Abstract
In this study, a refined approach for multicomponent fitting of active galactic nuclei (AGNs) spectra is presented utilizing the newly developed
Python
code Fully Automated pythoN Tool for ...AGN Spectra analYsis (
fantasy
). AGN spectra are modeled by simultaneously considering the underlying broken power-law continuum, predefined emission line lists, and an Fe
ii
model, which is here extended to cover the wavelength range 3700–11000 Å. The Fe
ii
model, founded solely on atomic data, effectively describes the extensive emission of the complex iron ion in the vicinity of the H
γ
and H
β
lines, as well as near the H
α
line, which was previously rarely studied. The proposed spectral fitting approach is tested on a sample of high-quality AGN spectra from the Sloan Digital Sky Survey Data Release 17. The results indicate that when Fe
ii
emission is present near H
β
, it is also detected redward from H
α
, potentially contaminating the broad H
α
line wings and thus affecting the measurements of its flux and width. The production of Fe
ii
emission is found to be strongly correlated with Eddington luminosity and appears to be controlled by a similar mechanism as the hydrogen Balmer lines. The study highlights the benefits of fitting type 1 AGN spectra with the
fantasy
code, pointing that it may be used as a robust tool for analyzing a large number of AGN spectra in the coming spectral surveys.
Most of the published results on solving operator equations are very restrictive i.e. they have been proved under certain additional assumptions and in fact we do not have general solvability ...conditions. There are many reasons why this is so, one of them being the fact that the usual methods employed when solving these equations involve the use of generalized inverses which exist and are bounded in the case of operators only under certain special conditions such as closedness of the range of operators. Using two previously considered systems of operator equations as examples, we will show that using a particular general approach we can give necessary and sufficient solvability conditions without any additional assumptions. We will consider the system AXC=C=CXA and generalize recent particular results from the paper C. Deng, et al. (Appl. Math. Letters 81, 86–92 (2018)), as well as BAX=B=XAB for which the particular results are given in the paper C. Deng, (J. Math. Anal. Appl. 398 (2013) 664–670). We intend to use our approach to initiate formulating various general solvability conditions for other systems of operator equations.
A generalization of the co-EP property Zou, Honglin; Cvetković Ilić, Dragana; Zuo, Kezheng
Communications in algebra,
08/2022, Volume:
50, Issue:
8
Journal Article
Peer reviewed
We establish different characterizations for the invertibility of ab − ba in a ring when
and
that are related to the invertibility of elements expressed as certain functions of a, b and suitable ...elements from the center of the ring. As a consequence we get some interesting results in the matrix and operator settings: for a co-EP matrix (or operator) A we list all linear combinations of
that are invertible independently of the choice of the scalars. In addition, we consider the co-EP-ness of idempotents and tripotents.
Improvements on the reverse order laws Cvetković Ilić, Dragana; Milenković, Jovana
Mathematische Nachrichten,
July 2023, 2023-07-00, 20230701, Volume:
296, Issue:
7
Journal Article
Peer reviewed
In many papers concerning properties of generalized inverses in different settings, we can find the results with many redundant instances of assuming regularity of certain elements. We have made an ...effort to widen the range of applicability of concrete results by considering more general cases of the problems without imposing any such additional assumptions. This was the main motivation for this paper, and we present several significant improvements of the reverse order laws on {1,3}$\lbrace 1,3\rbrace$ and {1,2,3}$\lbrace 1,2,3\rbrace$‐inverses in the ring setting.
Abstract
We report the results of a search for long-period (100 <
P
< 600 days) periodic variability in the SDSS Stripe 82 standards catalog. The SDSS coverage of Stripe 82 enables such a search ...because there are on average 20 observations per band in
ugriz
bands for about one million sources, collected over about 6 yr, with a faint limit of
r
∼ 22 mag and precisely calibrated 1%–2% photometry. We calculated the periods of variable source candidates in this sample using the Lomb–Scargle periodogram and considered the three highest periodogram peaks in each of the
gri
filters as relevant. Only those sources with
gri
periods consistent within 0.1% were later studied. We use the Kuiper statistic to ensure uniform distribution of data points in phased light curves. We present five sources with the spectra consistent with quasar spectra and plausible periodic variability. This SDSS-based search bodes well for future sensitive large-area surveys, such as the Rubin Observatory Legacy Survey of Space and Time, which, due to its larger sky coverage (about a factor of 60) and improved sensitivity (∼2 mag), will be more powerful for finding such sources.
