A Comprehensive Observational Analysis of V1324 Sco, the Most Gamma-Ray Luminous Classical Nova to Date

2.1 MB·

by  Thomas Finzell

Draft version January 12, 2017
PreprinttypesetusingLATEXstyleemulateapjv.5/2/11
A COMPREHENSIVE OBSERVATIONAL ANALYSIS OF V1324 SCO, THE MOST GAMMA-RAY LUMINOUS
CLASSICAL NOVA TO DATE
Thomas Finzell1, Laura Chomiuk1, Brian D. Metzger2, Frederick M. Walter3, Justin D. Linford4,5, Koji
Mukai6,7, Thomas Nelson8, Jennifer H. S. Weston9, Yong Zheng2, Jennifer L. Sokoloski2, Amy Mioduszewski10,
Michael P. Rupen11, Subo Dong12, Terry Bohlsen13, Christian Buil14, Jose Prieto15,16, R. Mark Wagner17,18,
Thomas Bensby19, I..A. Bond20, T. Sumi21, D.P. Bennett22, F. Abe23, N. Koshimoto24, D. Suzuki21, P.,J.
Tristram25, Grant W. Christie26, Tim Natusch26, Jennie McCormick27, Jennifer Yee28, and Andy Gould18
Draft version January 12, 2017
7 ABSTRACT
1 It has recently been discovered that some, if not all, classical novae emit GeV gamma-rays during
0 outburst, but the mechanics of this gamma-ray emission are still not well understood. We present
2 here a comprehensive, multi-wavelength dataset—from radio to X-rays—for the most gamma-ray
n luminousclassicalnovato-date,V1324Sco. Usingthisdataset,weshowthatV1324Scoisacanonical
a dusty Fe-II type nova, with a bulk ejecta velocity of 1150 40 km s−1and an ejecta mass of 2.0
J 0.4 10−5 M . However, despite it’s seeming normalcy, ±there is also evidence for complex shoc±k
(cid:12)
1 inte×ractions, including the aforementioned gamma-rays and early time high-brightness temperature
1 radio emission. To explain how a nova can be simultaneously ordinary and have the highest gamma-
rayluminositytodatewepresentasimplifiedmodeloftheejectainwhichthestrengthofgamma-ray

] emission is set by properties the fast ejecta component that collides with a slower component to
R
produce shocks. We conclude by detailing how this model can be tested using future gamma-ray
S detected novae.
. Subject headings: novae, cataclysmic variables, AAVSO, gamma rays: stars
h
p
-
o
r 1DepartmentofPhysicsandAstronomy,MichiganStateUni-
t veristy,567WilsonRoad,EastLansing,MI48824-2320
s 2Columbia Astrophysics Laboratory, Columbia University,
a
NewYork,NY10027,USA
[ 3DepartmentofPhysicsandAstronomy,StonyBrookUniver-
sity,StonyBrook,NY11794-3800
1 4DepartmentofPhysics,TheGeorgeWashingtonUniversity,
v Washington,DC20052,USA
4 5Astronomy,Physics,andStatisticsInstituteofSciences,The
9 GeorgeWashingtonUniversity,Washington,DC20052,USA
0 6CRESSTandX-rayAstrophysicsLaboratory,NASA/GSFC,
Greenbelt,MD20771,USA
3 7Department of Physics, University of Maryland, Baltimore
0 County,1000HilltopCircle,Baltimore,MD21250,USA
. 8School of Physics and Astronomy, University of Minnesota,
1
116ChurchStreetSE,Minneapolis,MN55455,USA
0 9GreenBankObservatory,P.O.Box2,GreenBank,WV24944
7 USA
1 10National Radio Astronomy Observatory, P.O. Box O, So-
corro,NM87801,USA
:
v 11NationalResearchCouncilofCanada,HerzbergAstronomy
i andAstrophysicsPrograms,DominionRadioAstrophysicalOb-
X servatory
12Kavli Institute for Astronomy and Astrophysics, Peking
r
University, Yi He Yuan Road 5, Hai Dian District, Beijing
a
100871,China
13Mirranook Observatory, Boorolong Rd Armidale, NSW,
2350,Australia
14Castanet Tolosan Observatory, 6 place Clemence Isaure, ofScience,OsakaUniversity,Toyonaka,Osaka560-0043,Japan
31320CastanetTolosan,France 22Laboratory for Exoplanets and Stellar Astrophysics,
15Nu´cleodeAstronom´ıadelaFacultaddeIngenier´ıa,Univer- NASA/Goddard Space Flight Center, Greenbelt, MD 20771,
sidadDiegoPortales,Av. Ej´ercito441,Santiago,Chile USA
16MillenniumInstituteofAstrophysics,Santiago,Chile 23InstituteforSpace-EarthEnvironmentalResearch,Nagoya
17LBT,UniversityofArizona,933N.CherryAve,Room552, University,Nagoya464-8601,Japan
Tucson,AZ85721,USA 24Department of Earth and Space Science, Graduate School
18Department of Astronomy, The Ohio State University, ofScience,OsakaUniversity,Toyonaka,Osaka560-0043,Japan
Columbus,OH43210,USA 25Mt. John University Observatory, P.O. Box 56, Lake
19LundObservatory,DepartmentofAstronomyandTheoret- Tekapo8770,NewZealand
icalPhysics,Box43,SE-22100Lund,Sweden 26AucklandObservatory,Auckland,NewZealand
20Institute of Information and Mathematical Sciences, 27FarmCoveObservatory,CentreforBackyardAstrophysics,
MasseyUniversity,PrivateBag102-904,NorthShoreMailCen- Pakuranga,Auckland,NewZealand
tre,Auckland,NewZealand 28Harvard-Smithsonian Center for Astrophysics, 60 Garden
21Department of Earth and Space Science, Graduate School Street,Cambridge,MA02138USA
2
1. INTRODUCTION metry in the mass ejection mechanism is necessary in
order to generate internal shocks. One idea put forward
Classical novae are the result of a thermonuclear run-
byChomiuketal.(2014)isthatthereisacommonenve-
awaytakingplaceonthesurfaceofawhitedwarfandare
lope phase during the mass ejection, resulting in a den-
fueled by matter accreted on to the white dwarf from a
sityenhancementinthebinaryorbitalplane. Aseparate,
companionstar. Theseoutburstsgiverisetoanincrease
inluminosityandejectbetween 10−3 10−7M ofma- fast, and diffuse wind propagates in the polar direction
terialatvelocities(cid:38)103 km s−1∼(Galla−gher&S(cid:12)tarrfield (e.g. perpendicular to the orbital plane). When these
twooutflows—denseequatorialanddiffusepolar—collide
1978; Prialnik 1986; Yaron et al. 2005; Shore 2012).
with one another, they produce shocks.
