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[show abstract]
[hide abstract]
ABSTRACT: We conducted Hubble Space Telescope (HST) Snapshot observations of the Type
IIb Supernova (SN) 2011dh in M51 at an age of ~641 days with the Wide Field
Camera 3. We find that the yellow supergiant star, clearly detected in pre-SN
HST images, has disappeared, implying that this star was almost certainly the
progenitor of the SN. Interpretation of the early-time SN data which led to the
inference of a compact nature for the progenitor, and to the expected survival
of this yellow supergiant, is now clearly incorrect. We also present
ground-based UBVRI light curves obtained with the Katzman Automatic Imaging
Telescope (KAIT) up to SN age ~70 days. From the light-curve shape including
the very late-time HST data, and from recent interacting binary models for SN
2011dh, we estimate that a putative surviving companion star to the now
deceased yellow supergiant could be detectable by late 2013, especially in the
ultraviolet. No obvious light echoes are detectable yet in the SN environment.
05/2013;
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[show abstract]
[hide abstract]
ABSTRACT: In this work we analyse late-time (t > 100 d) optical spectra of low-redshift
(z < 0.1) Type Ia supernovae (SNe Ia) which come mostly from the Berkeley
Supernova Ia Program dataset. We also present spectra of SN 2011by for the
first time. The BSNIP sample studied consists of 34 SNe Ia with 60 nebular
spectra, to which we add nebular spectral feature measurements of 20 SNe Ia
from previously published work (Maeda et al. 2011; Blondin et al. 2012),
representing the largest set of late-time SN Ia spectra ever analysed. The full
width at half-maximum intensity (FWHM) and velocities of the [Fe III]
{\lambda}4701, [Fe II] {\lambda}7155, and [Ni II] {\lambda}7378 emission
features are measured in most observations of spectroscopically normal objects
where the data have signal-to-noise ratios >20 px^-1 and are older than 160 d
past maximum brightness. The velocities of all three features are seen to be
relatively constant with time, increasing only a few to ~20 km/s/d. The nebular
velocity (v_neb, calculated by taking the average of the [Fe II] {\lambda}7155
and [Ni II] {\lambda}7378 velocities) is correlated with the
near-maximum-brightness velocity gradient and early-time ejecta velocity.
Nearly all high velocity gradient objects have redshifted nebular lines while
most low velocity gradient objects have blueshifted nebular lines. No
correlation is found between v_neb and {\Delta}m_15(B), and for a given
light-curve shape there is a large range of observed nebular velocities. The
data also indicate a correlation between observed (B-V)_max and v_neb.
11/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We present photometry and spectroscopy of the Type IIn supernova (SN) 2011ht,
identified previously as a SN impostor. The light curve exhibits an abrupt
transition from a well-defined ~120 day plateau to a steep bolometric decline.
Leading up to peak brightness, a hot emission-line spectrum exhibits signs of
interaction with circumstellar material (CSM), in the form of relatively narrow
P-Cygni features of H I and He I superimposed on broad Lorentzian wings. For
the remainder of the plateau phase the spectrum exhibits strengthening P-Cygni
profiles of Fe II, Ca II, and H-alpha. By day 147, after the plateau has ended,
the SN entered the nebular phase, heralded by the appearance of forbidden
transitions of [O I], [O II], and [Ca II] over a weak continuum. At this stage,
the light curve exhibits a low luminosity that is comparable to that
sub-luminous Type II-P supernovae, and a relatively fast visual-wavelength
decline that is significantly steeper than the Co-56 decay rate. However, the
total bolometric decline, including the IR luminosity, is consistent with Co-56
decay, and implies a low Ni-56 mass of ~0.01 M(Sun). We therefore characterize
SN 2011ht as a bona-fide core-collapse SN very similar to the peculiar SNe IIn
1994W and 2009kn. These three SNe define a subclass, which are Type IIn based
on their spectrum, but that also exhibit well-defined plateaus and produce low
Ni-56 yields. We therefore suggest Type IIn-P as a name for this subclass.
Possible progenitors of SNe IIn-P, consistent with the available data, include
8-10 M(Sun) stars, which undergo core collapse as a result of electron capture
after a brief phase of enhanced mass loss, or more massive M>25 M(Sun)
progenitors, which experience substantial fallback of the metal-rich
radioactive ejecta. In either case, the energy radiated by these three SNe
during their plateau must be dominated by CSM interaction (abridged).
