that are out-of-scope of the CPI-U. And finally, there are differences in the seasonal-adjustment routines and in the detailed price indexes used to construct the two indexes. Over the 2002:Q1-2007:Q2 time period, this analysis finds that almost half of the 0.4 percentage point difference in growth rates between the CPI-U and the PCE price index was explained by differences in index-number formulas. After adjusting for formula differences, differences in relative weights—primarily “rent of shelter”—more than accounted for the remaining difference in growth rates. Net scope differences, in contrast, partly offset the effect of relative weight differences.

A luminous, blue progenitor system for a type-Iax supernova

Type-Iax supernovae (SN Iax) are stellar explosions that are spectroscopically similar to some type-Ia supernovae (SN Ia) at maximum light, except with lower ejecta velocities. They are also distinguished by lower luminosities. At late times, their spectroscopic properties diverge from other SN, but their composition (dominated by iron-group and intermediate-mass elements) suggests a physical connection to normal SN Ia. These are not rare; SN Iax occur at a rate between 5 and 30% of the normal SN Ia rate. The leading models for SN Iax are thermonuclear explosions of accreting carbon-oxygen white dwarfs that do not completely unbind the star, implying they are "less successful" cousins of normal SN Ia, where complete disruption is observed. Here we report the detection of the luminous, blue progenitor system of the type-Iax SN 2012Z in deep pre-explosion imaging. Its luminosity, colors, environment, and similarity to the progenitor of the Galactic helium nova V445 Puppis, suggest that SN 2012Z was the explosion of a white dwarf accreting from a helium-star companion. Observations in the next few years, after SN 2012Z has faded, could test this hypothesis, or alternatively show that this supernova was actually the explosive death of a massive star.Comment: 9 pages, 5 figures; authors' version, accepted to Nature; final version available at http://dx.doi.org/10.1038/nature1361

Comprehensive Observations of the Bright and Energetic Type Iax SN 2012Z: Interpretation as a Chandrasekhar Mass White Dwarf Explosion

We present UV through NIR broad-band photometry, and optical and NIR spectroscopy of Type Iax supernova 2012Z. The data set consists of both early and late-time observations, including the first late phase NIR spectrum obtained for a spectroscopically classified SN Iax. Simple model calculations of its bolometric light curve suggest SN 2012Z produced ~0.3 M_sun of (56)Ni, ejected about a Chandrasekhar mass of material, and had an explosion energy of ~10^51 erg, making it one of the brightest and most energetic SN Iax yet observed. The late phase NIR spectrum of SN 2012Z is found to broadly resemble similar epoch spectra of normal SNe Ia; however, like other SNe Iax, corresponding visual-wavelength spectra differ substantially compared to all supernova types. Constraints from the distribution of IMEs, e.g. silicon and magnesium, indicate that the outer ejecta did not experience significant mixing during or after burning, and the late phase NIR line profiles suggests most of the (56)Ni is produced during high density burning. The various observational properties of SN 2012Z are found to be consistent with the theoretical expectations of a Chandrasekhar mass white dwarf progenitor that experiences a pulsational delayed detonation, which produced several tenths of a solar mass of (56)Ni during the deflagration burning phase and little (or no) (56)Ni during the detonation phase. Within this scenario only a moderate amount of Rayleigh-Taylor mixing occurs both during the deflagration and fallback phase of the pulsation, and the layered structure of the IMEs is a product of the subsequent denotation phase. The fact that the SNe Iax population does not follow a tight brightness-decline relation similar to SNe Ia can then be understood in the framework of variable amounts of mixing during pulsational rebound and variable amounts of (56)Ni production during the early subsonic phase of expansion.Comment: Submitted to A&A, manuscript includes response to referee's comments. 39 pages, including 16 figures, 9 table

Extensive HST Ultraviolet Spectra and Multi-wavelength Observations of SN 2014J in M82 Indicate Reddening and Circumstellar Scattering by Typical Dust

SN 2014J in M82 is the closest detected Type Ia supernova (SN Ia) in at least 28 years and perhaps in 410 years. Despite its small distance of 3.3 Mpc, SN 2014J is surprisingly faint, peaking at V = 10.6 mag, and assuming a typical SN Ia luminosity, we infer an observed visual extinction of A_V = 2.0 +/- 0.1 mag. But this picture, with R_V = 1.6 +/- 0.2, is too simple to account for all observations. We combine 10 epochs (spanning a month) of HST/STIS ultraviolet through near-infrared spectroscopy with HST/WFC3, KAIT, and FanCam photometry from the optical to the infrared and 9 epochs of high-resolution TRES spectroscopy to investigate the sources of extinction and reddening for SN 2014J. We argue that the wide range of observed properties for SN 2014J is caused by a combination of dust reddening, likely originating in the interstellar medium of M82, and scattering off circumstellar material. For this model, roughly half of the extinction is caused by reddening from typical dust (E(B-V ) = 0.45 mag and R_V = 2.6) and roughly half by scattering off LMC-like dust in the circumstellar environment of SN 2014J.Comment: 17 pages (excluding references and tables), 15 figures, accepted to MNRAS. A high-resolution HST image of SN 2014J in M82 is available upon reques

