Finding Supernova Ia Progenitors with the Chandra X-ray Observatory

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by  Mikkel T. B. Nielsen

Finding Supernova Ia Progenitors with the
Chandra X-ray Observatory
Mikkel Nielsen, Gijs Nelemans and Rasmus Voss
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1
0 DepartmentofAstrophysics,RadboudUniversityNijmegen,theNetherlands
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n Abstract. Weexaminepre-supernovaChandraimagestofindX-rayluminositiesoftypeIasuper-
a novaprogenitors.Atpresent,wehaveonepossibledirectdetectionandupperlimitsfortheX-ray
J
luminosities of a numberof other supernovaprogenitors.The methodhas also yieldeda possible

1 detectionofaX-raybinaryWolf-RayetsystemastheprogenitorofatypeIbsupernova.
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Keywords: binaries:close-supernovae:general-X-ray:binaries

] PACS: 97,98
E
H
Supernovae (SNe) Ia are highly luminous stellar explosions that can be used as cos-
.
h
mologicaldistanceindicators.TheyarealsothemainsourceofironintheUniverse.As
p
- such, they are an important phenomenon in both cosmology and galactic astrophysics.
o
However, the exact nature of their progenitor systems remains elusive. SNe Ia are be-
r
t lievedtoarisewhenwhitedwarfs(WDs)accretematterandapproachtheChandrasekhar
s
a mass.Ataround1.37M theyexplodeinathermonuclearrunawayascarbonisrapidly
⊙
[
fusedintoheavierelements.

