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Comparison of the time lag results between this study and previous studies. The calculated correlation coefficient of the two time lag measurements is 0.93, meaning that our results and the previous results agree well with each other.
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Reverberation mapping (RM) is one of the most efficient ways to investigate the broad-line region around the central supermassive black holes of active galactic nuclei (AGNs). A common way of performing the RM is to perform a long term spectroscopic monitoring of AGNs, but the spectroscopic monitoring campaign of a large number of AGNs requires an...
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The widely accepted active galactic nucleus (AGN) paradigm has been recently challenged by the discovery of the so-called ``changing-look'' (CL) phenomenon characterized by spectral-type transitions. By comparing the SDSS-V and SDSS DR16 spectroscopic datasets, here we report the identification of 14 new CL-AGNs (redshift $z<0.5$) exhibiting spectr...
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... Pozo Nuñez et al. (2012) computed a synthetic Hβ lightcurve by subtracting a scaled broadband lightcurve from the narrowband lightcurve to measure the BLR size of 3C 120, which was very close to the value obtained with SRM (Grier et al. 2012). In addition to the narrowband PRM, Kim et al. (2019) used three intermediate-band filters to get the time lags between the continuum and the Hα emission line of five AGNs, which are consistent with the SRM results. Jiang et al. (2016) combined the broad and intermediate bands and detected the Hα time lags for 13 AGNs at redshift 0.2 < z < 0.4. ...
Broadband photometric reverberation mapping (PRM) has been investigated for active galactic nuclei (AGNs) in recent years, but mostly on accretion disk continuum RM. Due to the small fraction of broad emission lines in the broad band, PRM for emission lines is very challenging. Here, we present an ICCF-Cut method for broadband PRM to obtain the H α broad-line lag and apply it to four Seyfert 1 galaxies: MCG+08-11-011, NGC 2617, 3C 120, and NGC 5548. All of them have high-quality broadband lightcurves with daily/subdaily cadences, which enable us to extract H α lightcurves from the line band by subtracting the contributions from the continuum and host galaxy. Their extracted H α lightcurves are compared with the lagged continuum-band lightcurves, as well as the lagged H β lightcurves obtained by spectroscopic RM (SRM) at the same epochs. The consistency of these lightcurves and the comparison with the SRM H β lags provide support for the H α lags of these AGNs, in a range from 9 to 19 days, obtained by the ICCF-Cut, JAVELIN, and χ ² methods. The simulations for evaluating the reliability of the H α lags and the comparisons between the SRM H β and PRM H α lags indicate that the consistency of the ICCF-Cut, JAVELIN, and χ ² results can ensure the reliability of the derived H α lags. These methods may be used to estimate the broad-line region sizes and black hole masses of a large sample of AGNs in large multi-epoch, high-cadence photometric surveys such as LSST in the future.
... Second, monitoring a sizable AGN sample for a long period and a sufficiently high cadence is extremely challenging, although it is clearly required to ensure that significant variability in both the seed (disk) and responsive emission components is properly recorded. Photometric RM alleviates some of these practical challenges, as it allows to robustly measure AGN time lags through photometric monitoring with various band widths instead of spectroscopy, as demonstrated by a growing number of studies (see, e.g., Chelouche & Zucker 2013;Chelouche et al. 2014;Ramolla et al. 2018;Kim et al. 2019b, and additional references below). ...
The Ultraviolet Transient Astronomy Satellite (ULTRASAT) is scheduled to be launched to geostationary orbit in 2026. It will carry a telescope with an unprecedentedly large field of view (204 deg$^2$) and NUV (230-290nm) sensitivity (22.5 mag, 5$\sigma$, at 900s). ULTRASAT will conduct the first wide-field survey of transient and variable NUV sources and will revolutionize our ability to study the hot transient universe: It will explore a new parameter space in energy and time-scale (months long light-curves with minutes cadence), with an extra-Galactic volume accessible for the discovery of transient sources that is $>$300 times larger than that of GALEX and comparable to that of LSST. ULTRASAT data will be transmitted to the ground in real-time, and transient alerts will be distributed to the community in $<$15 min, enabling a vigorous ground-based follow-up of ULTRASAT sources. ULTRASAT will also provide an all-sky NUV image to $>$23.5 AB mag, over 10 times deeper than the GALEX map. Two key science goals of ULTRASAT are the study of mergers of binaries involving neutron stars, and supernovae: With a large fraction ($>$50%) of the sky instantaneously accessible, fast (minutes) slewing capability and a field-of-view that covers the error ellipses expected from GW detectors beyond 2025, ULTRASAT will rapidly detect the electromagnetic emission following BNS/NS-BH mergers identified by GW detectors, and will provide continuous NUV light-curves of the events; ULTRASAT will provide early (hour) detection and continuous high (minutes) cadence NUV light curves for hundreds of core-collapse supernovae, including for rarer supernova progenitor types.
