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.Comment: 7 pages, 3 figures to be published in New Astronomy Review

A. Castera

A. Pécontal

B.C. Lee

Cabanela

D. Hardin

E. Gangler

E. Pécontal

G. Adam

G. Aldering

G. Smadja

Garnavich

Goldhaber

J. Siegrist

J.-P. Lemonnier

L. Wang

P. Antilogus

P. Astier

P. Nugent

Perlmutter

Pravdo

R. Bacon

R. Kessler

R. Pain

Riess

S. Loken

S. Perlmutter

W.M. Wood-Vasey

Y. Copin

English

arXiv

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 &lt; z &lt; 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

Wood-Vasey, W.M.

Aldering, G.

Lee, B.C.

Loken, S.

Nugent, P.

Perlmutter, S.

Siegrist, J.

Wang, L.

Antilogus, P.

Astier, P.

Hardin, D.

Pain, R.

Copin, Y.

Smadja, G.

Gangler, E.

Castera, A.

Adam, G.

Bacon, R.

Lemonnier, J.-P.

Pecontal, A.

Pecontal, E.

Kessler, R.

eScholarship - University of California

Lawrence Berkeley National LaboratoryLawrence Berkeley National LaboratoryTitleThe nearby supernova factoryPermalinkhttps://escholarship.org/uc/item/04f1z7r5AuthorsWood-Vasey, W.M.Aldering, G.Lee, B.C.et al.Publication Date2004-01-23eScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaarXiv:astro-ph/0401513 v1   23 Jan 2004The Nearby Supernova FactoryW. M. Wood-Vasey ∗, G. Aldering, B. C. Lee, S. Loken,P. Nugent, S. Perlmutter, J. Siegrist, L. WangLawrence Berkeley National Laboratory, One Cyclotron Road, Mailstop 50R232,Berkeley, CA, 94720, USAP. Antilogus, P. Astier, D. Hardin, R. PainLaboratoire de Physique Nucleaire et de Haute Energies de Paris, Paris, France(LPNHE)Y. Copin, G. Smadja, E. Gangler, A. CasteraInstitut de Physique Nucleaire de Lyon (IPNL), Lyon, FranceG. Adam, R. Bacon, J-P. Lemonnier, A. Pecontal, E. PecontalCentre de Recherche Astronomique de Lyon (CRAL), Lyon, FranceR. KesslerUniversity of Chicago, Chicago, Illinois, USAAbstractThe Nearby Supernova Factory (SNfactory) is an ambitious project to find andstudy in detail approximately 300 nearby Type Ia supernovae (SNe Ia) at redshifts0.03 < z < 0.08. This program will provide an exceptional data set of well-studiedSNe in the nearby smooth Hubble flow that can be used as calibration for the currentand 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 SNesystematically discovered in unprecedented numbers using the same techniques asthose used in distant SNe searches. In 2002, 35 SNe were found using our test-bedpipeline for automated SN search and discovery. The pipeline uses images fromthe asteroid search conducted by the Near Earth Asteroid Tracking group at JPL.Improvements in our subtraction techniques and analysis have allowed us to increaseour effective SN discovery rate to ∼12 SNe/month in 2003.Key words: supernovae, galaxiesPreprint submitted to Elsevier Science 26 January 20041 IntroductionType Ia supernovae (SNe Ia) have proven extremely useful as standardizablecandles to explore the expansion history of the Universe (Perlmutter et al.,1997, 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.,2002b), to extend the revolutionary result that the Universe is accelerating toprecise statements about the constituents and history of the Universe. How-ever, a key assumption underlying these experiments is that the current ob-served diversity in SNe Ia will be well-behaved and calibrated to allow for thedesired precision measurements. This assumption can be tested in large partusing nearby SNe Ia. Moreover, there is the possibility for such nearby stud-ies to uncover new relationships that will make SNe Ia even better standardcandles, much as the width-luminosity