A5082807649- Astrophysical Phenomena and Observations
- Galaxies: Formation, Evolution, Phenomena
- Astrophysics and Cosmic Phenomena
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- Radio Astronomy Observations and Technology
- Adaptive optics and wavefront sensing
- Stellar, planetary, and galactic studies
- Astrophysics and Star Formation Studies
- Pulsars and Gravitational Waves Research
- Particle Accelerators and Free-Electron Lasers
- Dark Matter and Cosmic Phenomena
- Advanced Measurement and Metrology Techniques
- Mechanics and Biomechanics Studies
- Plant Water Relations and Carbon Dynamics
- Particle Detector Development and Performance
- Advanced X-ray Imaging Techniques
- X-ray Spectroscopy and Fluorescence Analysis
- Gyrotron and Vacuum Electronics Research
- Nuclear Physics and Applications
- Radiation Detection and Scintillator Technologies
- Statistical and numerical algorithms
- Black Holes and Theoretical Physics
- Optical measurement and interference techniques
Aryabhatta Research Institute of Observational Sciences
2020-2024
Seoul National University
2018-2024
Turku Centre for Computer Science
2020-2021
University of Turku
2019-2021
Indian Institute of Astrophysics
2016-2020
Bhabha Atomic Research Centre
2019
Centre National de la Recherche Scientifique
2012-2017
Observatoire de la Côte d’Azur
2012-2017
Université Côte d'Azur
2014-2017
Quasi-periodic X-ray eruptions (QPEs) are a recently discovered phenomenon, the nature of which remains unclear. Based on their discovery in active galactic nuclei (AGN), explanations related to an AGN accretion disk, or potentially stellar tidal disruption event (TDE), were put forward. Following report QPEs apparently passive galaxies, alternatives including highly unequal mass compact object binaries have been proposed explain properties. We perform systematic study five known QPE host...
Abstract We present the main results from a long-term reverberation mapping campaign carried out for Seoul National University AGN Monitoring Project (SAMP). High-quality data were obtained during 2015–2021 32 luminous active galactic nuclei (AGNs; i.e., continuum luminosity in range of 10 44–46 erg s −1 ) at regular cadence, 20–30 days spectroscopy and 3–5 photometry. obtain time lag measurements between variability H β emission AGNs; 25 those have best based on our quality assessment,...
Binaries containing a compact object orbiting supermassive black hole are thought to be precursors of gravitational wave events, but their identification has been extremely challenging. Here, we report quasi-periodic variability in x-ray absorption, which interpret as outflows (QPOuts) from previously low-luminosity active galactic nucleus after an outburst, likely caused by stellar tidal disruption. We rule out several models based on observed properties and instead show using general...
Abstract We present results from a high-cadence multiwavelength observational campaign of the enigmatic changing-look active galactic nucleus 1ES 1927+654 2022 May to 2024 April, coincident with an unprecedented radio flare (an increase in flux by factor ∼60 over few months) and emergence spatially resolved jet at 0.1–0.3 pc scales. Companion work has also detected recurrent quasi-periodic oscillation (QPO) 2–10 keV band increasing frequency (1–2 mHz) same period. During this time, soft...
Abstract We present a new catalog of narrow-line Seyfert 1 (NLSy1) galaxies from the Sloan Digital Sky Survey Data Release 12 (SDSS DR12). This was obtained by systematic analysis through modeling continuum and emission lines spectra all 68,859 SDSS DR12 objects that are classified as “QSO” spectroscopic pipeline with <?CDATA $z\lt 0.8$?> median signal-to-noise ratio (S/N) > 2 pixel −1 . contains total 11,101 objects, which is about 5 times larger than previously known NLSy1 galaxies....
Abstract The detection of significant γ -ray emission from radio-loud narrow-line Seyfert 1 (NLSy1s) galaxies enables us to study jets in environments different than those blazars. However, due the small number known -ray-emitting NLSy1 ( -NLSy1) galaxies, a comprehensive could not be performed. Here, we report first four active galactic nuclei (AGNs), recently classified as their Sloan Digital Sky Survey (SDSS) optical spectrum. Three flat-spectrum radio quasars (FSRQs) present third Large...
