Supernova 2010ev: A reddened high velocity gradient type Ia supernova

1 MB·

by  Claudia P. Gutiérrez

Astronomy&Astrophysicsmanuscriptno.SN10ev (cid:13)c ESO2016
January29,2016
Supernova 2010ev: A reddened high velocity gradient type Ia
⋆
supernova
ClaudiaP.Gutie´rrez1,2,3,SantiagoGonza´lez-Gaita´n1,2,Gasto´nFolatelli4,GiulianoPignata5,1,JosephP.Anderson3,
MarioHamuy2,1,NidiaMorrell6,MaximilianStritzinger7,StefanTaubenberger8,9,FilomenaBufano1,5,10,Felipe
OlivaresE.1,5,JoshuaB.Haislip11,andDanielE.Reichart11
1 MillenniumInstituteofAstrophysics,Casilla36-D,Santiago,Chile,
6 2 DepartamentodeAstronom´ıa,UniversidaddeChile,Casilla36-D,Santiago,Chile
1 3 EuropeanSouthernObservatory,AlonsodeCo´rdova3107,Casilla19,Santiago,Chile
0 e-mail:[email protected]
4 InstitutodeAstrof´ısicadeLaPlata(IALP,CONICET),Argentina
2
5 DepartamentodeCienciasFisicas,UniversidadAndresBello,Avda.Repu´blica252,Santiago,Chile

n 6 CarnegieObservatories,LasCampanasObservatory,Casilla601,LaSerena,Chile
a 7 DepartmentofPhysicsandAstronomy,AarhusUniversity,NyMunkegade120,DK-8000AarhusC,Denmark
J 8 Max-Planck-Institutfu¨rAstrophysik,Karl-Schwarzschild-Str.1,85741Garching,Germany

8 9 EuropeanSouthernObservatory,Karl-Schwarzschild-Str.2,85748Garching,Germany
2 10 INAF-OsservatorioAstrofisicodiCatania,ViaSantaSofia,78,95123,Catania,Italy
11 UniversityofNorthCarolinaatChapelHill,CampusBox3255,ChapelHill,NC27599-3255,USA

]
E Preprintonlineversion:January29,2016
H
ABSTRACT
.
h
p Aims.WepresentandstudythespectroscopicandphotometricevolutionofthetypeIasupernova(SNIa)2010ev.
- Methods.Weobtainandanalyzemulti-bandopticallightcurvesandoptical/near-infraredspectroscopyatlowandmediumresolution
o spanningfrom−7daysto+300daysfromtheB-bandmaximum.
r Results.A photometric analysis shows that SN 2010ev is a SN Ia of normal brightness with a light curve shape of ∆m (B) =
t 15
s 1.12±0.02andastretch s = 0.94±0.01sufferingsignificantreddening.Fromphotometricandspectroscopicanalysis,wededuce
a acolorexcessof E(B−V) = 0.25±0.05andareddening lawofR = 1.54±0.65. Spectroscopically, SN2010ev belongstothe
[ broad-lineSNIagroup,showingstrongerthanaverageSiiiλ6355absvorptionfeatures.WealsofindthatSN2010evisahigh-velocity
1 gradientSN,withv˙Si =164±7kms−1d−1.ThephotometricandspectralcomparisonwithothersupernovaeshowsthatSN2010ev
v hassimilarcolorsandvelocitiestoSN2002bo andSN2002dj. Theanalysisofthenebularspectraindicatesthatthe[Feii]λ7155
3 and[Niii]λ7378linesareredshifted,asexpectedforahighvelocitygradientsupernova.Allthesecommonintrinsicandextrinsic
propertiesofthehighvelocitygradient(HVG)grouparedifferentfromthelowvelocitygradient(LVG)normalSNIapopulationand
6
suggestsignificantvarietyinSNIaexplosions.
8
7 Keywords.stars:supernovae:general stars:supernovae:individual:SN2010ev
0
.
1
0 1. Introduction els considered are: the single degenerate (SD) (Nomoto, 1982;
6
Iben&Tutukov, 1984), and the double degenerate (DD) sce-
1 Type Ia supernovae (SNe Ia) play an important role in stellar
nario(Iben&Tutukov, 1984;Webbink, 1984). Inthe former,a
: evolutionandinthechemicalenrichmentoftheuniverse,aswell
v whitedwarfaccretesmatterfromthecompanionwhichcanbea
i asin the determinationof extragalacticdistances,thanksto the sub-giantormainsequencestar,whileinthelattertheSNispro-
X relationbetweenthedeclinerateofthelightcurveanditspeak
ducedbythe mergingoftwo white dwarfs. SNe Ia are thought
r luminosity (Phillips, 1993; Hamuyetal., 1996; Phillipsetal.,
to explode near the Chandrasekhar mass, although recent sim-
a
1999) and between color and peak luminosity (Tripp, 1998).
ulationsof sub-Chandrasekharmass explosionshavebeen suc-
SNe Ia representa homogeneousclass andare thoughtto arise
cessfulforbothscenarios(Simetal.,2012;Kromeretal.,2010;
from the thermonuclear explosion of a carbon-oxygen white-
Pakmoretal.,2012).
dwarf either triggered by the interaction with the companion
The study of SN Ia spectral and photometricparametersin
in a close binary system (Hoyle&Fowler, 1960) or by direct
bothearlyandlateepochscangivekeyindicationsaboutthena-
collisions of white dwarfs. (Raskinetal., 2009). In the leading
tureoftheexplosion.StudiesofSNIaspectroscopicproperties
scenario of a close binary system, the nature of the explosion
reveal significant diversity among the population.Benettietal.
and of the companion star are still debated. Two of the mod-
(2005) defined a sub-classification of SNe Ia based on expan-
sion velocities, line ratios and light curve decline rates. They
⋆ This paper includes data gathered with the Du Pont Telescope at classified the SN Ia population in three different sub-groups:
LasCampanasObservatory,Chile;andtheGeminiObservatory,Cerro
High Velocity Gradient (HVG), Low Velocity Gradient (LVG)
Pachon,Chile(GeminiProgramGS-2010A-Q-14).Basedonobserva-
and FAINT objects. A parallel classification was proposed by
tionscollectedattheEuropeanOrganisationforAstronomicalResearch
Branchetal. (2006) based on absorption equivalent widths of
intheSouthernHemisphere,Chile(ESOProgramme085.D-0577)
1
Gutie´rrezetal.:SN2010ev:AreddenedHVGSN.
