Related papers: No missing flare in OJ~287
Episodically accreting black holes are thought to produce flares when a chunk of particles is accelerated to high velocity near the black hole horizon. This also seems to be the case of Sagittarius A* in the Galactic Center, where the…
We are carrying out a dense monitoring of the blazar OJ 287 with Swift since late 2015 as part of our project MOMO (Multiwavelength Observations and Modeling of OJ 287). This is the densest existing monitoring of OJ 287 involving X-ray and…
Changing-look quasars are a recently identified class of active galaxies in which the strong UV continuum and/or broad optical hydrogen emission lines associated with unobscured quasars either appear or disappear on timescales of months to…
In February 2017 the blazar OJ287, one of the best super-massive binary-black-hole-system candidates, was detected for the first time at very high energies (VHEs; E>100GeV) with the ground-based gamma-ray observatory VERITAS. Very high…
Quasi-periodic eruptions (QPEs) are rapid, recurring X-ray bursts from supermassive black holes, believed to result from interactions between accretion disks and surrounding matter. The galaxy SDSS1335+0728, previously stable for two…
We report the results from our study of the blazar S5 1803+784 carried out using the quasi-simultaneous $B$, $V$, $R$, and $I$ observations from May 2020 to July 2021 on 122 nights. Our observing campaign detected the historically bright…
In strong stellar and solar flares flare loops typically appear during the decay phase, providing an additional contribution to the flare emission and, possibly, obscuring the flare emission. Super-flares, common in active, cool stars,…
Blazars can be detected from very large distances due to their high luminosity. However, the detection of $\gamma$-ray emission of blazars beyond $z=3$ has only been confirmed for a small number of sources. Such observations probe the…
The ultraviolet/optical continuum of quasars is thought to be from an accretion flow around a supermassive black hole, and it dominates the radiative output of quasars. However, the nature of this emission, often called the Big Blue Bump,…
We present a noteworthy transient AT 2021aeuk exhibiting three distinct optical flares between 2018 and 2023. It is hosted in a radio-loud narrow-line Seyfert 1 (NLSy1) galaxy, with an optical image showing a minor tidal morphology and a…
Optical transient surveys have led to the discovery of dozens of stellar tidal disruption events (TDEs) by massive black hole in the centers of galaxies. Despite extensive searches, X-ray follow-up observations have produced no or only weak…
We present the results of a weekly monitoring of the new black hole candidate X-ray binary MAXI J1631-472 carried out with the MeerKAT radio interferometer, the Neil Gehrels Swift Observatory, and the Monitor of All-sky X-ray Image (MAXI)…
The recent detection of possible neutrino emission from the blazar TXS 0506+056 was the first high-energy neutrino associated with an astrophysical source, making this special type of active galaxies promising neutrino emitters. The fact…
We report the discovery of an anomalous flare in a bright blazar, namely, PKS 0208-512, one of the targets of the Yale/SMARTS optical-near-infrared (OIR) monitoring program of Fermi blazars. We identify three intervals during which PKS…
Swift J1357.2-0933 is a black hole transient of particular interest due to the optical, recurrent dips found during its first two outbursts (in 2011 and 2017), with no obvious X-ray equivalent. We present fast optical photometry during its…
We report periodic oscillations in the 15-year long optical light curve of the gravitationally lensed quasar QJ0158-4325. The signal is enhanced during a high magnification microlensing event undergone by the fainter lensed image of the…
Filament eruptions often result in flares and coronal mass ejections (CMEs). Most studies attribute the filament eruptions to their instabilities or magnetic reconnection. In this study, we report a unique observation of a filament eruption…
CTA 102, classified as a flat spectrum radio quasar at z=1.037, produced exceptionally bright optical flare in 2012 September. Following Fermi-LAT detection of enhanced gamma-ray activity, we densely monitored this source in the optical and…
This work presents comprehensive multi-frequency radio monitoring of the black hole low-mass X-ray binary Swift J1727.8$-$1613, which underwent its first recorded outburst after its discovery in August 2023. Through a considerable community…
Supermassive binary black holes (SMBBHs) are laboratories par excellence for relativistic effects, including precession effects in the Kerr metric and the emission of gravitational waves. Binaries form in the course of galaxy mergers, and…