A5086358001- Astrophysics and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Astrophysical Phenomena and Observations
- Neutrino Physics Research
- Astronomy and Astrophysical Research
- Astronomical Observations and Instrumentation
- Dark Matter and Cosmic Phenomena
- Stellar, planetary, and galactic studies
- Galaxies: Formation, Evolution, Phenomena
- Gamma-ray bursts and supernovae
- Solar and Space Plasma Dynamics
- Astrophysics and Star Formation Studies
- Gyrotron and Vacuum Electronics Research
- Particle Accelerators and Free-Electron Lasers
- Geophysics and Gravity Measurements
- Calibration and Measurement Techniques
- Adaptive optics and wavefront sensing
- Pulsars and Gravitational Waves Research
- Precipitation Measurement and Analysis
- High-pressure geophysics and materials
- Particle Detector Development and Performance
- Astro and Planetary Science
- Radio Wave Propagation Studies
- Ionosphere and magnetosphere dynamics
- Particle physics theoretical and experimental studies
Institute of Astronomy and National Astronomical Observatory
2013-2023
Turku Centre for Computer Science
2023
University of Turku
2023
Bulgarian Academy of Sciences
1999-2015
University of Alabama
2002-2005
Osservatorio Astronomico di Padova
2002
[Abridged] We have been exploring a spectroscopic unification for all known types of broad line emitting AGN. The 4D Eigenvector 1 (4DE1) parameter space shows promise as capable organizing quasar diversity on sequence primarily governed by Eddington ratio. This paper considers the role CIV 1549 measures with special emphasis shift principal 4DE1 diagnostic. use HST archival spectra 130 sources S/N high enough to permit reliable component (BC) measures. find BC profile blueshift that is...
Since the launch of Fermi satellite, BL Lacertae has been moderately active at gamma-rays and optical frequencies until May 2011, when source started a series strong flares. The exceptional sampling achieved by GLAST-AGILE Support Program (GASP) Whole Earth Blazar Telescope (WEBT) in collaboration with Steward Observatory allows us to perform detailed comparison daily gamma-ray observations Fermi. Discrete correlation analysis between emission reveals time lag 0 +- 1 d, which suggests...
We present a spectral atlas of the Hβ region for 215 type 1 AGNs (luminous Seyfert 1/radio galaxy nuclei and low-z quasars) up to z ≈ 0.8. Line profiles measures were derived from database intermediate resolution spectra (R ≳ 1000) with average continuum level S/N ratio ≈30. Parameters including rest frame equivalent width FWHM are provided Fe IIopt blend at λ4570, Hβ, He II λ4686, [O III] λλ4959, 5007 emission lines. extract clean broad component provide wavelength measurements 0, 1/4, 1/2,...
Recent work has shown that it is possible to systematize quasar spectral diversity in a parameter space called "Eigenvector 1" (E1). We present median active galactic nucleus (AGN) spectra for fixed regions of the E1 (optical) [FWHM(Hβ) vs. equivalent width ratio R = W(Fe II λ4570)/W(Hβ)]. Comparison shows considerable differences. suggest an E1-driven approach median/average emphasizes significant differences between AGNs and offers more insights into AGN physics than single-population...
We investigate the radial velocity difference between [O III] λλ4959, 5007 and Hβ lines for a sample of ≈200 low-redshift active galactic nuclei. identify seven objects showing an λ5007 blueshift relative to with amplitude larger than 250 km s-1 ("blue outliers"). These line shifts are found in sources where broad high-ionization (e.g., C IV λ1549) also show large systematic blueshift. Such blueshifts occur only population A region Eigenvector 1 parameter domain (that contains narrow-line...
Context. The quasar 3C 279 is among the most extreme blazars in terms of luminosity and variability flux at all wavebands. Its variations polarization are quite complex therefore require intensive monitoring observations multiple wavebands to characterise interpret observed changes.
