13,967 research outputs found
SOUSA's Swift Supernova Siblings
Swift has observed over three hundred supernovae in its first ten years.
Photometry from the Ultra-Violet Optical Telescope (UVOT) is being compiled in
the Swift Optical/Ultraviolet Supernovae Archive (SOUSA). The diversity of
supernovae leads to a wide dynamic range of intrinsic properties. The intrinsic
UV brightness of supernovae as a function of type and epoch allows one to
understand the distance ranges at which Swift can reliably detect supernovae.
The large Swift sample also includes supernovae from the same galaxy as other
Swift supernovae. Through the first ten years, these families include 34
supernovae from 16 host galaxies (two galaxies have each hosted three Swift
supernovae).Comment: Submitted to Proceedings of Science for the "10 Years of Swift"
Meeting held in Rome in December 201
The Ultraviolet Brightest Type Ia Supernova 2011de
We present and discuss the UV/optical photometric light curves and absolute
magnitudes of the Type Ia supernova (SN) 2011de from the Swift
Ultraviolet/Optical Telescope. We find it to be the UV brightest SN Ia yet
observed--more than a factor of ten brighter than normal SNe Ia in the
mid-ultraviolet. This object is an extreme example of the differences seen in
the ultraviolet for objects which do not appear remarkable in the optical. We
find that the UV/optical brightness and broad light curves are broadly
consistent with additional flux from the shock of the ejecta hitting a red
giant companion. SN~2011de is either the first external interaction of a SN Ia
discovered in the UV or an extreme example of the intrinsic UV variations in
SNe Ia.Comment: 6 pages, including 4 figures and 1 table Submitted to ApJ Letters
Swift/UVOT photometry available through the Swift Optical/Ultraviolet
Supernova Archive (SOUSA) at
http://swift.gsfc.nasa.gov/docs/swift/sne/swift_sn.htm
The First Ten Years of Swift Supernovae
The Swift Gamma Ray Burst Explorer has proven to be an incredible platform
for studying the multiwavelength properties of supernova explosions. In its
first ten years, Swift has observed over three hundred supernovae. The
ultraviolet observations reveal a complex diversity of behavior across
supernova types and classes. Even amongst the standard candle type Ia
supernovae, ultraviolet observations reveal distinct groups. When the UVOT data
is combined with higher redshift optical data, the relative populations of
these groups appear to change with redshift. Among core-collapse supernovae,
Swift discovered the shock breakout of two supernovae and the Swift data show a
diversity in the cooling phase of the shock breakout of supernovae discovered
from the ground and promptly followed up with Swift. Swift observations have
resulted in an incredible dataset of UV and X-ray data for comparison with
high-redshift supernova observations and theoretical models. Swift's supernova
program has the potential to dramatically improve our understanding of stellar
life and death as well as the history of our universe.Comment: Invited review paper accepted into the Journal of High Energy
Astrophysics for the dedicated issue: "Swift: Ten Years of Discovery" 8
pages, 4 figure
The Changing Fractions of Type Ia Supernova NUV-Optical Subclasses with Redshift
UV and optical photometry of Type Ia supernovae (SNe Ia) at low redshift have
revealed the existence of two distinct color groups, NUV-red and NUV-blue
events. The color curves differ primarily by an offset, with the NUV-blue u-
color curves bluer than the NUV-red curves by 0.4 mag. For a sample of 23 low-z
SNe~Ia observed with Swift, the NUV-red group dominates by a ratio of 2:1. We
compare rest-frame UV/optical spectrophotometry of intermediate and high-z SNe
Ia with UVOT photometry and HST spectrophotometry of low-z SNe Ia, finding that
the same two color groups exist at higher-z, but with the NUV-blue events as
the dominant group. Within each red/blue group, we do not detect any offset in
color for different redshifts, providing insight into how SN~Ia UV emission
evolves with redshift. Through spectral comparisons of SNe~Ia with similar peak
widths and phase, we explore the wavelength range that produces the UV/OPT
color differences. We show that the ejecta velocity of NUV-red SNe is larger
than that of NUV-blue objects by roughly 12% on average. This velocity
difference can explain some of the UV/optical color difference, but differences
in the strengths of spectral features seen in meanspectra require additional
explanation. Because of the different b-v colors for these groups, NUV-red SNe
will have their extinction underestimated using common techniques. This, in
turn, leads to under-estimation of the optical luminosity of the NUV-blue
SNe~Ia, in particular, for the high-redshift cosmological sample. Not
accounting for this effect should thus produce a distance bias that increases
with redshift and could significantly bias measurements of cosmological