... Pozo Nuñez et al. (2012) computed the synthetic Hβ lightcurve by subtracting a scaled broadband lightcurve from the narrow band lightcurve and measured the BLR size of 3C 120, which is very close to the value obtained with SRM (Grier et al. 2012). In addition to the narrow-band PRM, Kim et al. (2019) used three intermediate band filters to get the time lags between the continuum and the Hα emission line of five AGNs, which are consistent with the SRM results. Jiang et al. (2016) combined the broad and intermediate bands and detect the Hα time lags for 13 AGNs at redshift 0.2 < z < 0.4. ...
Broadband photometric reverberation mapping (PRM) have been investigated for AGNs in recent years, but mostly on accretion disk continuum RM. Due to the small fraction of broad emission lines in the broadband, PRM for emission lines is very challenging. Here we present an ICCF-Cut method for broadband PRM to obtain the Hα broad line lag and apply it to four Seyfert 1 galaxies, MCG+08-11-011, NGC 2617, 3C 120 and NGC 5548. All of them have high quality broadband lightcurves with daily/sub-daily cadence, which enables us to extract Hα lightcurves from the line band by subtracting the contributions from the continuum and host galaxy. Their extracted Hα lightcurves are compared with the lagged continuum band lightcurves, as well as the lagged Hβ lightcurves obtained by spectroscopic RM (SRM) at the same epochs. The consistency of these lightcurves and the comparison with the SRM Hβ lags provide supports to the Hα lags of these AGNs, in a range from 9 to 19 days, obtained by the ICCF-Cut, JAVELIN and χ 2 methods. The simulations to evaluate the reliability of Hα lags and the comparisons between SRM Hβ and PRM Hα lags indicate that the consistency of the ICCF-Cut, JAVELIN and χ 2 results can ensure the reliability of the derived Hα lags. These methods may be used to estimate the broad line region sizes and black hole masses of a large sample of AGNs in the large multi-epoch high cadence photometric surveys such as LSST in the future.
... Pozo Nuñez et al. (2012) computed the synthetic Hβ lightcurve by subtracting a scaled broadband lightcurve from the narrow band lightcurve and measured the BLR size of 3C 120, which is very close to the value obtained with SRM (Grier et al. 2012). In addition to the narrow-band PRM, Kim et al. (2019) used three intermediate band filters to get the time lags between the continuum and the Hα emission line of five AGNs, which are consistent with the SRM results. Jiang et al. (2016) combined the broad and intermediate bands and detect the Hα time lags for 13 AGNs at redshift 0.2 < z < 0.4. ...
Broadband photometric reverberation mapping (PRM) have been investigated for AGNs in recent years, but mostly on accretion disk continuum RM. Due to the small fraction of broad emission lines in the broadband, PRM for emission lines is very challenging. Here we present an ICCF-Cut method for broadband PRM to obtain the H$\alpha$ broad line lag and apply it to four Seyfert 1 galaxies, MCG+08-11-011, NGC 2617, 3C 120 and NGC 5548. All of them have high quality broadband lightcurves with daily/sub-daily cadence, which enables us to extract H$\alpha$ lightcurves from the line band by subtracting the contributions from the continuum and host galaxy. Their extracted H$\alpha$ lightcurves are compared with the lagged continuum band lightcurves, as well as the lagged H$\beta$ lightcurves obtained by spectroscopic RM (SRM) at the same epochs. The consistency of these lightcurves and the comparison with the SRM H$\beta$ lags provide supports to the H$\alpha$ lags of these AGNs, in a range from 9 to 19 days, obtained by the ICCF-Cut, JAVELIN and $\chi^2$ methods. The simulations to evaluate the reliability of H$\alpha$ lags and the comparisons between SRM H$\beta$ and PRM H$\alpha$ lags indicate that the consistency of the ICCF-Cut, JAVELIN and $\chi^2$ results can ensure the reliability of the derived H$\alpha$ lags. These methods may be used to estimate the broad line region sizes and black hole masses of a large sample of AGNs in the large multi-epoch high cadence photometric surveys such as LSST in the future.