Nova outbursts have also been detected in the GeV
Progress has been made on the theoretical front, by
gamma-ray regime with Fermi Gamma Ray Space Tele-
constraining the conditions necessary for both the ther-
scope (see e.g. Cheung et al. 2010, 2012a,b; Hays et al.
mal emission (Metzger et al. 2014) and non-thermal
2013; Cheung et al. 2015). The presence of gamma-rays
emission (Vlasov et al. 2016) observed in gamma-ray de-
imply that there are relativistic particles being gener-
tected novae. Work done in Metzger et al. (2015) found
ated in the nova event. There are two potential pro-
thatasignificantfraction(>10%)ofthebolometriclight
cesses for producing gamma-rays from relativistic parti-
should be coming from shock emission. However, there
cles: the leptonic process and the hadronic process. In
has been little in the way of in-depth, multi-wavelength,
the leptonic process electrons are accelerated up to rela-
analysis of these gamma-ray novae on the observational
tivistic speeds, and the gamma-rays are produced when
side, to constrain the properties of the shock.
photons inverse-Compton scatter off of the non-thermal
It is critical that a multi-wavelength analysis is used,
electrons (Blumenthal & Gould 1970). In the hadronic
as each of the different spectral regimes provides a dif-
process, it is ions that are being accelerated to relativis-
ferent piece of the puzzle. From the X-rays we can con-
ticspeeds; thesenon-thermalprotonsthencollidewitha
straintheshockenvironment(e.g.,Mukai&Ishida2001;
dense medium to produce π0 mesons, which then decay
Mukaietal.2008);fromtheopticalandIRwegaininfor-
to gamma-rays (Drury et al. 1994). The likely source of
mation about the energetics and structure of the ejecta
theacceleratedparticlesisstrongshocks,whichcangen-
(e.g.Hutchings1972;Hachisu&Kato2016);fromthera-
erate relativistic particles via the diffusive shock accel-
dio,wecandeterminebulkejectapropertiessuchasmass
erationmechanism(Blandford&Ostriker1978;Metzger
and velocity (e.g. Seaquist & Palimaka 1977; Hjellming
et al. 2014). The details of particle acceleration in novae
etal.1979). Finally,wemustalsoconstructamodelthat
still remains a poorly understood issue, despite the po-
can produce non-thermal particle acceleration, to facil-
tential for insight into the broader topic of high-energy
itate gamma-ray production. It is only possible to dis-
astrophysics (Metzger et al. 2015).
entanglethecomplexityofnovaeventsbyleveragingthe
The first nova detected by Fermi was V407 Cyg, and
information gained from each wavelength regime. Here
itreceivedconsiderableattention(Abdoetal.2010;Aliu
wepresentthefirstsuchmulti-wavelengthanalysisofthe
et al. 2012; Chomiuk et al. 2012; Esipov et al. 2012;
most gamma-ray luminous nova, V1324 Sco.
Mukai et al. 2012; Nelson et al. 2012; Orlando & Drake
We present the results from our analysis of V1324 Sco
2012; Shore et al. 2012; Martin & Dubus 2013). Given
using data from the optical/near-IR, radio, and X-ray
that V407 Cyg has a Mira giant secondary with a dense
(limits). This paper begins by presenting the complete
wind (a member of the symbiotic class of systems), a
multi-wavelength dataset we have gathered for V1324
model to explain the gamma-rays was proposed wherein
Sco: inSection2wediscusstheoptical/near-IRphotom-
ashockwasgeneratedasthenovaejectainteractedwith
etry; in Section 3 we discuss the optical spectra; in Sec-
the dense ambient medium.
tion4wedetailtheX-raylimits;andinSection5wedis-
This model, however, failed to explain subsequent no-
cussourradiodata. InSection6weshowthatV1324Sco
vae detected by Fermi: V1324 Sco, V959 Mon, V339
is—in all non-gamma-ray observations—a normal nova;
Del (Ackermann et al. 2014), V1369 Cen (Cheung et
we discuss how a normal nova can also be the most lu-
al. 2013), and V5668 Sgr (Cheung et al. 2015), almost
minous gamma-ray nova observed to date; we present a
all of which do not have a detectable red-giant compan-
modelthatexplainsthisseeminglyparadoxicalsituation;
ion (see, e.g., Finzell et al. 2015; Munari et al. 2013;
and we also present a means of testing said model. Fi-
Munari & Henden 2013; Hornoch 2013; the progenitor
nally,weconcludethepaperinSection7bysummarizing
of V5589 Sgr has yet to be determined). While it is
ourfindingsforV1324Scoandlessonslearnedforfuture
theoretically possible for these novae to have high den-
observations of gamma-ray novae.
sitycircumstellarmaterialdespitenothavingared-giant
companion (Spruit & Taam 2001), no evidence has yet
been found for dusty circumstellar material around cat- 2. OPTICAL/NEAR-IRPHOTOMETRY
aclysmic variables (Harrison et al. 2013). Thus the fact 2.1. Observations and Reduction
thatred-giantcompanionswerenotdetectedimpliesthat
V1324 Sco falls within one of the fields that the Mi-
these novae have main-sequence companions with low-
crolensing Observations in Astrophysics (MOA) Collab-
density circumstellar material.