relation has brought SNe Ia to theiralready impressive level of standardization.The Nearby Supernova Factory (SNfactory) project is designed to bring thisimproved understanding of SNe Ia (Aldering et al., 2002a; Pécontal et al.,2003; Lantz et al., 2003). Over the course of three years, it will study 300 SNe Iain the nearby smooth Hubble flow. These SNe will be observed with a dedi-cated instrument, the SuperNova Integral Field Spectrograph (SNIFS), whichis currently in the final stages of construction. SNIFS will provide simultaneousspectrophotometric coverage of both the SN and the host galaxy at 3–5 dayintervals during the rise and fall of each SN. This unprecedented dataset willprovide a wealth of information on SNe Ia and allow for an improved calibra-tion of SNe Ia for use in cosmology.2 The Supernova Search DatasetThe SNfactory searches for SNe using wide-field images obtained in collabo-ration with the Near Earth Asteroid Tracking (NEAT) group (Pravdo et al.,1999) at the Jet Propulsion Laboratory (JPL). In their quest for asteroids, theNEAT group observes hundreds of fields each night by taking three images ofeach field, spaced fifteen to thirty minutes apart, and searching for objectsthat move by more than a couple of arcseconds over this period. The SNfac-tory uses this temporal spacing to eliminate asteroids and reduce cosmic-raycontamination. The NEAT observing program covers the observable sky from∗ WMWV was supported in part by an NSF Graduate Research Fellowship.Email address: wmwood-vasey@lbl.gov (W. M. Wood-Vasey).URL: http://snfactory.lbl.gov (W. M. Wood-Vasey).2−40 to +40 degrees in declination every one to two weeks.Since 2001, the Palomar 1.2-m. Oschin telescope has been used by the SNfactory-NEAT collaboration. The NEAT group outfitted this telescope with an auto-mated system for control and observations and added a 3-chip, 3 ⊓⊔◦ field-of-view CCD camera (NEAT12GEN2) at the spherical focal plane of this Schmidtreflector. We spent 2001 designing, testing, and verifying the search pipelinewith the large data stream from this telescope. Full search operations began inthe fall of 2002 and continued through April of 2003 when the NEAT12GEN2camera was replaced by the Yale QUEST group (The QUEST Collaboration,2003) with a 112-chip, 9 ⊓⊔◦ field-of-view camera (QUESTII) capable of bothdrift-scan and point-and-track observations. QUESTII became operational inAugust 2003 and is now providing data for the SNfactory search. The NEATgroup also uses the Haleakala 1.2-m MSSS telescope, but as this telescope hasa smaller field of view and poor image quality, the SNfactory has focused itssearch efforts on the images from the Palomar Oschin telescope.3 Data ProcessingThe SNfactory, in collaboration with the High Performance Wireless Re-search and Education Network (Braun, 2003), has established a high-speed,6 Megabyte-per-second (MBps) radio internet link to the San Diego Supercom-puter Center (SDSC) from the Palomar observatory. Images are transmittedfrom the telescope and stored at the National Energy Research Supercomput-ing Center (NERSC) High Performance Storage System (HPSS). The band-width from SDSC to NERSC allows for near real-time transfer of 20–50 GBper night. From HPSS the data are transferred to the 200-node NERSC Par-allel Distributed Systems Facility (PDSF) and are submitted for simultaneousprocessing on the PDSF cluster in groups based on the dark frame taken clos-est in time. The processed images are then registered with our image database,renamed to match our canonical name format, and saved to HPSS.The