Related papers: The Seyfert Galaxy NGC 6814 -- a highly variable X…

We present a study of optical, UV and X-ray light curves of the nearby changing look active galactic nucleus in the galaxy NGC 1566 obtained with the Neil Gehrels Swift Observatory and the MASTER Global Robotic Network over the period 2007…

Evidence is emerging that the luminous X-ray sources in the cores of globular clusters may often consist of, or perhaps even as a class be dominated by, ultracompact (P < 1 hr) binary stars. To the two such systems already known, in NGC…

We report on daily monitoring of the Seyfert galaxy NGC 7469, around 95 GHz and 143 GHz, with the IRAM 30 m radio telescope, and with the Swift X-Ray and UV/Optical telescopes, over an overlapping period of 45 days. The source was observed…

We report on strong X-ray variability and the Fe K band spectrum of the Seyfert galaxy IRAS 18325-5926 obtained from the 2001 XMM-Newton EPIC pn observation of a 120 ks duration. While the X-ray source is highly variable, the 8-10 keV band…

We present the first result of a programme to search for large flux variations in the X-ray sources of the XMM Serendipitous Survey compared to previous ROSAT observations. An increase in X-ray flux by a factor >10 was discovered from the…

Using archival RXTE data, we show that the ultracompact X-ray binary in NGC 1851 exhibits large amplitude X-ray flux varations of more than a factor of 10 on timescales of days to weeks and undergoes sustained periods of months where the…

Timing analysis of a ~95 ks long XMM-Newton observation of the Seyfert 1 galaxy MCG-6-30-15 is presented. Model-independent tools have been used with the intent of resolving the different components that produce the observed flux and…

We report results from an 18-day ROSAT HRI monitoring campaign on the ultrasoft Narrow-Line Seyfert 1 (NLS1) class quasar PHL 1092. This luminous, radio-quiet quasar showed strong X-ray variability in a short ROSAT PSPC observation, and…

We present the results of photometric and spectroscopic monitoring campaigns of the changing look AGN NGC 3516 carried out in 2018 to 2020 covering the wavelength range from the X-ray to the optical. The facilities included the telescopes…

We report the discovery of eight X-ray sources with periodic variability in 487 ks of observations of the Galactic center with Chandra. The sources are identified from a sample of 285 objects detected with 100-4200 net counts. Their periods…

Context. Obscuration events caused by outflowing clumps or streams of high column density, low ionisation gas, heavily absorbing the X-ray continuum, have been witnessed in a number of Seyfert galaxies. Aims. We report on the X-ray…

We present the light curves obtained during an eight-year program of optical spectroscopic monitoring of nine Seyfert 1 galaxies: 3C 120, Akn 120, Mrk 79, Mrk 110, Mrk 335, Mrk 509, Mrk 590, Mrk 704, and Mrk 817. All objects show…

We report on the unveiling of the nature of the unidentified X-ray source 3XMM J005450.3-373849 as a Seyfert-2 galaxy located behind the spiral galaxy NGC 300 using Hubble Space Telescope data, new spectroscopic Gemini observations and…

We present a spectral and spatial analysis of the nuclear and circumnuclear X-ray emission of the prominent southern starburst/Seyfert galaxy NGC 1365. To describe the X-ray spectrum of the core source, we favour a two-component model…

We have characterized the energy-dependent X-ray variability properties of the Seyfert~1 galaxy NGC 3783 using archival XMM-Newton and Rossi X-ray Timing Explorer data. The high-frequency fluctuation power spectral density function (PSD)…

We report the discovery of a flaring X-ray source in the globular cluster NGC 6540, obtained during the EXTraS project devoted to a systematic search for variability in archival data of the XMM-Newton satellite. The source had a quiescent…

RE J2248-511 is one of only 14 non-blazar AGN detected in the far ultraviolet by the ROSAT Wide Field Camera implying a large ultrasoft X-ray flux. This soft X-ray excess is strongly variable on year timescales, a common property of Narrow…

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…

An XMM-Newton observation of the luminous Seyfert galaxy PG1211+143 in 2001 revealed the first clear evidence for a highly ionised high speed wind (in a non-BAL AGN), with a velocity of v~0.09c based on the identification of blue-shifted…

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…