oration continually observe with the MOAII 1.8 meter
It is in fact much more likely that the shocks are be-
telescope at Mt. Johns Observatory in New Zealand.
ing produced within the ejecta, due to different compo-
V1324 Sco was initially detected in 2012 May by their
nents of the ejecta colliding with one another (internal
high-cadence I-band photometry (Wagner et al. 2012).
shocks). There has already been long standing evidence
The initial detection showed a slow monotonic rise in
for internal shocks in classical novae from X-ray obser-
brightness between May 14 - May 31 (see Figure 1), fol-
vations (Mukai & Ishida 2001). However, some asym-
lowedbyaverylargeincreaseinbrightnessstartingJune
3
Phases of the Light Curve
6
Early Time Rise
Steep Optical Rise
Flattening of Optical Light Curve
8 Dust Event
Power Law Decline
10 Detected by Fermi
e
d
u
t12
ni
g
a
M
14
I
16
18
A B C D E
20
-50.0 -30.0 -10.0 -5.0-3.0 3.0 5.0 10.0 30.0 50.0 100.0 300.0500.0
Days Past 1 June 2012
Figure 1. I bandlightcurveforV1324Sco,generatedusingtheMOAdataset. Theplotstarts49daysbeforeprimaryopticalrise,at
thefirstdatewhereasingle observation(asopposedtoastackedobservation)yieldsa5σ detection. Thegrayshadedregiondenotesthe
timeperiodwhereV1324Scowasdetectedingamma-rays. Thankstotheextremelyhightime-resolutionoftheMOAdatasetwecansee
all of the different evolutionary phases of the optical light curve, as discussed in section 2.2. Note that the X-axis takes the date of the
primaryopticalrise(1June2012)tobeday0,sotheplotstartsonanegativevalue.
1 (Wagner et al. 2012). We will take June 1 to be day near-IR (J, H, K) filters going from day +35 to day
0. We also adopt the convention throughout this paper +124, while the AAVSO data have optical (V, B, R) fil-
that all dates with or + denote days before or after 1 ters, and goes from day +7 to day +445. A portion of
June 2012, respectiv−ely. the optical photometric data set is presented in Table 1;
All initial high-cadence observations, taken as part of theentiredatasetcanbefoundintheonlinepublication.
the regular MOA program, were taken in the I-broad Note that no attempt has been made to standardize the
band, and were reduced using the standard procedure photometry from different observatories.
(see Bond et al. 2001 for details). The MOA survey em-
phasizes rapid imaging of the Galactic bulge fields; on a
clear night an individual field will be reimaged every
40 minutes. The result of this high time cadence pho∼- 2.2. Timeline of Optical Light curve
tometry can be seen in Figure 1. It should be noted We give an overview of the different phases in the evo-
that the primary purpose of the high-cadence observa- lutionoftheopticallightcurve,tohelporientthereader
tions is difference imaging; as a result, the individual to the different qualitative variations. Throughout this
values should only be used to measure changes, not as overviewwewillreferenceFigure1,whichshowsthelight
an absolute measurement (Bond et al. 2001). curve generated from the MOA data set. We will also
After the steep optical rise a follow up campaign was referenceFigure2—whichshowsthelightcurveformul-
triggered by the MicroFUN group29, who believed that tiple photometric bands as well as the color evolution—
the transient was a potential microlensing event. Apart wheneverthereismulti-bandphotometryforagivenevo-
from the standard I-broad band filter, the MicroFUN lutionary phase.
follow up observations also used V and I Bessel filters.
2.2.1. Early Time Rise (Days −49 to 0)
Other observations were made in B, V, and I filters us-
ing the Small & Moderate Aperture Research Telescope ThefirstMOAobservationofV1324Scothatwasa5σ
System (SMARTS) 1.3 Meter telescope and Auckland detectionoccurredon13April2012. Followingthisthere
Observatories. was a monotonic increase in brightness that lasted until
Along with the MOA and MicroFUN data we also 31May2012. Thetotalincreaseinbrightnessduringthis
present multi-color photometry from Fred Walter’s on- periodwas∆I 2.5mags(about 0.05magsperday).
goingStonyBrook/SMARTSAtlasof(mostly)Southern This can be see≈n as phase A of Fig∼ure 1. An analysis of
Novae (see Walter et al. 2012 for further information on this initial rise can be found in Wagner et al. (In prep).