09/2012;
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Jeffrey M. Silverman, Mohan Ganeshalingam,
S. Bradley Cenko,
Alexei V. Filippenko,
Weidong Li,
Aaron J. Barth,
Daniel J. Carson,
Michael Childress,
Kelsey I. Clubb,
Antonino Cucchiara,
Melissa L. Graham,
G. H. Marion,
My L. Nguyen,
Liuyi Pei,
Brad E. Tucker,
Jozsef Vinko,
J. Craig Wheeler,
Gabor Worseck
[show abstract]
[hide abstract]
ABSTRACT: On 2012 May 17.2 UT, only 1.5 +/- 0.2 d after explosion, we discovered SN
2012cg, a Type Ia supernova (SN Ia) in NGC 4424 (d ~ 15 Mpc). As a result of
the newly modified strategy employed by the Lick Observatory SN Search, a
sequence of filtered images was obtained starting 161 s after discovery.
Utilizing recent models describing the interaction of SN ejecta with a
companion star, we rule out a ~1 M_Sun companion for half of all viewing angles
and a red-giant companion for nearly all orientations. SN 2012cg reached a
B-band maximum of 12.09 +/- 0.02 mag on 2012 June 2.0 and took ~17.3 d from
explosion to reach this, typical for SNe Ia. Our pre-maximum brightness
photometry shows a narrower-than-average B-band light curve for SN 2012cg,
though slightly overluminous at maximum brightness and with normal color
evolution (including some of the earliest SN Ia filtered photometry ever
obtained). Spectral fits to SN 2012cg reveal ions typically found in SNe Ia at
early times, with expansion velocities >14,000 km/s at 2.5 d past explosion.
Absorption from C II is detected early, as well as high-velocity components of
both Si II 6355 Ang. and Ca II. Our last spectrum (13.5 d past explosion)
resembles that of the somewhat peculiar SN Ia 1999aa. This suggests that SN
2012cg will have a slower-than-average declining light curve, which may be
surprising given the faster-than-average rising light curve.
06/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We present optical photometry and spectroscopy of the peculiar Type IIn/Ibn
supernova SN2011hw. Its light curve exhibits a slower decline rate than normal
SNeIbc, with a peak absolute magnitude of -19.5 (unfiltered) and a secondary
peak of -18.3 mag (R). Spectra of SN2011hw are unusual compared to normal SN
types, most closely resembling the spectra of SNeIbn. We center our analysis on
comparing SN 2011hw to the well-studied TypeIbn SN2006jc. While the two SNe
have many important similarities, the differences are quite telling: compared
to SN2006jc, SN2011hw has weaker HeI and CaII lines and relatively stronger H
lines, its light curve has a higher luminosity and slower decline rate, and
emission lines associated with the progenitor's CSM are narrower. One can
reproduce the unusual continuum shape of SN2011hw with equal contributions of a
6000K blackbody and a spectrum of SN2006jc. We attribute this emission
component and many other differences between the two SNe to extra opacity from
a small amount of additional H in SN2011hw, analogous to the small H mass that
makes SNeIIb differ from SNeIb. Slower speeds in the CSM and elevated H content
suggest a connection between the progenitor of SN2011hw and the class of
Ofpe/WN9 stars, which have been associated with LBVs in their hot quiescent
phases between outbursts, and are H-poor - but not H-free like classical
Wolf-Rayet (WR) stars. We conclude that the similarities and differences
between SN2011hw and SN2006jc can be largely understood if their progenitors
exploded at different points in the transitional evolution from an LBV to a WR
star.