... Paek et al. 2023, in preparation), the process of which includes bias and dark subtractions, flat-fielding, astrometry, and photometry calibration using point sources in the vicinity of AT2019cuk. We performed aperture photometry with a single aperture size to minimize the host galaxy contamination after convolving images from different epochs to have a common PSF using the HOTPANTS software (Becker 2015; see, e.g., Kim et al. 2018Kim et al. , 2019. Image convolution is necessary due to different seeing values on different nights, which may sample different amounts of the host galaxy light (when done with a variable aperture size that is proportional to the PSF size) or the nuclear transient (when done with a fixed aperture size; see, e.g., Kim et al. 2018). ...
The nuclear transient AT2019cuk/Tick Tock/SDSS J1430+2303 has been suggested to harbor a supermassive black hole (SMBH) binary near coalescence. We report results from high-cadence NICER X-ray monitoring with multiple visits per day from 2022 January to August, as well as continued optical monitoring during the same time period. We find no evidence of periodic/quasiperiodic modulation in the X-ray, UV, or optical bands; however, we do observe exotic hard X-ray variability that is unusual for typical active galactic nuclei (AGN). The most striking feature of the NICER light curve is repetitive hard (2–4 keV) X-ray flares that result in distinctly harder X-ray spectra compared to the nonflaring data. In its nonflaring state, AT2019cuk looks like a relatively standard AGN, but it presents the first case of day-long, hard X-ray flares in a changing-look AGN. We consider a few different models for the driving mechanism of these hard X-ray flares, including (1) corona/jet variability driven by increased magnetic activity, (2) variable obscuration, and (3) self-lensing from the potential secondary SMBH. We prefer the variable corona model, as the obscuration model requires rather contrived timescales and the self-lensing model is difficult to reconcile with a lack of clear periodicity in the flares. These findings illustrate how important high-cadence X-ray monitoring is to our understanding of the rapid variability of the X-ray corona and necessitate further high-cadence, multiwavelength monitoring of changing-look AGN like AT2019cuk to probe the corona-jet connection.
... We performed aperture photometry with a single aperture size to minimize the host galaxy contamination after convolving images from different epochs to have a common point-spread-function (PSF) using the HOTPANTS software (Becker 2015; see e.g. Kim et al. 2018Kim et al. , 2019. Image convolution is necessary due to different seeing values on different nights, which may sample different amounts of the host galaxy light (when done with a variable aperture size that is proportional to the PSF size) or the nuclear transient (when done with a fixed aperture size; see e.g. ...
The nuclear transient AT2019cuk/Tick Tock/SDSS J1430+2303 has been suggested to harbor a supermassive black hole (SMBH) binary near coalescence. We report results from high-cadence NICER X-ray monitoring with multiple visits per day from January-August 2022, as well as continued optical monitoring during the same time period. We find no evidence of periodic/quasi-periodic modulation in the X-ray, UV, or optical bands, however we do observe exotic hard X-ray variability that is unusual for a typical AGN. The most striking feature of the NICER light curve is repetitive hard (2-4 keV) X-ray flares that result in distinctly harder X-ray spectra compared to the non-flaring data. In its non-flaring state, AT2019cuk looks like a relatively standard AGN, but it presents the first case of day-long, hard X-ray flares in a changing-look AGN. We consider a few different models for the driving mechanism of these hard X-ray flares, including: (1) corona/jet variability driven by increased magnetic activity, (2) variable obscuration, and (3) self-lensing from the potential secondary SMBH. We prefer the variable corona model, as the obscuration model requires rather contrived timescales and the self-lensing model is difficult to reconcile with a lack of clear periodicity in the flares. These findings illustrate how important high-cadence X-ray monitoring is to our understanding of the rapid variability of the X-ray corona and necessitate further high-cadence, multi-wavelength monitoring of changing-look AGN like AT2019cuk to probe the corona-jet connection.