thisdataset), aswellasdatafromAmericanAssociation Thistypeofbehaviorhasneverbeenobservedinnovae
of Variable Star Observers (AAVSO)30. The SMARTS before, although this could be a selection effect. Most
data uses the ANDICAM instrument on the 1.3 meter early time information for novae comes from the Solar
telescope, and provide both optical (B, V, R, I) and Mass Ejection Imager (SMEI) (Hounsell et al. 2010),
whichhasalimitingmagnitudeofm 8,preventing
SMEI
29 http://www.astronomy.ohio-state.edu/~microfun/ it from seeing such faint early time rises.∼It is only with
30 https://www.aavso.org/data-download the type of dedicated, deep, high cadence observations
4
Table 1
TableofPhotometricData
ObservationDate JD t t0a Filter Mag MagError Observer/Group Telescope/SpecificFilterb
(D−ays)
2012Apr13 2456030.07502 -48.92499 I 18.700 0.150 MOA MJUO-Ibroad
2012Apr13 2456030.95591 -48.04410 I 18.770 0.090 MOA MJUO-Ibroad
2012Apr13 2456030.95714 -48.04287 I 18.590 0.090 MOA MJUO-Ibroad
2012Apr13 2456030.99663 -48.00338 I 18.800 0.110 MOA MJUO-Ibroad
2012Apr14 2456031.05194 -47.94807 I 18.760 0.090 MOA MJUO-Ibroad
2012Apr14 2456031.06304 -47.93697 I 18.900 0.110 MOA MJUO-Ibroad
2012Apr14 2456031.07414 -47.92587 I 18.850 0.090 MOA MJUO-Ibroad
2012Apr14 2456031.08652 -47.91348 I 18.860 0.110 MOA MJUO-Ibroad
2012Apr14 2456031.09762 -47.90238 I 19.030 0.110 MOA MJUO-Ibroad
2012Apr14 2456031.10976 -47.89024 I 18.660 0.070 MOA MJUO-Ibroad
2012Apr14 2456031.12211 -47.87789 I 18.930 0.120 MOA MJUO-Ibroad
2012Apr14 2456031.13321 -47.86679 I 18.890 0.100 MOA MJUO-Ibroad
2012Apr14 2456031.14435 -47.85566 I 18.830 0.100 MOA MJUO-Ibroad
2012Apr14 2456031.15670 -47.84331 I 18.860 0.090 MOA MJUO-Ibroad
2012Apr14 2456031.16781 -47.83220 I 18.950 0.110 MOA MJUO-Ibroad
2012Apr14 2456031.17893 -47.82108 I 18.890 0.090 MOA MJUO-Ibroad
2012Apr14 2456031.19127 -47.80874 I 18.910 0.090 MOA MJUO-Ibroad
2012Apr14 2456031.20237 -47.79764 I 18.880 0.120 MOA MJUO-Ibroad
2012Apr14 2456031.21348 -47.78653 I 18.850 0.090 MOA MJUO-Ibroad
2012Apr14 2456031.22585 -47.77416 I 18.880 0.100 MOA MJUO-Ibroad
2012Apr14 2456031.23825 -47.76176 I 18.750 0.090 MOA MJUO-Ibroad
2012Apr14 2456031.25182 -47.74818 I 18.870 0.090 MOA MJUO-Ibroad
2012Apr14 2456031.96000 -47.04001 I 18.610 0.080 MOA MJUO-Ibroad
2012Apr14 2456031.96123 -47.03877 I 18.700 0.080 MOA MJUO-Ibroad
2012Apr14 2456031.99908 -47.00093 I 18.880 0.120 MOA MJUO-Ibroad
2012Apr15 2456032.05184 -46.94817 I 18.740 0.100 MOA MJUO-Ibroad
2012Apr15 2456032.07405 -46.92596 I 18.840 0.130 MOA MJUO-Ibroad
2012Apr15 2456032.08742 -46.91258 I 18.920 0.100 MOA MJUO-Ibroad
2012Apr15 2456032.09855 -46.90146 I 18.810 0.100 MOA MJUO-Ibroad
2012Apr15 2456032.10966 -46.89035 I 18.770 0.090 MOA MJUO-Ibroad
2012Apr15 2456032.12200 -46.87801 I 18.880 0.150 MOA MJUO-Ibroad
2012Apr15 2456032.13311 -46.86690 I 18.740 0.100 MOA MJUO-Ibroad
2012Apr15 2456032.14421 -46.85580 I 18.850 0.100 MOA MJUO-Ibroad
2012Apr15 2456032.15655 -46.84346 I 18.740 0.090 MOA MJUO-Ibroad
2012Apr15 2456032.16869 -46.83132 I 18.780 0.090 MOA MJUO-Ibroad
2012Apr15 2456032.17989 -46.82012 I 18.910 0.090 MOA MJUO-Ibroad
2012Apr15 2456032.19224 -46.80777 I 18.960 0.100 MOA MJUO-Ibroad
2012Apr15 2456032.20335 -46.79666 I 18.890 0.080 MOA MJUO-Ibroad
2012Apr15 2456032.21445 -46.78556 I 18.800 0.080 MOA MJUO-Ibroad
2012Apr15 2456032.22683 -46.77317 I 18.840 0.070 MOA MJUO-Ibroad
2012Apr15 2456032.23920 -46.76081 I 18.840 0.100 MOA MJUO-Ibroad
2012Apr15 2456032.25030 -46.74971 I 18.820 0.080 MOA MJUO-Ibroad
2012Apr15 2456032.26264 -46.73736 I 18.960 0.190 MOA MJUO-Ibroad
... ... ... ... ... ... ... ...
Note. —Allofthisdata,aswelldatafrombothAAVSOand(Walteretal.2012),canbefoundonline.
a Takingt0 tobe1.0June2012
b ThisisakeyforthedifferentfacilitiesusedbytheMOAandMicroFUNgroups. MJUO:Mt. JohnUniversityObservatory;AUCK:
AucklandObservatory;CTIO:SMARTS1.3MeterTelescope.
like those of MOA that we can observe such a rise— to +12.9) the I band flux increased by a total of 9.1
although it may be possible in the future with deep sur- magnitudes, with most of that coming from the firs≈t 3
veyslikeLSST(LSSTScienceCollaborationetal.2009). days. This can be seen as phase B of Figure 1. ≈
2.2.3. Flattening of the Optical Light Curve (Days +11 to
2.2.2. Onset of Steep Optical Rise (Days 0 to +10)
+45)
The slow monotonic rise is followed by an extremely
The enormous increase in the optical is followed by a
rapid increase in brightness; between day 0 and day +2
period with a much smaller change in brightness, with I
thebrightnessincreasedby 2.2magsday−1. However,
thisisjustanaverage,asno∼measurementsweretakenon cdhaayns.giTnghibsyty≤pe1s.5omf flaagtstoevneinrgthinectohuerslieghotftchuervneexatre∼n3o0t
day+1. Betweendays+2.8and+3.3therateofincrease
unique to V1324 Sco; Strope et al. (2010) has 15 that
in brightness had dropped to 1.1 mags day−1, and show a similar flattening around peak, 10∼of which
then between days +5.6 and +6≈.8 the rate had dropped also show a dust event. This can be seen∼as phase C of
again, down to 0.3 mags day−1. This rate of increase Figure 1.
persistedforthe≈nexttwoobservationepochs(days+7.6 It is during the flattening of the optical light curve
to +7.9 and +8.7 to +9.2), before becoming flat (i.e. that we see both the gamma-ray emission as well as the
0 mags day−1) starting at the next observation epoch beginning of the initial radio bump (see section 6 for
(∼days +12.9 to +13.2). During this time period (day 0 further details). It should be noted that, of the gamma-
5
6 BBand
VBand
g) 8 RBand
a
M IBand
10
( JBand
s
es 12 HBand
n
t KBand
h 14
g
i
r
B 16
18
1
)
g
a
M
2
(
x
e B-V
d
n 3 V-R
I
or R-I
l
o I-J
C 4
J-H
H-K
5
3.0 10.0 30.0 100.0
DaysPast1June2012
Figure 2. Top panel: Light curves of V1324 Sco in the optical/near-IR bands. Bottom panel: Evolution of optical and near-IR colors.
