Abstract We present an algorithm to derive difference images for data taken with JWST with matched point-spread functions (PSFs). It is based on the saccadic fast Fourier transform method but with ...revisions to accommodate the rotations and spatial variations of the PSFs. It allows for spatially varying kernels in B-spline form with separately controlled photometric scaling and Tikhonov kernel regularization for harnessing the ultimate fitting flexibility. We present this method using the JWST/NIRCam images of galaxy cluster Abell 2744 acquired in JWST Cycle 1 as the test data. The algorithm can be useful for time-domain source detection and differential photometry with JWST. It can also coadd images of multiple exposures taken at different field orientations. The coadded images preserve the sharpness of the central cores of the PSFs, and the positions and shapes of the objects are matched precisely with B-splines across the field.
Image Subtraction in Fourier Space Hu, Lei; Wang, Lifan; Chen, Xingzhuo ...
The Astrophysical journal,
09/2022, Letnik:
936, Številka:
2
Journal Article
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Abstract
Image subtraction is essential for transient detection in time-domain astronomy. The point-spread function (PSF), photometric scaling, and sky background generally vary with time and across ...the field of view for imaging data taken with ground-based optical telescopes. Image subtraction algorithms need to match these variations for the detection of flux variability. An algorithm that can be fully parallelized is highly desirable for future time-domain surveys. Here we introduce the saccadic fast Fourier transform (SFFT) algorithm we developed for image differencing. SFFT uses a
δ
-function basis for kernel decomposition, and the image subtraction is performed in Fourier space. This brings about a remarkable improvement in computational performance of about an order of magnitude compared to other published image subtraction codes. SFFT can accommodate the spatial variations in wide-field imaging data, including PSF, photometric scaling, and sky background. However, the flexibility of the
δ
-function basis may also make it more prone to overfitting. The algorithm has been tested extensively on real astronomical data taken by a variety of telescopes. Moreover, the SFFT code allows for the spatial variations of the PSF and sky background to be fitted by spline functions.
Non-small cell lung cancer (NSCLC) is an aggressive malignancy with poor clinical outcomes. Accumulating evidence indicated that dysregulation of circular RNAs (circRNAs) plays a key role in multiple ...solid tumors. In this study, circ-RAD23B was explored. The expression of circ-RAD23B in NSCLC was detected by RT-qPCR. The clinical value of circ-RAD23B was analyzed by Fisher's exact test and Kaplan-Meier curves. Gain and loss of function experiments were carried out to elucidate the biological functions of circ-RAD23B in NSCLC cell lines. Dual luciferase reporter assay and rescue experiments were used to reveal the mechanism of circ-RAD23B. The findings demonstrated that circ-RAD23B, identified to be amplified and overexpressed in NSCLC, was associated with lymph node invasion, lower differentiation grade and shorter overall survival (OS). Furthermore, circ-RAD23B functions as an oncogene in NSCLC cells. Mechanistically, circ-RAD23B could sponge miR-593–3p and miR-653–5p and thus elevate CCND2 and TIAM1 expression, respectively. Rescue assays proved that circ-RAD23B promotes cell growth via miR-593–3p/CCND2 axis and facilitates cell invasion by miR-653–5p/TIAM1 pathway. Taken together, we propose circ-RAD23B as a promising biomarker and therapeutic target for NSCLC.
•Circ-RAD23B is upregulated in NSCLC tissues and cells.•Circ-RAD23B expression is associated with NSCLC patients' clinical severity.•Circ-RAD23B exerts oncogenic properties in NSCLC cells.•Circ-RAD23B could sponge miR-593–3p and miR-653–5p and thus elevate CCND2 and TIAM1 expression, respectively.•Circ-RAD23B promotes cell growth via miR-593–3p/CCND2 axis and facilitates cell invasion by miR-653–5p/TIAM1 pathway.
Abstract
We present a data-driven method based on long short-term memory (LSTM) neural networks to analyze spectral time series of Type Ia supernovae (SNe Ia). The data set includes 3091 spectra from ...361 individual SNe Ia. The method allows for accurate reconstruction of the spectral sequence of an SN Ia based on a single observed spectrum around maximum light. The precision of the spectral reconstruction increases with more spectral time coverages, but the significant benefit of multiple epoch data at around optical maximum is only evident for observations separated by more than a week. The method shows great power in extracting the spectral information of SNe Ia and suggests that the most critical information of an SN Ia can be derived from a single spectrum around the optical maximum. The algorithm we have developed is important for the planning of spectroscopic follow-up observations of future SN surveys with the LSST/Rubin and WFIRST/Roman telescopes.
Abstract
Observational signatures of the circumstellar material (CSM) around Type Ia supernovae (SNe Ia) provide a unique perspective on their progenitor systems. The pre-supernova evolution of the ...SN progenitors may naturally eject CSM in most of the popular scenarios of SN Ia explosions. In this study, we investigate the influence of dust scattering on the light curves and polarizations of SNe Ia. A Monte Carlo method is constructed to numerically solve the process of radiative transfer through the CSM. Three types of geometric distributions of the CSM are considered: spherical shell, axisymmetric disk, and axisymmetric shell. We show that both the distance of the dust from the SN and the geometric distribution of the dust affect the light curve and color evolutions of SN. We found that the geometric location of the hypothetical circumstellar dust may not be reliably constrained based on photometric data alone, even for the best observed cases such as SN 2006X and SN 2014J, due to the degeneracy of CSM parameters. Our model results show that a time sequence of broadband polarimetry with appropriate time coverage from a month to about one year after explosion can provide unambiguous limits on the presence of circumstellar dust around SNe Ia.