Siii λ5972 and λ6355 lines at maximum, which defines four
subtypes:Core-Normal(CN),Broad-Line(BL),Cool(CL)and
ShallowSilicon(SS).Wangetal.(2009)classifiedtheirSNeIa
sample in two groupsbased on the blueshiftedvelocityof Siii
absorptionlinesatmaximum:Normalvelocity(NV;v ∼ 10500
km s−1) and High velocity (HV; v ≥ 12000 km s−1) SNe.
Contemporary analyses of large samples of SNe Ia spectra
(e.g Branchetal., 2009; Blondinetal., 2012; Silvermanetal.,
2012; Silverman&Filippenko, 2012; Silvermanetal., 2013;
Folatellietal., 2013) have confirmedthis diversity and suggest
thatitcouldbekeytounderstandtheexplosionmechanism(s).In
fact,Maedaetal.(2010a)proposedanexplanationinwhichve-
locitygradientsvaryasaconsequenceofdifferentviewingdirec-
tions towards an aspherical explosion scenario. Nebular [Feii]
λ7155and[Niii]λ7378Ålinesareredshiftedandaregenerally
associatedwithHVGSNe,whileblueshiftedlinescorrespondto
LVGSNe.
Recentobservationalevidencesuggeststhepresenceofcir-
cumstellar material(CSM) aroundSN Ia progenitors,which in
principle could favor the SD model (Raskinetal., 2013), but
someDDmodelshavealsopresentedCSM (Shenetal.,2013).
Inobservedspectra,thetemporalevolutioninthenarrowNaID Fig.1.FindingchartshowingthepositionofSN2010evandthat
lineshasbeenattributedtoCSM(Patatetal.,2007;Simonetal., ofthelocalsequencestarsusedforphotometriccalibration.The
2009;Blondinetal.,2009),aswellasthefactthattheyhavean image was taken with PROMPT1 and covers an area of about
excessofblueshifts(Sternbergetal.,2011;Maguireetal.,2013; 8′×7′.Thecrosshairindicatesthepositionofthesupernova.
Phillipsetal.,2013).
IthasbeensuggestedthatsuchnearbyCSMcouldaffectthe
colors of SNe Ia (Goobar, 2008; Fo¨rsteretal., 2013), although pixel scale = 0.6′′per pixel). With PROMPT1, SN 2010evwas
other studiessuggestthat the dust responsibleforthe observed observed with the B, V, R and I Johnson-Kron-Cousinsfilters,
reddeningofSNeIaispredominantlylocatedintheinterstellar with PROMPT3 itwas observedwith Bfilter and theSloan u′,
medium(ISM)ofthehostgalaxiesandnotintheCSM associ- g′ filters, and in PROMPT5 using V, R and I and r′, i′ and z′
atedwiththeprogenitorsystem(e.gPhillipsetal.,2013).
In this paper we present the optical photometry and
optical/near-infraredspectroscopyofSN2010ev,aredSNwith Table1.MainparametersofSN2010evanditshostgalaxy
normal brightness. We discuss its characteristics and we com-
pareitwithothersimilar events.Thepaperisorganizedasfol- Hostgalaxy NGC3244
lows: A description of the observations and data reduction are Hostgalaxytype SA(rs)cd⋆
presentedinsection2.Thephotometryandspectroscopyarean- Redshift 0.0092⋆
Distancemodulusµ 32.31±0.60⋆
alyzedinsection3.Insection4wepresentthediscusion,andin
RA 10h25m28s.99
section5theconclusions. SN
Dec −39◦49′51′.′2
SN
E(B−V) 0.092mag∗
Gal
E(B−V) 0.25±0.05mag†
Host
2. Observationsanddatareduction ∆m (B) 1.12±0.02•
15
Stretchfactor(B) 0.94±0.01N
SN2010evwasdiscoveredbytheChileanAutomaticSupernova B epoch(JD) 2455384.60•
max
Search (CHASE) program on June 27.5 UT (Pignataetal.,
B epoch(UT) 2010July7.1
2010) in the spiral galaxy NGC 3244 (α = 10h25m28s.99, Bmax 14.94±0.02•
max
δ = −39◦49′51′.′2).TheSNlies1′.′6Eastand12′.′4Southofthe V 14.98±0.02•
max
center of the host galaxy (see Figure 1). Optical spectra of the V epoch(JD) 2455383.60•
max
SN 2010ev were obtained 3 days after discovery on June 30.9 Rmax 14.45±0.02•
UT with the GeminiSouth (GMOS-S) telescope by Stritzinger Rmaxepoch(JD) 2455385.60•
(2010).ThespectrumrevealedthatSN2010evwasayoung(∼ Imax 14.56±0.02•
I epoch(JD) 2455382.60•
7 days before maximum)SN Ia. Details on SN 2010evand its max
γ 1.63±0.03△
host-galaxypropertiesaresummarisedinTable1. B
γ 1.15±0.02△
V
γ 1.16±0.05△
R
γ 0.83±0.02△
I
2.1.Opticalphotometry ⋆ NED(NASA/IPACExtragalacticDatabase).
• ObtainedwithSNooPy.
Optical imaging of SN 2010ev was acquired with the
∗ Schlegeletal.(1998).
PROMPT1, PROMPT3 and PROMPT5 telescopes located at
† See§3.6
Cerro Tololo Interamerican Observatory, FORS2 at the ESO N ObtainedbySiFTO.