ThegrayshadedregiondenotesthetimeperiodwhenV1324Scowasdetectedingamma-rays. Notethatthisplothassignificantlyworse
time resolution than in Figure 1. Using this figure we can see how the dust event hits the bluer bands first and then moves to redder
wavelengths as time progresses. We can also see that the dust event caused a drop in brightness all the way out to the near-IR (JHK)
wavelengthregime.
ray detected novae, at least two—V1369 Cen and V5668 the signature of a dust event.
Sgr—hadsimilarflatteningoftheopticallightcurvenear A dust event occurs in a nova when the ejecta achieve
maximum(Cheungetal.2016),thoughbothhadalarge conditions that are conducive to the condensation of
(∆V >1Mag)oscillationsduringtheirperiodofflatten- dust—e.g. colder and shielded from ionizing radia-
ing. tion (Gallagher 1977). The newly formed dust has a
large optical depth; as a result a new, cooler, photo-
sphere is created at the site of dust condensation. Dust
2.2.4. Dust Event (Days +46 to +157)
events in novae are not a new phenomenon; McLaughlin
The flattening of the optical light curve is followed by (1936) first proposed dust condensation to explain the
anotherrapidchangeinbrightness,thistimedownwards. significant decline in optical light seen in DQ Her.
There was a very clear, very large, decline in optical and The standard model of novae posits that the total lu-
near-IR flux that took place from day +46 to day +78, minosity of the ejecta remains constant, being powered
and a subsequent recovery from day +79 to day +157. by the luminosity of the still hot white dwarf at the cen-
Only the MOA I band data had the cadence necessary teroftheejecta(Gallagher&Code1974;Bath&Shaviv
tocapturetheminimumofthedecrease; theI-bandflux 1976),suchthatthefractionoftheluminositythatislost
dropped by 8.5 magnitudes in the span of 30 days intheblueiscompensatedbyincreasedluminosityinthe
(Phase D in∼Figure 1). The observations in∼BVR did red. Thisisonlyfeasibleifthecooldustyphotosphereis
not have the sensitivity to detect V1324 Sco at the bot- significantlylargerthanthepre-dustphotosphere(Gehrz
tom of the decline. Figure 2 shows that this decline in etal.1992). However,thedetailsofthislargerdustpho-
flux occurred all the way out to the near-IR (although tosphere remain poorly understood. For a blackbody of
the decrease is much less in the near-IR bands, i.e. only constant luminosity R2 T4 R T2 , so even mod-
3.9 mags in K band). This decline in flux that pref- est changes in temperatu∝reerffeq→uire a∝sigenffificant increase
∼erentially affects the shorter wavelength (bluer) light is
6
Table 2
OpticalSpectroscopicObservations
UTDate t t0 Observer Telescope Instrument Dispersion WavelengthRange
(D−ays) (˚A) (˚A)
2012Jun04.0 +3 Bensby VLT UVES 0.02 3700 9500
2012Jun08.5 +7 Bohlsen VixenVC200L LISA 0.5 3800−8000
2012Jun14.5 +13 Bohlsen VixenVC200L LISA 0.5 3800−8000
2012Jun18.5 +17 Bohlsen VixenVC200L LISA 0.5 3800−8000
2012Jun20.9 +19 Buil 0.28meterCelestron LISA 0.6 3700−7250
2012Jun21.2 +20 Walter SMARTS1.5m RC ∼5.5 3240−9500
2012Jun23.1 +22 Walter SMARTS1.5m RC ∼1.0 5620−6940
2012Jun24.9 +24 Buil 0.28meterCelestron LISA ∼6.2 3700−7250
2012Jun25.1 +24 Walter SMARTS1.5m RC 1.5 3650−5420
2012Jul03.0 +32 Walter SMARTS1.5m RC ∼1.5 3650−5420
2012Jul07.1 +36 Walter SMARTS1.5m RC ∼1.0 5620−6940
2012Jul11.1 +40 Walter SMARTS1.5m RC ∼5.5 3240−9500
2012Jul15.0 +44 Walter SMARTS1.5m RC ∼1.0 5620−6940
2012Jul16.1 +45 Chomiuk ClayMagellan MIKE ∼0.035 3700−9200
2012Jul19.0 +48 Walter SMARTS1.5m RC 5.5 3240−9500
2013May20.0 +353 Wagner LBT MODS1 ∼0.5 3420 −10000
2013Aug04.0 +450 Chomiuk SOAR Goodman ∼1.0 3000− 7000
∼ −
in photosphere size. SOAR Goodman data were taken using 400 l/mm grat-
In the case of V1324 Sco, the drop in flux all the way ingcenteredat5000˚A,andwerereducedusingthestan-
out to the near-IR suggests that the dust photosphere dard procedure in IRAF with optimal extraction and
was very cold, and the change in temperature was sig- wavelength calibration using FeAr arcs. In the case
nificant. A rough calculation using the near-IR colors at of the spectra taken by C. Buil and T. Bohlsen, both
the epoch closest to the I band minimum suggest that observers used a LISA spectrograph attached to com-
thedustphotospherewas<1000K.Whilethesetypesof mercially available telescopes of different sizes (0.28 me-
dust episodes are not unheard of— Strope et al. (2010) ter Celestron for Buil; 0.22 meter Vixen VC200L for
gives 16 examples of other such novae—there are only a Bohlsen). Moreinformationabouttheirobservationscan
few novae with dust dips showing comparably cool pho- be found on their websites31,32.
tospheres(e.g. QVVulandV1280Sco;Gehrzetal.1992;
Sakon et al. 2015). For a more thorough analysis of the 3.2. Spectroscopic Evolution
dust event in V1324 Sco see Derdzinski et al. (2016).