SNfactory searches these data for SNe using image subtraction. The com-puters use a sophisticated suite of image tools, but there remains a significant,although ever-decreasing, amount of human interpretation needed to discrim-inate the good SN candidates from the bad. The same software used by theSNfactory to search for nearby (z ≤ 0.1) SNe is used by the Supernova Cosmol-ogy Project (SCP) to search for distant SNe. Our subtraction software beginsby spatially registering all of the images of a given field to a common referencesystem. The images to be used as a reference are stacked into a single coaddedimage, while the images to be searched are coadded into two separate imagesto allow for later checks for asteroids and cosmic rays. To account for differ-ences in the effective point-spread-function from variations in atmospheric and3telescope conditions, we calculate a convolution kernel to match each coaddedimage to the worst-seeing coadded image of the set. An automated scanningprogram looks for objects in the convolution-matched, subtracted image andapplies a variety of selection criteria to eliminate cosmic rays, asteroids, andsubtraction and detector artifacts. This program compiles a list of interestingcandidates to be looked at in more detail by a human scanner. Every day,human scanners consult the list of interesting candidates and decide whetheror not a computer-flagged candidate appears to be a real, variable object.Once we have a promising candidate, we submit it to the target list for thenext night of observation with NEAT. After obtaining confirmation images ofa candidate that reveal it to exhibit the appropriate behavior for a SN, weannounce the apparent SN in the IAU Circulars. A confirmation spectrum isdesirable but currently not always possible. When the SNIFS instrument isinstalled on the Hawaii 2.2-m telescope, it will be automatically scheduled toconfirm and follow SNe. Spectra will be taken of each SN at 3–5 day intervalsover a span of roughly 60 days.4 ResultsEighty-three SNe have been found using the techniques described above andhave been accepted by the International Astronomical Union. Fig. 1 shows the35 SNe we discovered in 2002. In the first five months of 2003, we found andreported an additional 48 SNe. In addition, our search identified another 17SNe that had already been reported by other groups. We are currently runningwith a very conservative set of selection criteria and need human eyes to scan∼ 5% of the successful subtractions for each night. However, many of the SNediscovered in 2003 could have been found using very restrictive criteria thatwould have required human scanning for < 1% of the subtractions. To furtherreduce our scanning burden, efforts are ongoing to understand the parameterspace of our candidate scores to uniquely identify the SNe.In order to understand our search results, we have developed a simple searchsimulator. We use a V-band lightcurve template from Goldhaber et al. (2001)to model the rise and fall of SNe Ia. 1 The simulator calculates the amountof time a supernova would be visible at a given redshift assuming a normal(stretch = 1) SN Ia. We considered a redshift range from 0 < z < 0.2, alimiting unfiltered magnitude of 19.5, and several different repeat coveragecadences for our simulations. We included the typical NEAT sky coveragerate, SD = 500 ⊓⊔◦/night, and assumed SO =10,000 ⊓⊔◦ of usable sky a night.There is a maximum effective cadence, Cmax, beyond which one is just idling1 We have found that the NEAT unfiltered magnitudes track V-band SN lightcurvesquite well.4Fig. 