Mario Hamuy

The High-Z Supernova Search: Measuring Cosmic Deceleration and Global Curvature of the Universe Using Type Ia Supernovae*

The High-Z Supernova Search is an international collaboration to discover and monitor Type Ia supernovae (SNe Ia) at z > 0.2 with the aim of measuring cosmic deceleration and global curvature. Our collaboration has pursued a basic understanding of supernovae in the nearby universe, discovering and observing a large sample of objects and developing methods to measure accurate distances with SNe Ia. This paper describes the extension of this program to z ≥ 0.2, outlining our search techniques and follow-up program. We have devised high-throughput filters that provide accurate two-color rest frame B and V light curves of SNe Ia, enabling us to produce precise, extinction-corrected luminosity distances in the range 0.25 M=-0.2 -->−0.8+1.0 if ΩΛ = 0. For a spatially flat universe composed of normal matter and a cosmological constant, we find Ω -->M=0.4 -->−0.4+0.5, Ω

Southern spectrophotometric standards. I

{Λ}

The reddening-free decline rate versus luminosity relationship for type ia supernovae

-->=0.6 -->−0.5+0.4. We demonstrate that with a sample of ~30 objects, we should be able to determine relative luminosity distances over the range 0 < z < 0.5 with sufficient precision to measure ΩM with an uncertainty of ±0.2.

Constraints on Cosmological Models from Hubble Space Telescope Observations of High-z Supernovae

We have obtained new observations of both secondary and tertiary spectrophotometric standards with the RC spectrographs and CCD cameras on the 1.5-m and 4-m telescopes at CTIO in the wavelength range of 3300-7550 angstroms, as well as UBV(RI)KC photometry for these stars. We have modified the monochromatic fluxes of the secondary spectrophotometric standards published by Taylor (1984) according to the new calibration of Vega provided by Hayes (1985). We have also uned the zero-point of the energy distribution of these stars by matching their V synthetic magnitudes to the observed magnitudes. We use these adjusted spectrophotometric standards in order to calculate ne fluxes for the tertiary standards of Stone and Baldwin (1983), as well as for three stars of the northern hemisphere from Stone (1977). We find that the synthetic magnitudes calculated from our spectra through the B and V bands agree extremely well with our photometry, to better than 1% on average. For the monochromatic fluxes, we find an internal precision better than 0.01 mag at all wavelengths, and a fair agreement with previous measurements of the tertiary standards. We present also a fine grid of averaged monochromatic fluxes (at continuous steps of 16 angstroms) for the ten secondary standards selected for our program, to be used in the flux calibration of high dispersion spectra.

The Absolute Luminosities of the Calan/Tololo Type IA Supernovae

We develop a method for estimating the host galaxy dust extinction for type Ia supernovae based on an observational coincidence first noted by Lira, who found that the B-V evolution during the period from 30 to 90 days after V maximum is remarkably similar for all events, regardless of light-curve shape. This fact is used to calibrate the dependence of the Bmax-Vmax and Vmax-Imax colors on the light-curve decline rate parameter Δm15(B), which can, in turn, be used to separately estimate the host galaxy extinction. Using these methods to eliminate the effects of reddening, we reexamine the functional form of the decline rate versus luminosity relationship and provide an updated estimate of the Hubble constant of H0 = 63.3 ± 2.2(internal) ± 3.5(external) km s-1 Mpc-1.

An asymptotic-giant-branch star in the progenitor system of a type Ia supernova

We have coordinated Hubble Space Telescope (HST) photometry with ground-based discovery for three supernovae: Type Ia supernovae near z ≈ 0.5 (SN 1997ce, SN 1997cj) and a third event at z = 0.97 (SN 1997ck). The superb spatial resolution of HST separates each supernova from its host galaxy and leads to good precision in the light curves. We use these light curves and relations between luminosity, light-curve shape, and color calibrated from low-z samples to derive relative luminosity distances that are accurate to 10% at z ≈ 0.5 and 20% at z = 1. When the HST sample is combined with the distance to SN 1995K (z = 0.48), analyzed by the same precepts, we find that matter alone is insufficient to produce a flat universe. Specifically, for Ωm+ΩΛ = 1, Ωm is less than 1 with more than 95% confidence, and our best estimate of Ωm is -0.1±0.5 if ΩΛ = 0. Although this result is based on a very small sample whose systematics remain to be explored, it demonstrates the power of HST measurements for high-redshift supernovae.