... PRM was able to estimate the BLR size and black hole masses in several local Seyfert-1 galaxies (Pozo Nu ˜ nez et al. 2012Nu ˜ nez et al. , 2013Edri et al. 2012 ;Ramolla et al. 2015Ramolla et al. , 2018Kim et al. 2019 ) with accuracy comparable to spectroscopic reverberation mapping (SRM) of the BLR (Blandford & McKee 1982 ;Gaskell & Sparke 1986 ;Peterson 1993 ;Grier et al. 2012 ). The feasibility of PRM has also been tested recently in high-redshift quasars (Read et al. 2020 ). ...
Photometric reverberation mapping can detect the radial extent of the accretion disc (AD) in Active Galactic Nuclei by measuring the time delays between light curves observed in different continuum bands. Quantifying the constraints on the efficiency and accuracy of the delay measurements is important for recovering the AD size-luminosity relation, and potentially using quasars as standard candles. We have explored the possibility of determining the AD size of quasars using next-generation Big Data surveys. We focus on the Legacy Survey of Space and Time (LSST) at the Vera C. Rubin Observatory, which will observe several thousand quasars with the Deep Drilling Fields and up to 10 million quasars for the main survey in six broadband filter during its 10-year operational lifetime. We have developed extensive simulations that take into account the characteristics of the LSST survey and the intrinsic properties of the quasars. The simulations are used to characterise the light curves from which AD sizes are determined using various algorithms. We find that the time delays can be recovered with an accuracy of 5 and 15% for light curves with a time sampling of 2 and 5 days, respectively. The results depend strongly on the redshift of the source and the relative contribution of the emission lines to the bandpasses. Assuming an optically thick and geometrically thin AD, the recovered time-delay spectrum is consistent with black hole masses derived with 30% uncertainty.
The Ultraviolet Transient Astronomy Satellite (ULTRASAT) is scheduled to be launched to geostationary orbit in 2027. It will carry a telescope with an unprecedentedly large field of view (204 deg ² ) and near-ultraviolet (NUV; 230–290 nm) sensitivity (22.5 mag, 5 σ , at 900 s). ULTRASAT will conduct the first wide-field survey of transient and variable NUV sources and will revolutionize our ability to study the hot transient Universe. It will explore a new parameter space in energy and timescale (months-long light curves with minutes cadence), with an extragalactic volume accessible for the discovery of transient sources that is >300 times larger than that of the Galaxy Evolution Explorer (GALEX) and comparable to that of the Vera Rubin Observatory’s Legacy Survey of Space and Time. ULTRASAT data will be transmitted to the ground in real time, and transient alerts will be distributed to the community in <15 minutes, enabling vigorous ground-based follow up of ULTRASAT sources. ULTRASAT will also provide an all-sky NUV image to >23.5 AB mag, over 10 times deeper than the GALEX map. Two key science goals of ULTRASAT are the study of mergers of binaries involving neutron stars, and supernovae. With a large fraction (>50%) of the sky instantaneously accessible, fast (minutes) slewing capability, and a field of view that covers the error ellipses expected from gravitational-wave (GW) detectors beyond 2026, ULTRASAT will rapidly detect the electromagnetic emission following binary neutron star/neutron star–black hole mergers identified by GW detectors, and will provide continuous NUV light curves of the events. ULTRASAT will provide early (hour) detection and continuous high-cadence (minutes) NUV light curves for hundreds of core-collapse supernovae, including for rarer supernova progenitor types.
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 (AGN) 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 dataset of long light-curves of eight AGN with peculiarities and the artificial datasets based on several idealized and LSST-like cadences. The SFs metric is assessed on synthetic datasets. The regression models (for both data types) predict similar cadences for time-lags and oscillation detection, whereas for light curves with low variability ($\sim 10\%$), cadences for oscillation detection differ. For higher variability ($\sim 20\%$), predicted cadences are larger than for $F_{var}\sim 10\%$. 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.