1. A mosaic of the 35 supernovae found by the Nearby Supernova Factorypipeline in 2002. Each image is centered on the respective supernova.the telescope: Cmax = SO/(SD−S0365 days). For the NEAT observation program,this cadence is approximately 20 days. An important goal of the SNfactory isto discover SNe early enough after explosion to follow them through their riseand fall. Fig. 3 shows a comparison of our simulations of the SNe discoveryphase with the actual discovery phase for SNe from the SNfactory searchhaving well-known dates of maximum. For shorter sky coverage cadences lesssky can be covered and so fewer SNe are discovered overall, although the epochof each SN can be better constrained. Fig. 3 clearly shows that the SNfactorysearch pipeline is successfully finding SNe Ia early in their lightcurves.5 ConclusionThe Nearby Supernova Factory search pipeline is operational and has proventhe ability to discover ∼ 12 SNe/month ⇒ ∼150 SNe/year. As 23of the su-pernovae discovered in our search have been SNe Ia, we expect to discover∼ 100 SNe Ia/year. Most of these supernovae have been discovered sufficientlyearly to enable detailed study starting before maximum light. This extensivestudy will enable improvements in the use of SNe Ia for cosmological measure-ments, and provide a wealth of information on the supernovae themselves.5 0 10 20 30 40 50 0  0.05  0.1  0.15  0.2 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4Supernovae Discovered / year / 0.02Magnitude ErrorRedshiftSNfactoryKAIT/LOTOSSVelocity+Cosmology ErrorFig. 2. The SNfactory is operating in the “sweet spot” redshift range between pecu-liar-velocity noise and cosmological uncertainty. The SNfactory curve is the redshiftdistribution of supernovae found and spectroscopically confirmed in our search todate scaled up to 100 SNe/year. The velocity error is for an assumed 300 km/svelocity dispersion. The cosmology error is modeled as the difference between anEinstein-de Sitter cosmology and a Universe with ΩM = 0.3 and ΩΛ = 0.7.-20 -15 -10 -5  0  5  10  15  20  25 0 1 2Predicted SNe found [arbitrary units]SNe found / 1 phase day binPhase [days]Expected phases of SNe  20 day cadence 12  8  4ObservedFig. 3. The distribution of discovery epoch for the SNe Ia with determined dates ofmaximum found in the SNfactory dataset compared with the simulations describedin the text. The model curves are not calculated in absolute units and have beenscaled for comparison with the observations. As the model curves show, a shortercadence gives fewer supernovae but better constraints on the epoch at discovery.6ReferencesAldering, G. et al. 2002b, Ed. Dressler, A. M. Proc. SPIE, 4835, pp. 146-157Aldering, G. et al. 2002a, Ed. Tyson, J. A.Proc. SPIE, 4836, pp. 61-72Braun, H.-W. 2003, High Performance Wireless Research and Education Net-work http://hpwren.ucsd.edu/Cabanela, J. E. et al. 2003, PASP, 115, 837Garnavich, P. M. et al. 2002, BAAS, 34, 1233Garnavich, P. M. et al. 1998, ApJ, 509, 74Goldhaber, G. et al. 2001, ApJ, 558, 359IAU. 2003, Minor Planet Checker http://scully.harvard.edu/˜cgi/CheckMPLantz, B. et al. 2003, in Proc. SPIE, in pressPécontal, E. et al. 2003, Proc. of the ESO/MPA/MPE July 2002, p. 404.Pain, R. et al. 2003. Proc. ESO/MPA/MPE July 2002, p. 408.Perlmutter, S. et al. 1997, ApJ, 483, 565Perlmutter, S. et al. 1998, Nature, 391, 51Perlmutter, S. et al. 1999, ApJ, 517, 565Riess, A. G. et al. 1998, AJ, 116, 1009Pravdo, S. H. et al. 1999, AJ, 117, 1616The QUEST Collaboration. 2003, The Palomar-QUEST Variability Surveyhttp://hepwww.physics.yale.edu/quest/palomar.html7

