56 research outputs found
Measuring the Hubble constant with Type Ia supernovae as near-infrared standard candles
The most precise local measurements of rely on observations of Type Ia
supernovae (SNe Ia) coupled with Cepheid distances to SN Ia host galaxies.
Recent results have shown tension comparing to the value inferred from
CMB observations assuming CDM, making it important to check for
potential systematic uncertainties in either approach. To date, precise local
measurements have used SN Ia distances based on optical photometry, with
corrections for light curve shape and colour. Here, we analyse SNe Ia as
standard candles in the near-infrared (NIR), where intrinsic variations in the
supernovae and extinction by dust are both reduced relative to the optical.
From a combined fit to 9 nearby calibrator SNe with host Cepheid distances from
Riess et al. (2016) and 27 SNe in the Hubble flow, we estimate the absolute
peak magnitude mag and
(statistical) 2.7 (systematic) km s Mpc. The 2.2
statistical uncertainty demonstrates that the NIR provides a compelling avenue
to measuring SN Ia distances, and for our sample the intrinsic (unmodeled) peak
magnitude scatter is just 0.10 mag, even without light curve shape or
colour corrections. Our results do not vary significantly with different sample
selection criteria, though photometric calibration in the NIR may be a dominant
systematic uncertainty. Our findings suggest that tension in the competing
distance ladders is likely not a result of supernova systematics that
could be expected to vary between optical and NIR wavelengths, like dust
extinction. We anticipate further improvements in with a larger
calibrator sample of SNe Ia with Cepheid distances, more Hubble flow SNe Ia
with NIR light curves, and better use of the full NIR photometric data set
beyond simply the peak -band magnitude.Comment: 13 pages, replaced to match published version in A&A, code available
at https://github.com/sdhawan21/irh
Potential signature of a quadrupolar Hubble expansion in Pantheon+ supernovae
The assumption of isotropy -- that the Universe looks the same in all
directions on large scales -- is fundamental to the standard cosmological
model. This model forms the building blocks of essentially all of our
cosmological knowledge to date. It is therefore critical to empirically test in
which regimes its core assumptions hold. Anisotropies in the cosmic expansion
are expected on small scales due to nonlinear structures in the late Universe,
however, the extent to which these anisotropies might impact our low-redshift
observations remains to be fully tested. In this paper, we use fully general
relativistic simulations to calculate the expected local anisotropic expansion
and identify the dominant multipoles in cosmological parameters to be the
quadrupole in the Hubble parameter and the dipole in the deceleration
parameter. We constrain these multipoles simultaneously in the new Pantheon+
supernova compilation. The fiducial analysis is done in the rest frame of the
CMB with peculiar velocity corrections. Under the fiducial range of redshifts
in the Hubble flow sample, we find a deviation from isotropy. We
constrain the eigenvalues of the quadrupole in the Hubble parameter to be
and
and place a upper limit on its amplitude of . We find no
significant dipole in the deceleration parameter, finding constraints of
. However, in the rest frame of the CMB
without corrections, we find , a
positive amplitude. We also investigate the impact of these anisotropies on the
Hubble tension. We find a maximal shift of km s Mpc in the
monopole of the Hubble parameter and conclude that local anisotropies are
unlikely to fully explain the observed tension.Comment: 12 pages, to be submitted to MNRA
Characterising the secondary maximum in the r-band for Type Ia Supernovae: Diagnostic for the ejecta mass
An increase in the number of studied Type Ia supernovae (SNe~Ia) has
demonstrated that this class of explosions has a greater diversity in its
observables than was previously assumed. The reasons (e.g. the explosion
mechanism, progenitor system) for such a diversity remain unknown. Here, we
analyse a sample of -band light curves of SNe~Ia, focusing on their
behaviour 2-4 weeks after maximum light, i.e. the second maximum. We
characterise the second maximum by its timing () and the integrated
flux (). We find that correlates with
the "colour-stretch" parameter s, which can be used as a proxy for
Ni mass, and , correlates with the
transparency timescale, t. Using , for a
sample of 199 SNe from the Palomar Transient Factory and intermediate Palomar
Transient Factory, we evaluate a distribution on t for a sample of SNe~Ia
found in an "untargeted" survey. Comparing this distribution to the predictions
of t ranges from models we find that the largest overlap in t values
between models and observations is for the sub-Chandrasekhar double detonation
models. We also compare our relations between t and
, with that from 1-D explosion models of
\citet{GK18} and confirm that , can be used as a
diagnostic of the total ejecta mass.Comment: 8 pages, 9 figures and 12 pages of table
The Biosafety Research Road Map: The Search for Evidence to Support Practices in the Laboratory—SARS-CoV-2
Introduction: The SARS-CoV-2 virus emerged as a novel virus and is the causative agent of the COVID-19 pandemic. It spreads readily human-to-human through droplets and aerosols. The Biosafety Research Roadmap aims to support the application of laboratory biological risk management by providing an evidence base for biosafety measures. This involves assessing the current biorisk management evidence base, identifying research and capability gaps, and providing recommendations on how an evidence-based approach can support biosafety and biosecurity, including in low-resource settings.
Methods: A literature search was conducted to identify potential gaps in biosafety and focused on five main sections, including the route of inoculation/modes of transmission, infectious dose, laboratory-acquired infections, containment releases, and disinfection and decontamination strategies.
Results: There are many knowledge gaps related to biosafety and biosecurity due to the SARS-CoV-2 virus's novelty, including infectious dose between variants, personal protective equipment for personnel handling samples while performing rapid diagnostic tests, and laboratory-acquired infections. Detecting vulnerabilities in the biorisk assessment for each agent is essential to contribute to the improvement and development of laboratory biosafety in local and national systems
Early-time spectroscopic modelling of the transitional Type Ia Supernova 2021rhu with TARDIS
An open question in SN Ia research is where the boundary lies between
'normal' Type Ia supernovae (SNe Ia) that are used in cosmological measurements
and those that sit off the Phillips relation. We present the spectroscopic
modelling of one such '86G-like' transitional SN Ia, SN 2021rhu, that has
recently been employed as a local Hubble Constant calibrator using a tip of the
red-giant branch measurement. We detail its modelling from -12 d until maximum
brightness using the radiative-transfer spectral-synthesis code tardis. We base
our modelling on literature delayed-detonation and deflagration models of
Chandrasekhar mass white dwarfs, as well as the double-detonation models of
sub-Chandrasekhar mass white dwarfs. We present a new method for 'projecting'
abundance profiles to different density profiles for ease of computation. Due
to the small velocity extent and low outer densities of the W7 profile, we find
it inadequate to reproduce the evolution of SN 2021rhu as it fails to match the
high-velocity calcium components. The host extinction of SN 2021rhu is
uncertain but we use modelling with and without an extinction correction to set
lower and upper limits on the abundances of individual species. Comparing these
limits to literature models we conclude that the spectral evolution of SN
2021rhu is also incompatible with double-detonation scenarios, lying more in
line with those resulting from the delayed detonation mechanism (although there
are some discrepancies, in particular a larger titanium abundance in SN 2021rhu
compared to the literature). This suggests that SN 2021rhu is likely a lower
luminosity, and hence lower temperature, version of a normal SN Ia.Comment: 25 pages, 22 figures, accepted for publication in MNRA
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