Very Large Telescope (VLT) and IMACS at Las Campanas △ Late-timedecline γ [Magnitudes per 100 days] between 175 and
Observatory. The PROMPT telescoples are equipped with an 290days.
Apogee Alta U47 E2V CCD47-10 CCD camera (1024×1024,
2
Gutie´rrezetal.:SN2010ev:AreddenedHVGSN.
filters. (Blondinetal.,2015,hereafter“B15”2).Hsiaoetal.(2007)use
Since the PROMPT cameras operate between -20 and -30 a sample of 28SNe Ia to characterizethe spectralfeaturesand
degrees Celsius, all optical images were dark subtracted to re- identify patterns in the data with principal componentanalysis
move the dark current. After flat-field corrections all images (PCA). Overall, these SNe show normal features. Meanwhile,
takenwithagivenfilterwereregisteredandstackedinorderto the B15 model is the result of a 1D non-local thermodynamic
produceafinaldeeperimage.PSFphotometryofthesupernova equilibrium radiative transfer simulation of a Chandrasekhar
was computed relative to a sequence of stars located close to massdelayed-detonationmodelwith0.51M of56Nithatclosely
⊙
theSNbutnotcontaminatedbyhostgalaxylight(seeFigure1). matches SN 2002bo. This model provides a reference for un-
The photometricsequence itself was calibrated to the standard derstanding SNe Ia similar to that prototype, as is the case for
JohnsonKron-CousinsandSloanphotometricsystemsusingob- SN2010ev.Thus,wecompareourresultswiththeH07template
servationsofphotometricstandardstars(Landolt1992;Landolt andtheB15model.
2007; Smithetal. 2002), respectively.The BVRI and u′g′r′i′z′
magnitudesofthelocalsequencearereportedinTableA.1.
3.1.Lightcurves
Given that SN 2010ev exploded in a region of significant
backgroundgalaxyflux, it was necessary to apply galaxy tem- SN 2010ev was observed in BVRI and u′g′r′i′z′ bands. We
platesubtractionstoalloftheopticalimages.Threetemplateim- have performed light curve fits to the multi-wavelength pho-
agesforeachfilterwereacquiredwiththePROMPTtelescopes tometry of SN 2010ev. For this purpose, we use SNooPy
between 2012 January 24–30, i.e. more than 565 days after B (Burnsetal.,2011)andSiFTO(Conleyetal.,2008)lightcurve
maximumbrightness.Thismakesusconfidentthattheresidual fitters.Figure2showsthe BVRI andu′g′r′i′z′ lightcurveswith
SNfluxonthetemplateimagesisnegligible.Eachfluxmeasure- both fits. This SN shows a normal decline rate, ∆m (B) =
15
mentwascomputedasaweightedaverageofthevaluesobtained 1.12±0.02andastretchparameters=0.94±0.01.This∆m (B)
15
fromthethreetemplates.Toaccountfortheerrorintroducedby is similar to those foundin highvelocitygradientSNe (HVG),
thetemplatesweaddinquadraturethermsfluxcomputedfrom such as SN 2002bo (∆m (B) = 1.13± 0.02) and SN 2002dj
15
the three measurements with errors obtained from the PSF fit- (∆m (B)=1.08±0.02).
15
tingandfluxcalibration.InTableA.2,wereportthe BVRI and
u′g′r′i′z′ photometry of SN 2010ev, together with their uncer-
tainties. Light curves of SN 2010ev
2.2.Opticalandnearinfraredspectroscopy 14
Opticalspectrawereobtainedat16epochsspanningphasesbe-
tween −6 and +270 days with respect to B-band maximum.
These observations were acquired with four different instru- 16
ments:X-ShooterandFORS2attheESOVeryLargeTelescope
(VLT), GMOS-S at the Gemini Observatory and the WFCCD
at the du Pont Telescope of the Las Campanas Observatory.
18
NearinfraredspectrawereobtainedwithX-Shootercovering9
epochsfrom−6to+15days.Alogofthespectroscopicobser-
vationsofSN2010evisreportedinTable2.
DatareductionforGMOS-S,WFCCDandFORS2wereper- 20
formedwithIRAF1usingthestandardroutines(biassubtraction,
flat-fieldcorrection,1Dextraction,andwavelengthcalibration),
while for X-Shooter the dedicated pipeline (Modiglianietal.,
22 SNooPy
2010) was employed for most of the process, leaving the tel-
SiFTO
luricline correctionandflux calibrationtobe donewith IRAF.
ToremovethetelluricopticalandNIRfeatures,theSNspectrum 0 20 40 60 80
was divided by the standard star spectrum observedduring the
samenight.TheSNspectrawereflux-calibratedusingresponse
curvesacquiredfromthespectraofstandardstars.
Fig.2. BVRI and u′g′r′i′z′ light curves of SN 2010ev. The
3. Results SNooPy fits are shown in solid lines while the SiFTO fits in
dotted lines. The light curves have been shifted by the amount
Inthissectionweshowthespectralandphotometricresultsob- showninthelabel.
tainedforSN2010ev.Theprincipalmeasurementsarecompared
withotherwell-studiedSNeIathathavesimilarcharacteristics,
such as colors, line ratios and velocities. In order to interpret UsingSNooPyweobtainapeak B-bandmagnitude Bmax =
our observationsand results, we compare them with the Hsiao 14.94 ± 0.02 on JD = 2455384.60 ± 0.30 (2010 July 7.1
SNIaspectraltemplate(Hsiaoetal.,2007,hereafter“H07”)and UT), which indicates that SN 2010ev was observed in BVRI
synthetic spectra computed from a delayed-detonation model and u′g′r′i′z′ from −7.5 to 289.5 days with respect to maxi-
mumlight.ThepeakVRI magnitudesareV = 14.98±0.02,
max
1 IRAF is distributed by the National Optical Astronomy Rmax = 14.45±0.02andImax = 14.56±0.01,thatoccurat−1,
Observatories (NOAO), which are operated by the Association
of Universities for Research in Astronomy (AURA), Inc., under 2 Synthetic spectra obtained from: https://www-
cooperativeagreementwiththeNationalScienceFoundation. n.oca.eu/supernova/snia/sn2002bo.html
3
Gutie´rrezetal.:SN2010ev:AreddenedHVGSN.
