298 research outputs found
Distance determination to 12 Type II-P Supernovae using the Expanding Photosphere Method
We use early-time photometry and spectroscopy of 12 Type II plateau
supernovae (SNe IIP) to derive their distances using the expanding photosphere
method (EPM). We perform this study using two sets of Type II supernova (SN II)
atmosphere models, three filter subsets (, , ), and
two methods for the host-galaxy extinction, which leads to 12 Hubble diagrams.
We find that systematic differences in the atmosphere models lead to 50%
differences in the EPM distances and to a value of between 52 and
101 . Using the filter subset we obtain the
lowest dispersion in the Hubble diagram, { mag}. We
also apply the EPM analysis to the well-observed SN IIP 1999em. With the
filter subset we derive a distance ranging from 9.3 0.5 Mpc to
13.9 1.4 Mpc depending on the atmosphere model employed.Comment: Accepted for publication in the Astrophysical Journa
A Study of the Type II-P Supernova 2003gd in M74
We present photometric and spectroscopic data of the type II-P supernova
2003gd, which was discovered in M74 close to the end of its plateau phase. SN
2003gd is the first type II supernova to have a directly confirmed red
supergiant progenitor. We compare SN 2003gd with SN 1999em, a similar type II-P
supernova, and estimate an explosion date of 18th March 2003. We determine a
reddening towards the supernova of E(B-V) = 0.14+/-0.06, using three different
methods. We also calculate three new distances to M74 of 9.6+/-2.8 Mpc,
7.7+/-1.7 Mpc and 9.6+/-2.2 Mpc. The former was estimated using the
Standardised Candle Method (SCM), for type II supernovae, and the latter two
using the Brightest Supergiants Method (BSM). When combined with existing
kinematic and BSM distance estimates, we derive a mean value of 9.3+/-1.8 Mpc.
SN 2003gd was found to have a lower tail luminosity compared to other
``normal'' type II-P SNe bringing into question the nature of this supernova.
We present a discussion concluding that this is a ``normal'' type II-P
supernova which is consistent with the observed progenitor mass of 8(+4/-2) Mo.Comment: 23 pages, 24 figures to appear in MNRA
A non-spherical core in the explosion of supernova SN 2004dj
An important and perhaps critical clue to the mechanism driving the explosion
of massive stars as supernovae is provided by the accumulating evidence for
asymmetry in the explosion. Indirect evidence comes from high pulsar
velocities, associations of supernovae with long-soft gamma-ray bursts, and
asymmetries in late-time emission-line profiles. Spectropolarimetry provides a
direct probe of young supernova geometry, with higher polarization generally
indicating a greater departure from spherical symmetry. Large polarizations
have been measured for 'stripped-envelope' (that is, type Ic) supernovae, which
confirms their non-spherical morphology; but the explosions of massive stars
with intact hydrogen envelopes (type II-P supernovae) have shown only weak
polarizations at the early times observed. Here we report multi-epoch
spectropolarimetry of a classic type II-P supernova that reveals the abrupt
appearance of significant polarization when the inner core is first exposed in
the thinning ejecta (~90 days after explosion). We infer a departure from
spherical symmetry of at least 30 per cent for the inner ejecta. Combined with
earlier results, this suggests that a strongly non-spherical explosion may be a
generic feature of core-collapse supernovae of all types, where the asphericity
in type II-P supernovae is cloaked at early times by the massive, opaque,
hydrogen envelope.Comment: Accepted for publication by Nature (results embargoed until 23 March
2006); 14 pages, 2 figure
Dust and the type II-Plateau supernova 2004dj
We present mid-infrared (MIR) spectroscopy of a Type II-plateau supernova, SN
2004dj, obtained with the Spitzer Space Telescope, spanning 106--1393 d after
explosion. MIR photometry plus optical/near-IR observations are also reported.
An early-time MIR excess is attributed to emission from non-silicate dust
formed within a cool dense shell (CDS). Most of the CDS dust condensed between
50 d and 165 d, reaching a mass of 0.3 x 10^{-5} Msun. Throughout the
observations much of the longer wavelength (>10 microns) part of the continuum
is explained as an IR echo from interstellar dust. The MIR excess strengthened
at later times. We show that this was due to thermal emission from warm,
non-silicate dust formed in the ejecta. Using optical/near-IR line-profiles and
the MIR continua, we show that the dust was distributed as a disk whose radius
appeared to be slowly shrinking. The disk radius may correspond to a grain
destruction zone caused by a reverse shock which also heated the dust. The
dust-disk lay nearly face-on, had high opacities in the optical/near-IR
regions, but remained optically thin in the MIR over much of the period
studied. Assuming a uniform dust density, the ejecta dust mass by 996 d was 0.5
+/- 0.1) x 10^{-4} Msun, and exceeded 10^{-4}Msun by 1393 d. For a dust density
rising toward the center the limit is higher. Nevertheless, this study suggests
that the amount of freshly-synthesized dust in the SN 2004dj ejecta is
consistent with that found from previous studies, and adds further weight to
the claim that such events could not have been major contributors to the cosmic
dust budget.Comment: ApJ in press; minor changes c.f. v
Photometry and Spectroscopy of GRB 030329 and Its Associated Supernova 2003dh: The First Two Months
We present extensive optical and infrared photometry of the afterglow of
gamma-ray burst (GRB) 030329 and its associated supernova (SN) 2003dh over the
first two months after detection (2003 March 30-May 29 UT). Optical
spectroscopy from a variety of telescopes is shown and, when combined with the
photometry, allows an unambiguous separation between the afterglow and
supernova contributions. The optical afterglow of the GRB is initially a
power-law continuum but shows significant color variations during the first
week that are unrelated to the presence of a supernova. The early afterglow
light curve also shows deviations from the typical power-law decay. A supernova
spectrum is first detectable ~7 days after the burst and dominates the light
after ~11 days. The spectral evolution and the light curve are shown to closely
resemble those of SN 1998bw, a peculiar Type Ic SN associated with GRB 980425,
and the time of the supernova explosion is close to the observed time of the
GRB. It is now clear that at least some GRBs arise from core-collapse SNe.Comment: 57 pages, 13 figures, accepted by ApJ, revised per referee's
comments, includes full photometry table. Data available at
ftp://cfa-ftp.harvard.edu/pub/kstanek/GRB030329 or through WWW at
http://cfa-www.harvard.edu/cfa/oir/Research/GRB
The Subluminous Supernova 2007qd: A Missing Link in a Family of Low-Luminosity Type Ia Supernovae
We present multi-band photometry and multi-epoch spectroscopy of the peculiar
Type Ia supernova (SN Ia) 2007qd, discovered by the SDSS-II Supernova Survey.
