20 research outputs found
Observation of dose-rate dependence in a Fricke dosimeter irradiated at low dose rates with monoenergetic X-rays
<p>Absolute measurements of the radiolytic yield of Fe3+ in a ferrous sulphate dosimeter formulation (6 mM Fe2+), with a 20 keV x-ray monoenergetic beam, are reported. Dose-rate suppression of the radiolytic yield was observed at dose rates lower than and different in nature to those previously reported with x-rays. We present evidence that this effect is most likely to be due to recombination of free radicals radiolytically produced from water. The method used to make these measurements is also new and it provides radiolytic yields which are directly traceable to the SI standards system. The data presented provides new and exacting tests of radiation chemistry codes.</p
Fast and Not-so-Furious: Case Study of the Fast and Faint Type IIb SN 2021bxu
We present photometric and spectroscopic observations and analysis of
SN~2021bxu (ATLAS21dov), a low-luminosity, fast-evolving Type IIb supernova
(SN). SN~2021bxu is unique, showing a large initial decline in brightness
followed by a short plateau phase. With
during the plateau, it is at the lower end of the luminosity distribution of
stripped-envelope supernovae (SE-SNe) and shows a distinct 10 day plateau
not caused by H- or He-recombination. SN~2021bxu shows line velocities which
are at least slower than typical SE-SNe. It is
photometrically and spectroscopically similar to Type IIb SNe during the
photospheric phases of evolution, with similarities to Ca-rich IIb SNe. We find
that the bolometric light curve is best described by a composite model of shock
interaction between the ejecta and an envelope of extended material, combined
with a typical SN~IIb powered by the radioactive decay of Ni. The
best-fit parameters for SN~2021bxu include a Ni mass of , an ejecta mass of
, and an ejecta
kinetic energy of . From the fits to the properties of the extended material of
Ca-rich IIb SNe we find a trend of decreasing envelope radius with increasing
envelope mass. SN~2021bxu has on the low end compared to
SE-SNe and Ca-rich SNe in the literature, demonstrating that SN~2021bxu-like
events are rare explosions in extreme areas of parameter space. The progenitor
of SN~2021bxu is likely a low mass He star with an extended envelope.Comment: 18 pages, 15 figures, submitted to MNRA
The absolute magnitudes of 1991T-like supernovae
1991T-like supernovae are the luminous, slow-declining extreme of the Branch shallow-silicon (SS) subclass of Type Ia supernovae. They are distinguished by extremely weak Ca ii H & K and Si ii λ6355 and strong Fe iii absorption features in their optical spectra at pre-maximum phases, and have long been suspected to be over-luminous compared to normal Type Ia supernovae. In this paper, the pseudo-equivalent width of the Si ii λ6355 absorption obtained at light curve phases from ≤ +10 days is combined with the morphology of the i-band light curve to identify a sample of 1991T-like supernovae in the Carnegie Supernova Project II. Hubble diagram residuals show that, at optical as well as near-infrared wavelengths, these events are over-luminous by ∼0.1–0.5 mag with respect to the less extreme Branch SS (1999aa-like) and Branch core-normal supernovae with similar B-band light-curve decline rates.The work of the CSP-II has been generously supported by the National Science Foundation under grants AST-1613426, AST-1613455, and AST-1613472. The CSP-II was also supported in part by the Danish Agency for Science and Technology and Innovation through a Sapere Aude Level 2 grant. M.S. acknowledges funding by a research grant (13261) from VILLUM FONDEN. E.B. is supported in part by NASA grant 80NSSC20K0538. L.G. acknowledges financial support from the Spanish Ministerio de Ciencia e Innovación (MCIN), the Agencia Estatal de Investigación (AEI) 10.13039/501100011033, and the European Social Fund (ESF) "Investing in your future" under the 2019 Ramón y Cajal program RYC2019-027683-I and the PID2020-115253GA-I00 HOSTFLOWS project, from Centro Superior de Investigaciones CientÃficas (CSIC) under the PIE project 20215AT016, and the program Unidad de Excelencia MarÃa de Maeztu CEX2020-001058-M. We gratefully acknowledge the use of WISeREP—https://wiserep.weizmann.ac.il. M.M.P. thanks Richard Scalzo for interesting discussions of extreme SNe Ia. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology.Peer reviewe
SN 2022crv: IIb, Or Not IIb: That is the Question
We present optical and near-infrared observations of SN~2022crv, a stripped
envelope supernova in NGC~3054, discovered within 12 hrs of explosion by the
Distance Less Than 40 Mpc Survey. We suggest SN~2022crv is a transitional
object on the continuum between SNe Ib and SNe IIb. A high-velocity hydrogen
feature (20,000 -- 16,000 ) was conspicuous in
SN~2022crv at early phases, and then quickly disappeared around maximum light.