Fundamental differences in the radio properties of red quasars (QSOs), as compared to blue QSOs, have been recently discovered, positioning them a potential key population evolution galaxies and black holes across cosmic time. To elucidate their nature, we exploited rich compilation photometry spectroscopic data model spectral energy distributions (SEDs) from UV FIR characterise emission-line properties. Following systematic comparison approach, infer AGN accretion, obscuration, host galaxy...
Spectral features from PAH molecules observed in the mid-IR range are typically used to infer amount of recent and ongoing star formation (SF) on kpc scales around AGN where more traditional methods fail. This assumes that excited predominantly by SF. With current ground-based telescopes upcoming JWST, much smaller spatial can be probed we aim at testing this assumption few tens hundreds pc. For that, spatially map emitted 11.3{\mu}m surface flux as a function distance 0.4-4 arcsec centre 28...
Abstract We investigate the torus size–luminosity relation of Type 1 active galactic nuclei (AGNs) based on reverberation-mapping analysis using light curves optical continuum and IR obtained with W1 W2 bands Wide-field Infrared Survey Explorer survey. The final sample consists 446 416 AGNs, respectively, for W1- W2-band curves, covering a large dynamic range bolometric luminosity from 10 43.4 to 47.6 erg s −1 , which show reliable lag measurements our quality assessment analysis. After...
We present results on a systematic study of flux variability hourly time-scales in large sample active galactic nuclei (AGN) the 3-79 keV band using data from Nuclear Spectroscopic Telescope Array. Our consists 4 BL Lac objects (BL Lacs), 3 flat spectrum radio quasars (FSRQs) 24 Seyfert 1, 42 2 and 8 narrow line 1 (NLSy1) galaxies. find that band, about 65% sources our show significant variations time scales. Using Mann-Whitney U-test Kolmogorov-Smirnov test, we no difference behaviour...
Abstract The broad-line region (BLR) size–luminosity relation has paramount importance for estimating the mass of black holes in active galactic nuclei (AGNs). Traditionally, size H β BLR is often estimated from optical continuum luminosity at 5100 Å, while α and its correlation with much less constrained. As a part Seoul National University AGN Monitoring Project, which provides 6 yr photometric spectroscopic monitoring data, we present our measurements lags high-luminosity AGNs. Combined...
We present results from a high cadence multi-wavelength observational campaign of the enigmatic changing look AGN 1ES 1927+654 May 2022- April 2024, coincident with an unprecedented radio flare (an increase in flux by factor $\sim 60$ over few months) and emergence spatially resolved jet at $0.1-0.3$ pc scales (Meyer et al. 2024). Companion work has also detected recurrent quasi-periodic oscillation (QPO) $2-10$ keV band increasing frequency ($1-2$ mHz) same period (Masterson al., 2025)....
Abstract We present velocity-resolved reverberation lags of H β for 20 active galactic nuclei (AGNs) from the Seoul National University AGN Monitoring Project. detect unambiguous structures in 12 AGNs, among which eight objects exhibit symmetric structures, two show inflow-like characteristics, and display outflow-like signatures. For we successfully measure different years, revealing evidence evolving broad-line region (BLR) kinematics. By combining our sample with literature lags, find...
We present measurements of the spectral properties for a total 526,265 quasars, out which 63% have continuum S/N$>3$ pixel$^{-1}$, selected from fourteenth data release Sloan Digital Sky Survey (SDSS-DR14) quasar catalog. performed careful and homogeneous analysis SDSS spectra these sources, to estimate line several emission lines such as H${\alpha}$, H${\beta}$, H${\gamma}$, Mg \textsc{ii}, C \textsc{iii]}, \textsc{iv} Ly${\alpha}$. From derived parameters, we estimated single-epoch virial...
We used the data from Fermi Gamma-ray Space Telescope to characterise {\gamma}-ray flux variability of blazars on month-like time scales. Our sample consists 1120 which 481 are flat spectrum radio quasars (FSRQs) and 639 BL Lac objects (BL Lacs). generated monthly binned light curves our for a period approximately nine years 2008 August 2017 December quantified by using excess variance (F_var). On scales, 371/481 FSRQs variable ( 80%), while only about 50% (304/639) Lacs variable. This...
Reverberation mapping (RM) estimates the size and kinematics of broad-line regions (BLR) in quasars type I AGNs. It yields size–luminosity relation to make QSOs standard cosmological candles, mass–luminosity study evolution black holes galaxies. The accuracy these relations is limited by unknown geometry BLR clouds distribution velocities. We analyse independent structure constraints given super-resolving differential interferometry. developed a three-dimensional model compute all...
