Related papers: Brightness and colour variability in NLSy1s
The well known relationship between metallicity and luminosity in AGN is addressed by introducing new metallicity measurements (based on the method of Hamann & Ferland 1993; HF93) for a sample of narrow-line Seyfert 1 (NLS1) galaxies. Our…
We present preliminary results on the variability properties of AGN above 20 keV in order to show the potential of the INTEGRAL IBIS/ISGRI and Swift/BAT instruments for hard X-ray timing analysis of AGN. The 15-50 keV light curves of 36 AGN…
Narrow-line Seyfert 1 (NLS1) galaxies are a type of active galactic nuclei (AGN) that were originally classified as sources with little to no radio emission. Although the class is rather unified from an optical perspective, their radio…
We made simultaneous single-dish and very long baseline interferometer (VLBI) observations of a narrow-line Seyfert 1 galaxy (NLS1) 1H 0323+342, showing gamma-ray activity revealed by Fermi/LAT observations. We found significant variation…
We investigate statistical and individual astrophysical properties of active galactic nuclei (AGNs), such as parsec-scale flux density, core dominance, angular and linear sizes, maximum observed brightness temperatures of VLBI core…
We present the second XMM-Newton observation (85 ks) of the narrow-line Seyfert 1 galaxy (NLS1) I Zw 1 and describe its mean spectral and timing characteristics. On average, I Zw 1 is ~35 per cent dimmer in 2005 than in the shorter (20 ks)…
The detection of significant $\gamma$-ray emission from radio-loud narrow line Seyfert 1 (NLSy1s) galaxies enables us to study jets in environments different than those in blazars. However, due to the small number of known $\gamma$-ray…
Variable sources probe a wide range of astrophysical phenomena. We present a catalog of over ten million variable source candidates found in Data Release 1 (DR1) of the Zwicky Transient Facility (ZTF). We perform a periodicity search up to…
We have collected an heterogeneous sample of galaxies at redshifts 0.001<z<3.35 with the aim of exploring the evolution of the physical parameters and of the element abundances calculated by modelling the observed spectra. The evolution…
Until recently, relativistic jets were ubiquitously found to be launched from giant elliptical galaxies. However, the detection by the Fermi-LAT of gamma-ray emission from radio-loud narrow-line Seyfert 1 (RL-NLSy1) galaxies raised doubts…
We present long term optical variability studies of bright X-ray sources in four nearby elliptical galaxies with {\it Chandra} Advanced CCD Imaging Spectrometer array (ACIS-S) and {\it Hubble Space Telescope (HST)} Advanced Camera for…
We present the observational results of multi-colour optical monitoring of eight red blazars from 2003 September to 2004 February. The aim of our monitoring is to investigate the spectral variability as well as the flux variations at short…
The narrow line Seyfert 1 (NLS1) IRAS 13224-3809 is the most X-ray variable active galactic nucleus (AGN), exhibiting 0.3-10 keV flux changes of over an order of magnitude within an hour. We report on the results of the 1.5 Ms 2016…
Studying large-scale environments of narrow-line Seyfert 1 (NLS1) galaxies gives a new perspective on their properties, particularly their radio loudness. The large-scale environment is believed to have an impact on the evolution and…
We have used the ROSAT Bright Source Catalogue to extract a complete sample of sources selected in the band from 0.1-0.4 keV. This 1/4 keV-selected sample is comprised of 54 Seyfert galaxies, 25 BL Lacertae objects, 4 clusters and 27…
The origin of the radio emission in active galactic nuclei (AGN) is still debated. Multiple physical mechanisms can contribute to the spectrum at these frequencies, including relativistic jets, the jet base, outflows, star formation, and…
The Zwicky Transient Facility (ZTF) is performing a three-day cadence survey of the visible Northern sky (~3$\pi$). The transient candidates found in this survey are announced via public alerts. As a supplementary product ZTF is also…
We present results from RXTE data obtained during a systematic monitoring program of four Seyfert galaxies (NGC5548, NGC5506, MCG-6-30-15 and NGC4051). We studied the variability of three hardness ratios derived from the light curves in…
We report the results of optical monitoring for a sample of 11 blazars including 10 BL Lacs and 1 Flat Spectrum Radio Quasar (FSRQ). We have measured the multiband optical flux and colour variations in these blazars on intra-day and…
Narrow-line Seyfert 1 galaxies (NLSy1) are intriguing due to their extreme continuum and emission line properties which are not yet well understood. This paper is motivated by the recent suggestion that NLSy1 galaxies might be young active…