82 research outputs found
Constraining Axions with ZTF J1901+1458
The axion-nucleon coupling enables the production of axions through the decay
of excited isotopes, and axions produced in the Sun
through this process are often a target of helioscope searches. We show for the
first time that hot, highly magnetic white dwarfs such as ZTF J1901+1458 are a
viable target to search for the X-ray signature of axions that were produced by
the transition in the core and then converted to photons
in the magnetosphere. We calculate that a 100 ks observation of ZTF J1901+1458
with NuSTAR would constrain the coupling of axions to nucleons and photons at a
level below the bounds of both current and future planned helioscopes.Comment: 6 pages, 2 figure
The origin of ultramassive white dwarfs: hints from Gaia EDR3
Gaia Data Release 2 revealed a population of ultramassive white dwarfs on the
Q branch that are moving anomalously fast for a local disc population with
their young photometric ages. As the velocity dispersion of stars in the local
disc increases with age, a proposed explanation of these white dwarfs is that
they experience a cooling delay that causes current cooling models to infer
photometric ages much younger than their true ages. To explore this
explanation, we investigate the kinematics of ultramassive white dwarfs within
200 pc of the Sun using the improved Gaia Early Data Release 3 observations. We
analyse the transverse motions of 0.95 - 1.25 white dwarfs,
subdivided by mass and age, and determine the distributions of the
three-dimensional components of the transverse velocities. The results are
compared to expectations based on observed kinematics of local main-sequence
stars. We find a population of photometrically young ( 0.5 - 1.5 Gyr)
ultramassive ( 1.15 - 1.25 ) white dwarfs for which the
transverse velocity component in the direction of Galactic rotation is more
dispersed than for local disc stars of any age; thus, it is too dispersed to be
explained by any cooling delay in white dwarfs originating from the local disc.
Furthermore, the dispersion ratio of the velocity components in the Galactic
plane for this population is also inconsistent with a local disc origin. We
discuss some possible explanations of this kinematically anomalous population,
such as a halo origin or production through dynamical effects of stellar triple
systems.Comment: 11 pages, 3 figures, published in MNRA
The Onset of Convective Coupling and Freezing in the White Dwarfs of 47 Tucanae
Using images from the Hubble Space Telescope Advanced Camera for Surveys, we
measure the rate of cooling of white dwarfs in the globular cluster 47 Tucanae
and compare it to modelled cooling curves. We examine the effects of the outer
convective envelope reaching the nearly isothermal degenerate core and the
release of latent heat during core crystallisation on the white dwarf cooling
rates. For white dwarfs typical of 47 Tuc, the onset of these effects occur at
similar times. The latent heat released during crystallisation is a small heat
source. In contrast, the heat reservoir of the degenerate core is substantially
larger. When the convective envelope reaches the nearly isothermal interior of
the white dwarf, the star becomes brighter than it would be in the absence of
this effect. Our modelled cooling curves that include this convective coupling
closely match the observed luminosity function of the white dwarfs in 47 Tuc.Comment: 6 pages, 5 figures. Submitted to MNRA
Optimal Summary Statistics for X-ray Polarization
We develop two new highly efficient estimators to measure the polarization
(Stokes parameters) in experiments that constrain the position angle of
individual photons such as scattering and gas-pixel-detector polarimeters, and
analyse in detail a previously proposed estimator. All three of these
estimators are at least fifty percent more efficient on typical datasets than
the standard estimator used in the field. We present analytic estimates of the
variance of these estimators and numerical experiments to verify these
estimates. Two of the three estimators can be calculated quickly and directly
through summations over the measurements of individual photons
Clinical benefit of adding oxaliplatin to standard neoadjuvant chemoradiotherapy in locally advanced rectal cancer: a meta-analysis : Oxaliplatin in neoadjuvant treatment for rectal cancer
Abstract. Background: To evaluate the treatment tolerance
and clinical outcomes in patients aged 70 years and older with
locally advanced oropharyngeal cancer treated by definitive
intensity-modulated radiation therapy (IMRT). Patients and
Methods: We retrospectively analyzed 15 consecutive elderly
patients, with histologically-proven squamous cell carcinoma
of the oropharynx, staged T3-4 with or without involved lymph
nodes at diagnosis, who received definitive sequential IMRT
(70 Gy; 2 Gy/fraction). Adult Comorbidity Evaluation-27
(ACE-27) score was calculated and its influence on treatment
tolerance and clinical outcomes was analyzed. Results: A total
of 15 patients were included with a median age of 77 years
(range=70-88 years). At baseline, 8 patients (53.3%) had an
ACE-27 score of 1, and the remainder (n=7, 46.7%) had a
comorbidity index of 0. All patients completed programmed
IMRT treatment, without any reduction of total dose. Oral
pain and mucositis were the most common acute side-effects,
classified as grade 3 in 6 patients (40%) only. Xerostomia was
reported in 13 patients (86.7%), without severe manifestation.
There was no hematological toxicity. ACE-27 score was not
related to higher severe acute toxicity. No patients experienced
grade 3 or more late toxicity. Five-year overall survival and
disease-free survival rates were 63.6% (95% confidence
interval=32.7-83.3%) and 55% (95% confidence
interval=24.4-77.6%), respectively. Comorbidity score did not
influence survival outcomes, both overall survival (p=0.46)
and disease-free survival (p=0.55). Conclusion: Treatment
tolerance, as well as survival outcomes were good in elderly
oropharyngeal cancer patients treated with definitive
sequential IMRT. Due to age and comorbidity, no dose or
volume reduction for IMRT should be considered in this
setting of patients. A prospective randomized trial with a large
sample size should be conducted to confirm our result
The Colibrì: taking the pulse of black holes and neutron stars
We propose a high-time-resolution, high-spectral-resolution X-ray telescope that uses transition-edge sensors (TES) as detectors and collector optics to direct the X-rays onto the focal plane, providing a large effective area in a small satellite. The key science driver of the instrument is to study neutron stars and accreting black holes. The proposed instrument is built upon two technologies that are already at high TRL: TES X-ray detectors and collector optics
The Colibrì: taking the pulse of black holes and neutron stars
We propose a high-time-resolution, high-spectral-resolution X-ray telescope that uses transition-edge sensors (TES) as detectors and collector optics to direct the X-rays onto the focal plane, providing a large effective area in a small satellite. The key science driver of the instrument is to study neutron stars and accreting black holes. The proposed instrument is built upon two technologies that are already at high TRL: TES X-ray detectors and collector optics
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