03/2012;
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Mohan Ganeshalingam,
Weidong Li,
Alexei V. Filippenko,
Jeffrey M. Silverman,
Ryan Chornock,
Ryan J. Foley,
Thomas Matheson,
Robert P. Kirshner,
Peter Milne,
Mike Calkins,
Ken J. Shen
[show abstract]
[hide abstract]
ABSTRACT: SN 2002es is a peculiar subluminous Type Ia supernova (SN Ia) with a
combination of observed characteristics never before seen in a SN Ia. At
maximum light, SN 2002es shares spectroscopic properties with the underluminous
SN 1991bg subclass of SNe Ia, but with substantially lower expansion velocities
(~6000 km/s) more typical of the SN 2002cx subclass. Photometrically, SN 2002es
differs from both SN 1991bg-like and SN 2002cx-like supernovae. Although at
maximum light it is subluminous (M_B=-17.78 mag), SN 2002es has a relatively
broad light curve (Dm15(B)=1.28 +/- 0.04 mag), making it a significant outlier
in the light-curve width vs. luminosity relationship. We estimate a 56Ni mass
of 0.17 +/- 0.05 M_sun synthesized in the explosion, relatively low for a SN
Ia. One month after maximum light, we find an unexpected plummet in the
bolometric luminosity. The late-time decay of the light curves is inconsistent
with our estimated 56Ni mass, indicating that either the light curve was not
completely powered by 56Ni decay or the ejecta became optically thin to
gamma-rays within a month after maximum light. The host galaxy is classified as
an S0 galaxy with little to no star formation, indicating the progenitor of SN
2002es is likely from an old stellar population. We also present a less
extensive dataset for SN 1999bh, an object which shares similar observed
properties. Both objects were found as part of the Lick Observatory Supernova
Search, allowing us to estimate that these objects should account for ~2.5% of
SNe Ia within a fixed volume. We find that current theoretical models are
unable to explain the observed of characteristics of SN 2002es.
02/2012;
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[show abstract]
[hide abstract]
ABSTRACT: In this third paper in a series we compare spectral feature measurements to
photometric properties of 108 low-redshift (z < 0.1) Type Ia supernovae (SNe
Ia) with optical spectra within 5 d of maximum brightness. We find the
pseudo-equivalent width (pEW) of the Si II 4000 line to be a good indicator of
light-curve width, and the pEWs of the Mg II and Fe II complexes are relatively
good proxies for SN colour. We also employ a combination of light-curve
parameters (specifically the SALT2 stretch and colour parameters x_1 and c,
respectively) and spectral measurements to calculate distance moduli. The
residuals from these models are then compared to the standard model which uses
only light-curve stretch and colour. Our investigations show that a distance
model that uses x_1, c, and the velocity of the Si II 6355 feature does not
lead to a decrease in the Hubble residuals. We also find that distance models
with flux ratios alone or in conjunction with light-curve information rarely
perform better than the standard (x_1,c) model. However, when adopting a
distance model which combines the ratio of fluxes near ~3750 Ang. and ~4550
Ang. with both x_1 and c, the Hubble residuals are decreased by ~10 per cent,
which is found to be significant at about the 2-sigma level. The weighted
root-mean-square of the residuals using this model is 0.130 +/- 0.017 mag (as
compared with 0.144 +/- 0.019 mag when using the same sample with the standard
model). This Hubble diagram fit has one of the smallest scatters ever published
and at the highest significance ever seen in such a study. Finally, these
results are discussed with regard to how they can improve the cosmological
accuracy of future, large-scale SN Ia surveys. [Abridged]
02/2012;
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Jeffrey M. Silverman,
Ryan J. Foley,
Alexei V. Filippenko, Mohan Ganeshalingam,
Aaron J. Barth,
Ryan Chornock,
Christopher V. Griffith,
Jason J. Kong,
Nicholas Lee,
Douglas C. Leonard, [......],
Dovi Poznanski,
Cassie A. Reuter,
James Scala,
Franklin J. D. Serduke,
Joseph C. Shields,
Brandon J. Swift,
John L. Tonry,
Schuyler D. Van Dyk,
Xiaofeng Wang,
Diane S. Wong
[show abstract]
[hide abstract]
ABSTRACT: In this first paper in a series we present 1298 low-redshift (z\leq0.2)
optical spectra of 582 Type Ia supernovae (SNe Ia) observed from 1989 through
2008 as part of the Berkeley SN Ia Program (BSNIP). 584 spectra of 199 SNe Ia
have well-calibrated light curves with measured distance moduli, and many of
the spectra have been corrected for host-galaxy contamination. Most of the data
were obtained using the Kast double spectrograph mounted on the Shane 3 m
telescope at Lick Observatory and have a typical wavelength range of
3300-10,400 Ang., roughly twice as wide as spectra from most previously
published datasets. We present our observing and reduction procedures, and we
describe the resulting SN Database (SNDB), which will be an online, public,
searchable database containing all of our fully reduced spectra and companion
photometry. In addition, we discuss our spectral classification scheme (using
the SuperNova IDentification code, SNID; Blondin & Tonry 2007), utilising our