We compare broad emission line profiles and estimate ratios for all major lines between Lyα Hβ in a sample of six quasars.The sources were chosen with two criteria mind: the existence high quality optical UV spectra as well possibility to spectroscopic diversity 4D Eigenvector 1 context (4DE1).In latter sense each source occupies region (bin) FWHM(Hβ) vs. Fe ii opt strength plane that is significantly different from others.High S/N are used templates modeling other (Lyα, Civλ1549, Heiiλ1640,...
We report on 18 months of multiwavelength observations the blazar 3C 454.3 (Crazy Diamond) carried out in July 2007-January 2009. show results AGILE campaigns which took place May-June 2008, July-August and October 2008-January During May 2009 period, source average flux was highly variable, from an gamma-ray F(E>100MeV) > 200E-8 ph/cm2/s to F(E>100MeV)~80E-8 The spectrum between 100 MeV 1 GeV can be fit by a simple power law (Gamma_GRID ~ 2.0 2.2). Only 3-sigma upper limits derived 20-60...
Abstract In an effort to locate the sites of emission at different frequencies and physical processes causing variability in blazar jets, we have obtained high time-resolution observations BL Lacertae over a wide wavelength range: with Transiting Exoplanet Survey Satellite (TESS) 6000–10000 Å 2 minute cadence; Neil Gehrels Swift satellite optical, UV, X-ray bands; Nuclear Spectroscopic Telescope Array hard Fermi Large Area γ -ray energies; Whole Earth Blazar for measurement optical flux...
We report the X-ray polarization properties of high-synchrotron-peaked (HSP) blazar PKS 2155−304 based on observations with Imaging Polarimetry Explorer (IXPE). observed source between Oct 27 and Nov 7, 2023. also conducted an extensive contemporaneous multiwavelength (MW) campaign. find that during first half ( T 1 ) IXPE pointing, exhibited highest degree detected for HSP thus far, (30.7 ± 2.0)%; this dropped to (15.3 2.1)% second 2 ). The angle remained stable pointing at 129.4° ±1.8°...
We present composite UV spectra for low-redshift type 1 active galactic nuclei binned to exploit the information content of eigenvector (E1) parameter space. Composite show high enough S/N and spectral resolution permit a decomposition C IV λ1549 line profile: one strongest high-ionization lines (HILs), fundamental in defining E1 The simplest into narrow-line region (NLR), broad-line (BLR), very broad (VBLR) components suggests that different have an analog Hβ with two major exceptions. VBLR...
<i>Context. <i/>Since 2001, the radio quasar 3C 454.3 has undergone a period of high optical activity, culminating in brightest state ever observed, during 2004-2005 outburst. The Whole Earth Blazar Telescope (WEBT) consortium carried out several multifrequency campaigns to follow source behaviour.<i>Aims. <i/>The GLAST-AGILE Support Program (GASP) was born from WEBT provide long-term continuous optical-to-radio monitoring sample <i>γ<i/>-loud blazars, operation AGILE and GLAST (now known as...
We have measured multiband optical flux and colour variations for a sample of 12 low-energy peaked blazars (LBLs) on short, day-to-month, time-scales. Our contains six BL Lacertae objects (BL Lacs) flat spectrum radio quasars (FSRQs). These photometric observations, made during 2008 September to 2009 June, used five telescopes, one in India four Bulgaria. detected short-term 11 these variability eight them. data indicate that (3C 66A, AO 0235+164, S5 0716+714, PKS 0735+178, OJ 287 3C 454.3)...
We report results from a 1 week multi-wavelength campaign to monitor the BL Lac object S5 0716+714 (on December 9-16, 2009). In radio bands source shows rapid (~ (0.5-1.5) day) intra-day variability with peak amplitudes of up ~ 10 %. The at 2.8 cm leads by about day 6 and 11 cm. This time lag more variations suggests an intrinsic contribution source's intraday cm, while interstellar scintillation (ISS) seems predominate. Large quasi-sinusoidal 0.8 mag were detected in V, R I-bands. X-ray...