Spectropolarimetry of Supernovae Wang, Lifan; Wheeler, J Craig
Annual review of astronomy and astrophysics,
01/2008, Letnik:
46, Številka:
1
Journal Article
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Overwhelming evidence has accumulated in recent years that supernova explosions are intrinsically three-dimensional phenomena with significant departures from spherical symmetry. We review the ...evidence derived from spectropolarimetry that has established several key results: Virtually all supernovae are significantly aspherical near maximum light; core-collapse supernovae behave differently than thermonuclear (Type Ia) supernovae; the asphericity of core-collapse supernovae is more pronounced in the inner layers, showing that the explosion process is strongly aspherical; core-collapse supernovae tend to establish a preferred direction of asymmetry; and the asphericity is stronger in the outer layers of thermonuclear supernovae, providing constraints on the burning process. We emphasize the utility of the Q/U plane as a diagnostic tool and revisit SN 1987A and SN 1993J in a contemporary context. An axially symmetric geometry can explain many basic features of core-collapse supernovae, but significant departures from axial symmetry are needed to explain most events. We introduce a spectropolarimetry type to classify the range of behavior observed in polarized supernovae. Understanding asymmetries in supernovae is important for phenomena as diverse as the origins of gamma-ray bursts and the cosmological applications of Type Ia supernovae in studies of the dynamics of the universe.
Evidence for two distinct populations of type Ia supernovae Wang, Xiaofeng; Wang, Lifan; Filippenko, Alexei V ...
Science (American Association for the Advancement of Science),
2013-Apr-12, 2013-04-12, 20130412, Letnik:
340, Številka:
6129
Journal Article
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Type Ia supernovae (SNe Ia) have been used as excellent standardizable candles for measuring cosmic expansion, but their progenitors are still elusive. Here, we report that the spectral diversity of ...SNe Ia is tied to their birthplace environments. We found that those with high-velocity ejecta are substantially more concentrated in the inner and brighter regions of their host galaxies than are normal-velocity SNe Ia. Furthermore, the former tend to inhabit larger and more luminous hosts. These results suggest that high-velocity SNe Ia likely originate from relatively younger and more metal-rich progenitors than do normal-velocity SNe Ia and are restricted to galaxies with substantial chemical evolution.
Abstract
The recent searches for
z
> 11 galaxies using the James Webb Space Telescope have resulted in an unexpectedly high number of candidate objects, which imply at least 1 order of magnitude ...higher number density of
z
> 11 galaxies than the previously favored predictions. A question has risen whether there are some new types of contaminants among these candidates. The candidate sample of Yan et al., totaling 87 dropouts, is the largest one, and we notice that a number of these candidates are pointlike. We hypothesize that the point-source dropouts could be supernovae at high redshifts. Further investigation shows that most of their spectral energy distributions indeed can be explained by supernovae at various redshifts from
z
∼ 1 to 15, which lends support to this hypothesis. Attributing such point-source dropouts to supernova contamination cannot eliminate the tension, however, because they only account for ∼10% of the Yan et al. sample. On the other hand, the discovery of “contaminant” supernovae at
z
> 3 will have a series of important implications. Ironically, the existence of supernovae at
z
> 10 would still imply that the previously favored picture of early galaxy formation severely underestimates the global star formation rate density such redshifts. Multiple-epoch JWST imaging will be the simplest and yet the most efficient way to further test this hypothesis.
SNe Ia play key roles in revealing the accelerating expansion of the universe, but our knowledge of their progenitors is still very limited. Here we report the discovery of a rigid dichotomy in ...circumstellar (CS) environments around two subclasses of SNe Ia as defined by their distinct photospheric velocities. For the SNe Ia with high photospheric velocities (HVs), we found a significant excess flux in blue light 60-100 days past maximum, while this phenomenon is absent for SNe with normal photospheric velocity. This blue excess can be attributed to light echoes by circumstellar dust located at a distance of about (1-2) × 1017 cm from the HV subclass. Moreover, we also found that the HV SNe Ia show systematically evolving Na i absorption line by performing a systematic search of variable Na i absorption lines in spectra of all SNe Ia, whereas this evolution is rarely seen in normal ones. The evolving Na i absorption can be modeled in terms of photoionization model, with the location of the gas clouds at a distance of about 2 × 1017 cm, in striking agreement with the location of CS dust inferred from B-band light-curve excess. These observations show clearly that the progenitors of HV subclass are likely from single-degenerate progenitor system (i.e., symbiotic binary), while the NV subclass may arise from double-degenerate system.
With growing data from ongoing and future supernova surveys, it is possible to empirically quantify the shapes of SNIa light curves in more detail, and to quantitatively relate the shape parameters ...with the intrinsic properties of SNIa. Building such relationships is critical in controlling systematic errors associated with supernova cosmology. Based on a collection of well-observed SNIa samples accumulated in the past years, we construct an empirical SNIa light curve model using a statistical method called the functional principal component analysis (FPCA) for sparse and irregularly sampled functional data. Using this method, the entire light curve of an SNIa is represented by a linear combination of principal component functions, and the SNIa is represented by a few numbers called "principal component scores." These scores are used to establish relations between light curve shapes and physical quantities such as intrinsic color, interstellar dust reddening, spectral line strength, and spectral classes. These relations allow for descriptions of some critical physical quantities based purely on light curve shape parameters. Our study shows that some important spectral feature information is being encoded in the broad band light curves; for instance, we find that the light curve shapes are correlated with the velocity and velocity gradient of the Si II λ6355 line. This is important for supernova surveys (e.g., LSST and WFIRST). Moreover, the FPCA light curve model is used to construct the entire light curve shape, which in turn is used in a functional linear form to adjust intrinsic luminosity when fitting distance models.
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