newly constructed set of SNID spectral templates. These templates allow us to
accurately classify our entire dataset, and by doing so we are able to
reclassify a handful of objects as bona fide SNe Ia and a few other objects as
members of some of the peculiar SN Ia subtypes. In fact, our dataset includes
spectra of nearly 90 spectroscopically peculiar SNe Ia. We also present
spectroscopic host-galaxy redshifts of some SNe Ia where these values were
previously unknown. [Abridged]
02/2012;
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Mansi M. Kasliwal,
S. R. Kulkarni,
Avishay Gal-Yam,
Peter E. Nugent,
Mark Sullivan,
Lars Bildsten,
Ofer Yaron,
Hagai B. Perets,
Iair Arcavi,
Sagi Ben-Ami, [......],
Nicholas M. Law,
Douglas C. Leonard,
Weidong Li,
Eran O. Ofek,
David Polishook,
Dovi Poznanski,
Robert M. Quimby,
Jeffrey M. Silverman,
Assaf Sternberg,
Dong Xu
[show abstract]
[hide abstract]
ABSTRACT: From the first two seasons of the Palomar Transient Factory, we identify
three peculiar transients (PTF09dav, PTF10iuv, PTF11bij) with five
distinguishing characteristics: peak luminosity in the gap between novae and
supernovae (M_R = 15.5 to -16.5), rapid photometric evolution (rise-time
~12--15 days), large photospheric velocities (~6000 to 11000 km/s), early
spectroscopic evolution into nebular phase (~1 to 3 months) and peculiar
nebular spectra dominated by Calcium. We also culled the extensive decade-long
Lick Observatory Supernova Search database and identified an additional member
of this group, SN 2007ke. Our choice of photometric and spectroscopic
properties was motivated by SN 2005E (Perets et al. 2010). To our surprise, as
in the case of SN 2005E, all four members of this group are also clearly offset
from the bulk of their host galaxy. Given the well-sampled early and late-time
light curves, we derive ejecta masses in the range of 0.4--0.7 Msun.
Spectroscopically, we find that there may be a diversity in the photospheric
phase, but the commonality is in the unusual nebular spectra. Our extensive
follow-up observations rule out standard thermonuclear and standard
core-collapse explosions for this class of "Calcium-rich gap" transients. If
the progenitor is a white dwarf, we are likely seeing a detonation of the white
dwarf core and perhaps, even shockfront interaction with a previously ejected
nova shell. In the less likely scenario of a massive star progenitor, a very
non-standard channel specific to a low-metallicity environment needs to be
invoked (e.g., ejecta fallback leading to black hole formation). Detection (or
lack thereof) of a faint underlying host (dwarf galaxy, cluster) will provide a
crucial and decisive diagnostic to choose between these alternatives.
11/2011;
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Nancy Elias-Rosa,
Schuyler D. Van Dyk,
Weidong Li,
Jeffrey M. Silverman,
Ryan J. Foley, Mohan Ganeshalingam,
Jon C. Mauerhan,
Erkki Kankare,
Saurabh Jha,
Alexei V. Filippenko,
John E. Beckman,
Edo Berger,
Jean-Charles Cuillandre,
and Nathan Smith
[show abstract]
[hide abstract]
ABSTRACT: We present early- and late-time photometric and spectroscopic observations of supernova (SN) 2009hd in the nearby spiral galaxy NGC 3627 (M66). This SN is one of the closest to us in recent years and provides an uncommon opportunity to observe and study the nature of SNe. However, the object was heavily obscured by dust, rendering it unusually faint in the optical given its proximity. We find that the observed properties of SN 2009hd support its classification as a possible Type II-Linear SN (SN II-L), a relatively rare subclass of core-collapse SNe. High-precision relative astrometry has been employed to attempt to identify an SN progenitor candidate, based on a pixel-by-pixel comparison between Hubble Space Telescope (HST) F555W and F814W images of the SN site prior to explosion and at late times. A progenitor candidate is identified in the F814W images only; this object is undetected in F555W. Significant uncertainty exists in the astrometry, such that we cannot definitively identify this object as the SN progenitor. Via insertion of artificial stars into the pre-SN HST images, we are able to constrain the progenitor's properties to those of a possible supergiant, with intrinsic absolute magnitude M 0 F555W –7.6 mag and intrinsic color (V – I)0 0.99 mag. The magnitude and color limits are consistent with a luminous red supergiant (RSG); however, they also allow for the possibility that the star could have been more yellow than red. From a comparison with theoretical massive-star evolutionary tracks which include rotation and pulsationally enhanced mass loss, we can place a conservative upper limit on the initial mass for the progenitor of M ini 20 M ☉. If the actual mass of the progenitor is near the upper range allowed by our derived mass limit, then it would be consistent with that for the identified progenitors of the SN II-L 2009kr and the high-luminosity SN II-Plateau (II-P) 2008cn. The progenitors of these three SNe may possibly bridge the gap between lower-mass RSGs that explode as SNe II-P and luminous blue variables, or more extreme RSGs, from which the more exotic SNe II-narrow may arise. Very late time imaging of the SN 2009hd site may provide us with more clues regarding the true nature of its progenitor.
