Related papers: Rapid Gamma-ray variability of NGC 1275

We present our photometric monitoring of a flat spectrum radio quasar (FSRQ) 3C 454.3 at Yunnan observatories from 2006 to 2011. We find that the optical color of 3C 454.3 shows obvious redder-when-brighter trend, which reaches a saturation…

In September 2016, the microquasar Cygnus X-3 underwent a giant radio flare, which was monitored for 6 days with the Medicina Radio Astronomical Station and the Sardinia Radio Telescope. Long observations were performed in order to follow…

Magnetars are slowly-rotating neutron stars with extremely strong magnetic fields ($10^{13-15}$ G), episodically emitting $\sim100$ ms long X-ray bursts with energies of $\sim10^{40-41}$ erg. Rarely, they produce extremely bright, energetic…

Intrigued by recent high-energy study results for nearby galaxies with gamma-ray emission and in particular NGC~1068 that has been detected as a neutrino-emitting source by the IceCube Neutrino Observatory, we conduct detailed analysis of…

We studied the evolution of the X-ray and gamma-ray spectra of the Crab pulsar utilizing the 11-year observations from the Rossi X-ray Timing Explorer (RXTE) and 9-year observations from the Fermi Gamma-ray Space Telescope (FGST). By…

We report on the discovery of \geq 100 MeV {\gamma} rays from the binary system PSR B1259-63/LS 2883 using the Large Area Telescope (LAT) on board Fermi. The system comprises a radio pulsar in orbit around a Be star. We report on LAT…

We present results of spectrometric studies based on the observations of very strong 3C 279 flares in high and very-high-energy bands and discuss their implications regarding the origin of radiation mechanisms. The FSRQ 3C 279 (z=0.536) is…

The solar disk is a bright gamma-ray source. Surprisingly, its flux is about one order of magnitude higher than predicted. As a first step toward understanding the physical origin of this discrepancy, we perform a new analysis in 1-100 GeV…

We report hard X-ray and gamma-ray observations of the impulsive phase of the SOL2017-09-06T11:55 X9.3 solar flare. We focus on a high-energy part of the spectrum, >100 keV, and perform time resolved spectral analysis for a portion of the…

We report the first detection of flux variability in the most luminous X-ray source in the southern ring of the Cartwheel galaxy. XMM--Newton data show that the luminosity has varied over a timescale of six months from L[0.5-10] keV \~1.3…

Optical and near-infrared photometry, optical spectroscopy, and soft X-ray and UV monitoring of the changing-look active galactic nucleus NGC 2617 show that it continues to have the appearance of a type-1 Seyfert galaxy. An optical light…

The prompt emission mechanism of gamma-ray bursts (GRBs) is still unclear, and the time-resolved spectral analysis of GRBs is a powerful tool for studying their underlying physical processes. We performed a detailed time-resolved spectral…

We present the main results of a deep timing analysis (in the 0.2-10 keV energy band) of the bright Seyfert-1 galaxy MCG-6-30-15 performed on XMM-Newton data. The light-curves and hardness ratios show that the source has large flux and…

The observations of the exceptionally bright gamma-ray burst (GRB) 130427A by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope provide constraints on the nature of such unique astrophysical sources. GRB 130427A had the…

Characterisation of the long-term variations in the broad line region in a luminous blazar, where Comptonisation of broad-line emission within a relativistic jet is the standard scenario for production of gamma-ray emission that dominates…

Optical Transients from gamma-ray burst sources, in addition to offering a distance determination, convey important information on the physics of the emission mechanism, and perhaps also about the underlying energy source. As the gamma-ray…

Between 1996 and 2002, we have carried out a spectral monitoring program for the Seyfert galaxy NGC 5548. High quality spectra (S/N>50), covering the spectral range (4000-7500)AA were obtained with the 6 m and 1 m telescopes of SAO (Russia)…

The Compton Gamma-Ray Observatory (CGRO) experiments EGRET and COMPTEL observed the Virgo sky region continuously for 7 weeks between December 10, 1996 and January 28, 1997. The prominent quasar 3C~273 was found to be the brightest source…

BL Lacertae had undergone a series of historical high flux activity over a year, from August 2020 in the optical to VHE $\gamma$-rays. In this paper, we report on optical flux and spectral variability of the first historical maxima outburst…

An analysis of the X-ray variability of the low luminosity Seyfert nucleus NGC 4395, based on a long XMM-Newton observation, is presented. The power spectrum shows a clear break from a flat spectrum (alpha ~ 1) to a steeper spectrum (alpha…