3.2.1. Onset of Steep Optical Rise (Days +4 to +7)
2.2.5. Power Law Decline (Days +157 to End of V1324 Sco presented initially as a standard Fe II type
Monitoring) nova. As seen in Figure 3 there were strong P-Cygni
absorption profiles starting at least as early as day +3.
Following the post-dust event rebound the evolution
The Hα emission component peaked at 180 km s−1
fto0lliosw1edJuanpeo2w0e1r2l)a.wTdheecliinnde,exwiotfhtIhe∝p(otw−etr0l)a0w.2 (iswhpeorse- oTnhedaHyα+P3-,CayngdnhiaadbsaoGrpatuiosnsiaconmFpWonHeMntoh∼fa∼d−a80F0WkmHMs−o1f.
itive because luminosity decreases when magnitudes in-
200 km s−1. The entirety of the Hα, including both
crease. This decline continues until the final observation ∼the primary emission feature as well as the P-Cygni ab-
form April 2014, when it fell below the MOA detection
sorption, extends out to 1100 km s−1 in the blue, or
threshold. In terms of Figure 1, the power-law decline is 900kms−1 awayfrom∼lin−epeak. WetaketheP-Cygni
phase E, between day +228 and +730. ∼absorptionprofiletobecomingfromthefastestmaterial,
meaning that—at this early time—the expansion veloc-
3. OPTICALSPECTRA
ity was 900 km s−1.
3.1. Observations and Reduction As dis∼cussed in Schwarz et al. (2001), one would nor-
We present the spectral observations in a manner sim- mally expect the bulk of the ejecta to be optically thick
ilar to the work of Surina et al. (2014)—who carried out at these early times and, as a result, one would expect
a multi-wavelength analysis of the 2011 outburst of T the spectral features to be absorption dominated. The
Pyx—by breaking up the analysis into sections based on presence of emission in the spectral features—which ne-
the phases of the light curve. However, unlike Surina et cessitatesanopticallythinregionintheejecta—suggests
al.(2014)—wherethetimeframeisrelativetothedateof thatthenovaatmosphereishighlyextended,evenatthis
V band maximum—all dates presented in this work are early stage.
relativetotheonsetofthesteepopticalrise(takentobe The second most prominent features—aside from the
1 June 2012). All spectroscopic observations—including Balmer lines—are the Fe II lines, all of which showed P-
date,telescope,andobserver—arelistedinTable2. Note Cygni profiles. This is evident in Figures 4 and 5, which
that all plots have been corrected to put them into the show the time evolution of the blue (3900 4950 ˚A) and
local standard of rest velocityframe, nottheheliocentric red (5700 6400 ˚A) spectral regions, re−spectively. In
frame. the UVES−spectrum taken on day +3 there were Fe II
The details of the data reduction for the UVES and
MIKEdatacanbefoundinFinzelletal.(2015)andWal- 31 http://users.northnet.com.au/~bohlsen/Nova/
ter et al. (2012) for the RC Spectrograph data. The 32 http://www.astrosurf.com/buil/index.htm
7
sorption features as being evidence of a slightly harder
ionizing radiation field at early times, as compared to
late times (Hillman et al. 2014).
+353Days
3.2.2. Flattening of the Optical Light Curve (Days +13 to
+45)
+45Days
This period is demarcated by two qualitative changes:
an increase in the Hα linewidth (see Figure 3), as well
+43Days as the onset of the optical decline (i.e. post-maximum
stage). This type of increase in the linewidths has
been seen before (for some more recent examples see,
e.g. Schwarz et al. 2001; Surina et al. 2014). In previ-
+35Days
ous works this increase in linewidth was attributed to a
gradually accelerating radiatively driven wind. We dis-
cuss this further in Section 6.2.1.
+24Days
x
u 3.2.3. Nebular Phase
Fl
y +23Days Within just a few days of the Magellan MIKE
r
a spectrum—taken on day +45—V1324 Sco underwent a
r
bit massive dust dip, dropping by > 8 mags in I band in
r +21Days 30 days, ultimately bottoming out at I 17.7. It was
A
∼atI >16.0magnitudeforthenext 50d(cid:39)ays. Although
it did eventually rebound out of the∼dust dip, there was
+19Days only a brief window of < 25 days before it went into
solar conjunction. As a∼result our spectroscopic cover-
age did not pick back up until 20 May 2013—355 days
+17Days after eruption—well into the nebular phase. All of our
analysis and line identification is done using the LBT
spectrum taken on day +355, as it had better resolution
and significantly better S/N.
+13Days
As seen in Figure 7 the strongest lines in the nebular
phase are the [O III] lines at 5007 and 4959 ˚A, followed
+7Days by Hα and [Fe VII] at 6084 ˚A. A list of all of the ob-
servednebularlinesisgiveninTable3. Mostofthelines
were matched using the table provided in the appendix
+3Days
of Williams (2012)
There are several lines that seem to have a match but,
3000 2000 1000 0 1000 2000 3000 assuming they are matched correctly, have a peak ve-
− − −
Velocity(Km/s) locity that is significantly different than the other lines.
Figure 3. Evolution of the Hα line as a function of time. We Such lines include He II at 8237 ˚A, which would have
take day 0 to be June 1 2012. All velocities are given in terms of a peak velocity of 0 km s−1, C I at 8335 ˚A, which
the local standard of rest. The blue dashed line indicates v = 0 would have a peak∼velocity of +100 km s−1, and [S
kms−1,whilethereddashedlines—usedtohelpguidetheeye—
givev= 1500kms−1. They axisissomearbitraryflux;these III] at 9531 ˚A, which would also have a peak velocity
relative fl±ux values are not to−scale. Note the expansion of the of +100 km s−1 . This is in contrast to most of the
velocity profile starting sometime between day +7 and +13, and
other lines, which have peak velocities between 200 to
continuinguntilday +35.