The progenitor and early evolution of the Type IIb SN 2016gkg

We report initial observations and analysis on the Type IIb SN~2016gkg in the nearby galaxy NGC~613. SN~2016gkg exhibited a clear double-peaked light curve during its early evolution, as evidenced by our intensive photometric follow-up campaign. SN~2016gkg shows strong similarities with other Type IIb SNe, in particular with respect to the \he~emission features observed in both the optical and near infrared. SN~2016gkg evolved faster than the prototypical Type~IIb SN~1993J, with a decline similar to that of SN~2011dh after the first peak. The analysis of archival {\it Hubble Space Telescope} images indicate a pre-explosion source at SN~2016gkg's position, suggesting a progenitor star with a $\sim$mid F spectral type and initial mass $15-20$\msun, depending on the distance modulus adopted for NGC~613. Modeling the temperature evolution within $5\,\rm{days}$ of explosion, we obtain a progenitor radius of $\sim\,48-124$\rsun, smaller than that obtained from the analysis of the pre-explosion images ($240-320$\rsun).Comment: 7 pages, 5 figures. Submitted to ApJ Letter

Supernova 2013by: A Type IIL Supernova with a IIP-like light curve drop

We present multi-band ultraviolet and optical light curves, as well as visual-wavelength and near-infrared spectroscopy of the Type II linear (IIL) supernova (SN) 2013by. We show that SN 2013by and other SNe IIL in the literature, after their linear decline phase that start after maximum, have a sharp light curve decline similar to that seen in Type II plateau (IIP) supernovae. This light curve feature has rarely been observed in other SNe IIL due to their relative rarity and the intrinsic faintness of this particular phase of the light curve. We suggest that the presence of this drop could be used as a physical parameter to distinguish between subclasses of SNe II, rather than their light curve decline rate shortly after peak. Close inspection of the spectra of SN 2013by indicate asymmetric line profiles and signatures of high-velocity hydrogen. Late (less than 90 days after explosion) near-infrared spectra of SN 2013by exhibit oxygen lines, indicating significant mixing within the ejecta. From the late-time light curve, we estimate that 0.029 solar mass of 56Ni was synthesized during the explosion. It is also shown that the V -band light curve slope is responsible for part of the scatter in the luminosity (V magnitude 50 days after explosion) vs. 56Ni relation. Our observations of SN 2013by and other SNe IIL through the onset of the nebular phase indicate that their progenitors are similar to those of SNe IIP.Comment: submitted 2014 December 5th, accepted 2015 January 28t

SN 2015ba: A type IIP supernova with a long plateau

We present optical photometry and spectroscopy from about a week after explosion to $\sim$272 d of an atypical Type IIP supernova, SN 2015ba, which exploded in the edge-on galaxy IC 1029. SN 2015ba is a luminous event with an absolute V-band magnitude of -17.1$\pm$0.2 mag at 50 d since explosion and has a long plateau lasting for $\sim$123 d. The distance to the SN is estimated to be 34.8$\pm$0.7 Mpc using the expanding photosphere and standard candle methods. High-velocity H-Balmer components constant with time are observed in the late-plateau phase spectra of SN 2015ba, which suggests a possible role of circumstellar interaction at these phases. Both hydrodynamical and analytical modelling suggest a massive progenitor of SN 2015ba with a pre-explosion mass of 24-26 M$_\odot$. However, the nebular spectra of SN 2015ba exhibit insignificant levels of oxygen, which is otherwise expected from a massive progenitor. This might be suggestive of the non-monotonical link between O-core masses and the zero-age main-sequence mass of pre-supernova stars and/or uncertainties in the mixing scenario in the ejecta of supernovae.Comment: 42 pages, 7 pages Appendix, 20 figures, 10 tables, Accepted for publication in MNRAS, 14-June-201

Revisiting Optical Tidal Disruption Events with iPTF16axa

We report the discovery by the intermediate Palomar Transient Factory (iPTF) of a candidate tidal disruption event (TDE) iPTF16axa at z = 0.108 and present its broadband photometric and spectroscopic evolution from three months of follow-up observations with ground-based telescopes and Swift. The light curve is well fitted with a t^(−5/3) decay, and we constrain the rise time to peak to be <49 rest-frame days after disruption, which is roughly consistent with the fallback timescale expected for the ~5 × 10^6 M_⊙ black hole inferred from the stellar velocity dispersion of the host galaxy. The UV and optical spectral energy distribution is well described by a constant blackbody temperature of T ~ 3 × 10^4 K over the monitoring period, with an observed peak luminosity of 1.1 × 10^(44) erg s^(−1). The optical spectra are characterized by a strong blue continuum and broad He ii and Hα lines, which are characteristic of TDEs. We compare the photometric and spectroscopic signatures of iPTF16axa with 11 TDE candidates in the literature with well-sampled optical light curves. Based on a single-temperature fit to the optical and near-UV photometry, most of these TDE candidates have peak luminosities confined between log(L [erg s^(−1)]) = 43.4–44.4, with constant temperatures of a few ×10^4 K during their power-law declines, implying blackbody radii on the order of 10 times the tidal disruption radius, that decrease monotonically with time. For TDE candidates with hydrogen and helium emission, the high helium-to-hydrogen ratios suggest that the emission arises from high-density gas, where nebular arguments break down. We find no correlation between the peak luminosity and the black hole mass, contrary to the expectations for TDEs to have M ∝ M_(BH)^(-1/2)