parameters.Comment: submitted to Ap
Reddened, Redshifted, or Intrinsically Red? Understanding Near-Ultraviolet Colors of Type Ia Supernovae
Understanding the intrinsic colors of Type Ia supernovae (SNe Ia) is
important to their use as cosmological standard candles. Understanding the
effects of reddening and redshift on the observed colors are complicated and
dependent on the intrinsic spectrum, the filter curves, and the wavelength
dependence of reddening. We present ultraviolet and optical data of a growing
sample of SNe Ia observed with the Ultra-Violet/Optical Telescope on the Swift
spacecraft and use this sample to re-examine the near-UV (NUV) colors of SNe
Ia. We find that a small amount of reddening (E(B-V)=0.2 mag) could account for
the difference between groups designated as NUV-blue and NUV-red, and a
moderate amount of reddening (E(B-V)=0.5 mag) could account for the whole
NUV-optical differences. The reddening scenario, however, is inconsistent with
the mid-UV colors and color evolution. The effect of redshift alone only
accounts for part of the variation. Using a spectral template of SN2011fe we
can forward model the effects of redshift and reddening and directly compare
with the observed colors. We find that some SNe are consistent with reddened
versions of SN2011fe, but most SNe Ia are much redder in the uvw1-v color than
SN2011fe reddened to the same b-v color. The absolute magnitudes show that two
of five NUV-blue SNe Ia are blue because their near-UV luminosity is high, and
the other three are optically fainter. We also show that SN2011fe is not a
"normal" SN Ia in the UV, but has colors placing it at the blue extreme of our
sample
Theoretical Clues to the Ultraviolet Diversity of Type Ia Supernovae
The effect of metallicity on the observed light of Type Ia supernovae (SNe
Ia) could lead to systematic errors as the absolute magnitudes of local and
distant SNe Ia are compared to measure luminosity distances and determine
cosmological parameters. The UV light may be especially sensitive to
metallicity, though different modeling methods disagree as to the magnitude,
wavelength dependence, and even the sign of the effect. The outer density
structure, ^56 Ni, and to a lesser degree asphericity, also impact the UV. We
compute synthetic photometry of various metallicity-dependent models and
compare to UV/optical photometry from the Swift Ultra-Violet/Optical Telescope.
We find that the scatter in the mid-UV to near-UV colors is larger than
predicted by changes in metallicity alone and is not consistent with reddening.
We demonstrate that a recently employed method to determine relative abundances
using UV spectra can be done using UVOT photometry, but we warn that accurate
results require an accurate model of the cause of the variations. The abundance
of UV photometry now available should provide constraints on models that
typically rely on UV spectroscopy for constraining metallicity, density, and
other parameters. Nevertheless, UV spectroscopy for a variety of SN explosions
is still needed to guide the creation of accurate models. A better
understanding of the influences affecting the UV is important for using SNe Ia
as cosmological probes, as the UV light may test whether SNe Ia are
significantly affected by evolutionary effects.Comment: 10 pages. Submitted to Ap
Interpreting Flux from Broadband Photometry
We discuss the transformation of observed photometry into flux for the
creation of spectral energy distributions and the computation of bolometric
luminosities. We do this in the context of supernova studies, particularly as
observed with the Swift spacecraft, but the concepts and techniques should be
applicable to many other types of sources and wavelength regimes. Traditional
methods of converting observed magnitudes to flux densities are not very
accurate when applied to UV photometry. Common methods for extinction and the
integration of pseudo-bolometric fluxes can also lead to inaccurate results.
The sources of inaccuracy, though, also apply to other wavelengths. Because of
the complicated nature of translating broad-band photometry into monochromatic
flux densities, comparison between observed photometry and a spectroscopic
model is best done by comparing in the natural units of the observations. We
recommend that integrated flux measurements be made using a spectrum or
spectral energy distribution which is consistent with the multi-band photometry
rather than converting individual photometric measurements to flux densities,
linearly interpolating between the points, and integrating. We also highlight
some specific areas where the UV flux can be mischaracterized.Comment: Accepted for publication in the Astronomical Journal. 16 pages, 9
figures. A PDF file with wide-screen friendly figures is linked from this
blog post
http://ultravioletsupernova.blogspot.com/2016/08/interpreting-flux-from-broadband.htm
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