The Astrophysical Journal 10/2011; 742(1):6. · 6.02 Impact Factor
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Weidong Li,
Joshua S. Bloom,
Philipp Podsiadlowski,
Adam A. Miller,
S. Bradley Cenko,
Saurabh W. Jha,
Mark Sullivan,
D. Andrew Howell,
Peter E. Nugent,
Nathaniel R. Butler, [......],
Alexei V. Filippenko, Mohan Ganeshalingam,
Jeffrey M. Silverman,
S. R. Kulkarni,
Nicholas M. Law,
Dovi Poznanski,
Robert M. Quimby,
Curtis McCully,
Brandon Patel,
Kate Maguire
[show abstract]
[hide abstract]
ABSTRACT: Type Ia supernovae (SNe) serve as a fundamental pillar of modern cosmology,
owing to their large luminosity and a well-defined relationship between
light-curve shape and peak brightness. The precision distance measurements
enabled by SNe Ia first revealed the accelerating expansion of the universe,
now widely believed (though hardly understood) to require the presence of a
mysterious "dark" energy. General consensus holds that Type Ia SNe result from
thermonuclear explosions of a white dwarf (WD) in a binary system; however,
little is known of the precise nature of the companion star and the physical
properties of the progenitor system. Here we make use of extensive historical
imaging obtained at the location of SN 2011fe/PTF11kly, the closest SN Ia
discovered in the digital imaging era, to constrain the visible-light
luminosity of the progenitor to be 10-100 times fainter than previous limits on
other SN Ia progenitors. This directly rules out luminous red giants and the
vast majority of helium stars as the mass-donating companion to the exploding
white dwarf. Any evolved red companion must have been born with mass less than
3.5 times the mass of the Sun. These observations favour a scenario where the
exploding WD of SN 2011fe/PTF11kly, accreted matter either from another WD, or
by Roche-lobe overflow from a subgiant or main-sequence companion star.
09/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We present new light curves and optical spectra for a number of extragalactic optical transients or ‘supernova impostors’ related to giant eruptions of luminous blue variables (LBVs), and we provide a comparative discussion of LBV-like giant eruptions known thus far. New data include photometry and spectroscopy of supernovae (SNe) 1999bw, 2000ch, 2001ac, 2002bu, 2006bv and 2010dn. SN 2010dn appears to be a carbon copy of SN 2008S and NGC 300-OT, whereas SN 2002bu shows spectral evolution from a normal LBV at early times to a twin of these cooler transients at late times. SN 2008S, NGC 300-OT and SN 2010dn appear to be special cases of a broader eruptive phenomenon where the progenitor star was enshrouded by dust, perhaps from a previous unseen eruptive episode. Evidence suggests that their progenitors have initial masses in the range 10–20 M⊙, extending the range of masses susceptible to the violent eruptive phenomenon below the canonical LBV mass range. Examining the full sample, SN impostors are characterized by strong photometric variability on a range of time-scales from a day to decades, potentially suffering multiple eruptions of the same source. The upper end of the luminosity distribution overlaps with the least-luminous core-collapse SNe, but in most cases a distinction can be made based on spectra. The low end of the luminosity distribution is far less well defined, and a distinction between LBV giant eruptions, S Doradus phases of LBVs, novae and possible eruptions of intermediate-mass stars is not entirely clear. We discuss observational clues concerning stellar winds or shocks as the relevant mass-loss mechanism, and we evaluate possible ideas for the physical mechanisms of outbursts, but there is still a great need for theoretical work on this problem. Although known examples of these eruptions are sufficient to illustrate their remarkably wide diversity in the peak absolute magnitude, duration, progenitor stars, outburst spectra and other observable properties, their statistical distribution is an area that will benefit greatly from current and upcoming transient surveys. Based on the distribution of these eruptive properties, we propose that the prototypical object SN 1961V was not a member of this class of impostors after all, but was instead a true core-collapse Type IIn SN that was preceded by a giant LBV eruption.