The nearby supernova factory

SupernovaeThe Nearby Supernova Factory (SNfactory) is an ambitious project to find and study in detail approximately 300 nearby Type Ia supernovae (SNe~Ia) at redshifts 0.0

HAL: Hyper Article en Ligne

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 &lt; z &lt; 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 {approx}12 SNe/month in 2003

Wood-Vasey, W. M.

Lee, B. C.

UNT (University of North Texas) Digital Library

arXiv:astro-ph/0401513 v1   23 Jan 2004The Nearby Supernova FactoryW. M. Wood-Vasey ∗, G. Aldering, B. C. Lee, S. Loken,P. Nugent, S. Perlmutter, J. Siegrist, L. WangLawrence Berkeley National Laboratory, One Cyclotron Road, Mailstop 50R232,Berkeley, CA, 94720, USAP. Antilogus, P. Astier, D. Hardin, R. PainLaboratoire de Physique Nucleaire et de Haute Energies de Paris, Paris, France(LPNHE)Y. Copin, G. Smadja, E. Gangler, A. CasteraInstitut de Physique Nucleaire de Lyon (IPNL), Lyon, FranceG. Adam, R. Bacon, J-P. Lemonnier, A. Pecontal, E. PecontalCentre de Recherche Astronomique de Lyon (CRAL), Lyon, FranceR. KesslerUniversity of Chicago, Chicago, Illinois, USAAbstractThe Nearby Supernova Factory (SNfactory) is an ambitious project to find andstudy in detail approximately 300 nearby Type Ia supernovae (SNe Ia) at redshifts0.03 < z < 0.08. This program will provide an exceptional data set of well-studiedSNe in the nearby smooth Hubble flow that can be used as calibration for the currentand 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 SNesystematically discovered in unprecedented numbers using the same techniques asthose used in distant SNe searches. In 2002, 35 SNe were found using our test-bedpipeline for automated SN search and discovery. The pipeline uses images fromthe asteroid search conducted by the Near Earth Asteroid Tracking group at JPL.Improvements in our subtraction techniques and analysis have allowed us to increaseour effective SN discovery rate to ∼12 SNe/month in 2003.Key words: supernovae, galaxiesPreprint submitted to Elsevier Science 26 January 20041 IntroductionType Ia supernovae (SNe Ia) have proven extremely useful as standardizablecandles to explore the expansion history of the Universe (Perlmutter et al.,1997, 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.,2002b), to extend the revolutionary result that the Universe is accelerating toprecise statements about the constituents and history of the Universe. How-ever, a key assumption underlying these experiments is that the current ob-served diversity in SNe Ia will be well-behaved and calibrated to allow for thedesired precision measurements. This assumption can be tested in large partusing nearby SNe Ia. Moreover, there is the possibility for such nearby stud-ies to uncover new relationships that will make SNe Ia even better standardcandles, much as the width-luminosity relation has brought SNe Ia to theiralready impressive level of standardization.The Nearby Supernova Factory (SNfactory) project is designed to bring thisimproved understanding of SNe Ia (Aldering et al., 2002a; Pécontal et al.,2003; Lantz et al., 2003). Over the course of three years, it will study 300 SNe Iain the nearby smooth Hubble flow. These SNe will be observed with a dedi-cated instrument, the SuperNova Integral Field Spectrograph (SNIFS), whichis currently in the final stages of construction. SNIFS will provide simultaneousspectrophotometric coverage of both the SN and the host galaxy at 3–5 dayintervals during the rise and fall of each SN. This unprecedented dataset willprovide a wealth of information on SNe Ia and allow for an improved calibra-tion of SNe Ia for use in cosmology.2 The Supernova Search DatasetThe SNfactory searches for SNe using wide-field images obtained in collabo-ration with the Near Earth Asteroid Tracking (NEAT) group (Pravdo et al.,1999) at the Jet Propulsion Laboratory (JPL). In their quest for asteroids, theNEAT group observes hundreds of fields each night by taking three images ofeach field, spaced fifteen to thirty minutes apart, and searching for objectsthat move by more than a couple of arcseconds over this period. The SNfac-tory uses this temporal spacing to eliminate asteroids and reduce cosmic-raycontamination. The NEAT observing program covers the observable sky from∗ WMWV was supported in part by an NSF Graduate Research Fellowship.Email address: wmwood-vasey@lbl.gov (W. M. Wood-Vasey).URL: http://snfactory.lbl.gov (W. M. Wood-Vasey).2−40 to +40 degrees in declination every one to two weeks.Since 2001, the Palomar 1.2-m. Oschin telescope has been used by the SNfactory-NEAT collaboration. The NEAT group outfitted