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SNANA and U-Band Anomaliesin Light Curve Fitting of Type Ia

Supernovae

Joe Duszynski

Advised by Professor David Cinabro 1

Overview of Projects

•SNANA•Supernova analysis software forsimulations and survey data

•Make it easy to install formost users

•Separate it from unnecessaryparts of CERNLIB

•Add to repositories or developa simple tarball to runconfigure; make

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Overview of ProjectsSupernova U-band discrepancies

•2009 paper found statisticallysignificant scattering indistance moduli when lightcurve fits excluded U-band

•What's going on with this?•Look more closely, check otherbands, use larger pool of data

•Determine how to proceed basedon what is found

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•Appeared to be a straightforwardprocess:•Write short install/updatescripts

•Isolate patchy and fcasplitfrom CERNLIB (small programs)

•Progress stalled at patchy:•Source code compiles•but doesn't actually doanything it's supposed to

SNANA

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SNANA - Patchy•Dr. Cinabro worked very hard toseparate patchy from CERNLIB anddebug the resulting mess.•But still no one understands what'sgoing on.

•Suspected bit arithmetic andcompiler changes over the decades

•Poor (absence of) any documentation•Patchy's development began in 1966,last version released ~1995; originalauthors very well may be dead 5

In the (near) future

•Looking to replace patchy withanother code expander (throughversion control software)•Mercurial•GNU Bazaar

•Rumored updated CERNLIB at DESY•Switching from hbook (part ofCERNLIB) to ROOT planned

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Supernovae U-BandDiscrepancies

•SDSS-II supernova analysis3 found(~6σ) the distance moduli were ~0.1mag higher when the U-band wasremoved (using MLCS2k2 and SALT-II)

•Ultimately, we didn't find anystrong indications of a distinctsubclass of supernovae, nor anyparticular strange or puzzlingbehavior.

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Approach

•Used SDSS and SNLS (4Shooter2,Keplercam, JRK07) survey data

•Avoided others with messy/vaguefiltering schemes, or ones suchas Low-z that mixed telescopesand are well-known headaches.•Resulting data set was rathersmall at 81 supernovae

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Approach (cont.)•Using generous cuts, SNANA'slight curve fitting function forSALT-II generated data files forresulting fit parameters, chi^2values, and so on

•Converted these files into ROOTfiles, and created histograms forchi^2/d.o.f. by survey, filtersused, and cumulative

•A natural cutoff occurred around(adjusted by degrees of freedom)chi^2 ~ 1.5

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Approach (cont.)•Manually inspected light curvefits with chi^2 >= 1.5 (35/486 ~7.2%)

•After removing duplicates (9), 14of 26 remaining had high chi^2sprimarily due to one or two badpoints.

•12/35 remained, and afteradjusting for duplicates in chi^2< 1.5, only about ~3% of thesample displayed potentially(true) aberrant behavior. 11

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Conclusions•Discrepancies most likelyexplained by occasional hardwareglitches in telescopes

•New supernova type/phenomena areunlikely, but sample size isquite small

•A recent paper5 discusses theimproved calibrations of SDSS(which had a calibration errorcorrected only discovered andcorrected recently) and SNLS,which would explain the anomalyobserved in the 2009 paper. 13

Color parameter

•Given smallsample sizes,doesn'tsupport anybizarrebehavior andis withinexpectedrange.

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Differences indistance moduli

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Chi^2/d.o.f. (cumulative)

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Chi^2/d.o.f.split at 1.5

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Flux difference•Expect to benear 0

•Poorresolutionfor highchi^2confirmspreviousconclusions

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Rest framewavelength (nm)

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Number of datapoints persupernova

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Point spreadfunction

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•Sample sizetoo small forthese minordifferences tobe significant

Time inearth/observer'sframe

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References1. SNANA website:http://sdssdp62.fnal.gov/sdsssn/SNANA-PUBLIC/

2. SNANA manual:http://sdssdp62.fnal.gov/sdsssn/SNANA-PUBLIC/doc/snana_manual.pdf

3. Kessler, R. et al. 2009, ApJS, 185, 32

4. http://cernlib.web.cern.ch/cernlib/

5. Betoule, M. et. al. 2013, Astronomy andAstrophysics, Volume 552, id.A124, 55 pp.

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