The LSST AGN Data Challenge: Selection Methods Savić, Đorđe V.; Jankov, Isidora; Yu, Weixiang ...
The Astrophysical journal,
08/2023, Volume:
953, Issue:
2
Journal Article, Web Resource
Peer reviewed
Open access
Abstract
Development of the Rubin Observatory Legacy Survey of Space and Time (LSST) includes a series of Data Challenges (DCs) arranged by various LSST Scientific Collaborations that are taking ...place during the project's preoperational phase. The AGN Science Collaboration Data Challenge (AGNSC-DC) is a partial prototype of the expected LSST data on active galactic nuclei (AGNs), aimed at validating machine learning approaches for AGN selection and characterization in large surveys like LSST. The AGNSC-DC took place in 2021, focusing on accuracy, robustness, and scalability. The training and the blinded data sets were constructed to mimic the future LSST release catalogs using the data from the Sloan Digital Sky Survey Stripe 82 region and the XMM-Newton Large Scale Structure Survey region. Data features were divided into astrometry, photometry, color, morphology, redshift, and class label with the addition of variability features and images. We present the results of four submitted solutions to DCs using both classical and machine learning methods. We systematically test the performance of supervised models (support vector machine, random forest, extreme gradient boosting, artificial neural network, convolutional neural network) and unsupervised ones (deep embedding clustering) when applied to the problem of classifying/clustering sources as stars, galaxies, or AGNs. We obtained classification accuracy of 97.5% for supervised models and clustering accuracy of 96.0% for unsupervised ones and 95.0% with a classic approach for a blinded data set. We find that variability features significantly improve the accuracy of the trained models, and correlation analysis among different bands enables a fast and inexpensive first-order selection of quasar candidates.
The photometric light curve of PG 1302-102 shows periodic variability, which makes this object one of the most plausible supermassive black hole binary candidates. Interestingly, the most recent ...study of its updated optical light curve reports a decrease in the significance of periodicity, which may suggest that the binary model is less favorable. Here we model the PG 1302-102 light curve, spanning almost 20 yr, with a supermassive black hole binary system in which a perturbation in the accretion disk of a more massive component is present. Our model reproduces well the observed light curve, with a slight perturbation of a sinusoidal feature, and predicts that a slightly larger period than previously reported, of about 1899 days, could arise owing to a cold spot in the disk of a more massive component of a close, unequal-mass ( ) black hole binary system. The light curve resembles the pattern of a sinusoid-like shape within a few years, which could be confirmed by future observations. In addition, using our hybrid method for periodicity detection, we show that the periods in the observed (1972 254 days) and modeled (1873 250 days) light curves are within 1 , which is also consistent with our physical model prediction and with previous findings. Thus, both the periodic nature and its slight fluctuation of the light curve of PG 1302-102 are evident from our physical model and confirmed by the hybrid method for periodicity detection.
ABSTRACT
Motivated by upcoming photometric and spectroscopic surveys Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST), Manuakea Spectroscopic Explorer, we design the statistical ...proxies to measure the cadence effects on active galactic nuclei (AGNs) variability-observables time-lags, periodicity, and structure-function (SF). We constructed a multiple-regression model to statistically identify the cadence-formal error pattern knowing AGN time-lags and periodicity from different surveys. We defined the simple metric for the SF’s properties, accounting for the ‘observed’ SF’s deviation relative to those obtained from the homogenously sampled light curves. We tested the regression models on different observing strategies: the optical data set of long light curves of eight AGN with peculiarities and the artificial data sets based on several idealized and LSST-like cadences. The SFs metric is assessed on synthetic data sets. The regression models (for both data types) predict similar cadences for time-lags and oscillation detection, whereas for light curves with low variability (${\sim}10{{\ \rm per\ cent}}$), cadences for oscillation detection differ. For higher variability (${\sim}20{{\ \rm per\ cent}}$), predicted cadences are larger than for $F_{var}\sim 10{{\ \rm per\ cent}}$. The predicted cadences are decreasing with redshift. SFs with dense and homogenous cadences are more likely to behave similarly. SFs with oscillatory signals are sensitive to the cadences, possibly impacting LSST-like operation strategy. The proposed proxies can help to select spectroscopic and photometric-surveys cadence strategies, and they will be tested further in larger samples of objects.
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