Monthly Notices of the Royal Astronomical Society 07/2011; 415(1):773 - 810. · 4.90 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Dust extinction is generally the least tractable systematic uncertainty in astronomy, and particularly in supernova science. Often in the past, studies have used the equivalent width of Na i D absorption measured from low-resolution spectra as proxies for extinction, based on tentative correlations that were drawn from limited data sets. We show here, based on 443 low-resolution spectra of 172 Type Ia supernovae for which we have measured the dust extinction as well as the equivalent width of Na i D, that the two barely correlate. We briefly examine the causes for this large scatter that effectively prevents one from inferring extinction using this method.
Monthly Notices of the Royal Astronomical Society Letters 07/2011; 415(1):L81 - L84.
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[show abstract]
[hide abstract]
ABSTRACT: We present an analysis of the B-band and V-band rise-time distributions of
nearby Type Ia supernovae (SNe Ia). We use a two-stretch template-fitting
method to measure the rise and decline of BV light curves. Our analysis of 61
SNe with high-quality light curves indicates that the longer the time between
explosion and maximum light (i.e., the rise time), the slower the decline of
the light curve after maximum. However, SNe with slower post-maximum decline
rates have a faster rise than would be expected from a single-parameter family
of light curves, indicating that SN Ia light curves are not a single-parameter
family of varying widths. Comparison of the B-band rise-time distribution for
spectroscopically normal SNe Ia to those exhibiting high-velocity spectral
features indicates that high-velocity (HV) SNe Ia have shorter B-band rise
times compared to their spectroscopically normal counterparts. After
normalising the B-band light curves to Dm15(B)= 1.1 mag (i.e., correcting the
post-maximum decline to have the same shape as our template), we find that
spectroscopically normal SNe Ia have a rise time of 18.03 +/- 0.24 d, while HV
SNe have a faster B-band rise time of 16.63 +/- 0.29 d. Despite differences in
the B band, we find that HV and normal SNe Ia have similar rise times in the V
band. The initial rise of a SN Ia B-band light curve follows a power law with
index 2.20 +0.27 -0.19, consistent with a parabolic rise in flux predicted by
an expanding fireball toy model. We compare our early-time B-band data to
models for the predicted signature of companion interaction arising from the
single-degenerate progenitor scenario. There is a substantial degree of
degeneracy between the adopted power-law index of the SN light-curve template,
the rise time, and the amount of shock emission required to match the data.
07/2011;
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Kevin Krisciunas,
Weidong Li,
Thomas Matheson,
D. Andrew Howell,
Maximilian Stritzinger,
Greg Aldering,
Perry L. Berlind,
M. Calkins,
Peter Challis,
Ryan Chornock, [......],
Peter E. Nugent,
M. Phelps,
Mark M. Phillips,
Yulei Qiu,
Robert Quimby,
K. Rines,
Jeffrey M. Silverman,
Nicholas B. Suntzeff,
Rollin C. Thomas,
Lifan Wang
[show abstract]
[hide abstract]
ABSTRACT: We present optical and near-infrared photometry, as well as ground-based
optical spectra and Hubble Space Telescope ultraviolet spectra, of the Type Ia
supernova (SN) 2001ay. At maximum light the Si II and Mg II lines indicated
expansion velocities of 14,000 km/sec, while Si III and S II showed velocities
of 9,000 km/sec There is also evidence for some unburned carbon at 12,000
km/sec. SN 2001ay exhibited a decline-rate parameter Delta m_15(B) = 0.68 \pm
0.05 mag; this and the B-band photometry at t > +25 d past maximum make it the
most slowly declining Type Ia SN yet discovered. Three of four
super-Chandrasekhar-mass candidates have decline rates almost as slow as this.
After correction for Galactic and host-galaxy extinction, SN 2001ay had M_B =
-19.19 and M_V = -19.17 mag at maximum light; thus, it was not overluminous in
optical bands. In near-infrared bands it was overluminous only at the 2-sigma
level at most. For a rise time of 18 d (explosion to bolometric maximum) the
implied Ni-56 yield was (0.58 \pm 0.15)/alpha M_Sun, with alpha = L_max/E_Ni
probably in the range 1.0 to 1.2. The Ni-56 yield is comparable to that of many
Type Ia supernovae. The "normal" Ni-56 yield and the typical peak optical
brightness suggest that the very broad optical light curve is explained by the
trapping of the gamma rays in the inner regions.
