Multi-pulsed GRB 190530A, detected by the GBM and LAT onboard Fermi, is the sixth most fluent GBM burst detected so far. This paper presents the timing, spectral, and polarimetric analysis of the prompt emission observed using AstroSat and Fermi to provide insight into the prompt emission radiation mechanisms. The time-integrated spectrum shows conclusive proof of two breaks due to peak energy and a second lower energy break. Time-integrated (55.43 ± 21.30 %) as well as time-resolved polarization measurements, made by the Cadmium Zinc Telluride Imager (CZTI) onboard AstroSat, show a hint of high degree of polarization. The presence of a hint of high degree of polarization and the values of low energy spectral index (αpt) do not run over the synchrotron limit for the first two pulses, supporting the synchrotron origin in an ordered magnetic field. However, during the third pulse, αpt exceeds the synchrotron line of death in few bins, and a thermal signature along with the synchrotron component in the time-resolved spectra is observed. Furthermore, we also report the earliest optical observations constraining afterglow polarization using the MASTER (P < 1.3 %) and the redshift measurement (z= 0.9386) obtained with the 10.4m GTC telescopes. The broadband afterglow can be described with a forward shock model for an ISM-like medium with a wide jet opening angle. We determine a circumburst density of n0 ∼ 7.41, kinetic energy EK ∼ 7.24 × 1054 erg, and radiated γ-ray energy Eγ, iso ∼ 6.05 × 1054 erg, respectively.

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Gamma-ray bursts (GRBs) are the most energetic and mysterious events in the Universe, which are observed in all ranges of electromagnetic spectrum. Most valuable results about physics of GRB are obtained by optical observations. GRBs are initially detected in gamma-rays with poor localization accuracy, and an optical counterpart should be found. The faster the counterpart is found, the more it can give to physics. This first phase, as a rule, corresponds to an early afterglow. The next phases of the observations are multicolor photometry, polarimetry, spectroscopy, and few days later the search for a supernova or kilonova associated with the GRB, and finally, observations of the host galaxy. To manage the problem of fast optical observations, telescopes with a small aperture are suitable. They can have a large field of view, which is necessary to cover initial localizations of GRBs. The sensitivity of the telescope+detector may be sufficient to record statistically significant light curve with fine time resolution. We describe one of the networks of telescopes with a small aperture IKI-GRB FuN, and present the results of early optical observation of GRB sources, and discuss the design requirements of the optical observations for effective GRB research in the next decade.

Orbital plane flips, a transition from prograde to retrograde motion or vice versa, is a phenomenon due to solar radiation pressure that is investigated. We consider initial near-circular orbits with different inclinations, including the vicinity of orbits of the GNSS satellites, GEO, geosynchronous orbits, and super-GEO region. Dynamical evolution of orbits is studied from a numerical simulation. Initial conditions for the objects are chosen in the GNSS orbit regions (GLONASS, GPS, BeiDou, Galileo) as well as 450-1100 km above to nominal semi-major axes of the navigation orbits, and in the vicinity of GEO, geosynchronous orbits, and super-GEO region. Initial data correspond to nearly circular orbits with the eccentricity 0.001. The initial inclination is varied from 55 • to 64.8 • . Initial values of longitude of ascending node are varied from 0 • to 350 • . High area-to-mass ratios are considered, at which orbital plane flips occur. Dynamical evolution covers periods of 24 and 240 years. The maximum inclination of the orbit is achieved when the longitude of the pericenter is sun-synchronous. Flips are possible only for objects with the area-to-mass ratio equal or more than 16 m 2 /kg (the radiation pressure coefficient is 1.44). The flips are caused precisely by solar radiation pressure. The Lidov-Kozai effect is suppressed by solar radiation pressure perturbations, affecting high area-to-mass ratio objects due to a secondary apsidal-nodal secular resonance.

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