Table2.SpectroscopicobservationsofSN2010ev.
UTdate M.J.D. Phase⋆ Range Telescope Arm/Grism•
[days] [Å] +Instrument∗
2010/06/30 55378.47 -6.1 3590-9640 GEM+GM B600-500&R600-750
2010/06/30 55378.48 -6.1 3500-25000 VLT+XS UV/VIS/NIR
2010/07/01 55379.49 -5.1 3580-9640 GEM+GM B600-500&R600-750
2010/07/03 55380.54 -4.1 3500-25000 VLT+XS UV/VIS/NIR
2010/07/04 55382.48 -2.1 3500-25000 VLT+XS UV/VIS/NIR
2010/07/05 55383.48 -1.1 3500-25000 VLT+XS UV/VIS/NIR
2010/07/06 55384.48 -0.1 3500-25000 VLT+XS UV/VIS/NIR
2010/07/07 55385.48 0.9 3500-25000 VLT+XS UV/VIS/NIR
2010/07/07 55385.49 0.9 3600-9212 DP+WF blue
2010/07/09 55387.49 2.9 3500-25000 VLT+XS UV/VIS/NIR
2010/07/11 55389.49 4.8 3635-9212 DP+WF blue
2010/07/13 55391.48 6.9 3500-25000 VLT+XS UV/VIS/NIR
2010/07/21 55399.50 14.9 3500-25000 VLT+XS UV/VIS/NIR
2010/07/26 55404.48 19.9 3590-8960 GEM+GM B600-500&R600-750
2010/12/31 55561.49 176.9 3600-10500 VLT+FS 300V
2011/04/03 55654.49 269.9 3600-10500 VLT+FS 300I+OG590
⋆ RelativetoBmax(MJD=2455384.60)
∗ GEM:GeminiObservatory,GM:GMOS-S,VLT:VeryLargeTelescope,XS:X-Shooter,DP:DuPontTelescope,WF:WFCCD,FS:FORS2.
• X-ShooterarmwavelengthrangesareUV[3000-5600]Å,VIS[5500-12200]Å,andNIR[10200-25000]Å.
1 and−2dayswith respectto Bmax. The I andi′ bandsshowa 0.1M⊙ of 56Ni synthesized during the explosion. Since these
secondarymaximumat∼20−25daysafterBmaximum,while SNehavesimilarpeakbolometricluminosity(see§4.1),thedi-
Randr′ bandsshowashoulderatthosetimes.Themainphoto- versityseeninFigure3couldbeattributedtoonlysmallchanges
metricparametersofSN2010evarereportedinTable1. in56Nimass,whichalsoaffectthetemperatureandionization.
DuringthenebularphasetheBVRImagnitudesfollowalin-
ear decline due to the exponentially decreasing rate of energy
inputbyradioactivedecay:1.63±0.03,1.15±0.02,1.16±0.05,
0.83±0.02magnitudesper100days,respectively.Theslopeof
the BlightcurveishigherthatthosefoundbyLairetal.(2006)
butlowerthatthoseintheV,RandIbands.Despitethesediffer- 1.5
ences,thesedeclineratesareconsistentwithotherwellstudied
1
SNeIa(e.g.,Stanishevetal.2007;Leloudasetal.2009),which
showthesameslowerdeclineintheIband. 0.5 SN 2010ev
SN 2002dj - B15
0 SN 2002er
SN 2002bo
3.2.ColorCurves
The (B− V), (V − R) and (V − I) color curves of SN 2010ev
0.5
arecomparedinFigure3withSN2002bo(Benettietal.,2004),
SN 2002dj(Pignataetal., 2008) andSN 2002er(Pignataetal.,
2004),aswellasthedelayed-detonationB15model(greylines) 0
forSN 2002bo.ThecolorshavebeencorrectedforMilkyWay
(MW) extinction exclusively. The B15 model colors were ob-
tainedwithsyntheticphotometrybyintegratingthemodelspec- 1
tralenergydistributions(SEDs).
0.5
Atmaximum,theseSNeallhaveredderB−Vcolorsthanthe
typicalaverageSN Iacolor(B−V ∼ 0),asrepresentedbythe 0
B15 model. Before maximum, SN 2002bo has redder (B−V)
-0.5
colors than SN 2010ev, but around 20 days they have similar
colors. Meanwhile, SN 2002dj and SN 2002er are bluer at all
-20 0 20 40 60 80
phases. The B15 model is bluer in B − V than all SNe at all
epochsindicatingthehighreddeninginthelineofsightwithin
thehostgalaxiesoftheseSNe.ThisistruewhenusingtheH07 Fig.3. Color evolution of SN 2010ev compared with high ve-
templateaswell. locity gradient (HVG) SNe Ia: SN 2002bo, SN 2002dj and
Thepeakofthe(B−V)colorevolutionhappensaround30 SN 2002er. The SN colors have been dereddened for MW ex-
days,comparedtoaround26daysintheB15model.Thisevolu- tinctiononly.WealsoshowthecolorsoftheB15modelwithout
tionissimilarin(V−R)and(V−I).Thedifferenceinthetimeof extinction(solidgreyline)andwiththehostextinction(dashed
(B−V)maximumandthecolorevolutionhaveshowntobevery greyline)obtainedinsection3.6.
important for SNe Ia (Burnsetal., 2014; Fo¨rsteretal., 2013).
