相关论文: A rapid occultation event in NGC 3227

We have analyzed survey and pointed \ros PSPC observations of the Seyfert galaxy NGC 3227. Large amplitude X-ray variability is detected, with a factor $\sim$ 15 change in count rate within about 3 years. Smaller changes are seen on the…

(Abridged) We present the results from {\it ASCA} observations of NGC 3227 along with those from a {\it ROSAT} observation. The 0.6--10 keV continuum is consistent with a powerlaw with $\Gamma \sim 1.6$, flatter than that typically observed…

Here we present the long-term optical spectral monitoring of a changing-look active galactic nuclei (AGN) NGC 3516 that covers 22 years (from 1996 to 2018). We explore a variability in the broad lines and continuum, finding that the…

The Seyfert-1 galaxy NGC 3516 has undergone major spectral changes in recent years. In 2017 we obtained Chandra, NuSTAR, and Swift observations during its new low-flux state. Using these observations we model the spectral energy…

We present an analysis of recent XMM-Newton and HST archive data of the ultraluminous X-ray source NGC 1313 X-2. Quasi-simultaneous observations taken with XMM-Newton, HST and VLT allow us to study both the X-ray light curve and its…

We report the discovery of a new ultraluminous X-ray source (ULX) associated with a globular cluster in the elliptical galaxy NGC 4649. The X-ray source was initially detected with a luminosity below 5 x 10^38 erg/s, but in subsequent…

NGC 1313 X-2 is one of the few known pulsating ultraluminous X-ray sources (PULXs), and so is thought to contain a neutron star that accretes at highly super-Eddington rates. However, the physics of this accretion remains to be determined.…

In this work, we study the X-ray spectral and temporal properties of an ultraluminous X-ray source (ULX) in NGC 628 by using multi-epoch archival X-ray data. The physical parameters were estimated in each epoch in order to constrain the…

We present an analysis of historical multi-wavelength emission of the Changing Look (CL) Active Galactic Nucleus (AGN) in NGC 2992, covering epochs ranging from 1978 to 2021, as well as new X-ray and optical spectra. The galaxy presents…

We report the results of a one year Swift X-ray/UV/optical programme monitoring the dwarf Seyfert nucleus in NGC 4395 in 2008-2009. The UV/optical flux from the nucleus was found to vary dramatically over the monitoring period, with a…

We present results from the major coordinated X-ray observing program on the ULX NGC 1313 X-1 performed in 2017, combining $XMM$-$Newton$, $Chandra$ and $NuSTAR$, focusing on the evolution of the broadband ($\sim$0.3-30.0 keV) continuum…

We present results of a 100 ks XMM observation of the Seyfert 1.5 NGC 3227. Our best-fit broadband model to the pn spectrum consists of a moderately flat (photon index 1.57) hard X-ray power-law absorbed by cold gas with N_H = 3 * 10^21…

NGC 7582 (z = 0.005264; D = 22.5 Mpc) is a highly variable, changing-look AGN. In this work, we explore the X-ray properties of this source using XMM-Newton and NuSTAR archival observations in the 3-40 keV range, from 2001 to 2016. NGC 7582…

We present the results of an intensive ground-based spectrophotometric monitoring campaign of the Seyfert galaxy NGC~4151 for a period of over two months, with a typical temporal resolution of one day. Light curves for four optical…

We present a complete spectral analysis of an XMM-Newton and Chandra campaign of the obscured AGN in NGC 4507, consisting of six observations spanning a period of six months, ranging from June 2010 to December 2010. We detect strong…

We have analyzed the two longest (elapsed time > 3 days) BeppoSAX observations of the X-ray brightest Seyfert galaxy, NGC 4151, to search for spectral variability on time-scales from a few tens of ksec to years. We found in both cases…

We present a spectral and temporal analysis of XMM-Newton data from a sample of six galaxies (NGC 3783, Mrk 279, Mrk 766, NGC 3227, NGC 7314, and NGC 3516). Using the hardness-ratio curves, we identify time-intervals in which clouds are…

We present the analysis of the X-ray variability and spectral timing properties of the ultraluminous X-ray source (ULX) NGC 5408 X-1, one of the most variable ULXs known so far. The variability properties are used as a diagnostic of the…

Using simultaneous Very Long Baseline Array and Neil Gehrels Swift Observatory X-ray Telescope observations of the active galactic nucleus (AGN) in NGC 2992 over a six-month observing campaign, we observed a large drop in core 5 cm radio…

We report the detection of flaring events in NGC 4395 ULX1, a nearby ultraluminous X-ray source (ULX), for the first time, using recent XMM-NEWTON observations. The flaring episodes are spectrally harder than the steady emission intervals,…