LecturesonCosmologywithTypeIaSupernovae:

CALIBRATION

R.Kessler(U.Chicago)

IIJaymeTiomnoSchoolofCosmologyRiodeJaneiro,Brazil

Aug6‐10,20121

Why?

•  BecausecalibrationuncertaintiescurrentlydominatethesystematicerrorbudgetforSNIacosmology.

2

Filters

3

UBVRI

ugriz

Bessell(1990):UsedformostnearbySNIa(CfA)

SDSSugriz:SimilarfiltersusedforSNLS,PS1,HSC,DES,LSST…

andCSP(nearby)

wavelength

IllustrationofCalibrationChallenge

4

UBVRI

ugriz

wavelength

Comparerest‐frameFlux(4400A)atz=0.05usingBband

to

samerest‐frameFluxatz=0.5,butusingrbandondifferenttelescope…andNOoverlappingmeasurementswithnearbySNfields!!!

5

Calibration:Overview

★★

★★

★★★

★

★

SDSS

★★

★★

★ ★SNLS

★★

★★

★ ★ESSENCE

★

★ ★

★★

★

★★

LowZ ✵

★

✵

Landolt/USNOsecondaryPrimary(Vega,BD+17)

Each SN sample is calibrated to Landolt or USNO stars within (or near) their survey field.

SDSS,SNLS filters ugriz require large color transformations to Bessell UBVRI.

6

CurrentCalibrationwithSNe

★★

★★

★★★

★

★

SDSS

★★

★★

★ ★SNLS

★★

★★

★ ★ESSENCE

★

★ ★

★★

★

★★

LowZ ✵

★

✵

Landolt/USNOsecondaryPrimary(Vega,BD+17)

Comparing SNe (❁) in different surveys involves a complex calibration path.

❁

❁

❁

❁

SNFlux‐ModelwithReference

7

Reference:(VegaorBD17)

Filtertransmission

SNFlux‐ModelwithReference

8

SNFlux‐ModelwithReference

9

SNFlux‐ModelwithReference

10

11

Landoltmags

HST‐measuredSEDsonLandoltstars

Solveδλ

FilterShifts,δλU,B,V,R,I

12

byJ.Marriner(inKessleretal,2009)

Usesground‐basedspectra

WavelengthShiftsforBessell(1990)Filters

CommentsonUBVRIFilterShifts

•  Discrepantfiltershiftsdependingonchoiceofspectro‐photometricstandards.

•  Simplewavelengthshiftislikelytoonaïve

•  BettersolutionistocollectnewnearbySNIawithknownfiltertransmissions:

CSP(Stritzingeretal.,2011)

CfA3(Hickenetal.,2009)

13

14

Exercise:Fora10ÅshiftintheVbandcentralwavelength,whatisthepeakSNmagnitudeshiftatz=0?atz=0.5?UseBD17SEDasthereference.

SNIaspectraltemplatevs.epoch:http://supernova.lbl.gov/~hsiao

BD17HSTspectrum:http://www.mmnt.net/db/0/1/ftp.stsci.edu/cdbs/testcdbs/calspec

BessellUBVRIFilters:http://supernovae.in2p3.fr/~guy/salt/download_instruments.html(thenclickSNLS3‐Landolt‐model‐5A.tar.gz)

15

ExerciseSupposewemeasurethefiltertransmissionin50ÅstepsusinganearlymonochromaticbeamwithaGaussianprofile(σλ=50Å).Wesimplyconnectthemeasurementswithstraightlinestoestimatethefilterresponse.

ForU, V, Ibands,whatistheerroronthesyntheticSNmagatpeak(z=0)?

Repeatfor200Åstepsandσλ=200Å.

MiscellaneousComplications

16

10%

12%

8%6%

4%

2%

0%

Wavelength(Å)

transm

ission

SDSS:Doiet.al.,AJ139,1628(2010)Filtertransmissioncanchangewithtime

uband

SNLS:Regnaultetal,A&A506,999(2009)Filtertransmissionisnotuniformoverfocalplane

MiscellaneousComplications:AtmosphereTransmission

17

DarkEnergySurveyFilters(approx)

MiscellaneousComplications:AtmosphereTransmission

18

ForSNIaatpeak,zbandmagerror(Δm)vs.redshiftfromignoringa50%increaseinH2O.