this telescope with an auto-mated system for control and observations and added a 3-chip, 3 ⊓⊔◦ field-of-view CCD camera (NEAT12GEN2) at the spherical focal plane of this Schmidtreflector. We spent 2001 designing, testing, and verifying the search pipelinewith the large data stream from this telescope. Full search operations began inthe fall of 2002 and continued through April of 2003 when the NEAT12GEN2camera was replaced by the Yale QUEST group (The QUEST Collaboration,2003) with a 112-chip, 9 ⊓⊔◦ field-of-view camera (QUESTII) capable of bothdrift-scan and point-and-track observations. QUESTII became operational inAugust 2003 and is now providing data for the SNfactory search. The NEATgroup also uses the Haleakala 1.2-m MSSS telescope, but as this telescope hasa smaller field of view and poor image quality, the SNfactory has focused itssearch efforts on the images from the Palomar Oschin telescope.3 Data ProcessingThe SNfactory, in collaboration with the High Performance Wireless Re-search and Education Network (Braun, 2003), has established a high-speed,6 Megabyte-per-second (MBps) radio internet link to the San Diego Supercom-puter Center (SDSC) from the Palomar observatory. Images are transmittedfrom the telescope and stored at the National Energy Research Supercomput-ing Center (NERSC) High Performance Storage System (HPSS). The band-width from SDSC to NERSC allows for near real-time transfer of 20–50 GBper night. From HPSS the data are transferred to the 200-node NERSC Par-allel Distributed Systems Facility (PDSF) and are submitted for simultaneousprocessing on the PDSF cluster in groups based on the dark frame taken clos-est in time. The processed images are then registered with our image database,renamed to match our canonical name format, and saved to HPSS.The SNfactory searches these data for SNe using image subtraction. The com-puters use a sophisticated suite of image tools, but there remains a significant,although ever-decreasing, amount of human interpretation needed to discrim-inate the good SN candidates from the bad. The same software used by theSNfactory to search for nearby (z ≤ 0.1) SNe is used by the Supernova Cosmol-ogy Project (SCP) to search for distant SNe. Our subtraction software beginsby spatially registering all of the images of a given field to a common referencesystem. The images to be used as a reference are stacked into a single coaddedimage, while the images to be searched are coadded into two separate imagesto allow for later checks for asteroids and cosmic rays. To account for differ-ences in the effective point-spread-function from variations in atmospheric and3telescope conditions, we calculate a convolution kernel to match each coaddedimage to the worst-seeing coadded image of the set. An automated scanningprogram looks for objects in the convolution-matched, subtracted image andapplies a variety of selection criteria to eliminate cosmic rays, asteroids, andsubtraction and detector artifacts. This program compiles a list of interestingcandidates to be looked at in more detail by a human scanner. Every day,human scanners consult the list of interesting candidates and decide whetheror not a computer-flagged candidate appears to be a real, variable object.Once we have a promising candidate, we submit it to the target list for thenext night of observation with NEAT. After obtaining confirmation images ofa candidate that reveal it to exhibit the appropriate behavior for a SN, weannounce the apparent SN in the IAU Circulars. A confirmation spectrum isdesirable but currently not always possible. When the SNIFS instrument isinstalled on the Hawaii 2.2-m telescope, it will be automatically scheduled toconfirm and follow SNe. Spectra will be taken of each SN at 3–5 day intervalsover a span of roughly 60 days.4 ResultsEighty-three SNe have been found using the techniques described above andhave been accepted by the International Astronomical Union. Fig. 1 shows the35 SNe we discovered in 2002. In the first five months of 2003, we found andreported an additional 48 SNe. In addition, our search identified another 17SNe that had already been reported by other groups. We are currently runningwith a very conservative set of selection criteria and need human eyes to scan∼ 5% of the successful subtractions for each night. However, many of the SNediscovered in 2003 could have been found using very restrictive criteria thatwould have required human scanning for < 1% of the subtractions. To furtherreduce our scanning burden, efforts are ongoing to understand the parameterspace of our candidate scores to uniquely identify the SNe.In order to