AccordingtoBlondinetal.(2015)ashiftof5daysearlier/later
in the (B− V) maximum correspond to a decrease/increase of
4
Gutie´rrezetal.:SN2010ev:AreddenedHVGSN.
Optical spectra
of SN 2010ev
-6.1 d
-6.1 d
-5.1 d
-4.1 d
-2.1 d
-1.1 d
-0.1 d
0.9 d
0.9 d
2.9 d
4.8 d
6.9 d
4.9 d
19.9 d
4000 6000 8000
Fig.4.SpectroscopicsequenceofSN2010evrangingfrom−6.1to19.9daysaroundB-bandmaximum.Eachspectrumhasbeen
correctedforMilkyWayreddeningandshiftedbyanarbitraryamountforpresentation.Weshowlowresolutionspectrainblueand
mediumresolutionspectrainblack.Thephasesarelabeledontheright.
3.3.Opticalspectralevolution turenearλ7600,Oiλ7774Åisalsodetected.ThenarrowNaiD
and Caii H & K from the host galaxy and the MW, as well as
3.3.1. Earlyphases diffuseinterstellarbands(DIBs)atλ5780andλ6283Åarealso
present,whichsuggestsignificantreddening.
Figure4showstheopticalspectraevolutionofSN2010evfrom In Figure 5 the optical spectrum of SN 2010ev at approxi-
-6.1 to 19.9 days. The spectra show that SN 2010ev is a nor- mately−4daysfromB-bandmaximumiscomparedatthesame
mal SN Ia with very prominent Siii λ6355 Å absorption. Pre- epoch with SNe with very prominent Siii λ6355 Å absorption
maximumspectraexhibitcharacteristicP-Cygniprofilesof Siii andsimilarcolors,suchasSN2002boandSN2002dj.TheH07
λ4130, λ5972 and λ6355; Caii H & K λ3945 and IR triplet templateandB15modelarealsoshownforcomparison.Ascan
λ8579;Siiλ5449andλ5622Å.OtherlinessuchasMgiiλ4481 be seen, SN 2010evshowsstronger Siii λ6355absorptionfea-
Å,andsomeblendscausedbyFeiiinthe4500to5500Årange turescomparedwithSN2002boandSN2002dj,andsimilarities
areclearlyvisible.Despitecontaminationfromthetelluricfea- inlineslikeCaiiandSii.SincetheB15modeliswellmatched
5
Gutie´rrezetal.:SN2010ev:AreddenedHVGSN.
03du 05cf 90N 94D
84A 02er 02dj 02bo
10ev B15 H07
H07 (-4.5d)
B15 (-4.5d)
2010ev (-4.1d)
2002dj (-4d)
2002bo (-3.7d)
2010ev (-4.1d)
4000 6000 8000
Fig.5. Comparison of pre-maximum (around −4 days) spectra Fig.6.EvolutionofR(Siii)forSN2010evcomparedwithasam-
of SN 2010ev, SN 2002bo, SN 2002dj, the H07 template and ple of HVG SNe (blue filled symbols) and LVG SNe (empty
B15model.ThespectrahavebeencorrectedbyMWreddening greensymbols).IngreyisshowntheevolutionofR(Siii)forthe
andredshift.Epochsaremarkedintheplot. B15modelandinpinkforH07template.
with SN 2002bo, their lines widths and the pseudo-continuum andbecomemoretransparent.
are very similar, while the H07 template shows smaller ab-
sorption lines of Siii λ6355 Å and the Caii IR triplet. The Oi
λ7774 Å line is more prominent in SN 2010ev than the other
3.3.2. Latephases
SNe, which could suggest either differences in the amount of
unburnedmaterial or in the oxygenabundance,producedby C In the nebular phase, two spectra were obtained at ∼177 and
burning.Consideringitsvelocity(∼ 14500kms−1),itcouldbe ∼270 days with FORS2. In this phase, the spectrum is mainly
attributedtounburntC(Blondinetal.,2015).However,wecan dominated by forbidden lines of iron-group elements: [Feii],
notconfirmthelatterusingthepossiblepresenceofCiiduetoa [Feiii], [Niiii], [Niiii] and [Coii], which were identified in
lackofveryearlyspectra. SN 2010ev (see Figure 7). The spectra also show typical lines
At maximum, the ratio of the depth of the Siii λ5972 of an Hii region at the SN site such as Hα, [Nii], and [Sii].
and λ6355 absorption features, R(Siii) (Nugentetal., 1995) The strongest feature at this epoch is the blend of [Feiii] lines
is R(Siii)= 0.20 ± 0.03, while the pseudo-equivalent widths at λ4701 Å (Maedaetal., 2010b). The velocity offset of peak
(pEWs)give150.80±1.21Åand15.91±0.72Å respectively. emissionshowsasignificanttemporalchangefrom1300±100
Based on the strength of the Siii lines defined by Branchetal. km s−1 at 177 days to 490± 20 km s−1 at 270 days from the
(2006), SN 2010ev is a Broad-Line (BL) SN. The evolution rest position. This behavior is consistent with that found by
of R(Siii) of SN 2010ev is compared in Figure 6 with HVG Maedaetal. (2010b) for a sample of 20 SNe Ia with late-time
and low velocity gradient (LVG, Benettietal. 2005) SNe. As nebular spectra and different velocities, light-curve widths and
can be seen, SN 2010evshowsa dramaticdecline beforemax- colors. Meanwhile, the FWHM velocities show the opposite
imum from R(Siii)= 0.40 at −6 days to R(Siii)= 0.20 around trend: At 177 days, the FWHM=14800± 300 km s−1 and in-
maximum. Then, it shows a flat evolution, which is consistent creasesto16400±600kms−1at270days.Takinganaverageof
withHVGSNe.Thisbehaviorreflectslowertemperaturesbefore the relation derivedby Mazzalietal. (1998) and more recently
maximuminthespectrum-formingregion,whichthenincrease. by Blondinetal. (2012), we can infer ∆m15(B) = 1.10±0.03
Figure 6 also shows the evolution of R(Siii) for H07 template based on the FWHM velocities of [Feiii] at t > 200d, which
andB15model.TheB15modelisconsistentwiththeevolution is consistent with the one obtained with SNooPy. However, it
oftheHVGSN2002bo;meanwhile,theevolutionofH07tem- shouldbenotedthatthisrelationisnotsignificantwhensublumi-
plateshowsabehaviorsimilartoLVGSNe. nouseventsareexcluded(Blondinetal.,2012;Silvermanetal.,
Aftermaximum,theCaiiIRtriplet(Figure4)becomesvery 2013).
