The Nearby Supernova Factory

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Abstract

The Nearby Supernova Factory (SNfactory) is an ambitious project to find and study in detail approximately 300 nearby Type Ia supernovae (SNe Ia) at redshifts 0.03<z<0.08. This program will provide an exceptional data set of well-studied SNe in the nearby smooth Hubble flow that can be used as calibration for the current and future programs designed to use SNe to measure the cosmological parameters. The first key ingredient for this program is a reliable supply of Hubble-flow SNe systematically discovered in unprecedented numbers using the same techniques as those used in distant SNe searches. In 2002, 35 SNe were found using our test-bed pipeline for automated SN search and discovery. The pipeline uses images from the asteroid search conducted by the Near Earth Asteroid Tracking group at JPL. Improvements in our subtraction techniques and analysis have allowed us to increase our effective SN discovery rate to ∼12 SNe/month in 2003.

Introduction

Type Ia supernovae (SNe Ia) have proven extremely useful as standardizable candles to explore the expansion history of the Universe (Perlmutter et al., 1997; Perlmutter et al., 1998; Garnavich et al., 1998; Riess et al., 1998; Perlmutter et al., 1999). Ambitious follow-on experiments are just starting, SNLS (Pain et al., 2003), ESSENCE (Garnavich et al., 2002), or have been planned, SNAP (Aldering et al., 2002), to extend the revolutionary result that the Universe is accelerating to precise statements about the constituents and history of the Universe. However, a key assumption underlying these experiments is that the current observed diversity in SNe Ia will be well-behaved and calibrated to allow for the desired precision measurements. This assumption can be tested in large part using nearby SNe Ia. Moreover, there is the possibility for such nearby studies to uncover new relationships that will make SNe Ia even better standard candles, much as the width-luminosity relation has brought SNe Ia to their already impressive level of standardization.

The Nearby Supernova Factory (SNfactory) project is designed to bring this improved understanding of SNe Ia (Aldering et al., 2002; Pécontal et al., 2003; Lantz et al., 2003). Over the course of 3 years, it will study 300 SNe Ia in the nearby smooth Hubble flow (see Fig. 1). These SNe will be observed with a dedicated instrument, the SuperNova Integral Field Spectrograph (SNIFS), which is currently in the final stages of construction. SNIFS will provide simultaneous spectrophotometric coverage of both the SN and the host galaxy at 3–5 day intervals during the rise and fall of each SN. This unprecedented dataset will provide a wealth of information on SNe Ia and allow for an improved calibration of SNe Ia for use in cosmology.

Section snippets

The supernova search dataset

The SNfactory searches for SNe using wide-field images obtained in collaboration with the Near Earth Asteroid Tracking (NEAT) group (Pravdo et al., 1999) at the Jet Propulsion Laboratory (JPL). In their quest for asteroids, the NEAT group observes hundreds of fields each night by taking three images of each field, spaced fifteen to thirty minutes apart, and searching for objects that move by more than a couple of arcseconds over this period. The SNfactory uses this temporal spacing to eliminate

Data processing

The SNfactory, in collaboration with the High Performance Wireless Research and Education Network (Braun, 2003), has established a high-speed, 6 Megabyte-per-second (MBps) radio internet link to the San Diego Supercomputer Center (SDSC) from the Palomar observatory. Images are transmitted from the telescope and stored at the National Energy Research Supercomputing Center (NERSC) High Performance Storage System (HPSS). The bandwidth from SDSC to NERSC allows for near real-time transfer of 20–50

Results

Eighty-three SNe have been found using the techniques described above and have been accepted by the International Astronomical Union. Fig. 2 shows the 35 SNe we discovered in 2002. In the first five months of 2003, we found and reported an additional 48 SNe. In addition, our search identified another 17 SNe that had already been reported by other groups. We are currently running with a very conservative set of selection criteria and need human eyes to scan ∼5% of the successful subtractions for

Conclusion

The Nearby Supernova Factory search pipeline is operational and has proven the ability to discover ∼12 SNe/month  ∼150 SNe/year. As 23 of the supernovae discovered in our search have been SNe Ia, we expect to discover ∼100 SNe Ia/year. Most of these supernovae have been discovered sufficiently early to enable detailed study starting before maximum light. This extensive study will enable improvements in the use of SNe Ia for cosmological measurements, and provide a wealth of information on the

Further reading

Cabanela et al. (2003), IAU (2003).

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WMWV was supported in part by an NSF Graduate Research Fellowship.

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