132 research outputs found
Measuring the Evolution of the NuSTAR Detector Gains
The memo describes the methods used to track the long-term gain variations in
the NuSTAR detectors. It builds on the analysis presented in Madsen et al.
(2015) using the deployable calibration source to measure the gain drift in the
NuSTAR CdZnTe detectors. This is intended to be a live document that is
periodically updated as new entries are required in the NuSTAR gain CALDB
files. This document covers analysis up through early-2022 and the gain v011
CALDB file released in version 20240226.Comment: 11 page, 7 figures. Intended as a living, easy-to-find document. No
intention of submitting this to a journa
Locating the most energetic electrons in Cassiopeia A
We present deep (2.4 Ms) observations of the Cassiopeia A supernova
remnant with {\it NuSTAR}, which operates in the 3--79 keV bandpass and is the
first instrument capable of spatially resolving the remnant above 15 keV. We
find that the emission is not entirely dominated by the forward shock nor by a
smooth "bright ring" at the reverse shock. Instead we find that the 15 keV
emission is dominated by knots near the center of the remnant and dimmer
filaments near the remnant's outer rim. These regions are fit with unbroken
power-laws in the 15--50 keV bandpass, though the central knots have a steeper
() spectrum than the outer filaments ().
We argue this difference implies that the central knots are located in the 3-D
interior of the remnant rather than at the outer rim of the remnant and seen in
the center due to projection effects. The morphology of 15 keV emission does
not follow that of the radio emission nor that of the low energy (12 keV)
X-rays, leaving the origin of the 15 keV emission as an open mystery. Even
at the forward shock front we find less steepening of the spectrum than
expected from an exponentially cut off electron distribution with a single
cutoff energy. Finally, we find that the GeV emission is not associated with
the bright features in the {\it NuSTAR} band while the TeV emission may be,
suggesting that both hadronic and leptonic emission mechanisms may be at work.Comment: 12 pages, 11 figures, accepted for publication in Ap
Morphological, genetic and molecular characteristics of barley root hair mutants
Root hairs are tubular outgrowths of specialized
epidermal cells called trichoblasts. They affect anchoring plants
in soil, the uptake of water and nutrients and are the sites of the
interaction between plants and microorganisms. Nineteen root
hair mutants of barley representing different stages of root hair
development were subjected to detailed morphological and
genetic analyses. Each mutant was monogenic and recessive.
An allelism test revealed that nine loci were responsible for the
mutated root hair phenotypes in the collection and 1–4 mutated
allelic forms were identified at each locus. Genetic relationships
between the genes responsible for different stages of root
hair formation were established. The linkage groups of four loci
rhl1, rhp1, rhi1 and rhs1, which had previously been mapped
on chromosomes 7H, 1H, 6H and 5H, respectively, were
enriched with new markers that flank the genes at a distance
of 0.16 cM to 4.6 cM. The chromosomal position of three new
genes – two that are responsible for the development of short
root hairs (rhs2 and rhs3) and the gene that controls an irregular
root hair pattern (rhi2) – were mapped on chromosomes 6H,
2H and 1H, respectively. A comparative analysis of the
agrobotanical parameters between some mutants and their respective
parental lines showed that mutations in genes responsible
for root hair development had no effect on the
agrobotanical performance of plants that were grown under
controlled conditions. The presented mutant collection is a
valuable tool for further identification of genes controlling root
hair development in barley
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Production of haploids and doubled haploids in oil palm
Background: Oil palm is the world’s most productive oil-food crop despite yielding well below its theoretical
maximum. This maximum could be approached with the introduction of elite F1 varieties. The development of
such elite lines has thus far been prevented by difficulties in generating homozygous parental types for F1
generation.
Results: Here we present the first high-throughput screen to identify spontaneously-formed haploid (H) and
doubled haploid (DH) palms. We secured over 1,000 Hs and one DH from genetically diverse material and derived
further DH/mixoploid palms from Hs using colchicine. We demonstrated viability of pollen from H plants and
expect to generate 100% homogeneous F1 seed from intercrosses between DH/mixoploids once they develop
female inflorescences.