prominent,whiletheSiiiλ5972andSiilinesfaderapidly.The Other lines in the spectra seem to have no significant evo-
Sii linesare notdetectable∼ 2 weeksaftermaximumwhereas lution, exceptthe emission lines near ∼ 6000Å, which appear
Siiiλ6355isvisiblefor∼ 20days.At14daysaftermaximum todecreasewithtime,andtheblendof [Feii]λ7155and[Niii]
the Oi λ7774 line disappears and Caii H & K decreases λ7378featuresthatdevelopadouble-peakedprofile.
significantly.Ataround20dayslinesfromiron-groupelements In Figure 7 the nebular spectra of SN 2010ev are com-
start to dominate the spectrum, as the SN ejecta layers expand pared with SN 2003du (Stanishevetal., 2007) and SN 2002dj
6
Gutie´rrezetal.:SN2010ev:AreddenedHVGSN.
6
4
2
0
4000 6000 8000
Fig.7.NebularspectraofSN2010evtakenat177and270dayscomparedwithSN2003du,andSN2002djaround270days.The
spectrahavebeencorrectedforredshiftandnormalizedwithrespecttotheSN2010evfluxinV-band(andshiftedbyanarbitrary
constant).Themainfeatureshavebeenlabeled,whiletheepochsandtheSNnameareshownontheright.Thedashedlinesarethe
restpositionof[Feii]λ7155and[Niii]λ7378
(Pignataetal.,2008)around270days.The∼ 4700Åfeatureis (2007)suggestthatthelineisSiiii.Ciλ10693isnotdetectedin
similar in SN 2010ev and SN 2002dj, although slightly more ourspectra,butpossiblycontributestoMgiiλ10927.
pronounced in the latter. In SN 2003du this feature appears
to be stronger. Also, the [Feii] λ7155 and [Niii] λ7378 lines
are blueshifted. This shift may suggest an asymmetry during
the initial deflagration of the explosion in the direction away
The H-bandbreakratio (R = f /f ) definedby Hsiaoetal.
from the observer (Maedaetal., 2010a). At 270 days, we find 1 2
v = 2150 ± 220 km s−1, inferred from the average of the (2013) as the ratio between the maximum flux level redwards
neb
Dopplershiftsoftheemissionlinesof[Feii]λ7155and[Niii] of 1.5 µm (f1) and the maximum flux just bluewards of 1.5
µm (f ), can be seen in the spectra of SN 2010ev at 2.9 days.
λ7378. Redshifted nebular velocities have been seen to relate 2
The break at this epoch increases from R = 1.26 ± 0.14 to
with HVG and reddercolors(Maedaetal., 2011;Fo¨rsteretal.,
2012) and with narrow Nai D equivalent width (Fo¨rsteretal., 2.14± 0.11 at 6.9 days and takes the maximum value at 14.9
days (R = 3.11 ± 0.09). Hsiaoetal. (2013) found that this
2012).WeconfirmthesetrendswithSN2010ev.
parameter appears to peak uniformly around 12 days past
B-bandmaximum,andthatitiscorrelatedwith∆m (B).Using
15
3.4.NIRSpectralevolution the mean decline rate estimated by Hsiaoetal. (2013) for a
sample of SNe Ia, we measure the ratio at 12 days and find
TheNIRspectraofSN2010evbetween−6to15dayswithre- R = 3.39±0.15, which corresponds well with our ∆m (B)
12 15
specttoB arepresentedinFigure8.Theearlyspectrashowa estimate(Hsiaoetal.2013,Figure11).
max
bluepseudo-continuumwithaweakfeatureat∼10500Å which At6.9daysthespectrumshowsemissionfeaturespresentat
correspondstoMgiiλ10927(Wheeleretal.,1998).Thestrength 15500 Å and 17500 Å. These features are attributed to blends
ofthisfeatureseemstobeconstantwithtime,whileotherlines ofirongoupelements:Coii,FeiiandNiii(Wheeleretal.1998;
are getting stronger.Near ∼ 16500Å a weak feature is clearly Marionetal. 2003). Above 20000 Å, lines of Coii dominate
visible, which has been identified as Siii by Galletal. (2012) the spectrum (Marionetal., 2009). The presence of these lines
and as Feiii by Hsiaoetal. (2013). Near ∼ 20800Å we detect meansthatthespectrum-formingregionhasrecededenoughto
afeaturewhichhasnotbeenclearlyidentified,butaccordingto reachtheirongroupdominatedregion.
Benettietal.(2004)thislineisduetoSiii,whileStanishevetal.
7
Gutie´rrezetal.:SN2010ev:AreddenedHVGSN.
NIR spectra
-6.1 d of SN 2010ev
-4.1 d
-2.1 d
-1.1 d
-0.1 d
+0.9 d
+2.9 d
+6.9 d
+14.9 d
1.0 1.5 2.0 2.5
Fig.8.NIRSpectraofSN2010evtakenbetween∼ −7and∼15dayswithX-Shooter.Thespectraaredisplayedinlogscale.Each
spectrumhavebeencorrectedforredshiftandshiftedbyanarbitraryamountforpresentation.Thephasesarelabeledontheleft.