SimulationforDES(byRK&V.Braganca)

Δm

DarkEnergySurveyFilters(approx)

−−

Inter‐calibrationBetweenSurveys

•  CombiningSNfromdifferentsurveysrequirespreciseinter‐calibrationwithoutcrosschecks.

•  Inter‐calibrationeffortshaverecentlystarted,whereindependenttelescopesobservethesameobjectswithintheirfields(beyondLandoltstars)

19

CSPvs.SDSSMosheretal,AJ144,17,(2012)

•  CSP&SDSSsimultaneouslyobserved9liveSNIa.Usemeasuredfiltertransmissionstocorrectandcomparemags.

20

CSPvs.SDSS•  CSP&SDSSsimultaneouslyobserved9liveSNIa.Use

measuredfiltertransmissionstocorrectandcomparemags.

21‐10010203040rest‐frameepoch(days)

16

18

20

22

24

magnitdue

+SDSS• CSP(transformed)

InterpolateSDSSobstoCSPobs

CSPvs.SDSS•  CSP&SDSSsimultaneouslyobserved9liveSNIa.Use

measuredfiltertransmissionstocorrectandcomparemags.

22‐10010203040rest‐frameepoch(days)

16

18

20

22

24

magnitdue

+SDSS• CSP(transformed)

InterpolateSDSSobstoCSPobs

SDSSvs.SNLS(M.Betouleetal,inprep)

•  SNLSobservedSDSSfieldstocomparemagsforthousandsofstars(nosimultaneousSNIa)

23

SDSS

SolarAnalogs

Landolt

SDSS

SolarAnalogs

Landolt

‐0.0200.02 ‐0.0200.02 ‐0.0200.02magdifferencew.r.t.SNLS

preliminary

Calibration:Oldvs.New

24

Oldsurveys:SNLS,ESSENC,SDSS

NewSurveys:PS1,DES,LSST…

Filtertransmission Onceeveryfewyearsinalab

weekly/monthlyin‐situ

Filteruniformity Whatevertheygot Strictspecifications

Calibration:Oldvs.New

25

Oldsurveys:SNLS,ESSENC,SDSS

NewSurveys:PS1,DES,LSST…

Filtertransmission Onceeveryfewyearsinalab

weekly/monthlyin‐situ

Filteruniformity Whatevertheygot Strictspecifications

Atmosphere Photometricnightbyvisualinspectionor10umcamera

Monitorbrightstarswithmulti‐bandcameraorspectrograph.GPSforwatervapor.

Spectrophotometricstandards

HSTCalSpec,WhiteDwarfModels

Same,butmoreWhiteDwarfs

In‐SituMeasurementofTelescopeEfficiency

26

CTIO4m

ScreenforDES

In‐SituMeasurementofTelescopeEfficiency

27

Monochromaticlightsourceilluminatesscreen

ReflectedlightgoesintotelescopeandintoPINdiode.Eff=Nγ

tel/NγPIN

Mapoutefficiencyvs.λ

SeveralexistingsystemsbuiltbyC.StubbsandD.Depoy.

CTIO4m

ScreenforDES

HolyGrailofCalibration(fromC.StubbstalkatFNALCalibconf,April2012)

Instri

InstrumentalSensitivity

Instri

AtmosphericTransmission

Instri

SpectrophotometricStandards

Instri

Predictobservedphotometry

HolyGrailofCalibration(fromC.StubbstalkatFNALCalibconf,April2012)

Instri

InstrumentalSensitivity

Instri

AtmosphericTransmission

Instri

SpectrophotometricStandards

Instri

Predictobservedphotometry

PanStarrs‐1comeswithin5%rmsTonryetal.,AJ750,99,(2012)Long‐termgoalissub‐percent.