Context. The international whole earth blazar telescope (WEBT) consortium planned and carried out three days of intensive micro-variability observations S5 0716+714 from February 22, 2009 to 25, 2009. This object was chosen due its bright apparent magnitude range, high declination, very large duty cycle for micro-variations. Aims. We report here on the long continuous optical light curve obtained during multi-site observing campaign which Blazar showed almost constant variability over a 0.5...
We examine the 2008-2016 $γ$-ray and optical light curves of three bright BL Lac objects, 0716+714, MRK 421, Lac, which exhibit large structured variability. searched for periodicities by using a fully Bayesian approach. For two out sources investigated no significant periodic variability was found. In case we detected periodicity ~ 680 days. Although signal related to this is modest, coincidence periods in both gamma bands indicative physical relevance. Considering previous literature...
We present our optical photometric observations of three TeV blazars, PKS 1510-089, PG 1553+113 and Mrk 501 taken using two telescopes in India, one Bulgaria, Greece Serbia during 2012 - 2014. These covered a total 95 nights with 202 B filter frames, 247 images V band, 817 R band while 229 were the I filter. This work is focused on multi-band flux colour variability studies these blazars diverse timescales which are useful understanding emission mechanisms. studied characteristics above...
After several years of quiescence, the blazar CTA 102 underwent an exceptional outburst in 2012 September–October. The flare was tracked from γ-ray to near-infrared (NIR) frequencies, including Fermi and Swift data as well photometric polarimetric observatories. An intensive Glast-Agile support programme Whole Earth Blazar Telescope (GASP–WEBT) collaboration campaign optical NIR bands, with addition previously unpublished archival extension through fall 2015, allows comparison this previous...
We report the results of decade-long (2008-2018) $\gamma$-ray to 1 GHz radio monitoring blazar 3C 279, including GASP/WEBT, $\it{Fermi}$ and $\it{Swift}$ data, as well polarimetric spectroscopic data. The X-ray light curves correlate well, with no delay > 3 hours, implying general co-spatiality emission regions. $\gamma$-ray-optical flux-flux relation changes activity state, ranging from a linear more complex dependence. behaviour Stokes parameters at optical wavelengths, 43 VLBA images,...
ABSTRACT In 2021 BL Lacertae underwent an extraordinary activity phase, which was intensively followed by the Whole Earth Blazar Telescope (WEBT) Collaboration. We present WEBT optical data in BVRI bands acquired at 36 observatories around world. mid-2021 source showed its historical maximum, with R = 11.14. The light curves display many episodes of intraday variability, whose amplitude increases brightness, agreement a geometrical interpretation long-term flux behaviour. This is also...
ABSTRACT In this work, we report the presence of rapid intra-night optical variations in both flux and polarization blazar BL Lacertae during its unprecedented 2020–2021 high state brightness. The object showed significant variability some colour changes, but no firmly detectable time delays between bands. linear was also highly variable degree angle (electric vector angle). observed from several observatories throughout world, covering a total almost 300 h 66 nights. Based on our results,...
From October 2014 until now (about 10 years) we have done astronomical observations of the Gaia Alerts or Follow Up Network for Transients Objects (Gaia- FUN-TO). In 2013 organized our local cooperation Serbian-Bulgarian mini-network telescopes to get better results. Also, mentioned and investigations are in line with actual joint research SANU-BAN project astrometry fast variable objects from 2023 2025; Serbian Bulgarian Academies Sciences. Now, there 8 instruments at two sites Bulgaria (at...
Blazars are relativistic jet-dominated active galactic nuclei, whose emission in the optical region is mostly synchrotron nature and consequently polarized. We monitored several objects on night-to-night long-term time scales order to study their flux polarization variability. Our primary goal was variability of blazars its relation X-ray polarization, which had been measured for a number with newly introduced IXPE orbital observatory. Among we studied were BL Lacertae, S4 0954+65, S5...