The Carnegie Supernova Project: Analysis of the First Sample of Low-Redshift Type-Ia Supernovae

We examine the absolute luminosities of 29 SNe Ia in the Calan/Tololo survey. We confirm a relation between the peak luminosity of the SNe and the decline rate as measured by the light curve, as suggested by Phillips (1993). We derive linear slopes to this magnitude-decline rate relation in BV(I)kc colors, using a sample with Bmax-Vmax < 0.2 mag. The scatter around this linear relation (and thus the ability to measure SNe Ia distances) ranges from 0.13 mag (in the I band) to 0.17 mag (in the B band). We also find evidence for significant correlations between the absolute magnitudes or the decline rate of the light curve, and the morphological type of the host galaxy.

A relativistic type Ibc supernova without a detected γ-ray burst

Stars that explode as supernovae come in two main classes. A type Ia supernova is recognized by the absence of hydrogen and the presence of elements such as silicon and sulphur in its spectrum; this class of supernova is thought to produce the majority of iron-peak elements in the Universe. They are also used as precise ‘standard candles’ to measure the distances to galaxies. While there is general agreement that a type Ia supernova is produced by an exploding white dwarf star, no progenitor system has ever been directly observed. Significant effort has gone into searching for circumstellar material to help discriminate between the possible kinds of progenitor systems, but no such material has hitherto been found associated with a type Ia supernova. Here we report the presence of strong hydrogen emission associated with the type Ia supernova SN2002ic, indicating the presence of large amounts of circumstellar material. We infer from this that the progenitor system contained a massive asymptotic-giant-branch star that lost several solar masses of hydrogen-rich gas before the supernova explosion.

SN 1991bg - A type Ia supernova with a difference

An analysis of the first set of low-redshift (z < 0.08) Type Ia supernovae (SNe Ia) monitored by the Carnegie Supernova Project between 2004 and 2006 is presented. The data consist of well-sampled, high-precision optical (ugriBV) and near-infrared (NIR; YJHKs ) light curves in a well-understood photometric system. Methods are described for deriving light-curve parameters, and for building template light curves which are used to fit SN Ia data in the ugriBVYJH bands. The intrinsic colors at maximum light are calibrated using a subsample of supernovae (SNe) assumed to have suffered little or no reddening, enabling color excesses to be estimated for the full sample. The optical-NIR color excesses allow the properties of the reddening law in the host galaxies to be studied. A low average value of the total-to-selective absorption coefficient, RV 1.7, is derived when using the entire sample of SNe. However, when the two highly reddened SNe (SN 2005A and SN 2006X) in the sample are excluded, a value RV 3.2 is obtained, similar to the standard value for the Galaxy. The red colors of these two events are well matched by a model where multiple scattering of photons by circumstellar dust steepens the effective extinction law. The absolute peak magnitudes of the SNe are studied in all bands using a two-parameter linear fit to the decline rates and the colors at maximum light, or alternatively, the color excesses. In both cases, similar results are obtained with dispersions in absolute magnitudes of 0.12-0.16?mag, depending on the specific filter-color combination. In contrast to the results obtained from the comparison of the color excesses, these fits of absolute magnitude give RV 1-2 when the dispersion is minimized, even when the two highly reddened SNe are excluded. This discrepancy suggests that, beyond the normal interstellar reddening produced in the host galaxies, there is an intrinsic dispersion in the colors of SNe Ia which is correlated with luminosity but independent of the decline rate. Finally, a Hubble diagram for the best-observed subsample of SNe is produced by combining the results of the fits of absolute magnitude versus decline rate and color excess for each filter. The resulting scatter of 0.12 mag appears to be limited by the peculiar velocities of the host galaxies as evidenced by the strong correlation between the distance-modulus residuals observed in the individual filters. The implication is that the actual precision of SNe Ia distances is 3%-4%.

Photometry and Spectroscopy of GRB 030329 and Its Associated Supernova 2003dh: The First Two Months

Long duration γ-ray bursts (GRBs) mark the explosive death of some massive stars and are a rare sub-class of type Ibc supernovae. They are distinguished by the production of an energetic and collimated relativistic outflow powered by a central engine (an accreting black hole or neutron star). Observationally, this outflow is manifested in the pulse of γ-rays and a long-lived radio afterglow. Until now, central-engine-driven supernovae have been discovered exclusively through their γ-ray emission, yet it is expected that a larger population goes undetected because of limited satellite sensitivity or beaming of the collimated emission away from our line of sight. In this framework, the recovery of undetected GRBs may be possible through radio searches for type Ibc supernovae with relativistic outflows. Here we report the discovery of luminous radio emission from the seemingly ordinary type Ibc SN 2009bb, which requires a substantial relativistic outflow powered by a central engine. A comparison with our radio survey of type Ibc supernovae reveals that the fraction harbouring central engines is low, about one per cent, measured independently from, but consistent with, the inferred rate of nearby GRBs. Independently, a second mildly relativistic supernova has been reported.