By comparing with hydrodynamic modeling, we find that a hydrogen envelope of
\msun{} can reproduce the behaviour of the hydrogen feature
observed in SN~2022crv. The early light curve of SN~2022crv did not show
envelope cooling emission, implying that SN~2022crv had a compact progenitor
with extremely low amount of hydrogen. The analysis of the nebular spectra
shows that SN~2022crv is consistent with the explosion of a He star with a
final mass of 4.5 -- 5.6 \msun{} that has evolved from a 16 -- 22
\msun{} zero-age main sequence star in a binary system with about 1.0 -- 1.7
\msun{} of oxygen finally synthesized in the core. The high metallicity at the
supernova site indicates that the progenitor experienced a strong stellar wind
mass loss. In order to retain a small amount of residual hydrogen at such a
high metallicity, the initial orbital separation of the binary system is likely
larger than 1000~. The near-infrared spectra of SN~2022crv
show a unique absorption feature on the blue side of He I line at
1.005~m. This is the first time that such a feature has been
observed in a Type Ib/IIb, and could be due to \ion{Sr}{2}. Further detailed
modelling on SN~2022crv can shed light on the progenitor and the origin of the
mysterious absorption feature in the near infrared.Comment: 33 pages, 23 figures, submitted to Ap
Strong Carbon Features and a Red Early Color in the Underluminous Type Ia SN 2022xkq
We present optical, infrared, ultraviolet, and radio observations of SN
2022xkq, an underluminous fast-declining type Ia supernova (SN Ia) in NGC 1784
( Mpc), from to 180 days after explosion. The
high-cadence observations of SN 2022xkq, a photometrically transitional and
spectroscopically 91bg-like SN Ia, cover the first days and weeks following
explosion which are critical to distinguishing between explosion scenarios. The
early light curve of SN 2022xkq has a red early color and exhibits a flux
excess which is more prominent in redder bands; this is the first time such a
feature has been seen in a transitional/91bg-like SN Ia. We also present 92
optical and 19 near-infrared (NIR) spectra, beginning 0.4 days after explosion
in the optical and 2.6 days after explosion in the NIR. SN 2022xkq exhibits a
long-lived C I 1.0693 m feature which persists until 5 days post-maximum.
We also detect C II 6580 in the pre-maximum optical spectra. These
lines are evidence for unburnt carbon that is difficult to reconcile with the
double detonation of a sub-Chandrasekhar mass white dwarf. No existing
explosion model can fully explain the photometric and spectroscopic dataset of
SN 2022xkq, but the considerable breadth of the observations is ideal for
furthering our understanding of the processes which produce faint SNe Ia.Comment: 38 pages, 16 figures, accepted for publication in ApJ, the figure 15
input models and synthetic spectra are now available at
https://zenodo.org/record/837925
Dataset: Observation of dose-rate dependence in a Fricke dosimeter irradiated at low dose rates with monoenergetic X-rays
Data relevant to our forthcoming Sci. Rep. paper "Observation of dose-rate dependence in a Fricke dosimeter irradiated at low dose rates with monoenergetic X-rays". Data produced on Diamond sessions: MT11529-1, EE15073-1 and EE15073-2, MT16218-1, and EE17519-1