06/2011;
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[show abstract]
[hide abstract]
ABSTRACT: Recent observations suggest that Type IIn supernovae (SNe IIn) may exhibit
late-time (>100 days) infrared (IR) emission from warm dust more than other
types of core-collapse SNe. Mid-IR observations, which span the peak of the
thermal spectral energy distribution, provide useful constraints on the
properties of the dust and, ultimately, the circumstellar environment,
explosion mechanism, and progenitor system. Due to the low SN IIn rate (<10% of
all core-collapse SNe), few IR observations exist for this subclass. The
handful of isolated studies, however, show late-time IR emission from warm dust
that, in some cases, extends for five or six years post-discovery. While
previous Spitzer/IRAC surveys have searched for dust in SNe, none have targeted
the Type IIn subclass. This article presents results from a warm Spitzer/IRAC
survey of the positions of all 68 known SNe IIn within a distance of 250 Mpc
between 1999 and 2008 that have remained unobserved by Spitzer more than 100
days post-discovery. The detection of late-time emission from ten targets
(~15%) nearly doubles the database of existing mid-IR observations of SNe IIn.
Although optical spectra show evidence for new dust formation in some cases,
the data show that in most cases the likely origin of the mid-IR emission is
pre-existing dust, which is continuously heated by optical emission generated
by ongoing circumstellar interaction between the forward shock and
circumstellar medium. Furthermore, an emerging trend suggests that these SNe
decline at ~1000--2000 days post-discovery once the forward shock overruns the
dust shell. The mass-loss rates associated with these dust shells are
consistent with luminous blue variable (LBV) progenitors.
04/2011;
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Io K. W. Kleiser,
Dovi Poznanski,
Daniel Kasen,
Timothy R. Young,
Ryan Chornock,
Alexei V. Filippenko,
Peter Challis, Mohan Ganeshalingam,
Robert P. Kirshner,
Weidong Li,
Thomas Matheson,
Peter E. Nugent,
Jeffrey M. Silverman
[show abstract]
[hide abstract]
ABSTRACT: The vast majority of Type II supernovae (SNe) are produced by red supergiants
(RSGs), but SN 1987A revealed that blue supergiants (BSGs) can produce members
of this class as well, albeit with some peculiar properties. This best studied
event revolutionized our understanding of SNe, and linking it to the bulk of
Type II events is essential. We present here optical photometry and
spectroscopy gathered for SN 2000cb, which is clearly not a standard Type II SN
and yet is not a SN 1987A analog. The light curve of SN 2000cb is reminiscent
of that of SN 1987A in shape, with a slow rise to a late optical peak, but on
substantially different time scales. Spectroscopically, SN 2000cb resembles a
normal SN II but with ejecta velocities that far exceed those measured for SN
1987A or normal SNe II, above 18000 km/s for H-alpha at early times. The red
colours, high velocities, late photometric peak, and our modeling of this
object all point toward a scenario involving the high-energy explosion of a
small-radius star, most likely a BSG, producing 0.1 solar masses of Ni-56.
Adding a similar object to the sample, SN 2005ci, we derive a rate of about 2%
of the core-collapse rate for this loosely defined class of BSG explosions.
01/2011;
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Mohan Ganeshalingam,
Weidong Li,
Alexei V. Filippenko,
Carmen Anderson,
Griffin Foster,
Elinor L. Gates,
Christopher V. Griffith,
Bryant J. Grigsby,
Niels Joubert,
Joel Leja,
Thomas B. Lowe,
Brent Macomber,
Tyler Pritchard,
Patrick Thrasher,
and Dustin Winslow
[show abstract]
[hide abstract]
ABSTRACT: We present BVRI light curves of 165 Type Ia supernovae (SNe Ia) from the Lick Observatory Supernova Search follow-up photometry program from 1998 through 2008. Our light curves are typically well sampled (cadence of 3-4 days) with an average of 21 photometry epochs. We describe our monitoring campaign and the photometry reduction pipeline that we have developed. Comparing our data set to that of Hicken et al., with which we have 69 overlapping supernovae (SNe), we find that as an ensemble the photometry is consistent, with only small overall systematic differences, although individual SNe may differ by as much as 0.1 mag, and occasionally even more. Such disagreement in specific cases can have significant implications for combining future large data sets. We present an analysis of our light curves which includes template fits of light-curve shape parameters useful for calibrating SNe Ia as distance indicators. Assuming the B – V color of SNe Ia at 35 days past maximum light can be presented as the convolution of an intrinsic Gaussian component and a decaying exponential attributed to host-galaxy reddening, we derive an intrinsic scatter of σ = 0.076 ± 0.019 mag, consistent with the Lira-Phillips law. This is the first of two papers, the second of which will present a cosmological analysis of the data presented herein.