∼ 350 km s−1. −
lines at 4297 ˚A, 4556 ˚A, 4584 ˚A, 4629 ˚A, 4921 ˚A, and −
6456 ˚A. There are further lines in the region between 4. X-RAY
4450 - 4540 angstroms; however, their morphology and
Multiple X-ray observations were made using the
velocity structure make them difficult to identify. There
Swift X-Ray Telescope (XRT), all of them yielding non-
is also a feature that could not be identified using the
detections. That is, we did not detect thermal X-rays
table provided in Williams (2012) that shows a P-Cygni
from the shocked plasma, and we did not detect non-
profile and peaks around 4485 ˚A. It is possible that this
thermal (hard) X-rays from the population of acceler-
isablendoftheMgIIfeatureat4481˚AandFeIIfeature ated particles. This is especially noteworthy given that
at 4491 ˚A. the extremely high gamma-ray luminosity should imply
During this early time we see transitory Si II absorp- a relatively strong shock which, in turn, would gener-
tionfeaturesat3858˚A,5958/78˚Aand6347/71˚A.While ate a significant amount of hard X-rays (Mukai & Ishida
present on day +3 all evidence of them disappears by 2001). As discussed in Vurm & Metzger (2016), this ap-
day +22, when the next medium-resolution spectrum parentcontradictioncanbeexplainedbyeitherthepres-
was taken. These are the highest excitation lines we ence of high densities behind the radiative shock—due
see at this early time—having an ionization potential of to coulomb collisions sapping energy from what would
16.3 eV—so we attribute the appearance of these ab- otherwise be X-ray emitting particles—or by bound-free
8
3.5 I
I
β Fe
H
I
I I
23..50 SiII CaII CaII (cid:15)H FeII FeII FeII γH Unidentified FeI FeIIFe FeII
+45Days
x
u +35Days
l
F2.0
y
r
a
r
t +31Days
bi1.5
r
A
+23Days
1.0
+19Days
0.5
+3Days
0.0
4000 4200 4400 4600 4800
Wavelength (Angstroms)
Figure 4. Evolutionoftheblue(3900 4950˚A)spectralregion. Allwavelengthshavebeencorrectedtobeinthelocalstandardofrest
frame. Noneofthesespectrahavebeenc−orrectedforTelluricfeatures.
gen line ratios to show such high column densities are
Table 3 plausible.
NebularPhaseSpectralLines
Note that, along with the peculiar lack of hard X-rays
from non-thermal particle acceleration, there was also a
Feature Wavelength PeakVelocity
lack of soft X-rays, which are usually seen at later times
(˚A) ((kms−1))
(see, e.g., Schwarz et al. 2011). However, V1324 Sco
[OIII] 4363 140 120 was both distant ( 6.5 kpc Finzell et al. 2015) and
NHeIIII 44663886 −200±0±101000 had a large absorbi≥ng column density. The only other
Hβ 4861 −130±170 nova given in Schwarz et al. (2011) with both of these
[OIII] 4959 −150±100 characteristics is V1663 Aql, a nova that was also never
[OIII] 5007 −160± 90 detected as a super soft source.
[FeVII] 5176 −250 ±100
[FeVI] 5424 200− 200±(lowS/N) We present the X-ray limits obtained from the Swift
[FeVII] 5721 − ±200 100 observations in Table 4. The quoted limits are the 3σ
[NII] 5755 −250±100 upper limits, derived using the Bayesian upper limit
[FeVII] 6084 −280±120 method outlined in Kraft et al. (1991). The count rates
[ArV] 7006 −250±100
Hα 6563 −400±100 wereconvertedintoluminositiesassumingemissionfrom
[ArV] 7006 −250±100 a thermal plasma with characteristic temperature 1 keV
[CaII] 7057 − 80±40 and a distance of 6.5 kpc(which is lower limit derived
[ArIII] 7136 −250±100 in Finzell et al. 2015). These limits are for X-ray lumi-
[ArIV] 7237 −250±100
[OII] 7320/7330 ?? (−Lines±blended) nonoslyiticeosrirnectthfeorraanbgseor0p.3ti−on10byketVhe. TIShMe,luamssiunmosiintyg laimcoitls-
[SI] 7725 350 20
HeII 8237 +−100±20 umn density of 8 1021 cm−2. The column density was
CI 8335 0 ±50 derivedusingthe×reddeningvaluesofFinzelletal.(2015)
[SIII] 9069 0±80
[SIII] 9531 +10±0 20 and the relationship of Gu¨ver & Oumlzel (2009). These
± limits were used in the analysis of Metzger et al. (2014)
and we are publishing the actual numbers here for com-
pleteness.
(photoelectric) absorption or inelastic Compton down-
scattering if there is a large column of material ((cid:38) 1025
cm−2) ahead of the shock. In Appendix B we use oxy- 5. RADIODATA
9
I]
O
5 [OI] NaD II IIII FeII FeII [ SiII[OI]SiII
Si SiFe
+45Days
4
+43Days
x
u
Fl3 +35Days
y
r
a
r +35Days
t
i
b
r
A2
+21Days
+19Days
1
+3Days
0
5700 5800 5900 6000 6100 6200 6300 6400
Wavelength (Angstroms)
Figure 5. Evolutionofthered(5700 6400˚A)spectralregion. Allwavelengthshavebeencorrectedtobeinthelocalstandardofrest
frame. None of these spectra have been−corrected for Telluric features. The UVES spectrum taken on day +3 has contamination from
Telluricabsorptionlinesbetween6280˚Aand6320˚A.
