2,168 research outputs found
Optimal binning of X-ray spectra and response matrix design
A theoretical framework is developed to estimate the optimal binning of X-ray
spectra. We derived expressions for the optimal bin size for model spectra as
well as for observed data using different levels of sophistication. It is shown
that by taking into account both the number of photons in a given spectral
model bin and their average energy over the bin size, the number of model
energy bins and the size of the response matrix can be reduced by a factor of
. The response matrix should then contain the response at the bin
centre as well as its derivative with respect to the incoming photon energy. We
provide practical guidelines for how to construct optimal energy grids as well
as how to structure the response matrix. A few examples are presented to
illustrate the present methods.Comment: 16 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
Adaptive radiotherapy for preoperative gastric cancer
Preoperative radiotherapy for gastric cancer is a novel treatment approach, aiming to precisely irradiate the target while sparing the surrounding healthy tissue to limit potential adverse side effects. However, the stomach's inherent motion and deformation, as well as its proximity to vital organs, pose challenges for precise irradiation. A promising solution is adaptive radiotherapy, which adjusts the treatment plan to match daily anatomical variations. One such approach is a Library of Plans (LoP), where multiple treatment plans covering various anatomical variations are created, and the most suitable plan is selected daily. This thesis explored a CBCT-guided adaptive strategy for preoperative gastric cancer radiotherapy. The observed substantial stomach motion and deformation highlights the need for an adaptive strategy. The feasibility of a CBCT-guided LoP was demonstrated through observer evaluations, showing that a range of observers can consistently select the most appropriate treatment plan. Furthermore, using a gastric deformation model, stomach shape was predicted from stomach volumes. A dosimetric comparison between the LoP and a single-plan approach showed that the LoP reduces the average irradiated volume and the dose to organs at risk while maintaining equal target coverage. Hence, this research underscores the benefit of an adaptive strategy for preoperative gastric cancer radiotherapy and contributes to understanding the challenges and potential solutions in this field
The mass and energy budget of Cassiopeia A
Further analysis of X-ray spectroscopy results recently obtained from the MOS
CCD cameras on-board XMM-Newton provides a detailed description of the hot and
cool X-ray emitting plasma in Cas A. Measurement of the Doppler broadening of
the X-ray lines is consistent with the expected ion velocities, ~1500 km/s
along the line of sight, in the post shock plasma. Assuming a constant total
pressure throughout the remnant we estimate the total remnant mass as 10 Msun
and the total thermal energy as 7E43 J. We derive the differential mass
distribution as a function of ionisation age for both X-ray emitting
components. This distribution is consistent with a hot component dominated by
swept up mass heated by the primary shock and a cool component which are
ablated clumpy ejecta material which were and are still being heated by
interaction with the preheated swept up material. We calculate a balanced mass
and energy budget for the supernova explosion giving 1E44 J in ejected mass;
approximately 0.4 Msun of the ejecta were diffuse with an initial rms velocity
of 15000 km/s while the remaining ~1.8 Msun were clumpy with an initial rms
velocity of ~2400 km/s. Using the Doppler velocity measurements of the X-ray
spectral lines we can project the mass into spherical coordinates about the
remnant. This provides quantitative evidence for mass and energy beaming in the
supernova explosion. The mass and energy occupy less than 4.5 sr (<40 % of the
available solid angle) around the remnant and 64 % of the mass occurs in two
jets within 45 degrees of a jet axis. We calculate a swept up mass of 7.9 Msun
in the emitting plasma and estimate that the total mass lost from the
progenitor prior to the explosion could be as high as ~20 Msun.Comment: 8 pages, 7 figures, submitted to Astronomy & Astrophysic
Proper Motions of H-alpha filaments in the Supernova Remnant RCW 86
We present a proper motion study of the eastern shock-region of the supernova
remnant RCW 86 (MSH 14-63, G315.4-2.3), based on optical observations carried
out with VLT/FORS2 in 2007 and 2010. For both the northeastern and southeastern
regions, we measure an average proper motion of H-alpha filaments of 0.10 +/-
0.02 arcsec/yr, corresponding to 1200 +/- 200 km/s at 2.5kpc. There is
substantial variation in the derived proper motions, indicating shock
velocities ranging from just below 700 km/s to above 2200 km/s.
The optical proper motion is lower than the previously measured X-ray proper
motion of northeastern region. The new measurements are consistent with the
previously measured proton temperature of 2.3 +/- 0.3 keV, assuming no
cosmic-ray acceleration. However, within the uncertainties, moderately
efficient (< 27 per cent) shock acceleration is still possible. The combination
of optical proper motion and proton temperature rule out the possibility that
RCW 86 has a distance less than 1.5kpc.
The similarity of the proper motions in the northeast and southeast is
peculiar, given the different densities and X-ray emission properties of the
regions. The northeastern region has lower densities and the X-ray emission is
synchrotron dominated, suggesting that the shock velocities should be higher
than in the southeastern, thermal X-ray dominated, region. A possible solution
is that the H-alpha emitting filaments are biased toward denser regions, with
lower shock velocities. Alternatively, in the northeast the shock velocity may
have decreased rapidly during the past 200yr, and the X-ray synchrotron
emission is an afterglow from a period when the shock velocity was higher.Comment: Accepted for publication in MNRA
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