3.5.Expansionvelocities findingsofHsiaoetal.(2013),whoshowthatthevelocityisre-
markably constant after a short period of decline in very early
The analysis of the spectra indicate large and rapidly decreas- phases.After1daypastmaximum,theMgiifeatureisdifficult
ing expansion velocities due to the rapidly receding spectrum- tomeasureduetotheblendwithotherlines.
forming region to deeper layers with time. In Figure 9, we From the velocity evolution of Siii λ6355 between max-
presentthevelocityevolutionforselectedlinesofSiii,Caii,Sii imum and 20 days, we obtain a velocity gradient of v˙ =
Si
andMgii.Itclearlyshowsthattheexpansionvelocityof Caiiis 164±7 km s−1 d−1, whichplacesSN 2010evamongthe HVG
higherthanSiii.TheSiiiminimumevolvesfrom14800kms−1 group (Benettietal., 2005). This result is comparable with the
at-7daysto10200kms−1 at19days,whileatthesameepoch definitions of velocity gradient put forward by Blondinetal.
CaiiH&Kdecreasefrom20100to14000kms−1 andtheCaii (2012) and Folatellietal. (2013). In the former we obtain
IR triplet from 17000 to 11900 km s−1. This implies that the ∆v /∆t =166±14kms−1d−1,whileinthelatterwefind
Caiilinesmostlyformintheoutershelloftheejecta,whileSii, ∆vabs(Si)[=+0,3+1201]0±183kms−1.Tobeconsistentwiththeunits,
20
whichhasahigherionizationpotential,formsindeeperlayers, we dividethislast valueby20 daysandwe obtain160.5±9.2
resultinginlowerabsorptionvelocities(11400at-7daysto8600 kms−1d−1.SincetheSiiivelocityinSN2010evisquasi-linear,
kms−1at5daysandthendisappears).Meanwhile,Mgiiλ10900 allthreegradientsagreewitheachother.
Åshowsanearlyconstantvelocity,whichisconsistentwiththe
8
Gutie´rrezetal.:SN2010ev:AreddenedHVGSN.
CaII H & K 3945
2010ev
SiII 4130
2009Y
SII 5449
2006X
SII 5622
2005cf
SiII 5972
2004dt
SiII 6355
CaII IR 8578 2003du
Mg IR 10927 2002dj
2002bo
1994D
B15 Model
H07 Template
Fig.9.Evolutionof expansionvelocitiesof SN 2010evderived Fig.10.Siiiλ6355expansionvelocityevolutionofSN 2010ev
fromthemaximumabsorptionsofdifferentlines. derivedfromtheminimumoftheabsorptionline,comparedwith
otherSNe:SN2009Y,SN2006X(Wangetal.,2008),SN2005cf
(Pastorelloetal., 2007), SN2004dt (Altavillaetal., 2007),
InFigure10wecomparethetimeevolutionoftheexpansion SN2003du (Stanishevetal., 2007), SN2002dj (Pignataetal.,
velocityofSiiiλ6355witheightwellstudiedSNeIa.Itcanbe 2008), SN2002bo (Benettietal., 2004), SN1994D (Patatetal.,
1996),H07template,andB15model.
clearlyseenthatthevelocityevolutionofSN2010ev,SN2002bo
and SN 2002djare consistent with the HVG class. In contrast,
SN 1994D and SN 2005cf belong to the LVG group. Table 3
3.6.Extinctionfromthelight-curve
showsthevelocitygradientfortheseSNemeasuredindifferent
ways.SN2010evhasoneofthehighestv˙Sivalue.Figure10also ThenatureofredcolorstowardsSNIaisstilldebated.Itisnot
showsthe velocityevolutionfor H07templateandB15 model. clear what is intrinsic to the SN and what is due to reddening
Asnotedabove,theB15modelgivesbetteragreementwithour frommaterialinthelineofsight.Recentclaimsofcircumstellar
SN, while the H07 templete gives better results for the LVG interaction have fed the question of whether their color evolu-
group. tion and the atypical inferred host extinction laws actually re-
latetonearbymaterialejectedclosetoexplosion.Inthissection
weexploredifferentmethodstoestimatethereddeningandex-
Table3.VelocitydeclineforthesampleusedinFigure10.The tinctionlawtowardsSN2010ev,aswellasanyotherevidences
secondcolumnisthemeanvelocitydeclinebetweenmaximum for CSM from a photometric perspective. The B − V color at
and +10 days (Blondinetal., 2012). The third column is es- B obtained from SiFTO is 0.29±0.06. This value is above
max
timated in the same way but between maximum and 20 days thetypicalvaluesofthetypeIaSNewhichhavecoloratmaxi-
(Folatellietal., 2013). The last column is derived doing a fit mumbetween−0.2 < B−V < 0.2(e.gGonza´lez-Gaita´netal.,
between maximum and the last available value (Benettietal., 2014),sothatthehost-galaxyextinctionappearstobesignificant
2005). fromaphotometricpointofview.Withtherelationproposedby
Phillipsetal. (1999), using the maximum-light colors we esti-
SN ∆vabs/∆t[+0,+10] ∆v20(Si)/20 v˙Si⋆ mate E(B−V)Host = 0.26±0.07.Thisresultisconsistentwith
[kms−1d−1] [kms−1d−1] [kms−1d−1] thevalueobtainedthroughtherelationofFolatellietal.(2010):
2003du 17 33 31 E(B−V) =0.29±0.05andwithE(B−V) =0.29±0.02
Host Host
2005cf 52 54 35
givenbySNooPy.WesummarizethesefindingsinTable4.
1994D 64 54 39
Extensiveevidence(e.gRiessetal.,1996;Elias-Rosaetal.,
2009Y 96 86 125
2006;Conleyetal.,2007;Krisciunasetal.,2007;Goobaretal.,
2002bo 122 115 110
2014) suggests that at least some SNe Ia suffer from a lower
2002dj 145 132 86
2010ev 166 160 164 characteristicRV reddeninglawthantheGalacticaveragevalue
2006X 235 179 123 of RV = 3.1 (Fitzpatrick&Massa, 2007). It has been claimed
2004dt 244 245 160 that such variation could be attributed to CSM near the super-
nova(Wang,2005;Goobar,2008;Amanullah&Goobar,2011).