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Currently, two progenitor scenarios are considered: the single degenerate (SD) and
v
9 doubledegenerate(DD)scenarios.IntheSDscenario,aWDaccretesmassfromacom-
4 panion star and eventually explodes. In the DD scenario, two sub-Chandrasekhar mass
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WDs merge to form a single WD above the Chandrasekhar mass which subsequently
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. explodes.Bothscenariosfaceconsiderableproblems,however,andafullunderstanding
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ofthepropertiesofSNe Iaprogenitorsissorely needed [1].
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1 A sufficiently massiveWD accreting mass from a companion star will burn accreted
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materialat itssurface. Theenergy producedinthisprocesshasbeen showntodominate
:
v over the acceleration of the infalling mass (unlike for more compact X-ray accretors,
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X i.e. neutron stars or black holes, where the acceleration of matter dominates) and will
r produce soft X-rays at luminosities around ∼ 1037−1038 erg/s. DD progenitors likely
a
havenoorweakerX-rayemission.Therfore,weexaminepre-explosionarchivalimages
from the Chandra satellite to find the X-ray brightness of the progenitors and thereby
determinewhethertheyareSD ornot.
By this approach Voss & Nelemans [2] found evidence of an X-ray emitting pro-
genitor of SN2007on. However, later analyses indicate what might have been a chance
alignmentbetween the progenitorand an unidentified X-ray source [3]. At present, it is
unclear whether the X-ray source in question was in fact the progenitor of SN2007on.
MoreSNe need tobestudied.
Pre-SN Chandra images of nearby SNe Ia allow upper limits to be calculated for X-
ray luminosities of progenitors (see table 1). We note that these are close to theoretical
predictionsforaccretingwhitedwarfs.MorenearbySNeIaarelikelytofurtherconstrain
TABLE 1. 3s upperlimits onX-
ray luminosities of SN Ia progeni-
tors
SN L
X
2008fp 1.5·1038erg/s
2007sr 1.9·1037erg/s
2007on 5.1·1038erg/s
2007gi 3.6·1038erg/s
2006mr 4.8·1038erg/s
2006dd 3.1·1038erg/s
2006X 2.5·1039erg/s
2004W 4.0·1037erg/s
2003cg 1.6·1039erg/s
2002cv 1.9·1038erg/s
thesevaluesand/orprovideadirect detectionofaprogenitor.
To generate our sample we use the list of SNe provided by the Harvard CfA
(http://www.cfa.harvard.edu/iau/lists/Supernovae.html). Chan-
dra became operational in October 1999 so we only consider SNe later than this time.
Since luminosities of ∼1037 erg/s are unlikely to be detectable at larger distances than
25 Mpc we use NED (http://nedwww.ipac.caltech.edu/) to give us only
thoseSNeIa whosehostgalaxiesarewithinthisdistance.
The total number of SNe Ia with known distances is 608. Figure 1 plots the number
of SNe Ia as a function of NED distance and for a cut-off distance of 25 Mpc we arrive
at a sample of 34 SNe Ia. Of this sample, we find 10 with pre-SN images (figure 3).
This corresponds to approximately one SN Ia having pre-SN images per year, although
this number is obviously subject to large uncertainties due to small number statistics.
Completenessis alsoan issueofsomeconcern, seefigure2.
In our work, we have also examined Chandra archival images for evidence of pro-
genitors of other types of SNe (Ib/c, II). Evidence for an X-ray source was found for
SN2010O,and thishas been interpreted as an X-ray binaryin aWolf-Rayet system[4].
Our conclusionis that themethodworks and havealready produced a possibledirect
detection in additionto interestingupper limitsto X-ray luminositiesof the progenitors
ofnineSNeIa.Themethodmayprovehelpfulinthefieldofcore-collapseSNeaswell.
As time progresses we expect more SNe Ia to occur that have pre-SN images available
andit appears likelythatthiswillhappensoon.
REFERENCES
1. R.DiStefano,ApJ712,728–733(2010).
2. R.Voss,andG.Nelemans,Nature451,802–804(2008).
3. G.Roelofs,C.Bassa,R.Voss,andG.Nelemans,MNRAS391,290–296(2008).
4. G.Nelemans,R.Voss,M.T.B.Nielsen,andG.Roelofs,MNRAS405,L71–L75(2010).
number of SNe, by distance
25
20
15
10
5
0
0 50 100 150 200 250 300 350
distance to SNe [Mpc]
FIGURE1. SNeIainhostgalaxiesatknowndistances.
SNe Ia apparent magnitude vs. distance
350
300
250
c]
p
M
e [200
c
n
a
st
di150
D
E
N
100
50
0
12 13 14 15 16 17 18 19 20
apparent magnitude
FIGURE 2. Distance to nearby (d ≤25Mpc) SNe Ia as a function of apparent magnitude. We note
the largescatter in apparentmagnitudes,from12.4as the brightest(SN2006ce)to 19.0as the dimmest
(SN2002cv).NearbySNeareoftendiscoveredbyamateurastronomerswhosetelescopesarehardpressed
todetectanythingbelowmagnitude17orso,henceweexpectasignificantnumberofdim,undiscovered
nearbySNe.Thisraisesseriousconcernswithrespecttothecompletenessofoursample.
SNe Ia covered by Chandra observations
2008fp
2007sr
2007on
2007gi
2006mr
2006dd
2006X
2005ke
22000044aWb
2003if
2003cg
2002cv
2002bo
1998 2000 2002 2004 2006 2008 2010
year
FIGURE 3. Timeline of SNe Ia covered by Chandra. Each horizontal line on the plot corresponds
to a nearby SN for which Chandra data is available: 2002bo,2002cv,2003cg,2003if, 2004W, 2004ab,
2005ke,2006X,2006dd,2006mr,2007gi,2007on,2007sr,& 2008fp.Squaresmark the date of SNe Ia
while triangles mark observations covering the position of the SN. Hence, triangles to the left of the
squareonthesamelineindicatepre-SNimages.Ascanbeseen,thereisaroughlyconstantdistribution
ofobservations.WenotethatthereisacuriousabsenceofChandra-coveredSNefrom1999to2002.We
wouldexpecttheretobeatleastacoupleofSNewithpost-SNimagesinthisregion.