1,269 research outputs found
What can be learnt from a highly informative X-ray occultation event in NGC 6814? A marvellous absorber
A unique X-ray occultation event in NGC 6814 during an XMM-Newton observation
in 2016 has been reported, providing useful information of the absorber and the
corona. We revisit the event with the aid of the hardness ratio (HR) - count
rate (CR) plot and comparison with two other absorption-free XMM exposures in
2009 and 2021. NGC 6814 exhibits a clear "softer-when-brighter" variation
pattern during the exposures, but the 2016 exposure significantly deviates from
the other two in the HR - CR plot. While spectral fitting does yield transient
Compton-thin absorption corresponding to the eclipse event in 2016, rather than
easing the tension between exposures in the HR - CR plot, correcting the
transient Compton-thin absorption results in new and severe deviation within
the 2016 exposure. We show that the eclipsing absorber shall be clumpy (instead
of a single Compton-thin cloud), with an inner denser region composed of both
Compton-thin and Compton-thick clouds responsible for the previously identified
occultation event, and an outer sparser region with Compton-thin clouds which
eclipses the whole 2016 exposure. With this model, all the tension in the HR -
CR plots could be naturally erased, with the observed spectral variability
during the 2016 exposure dominated by the variation of absorption. Furthermore,
the two warm absorbers (with different ionization and column densities but
similar outflowing velocities) detected in the 2016 exposure shall also
associate with the transient absorber, likely due to ablated or tidal
stretched/disrupted fragments. This work highlights the unique usefulness of
the HR - CR plot while analysing rare occultation events.Comment: 13 pages, 9 figures, accepted by MNRAS. For the video of the
eclipsing cloud, see
https://drive.google.com/file/d/1CEsPEWE-b5W8PfZINyI5K1sE6klHaYMa/view?usp=sharing
. Comments are welcome
RAWIW: RAW Image Watermarking Robust to ISP Pipeline
Invisible image watermarking is essential for image copyright protection.
Compared to RGB images, RAW format images use a higher dynamic range to capture
the radiometric characteristics of the camera sensor, providing greater
flexibility in post-processing and retouching. Similar to the master recording
in the music industry, RAW images are considered the original format for
distribution and image production, thus requiring copyright protection.
Existing watermarking methods typically target RGB images, leaving a gap for
RAW images. To address this issue, we propose the first deep learning-based RAW
Image Watermarking (RAWIW) framework for copyright protection. Unlike RGB image
watermarking, our method achieves cross-domain copyright protection. We
directly embed copyright information into RAW images, which can be later
extracted from the corresponding RGB images generated by different
post-processing methods. To achieve end-to-end training of the framework, we
integrate a neural network that simulates the ISP pipeline to handle the
RAW-to-RGB conversion process. To further validate the generalization of our
framework to traditional ISP pipelines and its robustness to transmission
distortion, we adopt a distortion network. This network simulates various types
of noises introduced during the traditional ISP pipeline and transmission.
Furthermore, we employ a three-stage training strategy to strike a balance
between robustness and concealment of watermarking. Our extensive experiments
demonstrate that RAWIW successfully achieves cross-domain copyright protection
for RAW images while maintaining their visual quality and robustness to ISP
pipeline distortions
Light-cone distribution amplitudes of a light baryon in large-momentum effective theory
Momentum distributions of quarks/gluons inside a light baryon in a hard
exclusive process are encoded in the light-cone distribution amplitudes
(LCDAs). In this work, we point out that the leading twist LCDAs of a light
baryon can be obtained through a simulation of a quasi-distribution amplitude
calculable on lattice QCD within the framework of the large-momentum effective
theory. We calculate the one-loop perturbative contributions to LCDA and
quasi-distribution amplitudes and explicitly demonstrate the factorization of
quasi-distribution amplitudes at the one-loop level. Based on the perturbative
results, we derive the matching kernel in the scheme and
regularization-invariant momentum-subtraction scheme. Our result provides a
first step to obtaining the LCDA from first principle lattice QCD calculations
in the future.Comment: 19 pages, 2 figure
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