⋆ Taken fromMaedaetal.(2010a),except thevalue ofSN2010ev,
Infact,thereisanintriguingtrendoflowR ’sandhighextinc-
V
whichwasestimatedinthiswork.
tion towards SNe (Mandeletal., 2011; Kawabataetal., 2014)
which raises the question of whether interstellar extinction to-
wards extragalactic sites with large amounts of dust is differ-
9
Gutie´rrezetal.:SN2010ev:AreddenedHVGSN.
Table4.LineofsightextinctionA ,reddeninglawR andcolorexcessE(B−V)forSN2010evaccordingtodifferentspectroscopic
V V
andphotometrictechniques.
A R E(B−V) Reference
V V
MILKYWAY
0.28±0.06⋆ ··· ··· MWdustextinctionmaps(Schlafly&Finkbeiner,2011)
··· ··· 0.147±0.003 EW(NaiD)viaTurattoetal.(2003)
··· ··· 0.169±0.034 EW(NaiD)viaPoznanskietal.(2012)
0.28±0.02 ··· ··· MWNaiDcolumndensity(Phillipsetal.,2013)
HOST
··· ··· 0.26±0.07 MaximumlightcolorsviaPhillipsetal.(1999)
··· ··· 0.29±0.05 MaximumlightcolorsviaFolatellietal.(2010)
··· ··· 0.29±0.02 SNooPyfit(Burnsetal.,2011)
0.50+0.17 1.54+0.57 ··· MCMClight-curvefit(Phillipsetal.,2013;Burnsetal.,2014)
−0.19 −0.59
– 1.54±0.65 0.25±0.05 Colorexcessfit(thiswork)
··· ··· 0.107±0.008 EW(NaiD)via(Turattoetal.,2003)
··· ··· 0.085±0.050 EW(NaiD)via(Poznanskietal.,2012)
0.38±0.02 ··· ··· NaiDcolumndensity(Phillipsetal.,2013)
··· ··· 0.53±0.09 EW(DIB)λ5780Åvia(Lunaetal.,2008)
1.18±0.01 ··· ··· EW(DIB)λ5780Å(Phillipsetal.,2013)
··· ··· 0.50±0.04 EW(DIB)λ6283Åvia(Lunaetal.,2008)
0.24±0.03 ··· ··· Kicolumndensity(Phillipsetal.,2013)
··· .2 ··· Continuumpolarization(Zelayaetal.,2015)
⋆ TheerroriscalculatedfromthedifferencewithSchlegeletal.(1998).
ent from the Milky Way (MW), or if some nearbymaterial af-
fectsthe colorof SNe Ia in such a way as to mimic thiseffect.
0.5
SN2010evisreddenedandisthusagoodcandidateforlowR .
V
CCM MW
In order to estimate a reddening law for SN 2010ev, we
CCM Rv= 1.53+/-0.64
calculate the color excesses at maximum at different wave- Goobar p=-1.6+/-0.48
SALT2 c=0.19+/-0.01
lengths to fit them to various reddening laws in a similar way
toFolatellietal.(2010).Firstly,weobtaincolors(V −X)at B-
bandmaximumlightfor bands X = u′,B,g′,r′ and i′ obtained
fromourSiFTOfit.ThesecolorshavebeenK-correctedthrough 0
the H07 template warped to the observed photometric colors,
andthencorrectedforMWextinction.Toobtaincolorexcesses
weuseintrinsiccolorsfromboththeH07templateandtheB15
model.
The resulting colorexcessesusing intrinsic colorsfromthe
B15 model are shown in Figure 11, where we also show dif-
-0.5
ferent reddening law fits. The best reddening law we find for
Cardellietal. (1989), modifiedby O’Donnell(1994) (CCM) is
R =1.54±0.65withE(B−V)=0.25±0.05,whichisconsis-
v
tentwiththemodelbyFitzpatrick(1999)(R =1.72±0.60),and
v
is also consistent with the reddeninglaw of Goobar (2008) for 1 1.5 2 2.5 3
circumstellardust.ThereddeninglawofSN2010evisdifferent
from standard values for the MW and is consistent with other
valuesofreddenedSNe.Thisarguesfordifferentdustproperties
suchassizeintheCSMorISMaroundtheSN,oracombination
Fig.11.Color excesses E(V −X) vs 1/λforSN 2010ev.Lines
of normal dust from CSM and ISM (Foleyetal., 2014). If we
arefitstotheexcesseswithastandardR =3.1(solidblack)and
weretousetheintrinsiccolorsoftheH07templateinstead,the v
free R = 1.54 (black dotted) Cardellietal. (1989) extinction
R obtainedwouldbeevenlower.SuchalowR forSN2010ev v
V V
law,aGoobar(2008)law(bluedashed)andaSALT2colorlaw
has recently also been constrained by Burnsetal. (2014) who
(Guyetal.,2007)fit(dotteddashedred).
applied a detailed Baysian analysis to a large sample of SN Ia
lightcurves.They obtainedR = 1.54+0.57 and A = 0.50+0.17
V −0.59 V −0.19
whichyieldsE(B−V)=0.32,consistentwithourapproach.One
canseethattheu′bandiscrucialtodifferentiatebetweendiffer- vestigatetheevolutionofthereddeninglaw.Wedonotfindany
entreddeninglawvalues.TheNIRcouldhelptoconstrainthese significant change for R nor E(B − V) between −4 and +15
V
estimatesfurther,howeverwedonothaveNIRphotometry. daysfrommaximum.Thisarguesfornoevolutionandtherefore
We did similar fits to data at other epochs, in order to in- no nearby dust. We note that for SN 2014J, a highly redenned
10