We obtained sensitive radio observations of V1324 Sco
Table 4 between 2012 June 26 and 2014 December 19 with the
X-rayUpperLimitsfromSwift XRT
Karl G. Jansky Very Large Array (VLA) through pro-
grams S4322, 12A-483, 12B-375, 13A-461, 13B-057, and
(DUaTte) (tD−ayts0) Cou(nst−R1)atea (erLgusms−in1oscimty−a2) S61420. Over the course of the nova, the VLA was op-
erated in all configurations, and data were obtained in
2012Jun22 +21 0.0031 1.66465E+33 the C (4–8 GHz), Ku (12–18 GHz), and Ka (26.5–40
2012Jun27 +26 0.0054 2.9068E+33
GHz) bands, resulting in coverage from 4–37 GHz. Ob-
2012Jun28 +27 0.0151 8.112E+33
2012Jul4 +33 0.0038 2.0449E+33 servations were acquired with 2 GHz of bandwidth and
2012Jul10 +39 0.012 6.4389E+33 8-bit samplers, split between two independently tunable
2012Jul13 +42 0.0055 2.9575E+33 1-GHz-wide basebands. The details of our observations
2012Aug14 +74 0.0031 1.66465E+33
are given in Table 5. V1324 Sco was unresolved in all
2012Oct16 +137 0.0023 1.23539E+33
2013May22 +355 0.003 1.61226E+33 observations.
2013Nov3 +520 0.0037 1.9942E+33 At the lower frequencies (C band), the source J1751-
2524 was used as the complex gain calibrator, while
a 3σUpperlimits J1744-3116 was used for gain calibration at the higher
frequencies (Ku and Ka bands). The absolute flux den-
sity scale and bandpass were calibrated during each run
Radioemissionfromnovaeisacrucialtoolinouranal-
with either 3C48 or 3C286. Referenced pointing scans
ysis, as the opacity at radio frequencies is directly pro-
wereusedatKuandKabandstoensureaccuratepoint-
portionaltotheemissionmeasure—definedforsomeline
of sight z as EM = (cid:82) n2dz—of the emitting material, ing; pointing solutions were obtained on both the flux
z e calibrator and gain calibrator, and the pointing solution
so we can map out the density profile of the ejecta just
fromthegaincalibratorwassubsequentlyappliedtoour
by watching the evolution of the radio emission (Bode
observations of V1324 Sco. Fast switching was used for
& Evans 2008). The early time radio can also show un-
high-frequency calibration, with a cycle time of 2 min-
expected behavior that can be used to constrain other
utes. Datareductionwascarriedoutusingstand∼ardrou-
parameters of the nova event.
tinesinAIPSandCASA.Eachreceiverbandwasedited
and calibrated independently. The calibrated data were
5.1. Observations and Reduction
10
3.5 I
O
3.0 6
1
3
Pa 5 4 1
I 1 1 a 2
O gII OI Pa Pa P Pa1 a11
2.5 M P +45Days
x
u
l
F2.0
y
r +35Days
a
r
t
bi1.5
r
A
+19Days
1.0
0.5 +3Days
0.0
7800 8000 8200 8400 8600 8800 9000 9200
Wavelength (Angstroms)
Figure 6. Evolutionofthenear-infrared(7700 9000˚A)spectralregion. Allwavelengthshavebeencorrectedtobeinthelocalstandard
of rest frame. None of these spectra have been−corrected for Telluric features. The UVES spectrum taken on day +3 has prominent
contaminationfromTelluricabsorptionlinesbetween8200˚A 8300˚Aandbetween8900˚A 9200˚A.
− −
split into their two basebands and imaged, thereby pro- V1324Scowasdetectedduringthefirstradioobserva-
viding two frequency points. tion(day+25),coincidentwiththeendofthegamma-ray
An observation in A configuration (the most extended emission and one day before the second X-ray observa-
VLA configuration) from 2012 Dec 16 suffered severe tion. In subsequent radio observations the light curve
phase decorrelation at higher frequencies. Despite ef- showed an initial bump, peaking on day +72. The emis-
forts to self calibrate, we could not reliably recover the sionaftertheinitialbump—whichwerefertoasthesec-
source and we therefore do not include these measure- ondbump—wasseen30to50dayslater(days+102and
ments here. +152, respectively; see Figure 8).
In each image, the flux density of V1324 Sco was mea- The radio spectrum during the initial bump started
sured by fitting a gaussian to the imaged source with out flat, with α = 0.3 0.7 on day +25 (where α is
the tasks JMFIT in AIPS and gaussfit in CASA. We defined such that f− να±). It then transitioned to α =
ν
record the integrated flux density of the gaussian; in 2.0 0.4 on day +65∝, which is consistent with optically
most cases, there was sufficient signal on V1324 Sco to thic±kthermalemission. Thespectrumthenflattenedout
allow the width of the gaussian to vary slightly, but in again(α=0.6 0.1onday+72). Notethatthefirsttwo
cases of low signal-to-noise ratio, the width of the gaus- epochswereon±lybasedontwofrequencies(4.5GHzand
sian was kept fixed at the dimensions of the synthesized 7.8 GHz) while the epoch on day +72 included higher
beam. Errors were estimated by the gaussian fitter, and frequency observations (27.5 GHz and 36.5 GHz). As
addedin quadraturewithestimatedcalibrationerrors of a result, the early time fits should be interpreted with
5% at lower frequencies (<10 GHz) and 10% at higher some caution.
frequencies (>10 GHz). All resulting flux densities and Afulldiscussionoftheimplicationsforthisinitialradio
uncertainties are presented in Table 5. bump is given in Section 6.2.2.
5.2.2. Second Radio Bump (Days +137 to +900)
5.2. Timeline of Radio Light Curve
After this initial radio bump, a secondary radio bump
Here we discuss the different phases of the radio light
occurred, starting sometime between September 15 2012
curveevolution. TheradioemissionisshowninFigure8
and October 15 2012 (+106 and +136 days after 1 June
(radio light curve) and Figure 9 (radio spectra).
2012), starting with high frequencies and progressing to
lower frequencies. During this secondary radio bump,
5.2.1. Initial Radio Bump (Days +25 to +136)
V1324 Sco peaked at 6.23 mJy at high frequencies
∼