Conclusions: This study has generated genetically diverse H/DH palms from which parental clones can be selected
in sufficient numbers to enable the commercial-scale breeding of F1 varieties. The anticipated step increase in
productivity may help to relieve pressure to extend palm cultivation, and limit further expansion into biodiverse
rainforest
Radical chemistry and ozone production at a UK coastal receptor site
OH, HO2, total and partially speciated RO2, and OH reactivity (kOH′) were measured during the July 2015 ICOZA (Integrated Chemistry of OZone in the Atmosphere) project that took place at a coastal site in north Norfolk, UK. Maximum measured daily OH, HO2 and total RO2 radical concentrations were in the range 2.6–17 × 106, 0.75–4.2 × 108 and 2.3–8.0 × 108 molec. cm−3, respectively. kOH′ ranged from 1.7 to 17.6 s−1, with a median value of 4.7 s−1. ICOZA data were split by wind direction to assess differences in the radical chemistry between air that had passed over the North Sea (NW–SE sectors) and that over major urban conurbations such as London (SW sector). A box model using the Master Chemical Mechanism (MCMv3.3.1) was in reasonable agreement with the OH measurements, but it overpredicted HO2 observations in NW–SE air in the afternoon by a factor of ∼ 2–3, although slightly better agreement was found for HO2 in SW air (factor of ∼ 1.4–2.0 underprediction). The box model severely underpredicted total RO2 observations in both NW–SE and SW air by factors of ∼ 8–9 on average. Measured radical and kOH′ levels and measurement–model ratios displayed strong dependences on NO mixing ratios, with the results suggesting that peroxy radical chemistry is not well understood under high-NOx conditions. The simultaneous measurement of OH, HO2, total RO2 and kOH′ was used to derive experimental (i.e. observationally determined) budgets for all radical species as well as total ROx (i.e. OH + HO2 + RO2). In NW–SE air, the ROx budget could be closed during the daytime within experimental uncertainty, but the rate of OH destruction exceeded the rate of OH production, and the rate of HO2 production greatly exceeded the rate of HO2 destruction, while the opposite was true for RO2. In SW air, the ROx budget analysis indicated missing daytime ROx sources, but the OH budget was balanced, and the same imbalances were found with the HO2 and RO2 budgets as in NW–SE air. For HO2 and RO2, the budget imbalances were most severe at high-NO mixing ratios, and the best agreement between HO2 and RO2 rates of production and destruction rates was found when the RO2 + NO rate coefficient was reduced by a factor of 5. A photostationary-steady-state (PSS) calculation underpredicted daytime OH in NW–SE air by ∼ 35 %, whereas agreement (∼ 15 %) was found within instrumental uncertainty (∼ 26 % at 2σ) in SW air. The rate of in situ ozone production (P(Ox)) was calculated from observations of ROx, NO and NO2 and compared to that calculated from MCM-modelled radical concentrations. The MCM-calculated P(Ox) significantly underpredicted the measurement-calculated P(Ox) in the morning, and the degree of underprediction was found to scale with NO.</p
Orbital Decay in M82 X-2
© 2022. The Author(s). Published by the American Astronomical Society. This is an open access article distributed under the Creative Commons Attribution License, to view a copy of the license, https://creativecommons.org/licenses/by/4.0/M82 X-2 is the first pulsating ultraluminous X-ray source discovered. The luminosity of these extreme pulsars, if isotropic, implies an extreme mass transfer rate. An alternative is to assume a much lower mass transfer rate, but with an apparent luminosity boosted by geometrical beaming. Only an independent measurement of the mass transfer rate can help discriminate between these two scenarios. In this paper, we follow the orbit of the neutron star for 7 yr, measure the decay of the orbit ( Ṗorb/Porb≈−8·10−6yr−1 ), and argue that this orbital decay is driven by extreme mass transfer of more than 150 times the mass transfer limit set by the Eddington luminosity. If this is true, the mass available to the accretor is more than enough to justify its luminosity, with no need for beaming. This also strongly favors models where the accretor is a highly magnetized neutron star.Peer reviewe
The distribution of radioactive 44Ti in Cassiopeia A
The distribution of elements produced in the innermost layers of a supernova explosion is a key diagnostic for studying the collapse of massive stars. Here we present the results of a 2.4 Ms NuSTAR observing campaign aimed at studying the supernova remnant Cassiopeia A (Cas A). We perform spatially resolved spectroscopic analyses of the 44Ti ejecta, which we use to determine the Doppler shift and thus the three-dimensional (3D) velocities of the 44Ti ejecta. We find an initial 44Ti mass of (1.54 ± 0.21) × 10−4 M⊙, which has a present-day average momentum direction of 340° ± 15° projected onto the plane of the sky (measured clockwise from celestial north) and is tilted by 58° ± 20° into the plane of the sky away from the observer, roughly opposite to the inferred direction of motion of the central compact object. We find some 44Ti ejecta that are clearly interior to the reverse shock and some that are clearly exterior to it. Where we observe 44Ti ejecta exterior to the reverse shock we also see shock-heated iron; however, there are regions where we see iron but do not observe 44Ti. This suggests that the local conditions of the supernova shock during explosive nucleosynthesis varied enough to suppress the production of 44Ti by at least a factor of two in some regions, even in regions that are assumed to be the result of processes like α-rich freezeout that should produce both iron and titanium
The NuSTAR ULX program
We present the results of the first large program of broadband ULX observations with NuSTAR, XMM-Newton and Suzaku, yielding high-quality spectra and timing measurements from 0.3-30 keV in 6 ULXs, providing powerful information for understanding the accretion modes and nature of the central BHs. In particular, we find that all ULXs in our sample have a clear cutoff above 10 keV. This cutoff is less pronounced than expected by Comptonization from a cold, thick corona. We confirm the presence of a soft excess at low energies in the brightest ULXs, with temperatures below ~ 0.5 keV. We make an estimates on the masses of several ULXs based on spectral variability and model fitting
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