We studied optical variability (OV) of a large sample narrow-line Seyfert 1 (NLSy1) and broad-line (BLSy1) galaxies with z<0.8 to investigate any differences in their OV properties. Using archival V-band light curves from the Catalina Real Time Transient Survey that span 5-9 years modeling them using damped random walk, we estimated amplitude variability. found NLSy1 as class show lower than counterparts. In both BLSy1 galaxies, radio-loud sources are have higher radio-quiet sources....
ABSTRACT Blazars show optical and γ-ray flux variations that are generally correlated, although there exceptions. Here we present anomalous behaviour seen in the blazar 3C 454.3 based on an analysis of quasi-simultaneous data at optical, ultraviolet, X-ray, energies, spanning about 9 yr from 2008 August to 2017 February. We have identified four time intervals (epochs), A, B, D, E, when source showed large-amplitude flares. In epochs A B flares while D E corresponding γ-rays weak or absent....
Abstract We investigate the connection between ionized gas outflows and star formation activity using a large sample of type 1 2 active galactic nuclei (AGNs) with far-infrared detections or rate (SFR) estimates. The strength outflows, measured by velocity dispersion shift [O iii ] emission line, clearly shows correlation SFR. specific (sSFR) indicates that AGNs stronger are hosted galaxies higher Compared star-forming in main sequence, both show sSFRs similar to non-AGN galaxies, indicating...
Abstract We explore the relationship between ionized gas outflows and radio activity using a sample of ∼6000 active galactic nuclei (AGNs) at z < 0.4 with kinematical measurement based on <?CDATA $\left[{\rm{O}}\,{\rm\small{III}}\right]$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close="]" open="["> <mml:mrow> <mml:mi mathvariant="normal">O</mml:mi> <mml:mspace width="0.25em" /> mathsize="small" mathvariant="normal">III</mml:mi> </mml:mrow>...
Abstract The gamma-ray blazar OJ 287 was in a high activity state during 2015 December–2016 February. Coinciding with this brightness state, we observed source for photometry on 40 nights R -band and polarimetry nine epochs UBV RI bands. During the period of our observations, varied from 13.20 ± 0.04 mag to 14.98 degree polarization ( P ) fluctuated between 6.0% 0.3% 28.3% 0.8% -band. Focusing intranight optical variability (INOV), find duty cycle about 71% using χ 2 -statistics, similar...
The time delay between flux variations in different wavelength bands can be used to probe the inner regions of active galactic nuclei (AGN). Here, we present first measurements optical and near-infrared (NIR) H0507+164, a nearby Seyfert 1.5 galaxy at z = 0.018. observations V -band NIR J, H Ks carried over 35 epochs during period October 2016 April 2017 were estimate radius dusty torus. From careful reduction analysis data using cross-correlation techniques, found delayed responses light...
Abstract We present a systematic study of ionized gas outflows based on the velocity shift and dispersion [O iii ] λ 5007 emission line using sample ∼5000 Type 1 AGNs at z < 0.3 selected from Sloan Digital Sky Survey. This analysis is supplemented by kinematics 2 Woo et al. For majority (i.e., ∼89%), profile best represented double Gaussian model, presenting kinematic signature nonvirial motion. Blueshifted more frequently detected than redshifted factor 3.6 in AGNs, while ratio between...
We present a detailed comparative systematic study using sample of 221 Narrow-line Seyfert 1 (NLSy1) galaxies in comparison to redshift matched 154 Broad-line (BLSy1) based on their observations ROSAT and/or XMM-Newton telescopes soft X-ray band (0.1-2.0 keV). A homogeneous analysis is carried out estimate photon indices ($\Gamma^{s}_{X}$) and its correlations with other parameters nuclear activities such as Eddington ratios (R$_\mathrm{Edd}$), bolometric luminosities (L$_\mathrm{bol}$),...
We present long term optical and near infrared flux variability analysis of 37 blazars detected in the $\gamma$-ray band by {\it Fermi Gamma-Ray Space Telescope}. Among them, 30 are flat spectrum radio quasars (FSRQs) 7 BL Lac objects (BL Lacs). The photometric data (BVR) (JK) bands were from Small Moderate Aperture Research Telescope System acquired between 2008$-$2018. From cross-correlation light curves at different wavelengths, we did not find significant time delays variations except...