It possesses physical properties intermediate to those of the peculiar SN
2002cx and the extremely low-luminosity SN 2008ha. Optical photometry indicates
that it had an extraordinarily fast rise time of <= 10 days and a peak absolute
B magnitude of -15.4 +/- 0.2 at most, making it one of the most subluminous SN
Ia ever observed. Follow-up spectroscopy of SN 2007qd near maximum brightness
unambiguously shows the presence of intermediate-mass elements which are likely
caused by carbon/oxygen nuclear burning. Near maximum brightness, SN 2007qd had
a photospheric velocity of only 2800 km/s, similar to that of SN 2008ha but
about 4000 and 7000 km/s less than that of SN 2002cx and normal SN Ia,
respectively. We show that the peak luminosities of SN 2002cx-like objects are
highly correlated with both their light-curve stretch and photospheric
velocities. Its strong apparent connection to other SN 2002cx-like events
suggests that SN 2007qd is also a pure deflagration of a white dwarf, although
other mechanisms cannot be ruled out. It may be a critical link between SN
2008ha and the other members of the SN 2002cx-like class of objects.Comment: To be published in the Astrophysical Journal; 37 pages, 13 figures, 4
table
A Precision Photometric Comparison between SDSS-II and CSP Type Ia Supernova Data
Consistency between Carnegie Supernova Project (CSP) and SDSS-II supernova
(SN) survey ugri measurements has been evaluated by comparing SDSS and CSP
photometry for nine spectroscopically confirmed Type Ia supernova observed
contemporaneously by both programs. The CSP data were transformed into the SDSS
photometric system. Sources of systematic uncertainty have been identified,
quantified, and shown to be at or below the 0.023 magnitude level in all bands.
When all photometry for a given band is combined, we find average magnitude
differences of equal to or less than 0.011 magnitudes in ugri, with rms scatter
ranging from 0.043 to 0.077 magnitudes. The u band agreement is promising, with
the caveat that only four of the nine supernovae are well-observed in u and
these four exhibit an 0.038 magnitude supernova-to-supernova scatter in this
filter.Comment: This paper has been accepted for publication in The Astronomical
Journa
The JCMT Nearby Galaxies Legacy Survey VII: H\alpha{} imaging and massive star formation properties
We present H\alpha{} fluxes, star formation rates (SFRs) and equivalent
widths (EWs) for a sample of 156 nearby galaxies observed in the 12CO J=3-2
line as part of the James Clerk Maxwell Telescope Nearby Galaxies Legacy
Survey. These are derived from images and values in the literature and from new
H\alpha{} images for 72 galaxies which we publish here. We describe the sample,
observations and procedures to extract the H\alpha{} fluxes and related
quantities. We discuss the SFR properties of our sample and confirm the
well-known correlation with galaxy luminosity, albeit with high dispersion. Our
SFRs range from 0.1 to 11 Msun yr-1 with a median SFR value for the complete
sample of 0.2 Msun yr-1. This median values is somewhat lower than similar
published measurements, which we attribute, in part, to our sample being
HI-selected and, thus, not biased towards high SFRs as has frequently been the
case in previous studies. Additionally, we calculate internal absorptions for
the H\alpha{} line, A(H\alpha{}), which are lower than many of those used in
previous studies. Our derived EWs, which range from 1 to 880\AA{} with a median
value of 27\AA{}, show little dependence with luminosity but rise by a factor
of five from early- to late-type galaxies. This paper is the first in a series
aimed at comparing SFRs obtained from H\alpha{} imaging of galaxies with
information derived from other tracers of star formation and atomic and
molecular gas.Comment: Accepted for publication in MNRAS. 47 pages, 18 figure
Supernovae and radio transients in M 82
We present optical and near-infrared (IR) photometry and near-IR spectroscopy
of SN 2004am, the only optically detected supernova (SN) in M 82. These
demonstrate that SN 2004am was a highly reddened type II-P SN similar to the
low luminosity type II-P events such as SNe 1997D and 2005cs. We show that SN
2004am was located coincident with the obscured super star cluster M 82-L, and
from the cluster age infer a progenitor mass of 12 +7/-3 Msun. In addition to
this, we present a high spatial resolution Gemini-N K-band adaptive optics
image of the site of SN 2008iz and a second transient of uncertain nature, both
detected so far only at radio wavelengths. Using image subtraction techniques
together with archival data from the Hubble Space Telescope, we are able to
recover a near-IR transient source co-incident with both objects. We find the
likely extinction towards SN 2008iz to be not more than Av ~ 10. The nature of
the second transient remains elusive and we regard an extremely bright
microquasar in M 82 as the most plausible scenario.Comment: 14 pages, 8 figures, accepted for publication in MNRA
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