understand our search results, we have developed a simple searchsimulator. We use a V-band lightcurve template from Goldhaber et al. (2001)to model the rise and fall of SNe Ia. 1 The simulator calculates the amountof time a supernova would be visible at a given redshift assuming a normal(stretch = 1) SN Ia. We considered a redshift range from 0 < z < 0.2, alimiting unfiltered magnitude of 19.5, and several different repeat coveragecadences for our simulations. We included the typical NEAT sky coveragerate, SD = 500 ⊓⊔◦/night, and assumed SO =10,000 ⊓⊔◦ of usable sky a night.There is a maximum effective cadence, Cmax, beyond which one is just idling1 We have found that the NEAT unfiltered magnitudes track V-band SN lightcurvesquite well.4Fig. 1. A mosaic of the 35 supernovae found by the Nearby Supernova Factorypipeline in 2002. Each image is centered on the respective supernova.the telescope: Cmax = SO/(SD−S0365 days). For the NEAT observation program,this cadence is approximately 20 days. An important goal of the SNfactory isto discover SNe early enough after explosion to follow them through their riseand fall. Fig. 3 shows a comparison of our simulations of the SNe discoveryphase with the actual discovery phase for SNe from the SNfactory searchhaving well-known dates of maximum. For shorter sky coverage cadences lesssky can be covered and so fewer SNe are discovered overall, although the epochof each SN can be better constrained. Fig. 3 clearly shows that the SNfactorysearch pipeline is successfully finding SNe Ia early in their lightcurves.5 ConclusionThe Nearby Supernova Factory search pipeline is operational and has proventhe ability to discover ∼ 12 SNe/month ⇒ ∼150 SNe/year. As 23of the su-pernovae discovered in our search have been SNe Ia, we expect to discover∼ 100 SNe Ia/year. Most of these supernovae have been discovered sufficientlyearly to enable detailed study starting before maximum light. This extensivestudy will enable improvements in the use of SNe Ia for cosmological measure-ments, and provide a wealth of information on the supernovae themselves.5 0 10 20 30 40 50 0  0.05  0.1  0.15  0.2 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4Supernovae Discovered / year / 0.02Magnitude ErrorRedshiftSNfactoryKAIT/LOTOSSVelocity+Cosmology ErrorFig. 2. The SNfactory is operating in the “sweet spot” redshift range between pecu-liar-velocity noise and cosmological uncertainty. The SNfactory curve is the redshiftdistribution of supernovae found and spectroscopically confirmed in our search todate scaled up to 100 SNe/year. The velocity error is for an assumed 300 km/svelocity dispersion. The cosmology error is modeled as the difference between anEinstein-de Sitter cosmology and a Universe with ΩM = 0.3 and ΩΛ = 0.7.-20 -15 -10 -5  0  5  10  15  20  25 0 1 2Predicted SNe found [arbitrary units]SNe found / 1 phase day binPhase [days]Expected phases of SNe  20 day cadence 12  8  4ObservedFig. 3. The distribution of discovery epoch for the SNe Ia with determined dates ofmaximum found in the SNfactory dataset compared with the simulations describedin the text. The model curves are not calculated in absolute units and have beenscaled for comparison with the observations. As the model curves show, a shortercadence gives fewer supernovae but better constraints on the epoch at discovery.6ReferencesAldering, G. et al. 2002b, Ed. Dressler, A. M. Proc. SPIE, 4835, pp. 146-157Aldering, G. et al. 2002a, Ed. Tyson, J. A.Proc. SPIE, 4836, pp. 61-72Braun, H.-W. 2003, High Performance Wireless Research and Education Net-work http://hpwren.ucsd.edu/Cabanela, J. E. et al. 2003, PASP, 115, 837Garnavich, P. M. et al. 2002, BAAS, 34, 1233Garnavich, P. M. et al. 1998, ApJ, 509, 74Goldhaber, G. et al. 2001, ApJ, 558, 359IAU. 2003, Minor Planet Checker http://scully.harvard.edu/˜cgi/CheckMPLantz, B. et al. 2003, in Proc. SPIE, in pressPécontal, E. et al. 2003, Proc. of the ESO/MPA/MPE July 2002, p. 404.Pain, R. et al. 2003. Proc. ESO/MPA/MPE July 2002, p. 408.Perlmutter, S. et al. 1997, ApJ, 483, 565Perlmutter, S. et al. 1998, Nature, 391, 51Perlmutter, S. et al. 1999, ApJ, 517, 565Riess, A. G. et al. 1998, AJ, 116, 1009Pravdo, S. H. et al. 1999, AJ, 117, 1616The QUEST Collaboration. 2003, The Palomar-QUEST Variability Surveyhttp://hepwww.physics.yale.edu/quest/palomar.html7

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

The Nearby Supernova Factory

Abstract

Similar works

Full text

Available Versions

eScholarship - University of California

HAL: Hyper Article en Ligne

UNT (University of North Texas) Digital Library

HAL-IN2P3

HAL-INSU

HAL-ENS-LYON

HAL-IN2P3