The Astrophysical Journal Supplement Series 09/2010; 190(2):418. · 13.46 Impact Factor
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Peter A. Milne,
Peter J. Brown,
Peter W. A. Roming,
Stephen T. Holland,
Stefan Immler,
Alexei V. Filippenko, Mohan Ganeshalingam,
Weidong Li,
Maximilian Stritzinger,
Mark M. Phillips,
Malcolm Hicken,
Robert P. Kirshner,
Peter J. Challis,
Paolo Mazzali,
Brian P. Schmidt,
Filomena Bufano,
Neil Gehrels,
and Daniel Vanden Berk
[show abstract]
[hide abstract]
ABSTRACT: We present ultraviolet (UV) and optical photometry of 26 Type Ia supernovae (SNe Ia) observed from 2005 March to 2008 March with the NASA Swift Ultraviolet and Optical Telescope (UVOT). The dataset consists of 2133 individual observations, making it by far the most complete study of the UV emission from SNe Ia to date. Grouping the SNe into three subclasses as derived from optical observations, we investigate the evolution of the colors of these SNe, finding a high degree of homogeneity within the normal subclass, but dramatic differences between that group and the subluminous and SN 2002cx-like groups. For the normal events, the redder UV filters on UVOT (u, uvw1) show more homogeneity than do the bluer UV filters (uvm2, uvw2). Searching for purely UV characteristics to determine existing optically based groupings, we find the peak width to be a poor discriminant, but we do see a variation in the time delay between peak emission and the late, flat phase of the light curves. The UV light curves peak a few days before the B band for most subclasses (as was previously reported by Jha et al.), although the SN 2002cx-like objects peak at a very early epoch in the UV. That group also features the bluest emission observed among SNe Ia. As the observational campaign is ongoing, we discuss the critical times to observe, as determined by this study, in order to maximize the scientific output of future observations.
The Astrophysical Journal 09/2010; 721(2):1627. · 6.02 Impact Factor
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Weidong Li,
Jesse Leaman,
Ryan Chornock,
Alexei V. Filippenko,
Dovi Poznanski, Mohan Ganeshalingam,
Xiaofeng Wang,
Maryam Modjaz,
Saurabh Jha,
Ryan J. Foley,
Nathan Smith
[show abstract]
[hide abstract]
ABSTRACT: This is the second paper of a series in which we present new measurements of the observed rates of supernovae (SNe) in the local Universe, determined from the Lick Observatory Supernova Search (LOSS). In this paper, a complete SN sample is constructed, and the observed (uncorrected for host-galaxy extinction) luminosity functions (LFs) of SNe are derived. These LFs solve two issues that have plagued previous rate calculations for nearby SNe: the luminosity distribution of SNe and the host-galaxy extinction. We select a volume-limited sample of 175 SNe, collect photometry for every object, and fit a family of light curves to constrain the peak magnitudes and light-curve shapes. The volume-limited LFs show that they are not well represented by a Gaussian distribution. There are notable differences in the LFs for galaxies of different Hubble types (especially for SNe Ia). We derive the observed fractions for the different subclasses in a complete SN sample, and find significant fractions of SNe II-L (10%), IIb (12%), and IIn (9%) in the SN II sample. Furthermore, we derive the LFs and the observed fractions of different SN subclasses in a magnitude-limited survey with different observation intervals, and find that the LFs are enhanced at the high-luminosity end and appear more "standard" with smaller scatter, and that the LFs and fractions of SNe do not change significantly when the observation interval is shorter than 10 days. We also discuss the LFs in different galaxy sizes and inclinations, and for different SN subclasses. Some notable results are ... (abridged). Comment: Submitted to MNRAS (Paper II of a series). For high-res figures, latex source, landscape tables, and online data, please visit http://astro.berkeley.edu/~weidong/rate/
06/2010;
