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This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., We present a detailed prompt emission and early optical afterglow analysis of the two very-high-energy (VHE) detected bursts GRB 201015A and GRB 201216C, and their comparison with a subset of similar bursts. Time-resolved spectral analysis of multistructured GRB 201216C using the Bayesian binning algorithm revealed that during the entire duration of the burst, the low-energy spectral index (αpt) remained below the limit of the synchrotron line of death. However, statistically some of the bins supported the additional thermal component. Additionally, the evolution of spectral parameters showed that both the peak energy (Ep) and αpt tracked the flux. These results were further strengthened using the values of the physical parameters obtained by synchrotron modeling of the data. Our earliest optical observations of both bursts using the F/Photometric Robotic Atmospheric Monitor Observatorio del Roque de los Muchachos and Burst Observer and Optical Transient Exploring System robotic telescopes displayed a smooth bump in their early optical light curves, consistent with the onset of the afterglow due to synchrotron emission from an external forward shock. Using the observed optical peak, we constrained the initial bulk Lorentz factors of GRB 201015A and GRB 201216C to Γ0 = 204 and Γ0 = 310, respectively. The present early optical observations are the earliest known observations constraining outflow parameters and our analysis indicate that VHE detected bursts could have a diverse range of observed luminosity within the detectable redshift range of present VHE facilities. © 2023. The Author(s). Published by the American Astronomical Society., R.G. and S.B.P. acknowledge the financial support of ISRO under AstroSat archival Data utilization program (DS_2B-13013(2)/1/2021-Sec.2). A.A. acknowledges funds and assistance provided by the Council of Scientific & Industrial Research (CSIR), India with file No. 09/948(0003)/2020-EMR-I. A.J.C.T. acknowledges support from the Spanish Ministry project PID2020-118491GB-I00 and Junta de Andalucia grant P20_010168. Y.D.H. acknowledges support under the additional funding from the RYC2019-026465-I. M.C.G. acknowledges support from the Ramón y Cajal Fellowship RYC2019-026465-I (funded by the MCIN/AEI/10.13039/501100011033 and the European Social Funding). This research has used data obtained through the HEASARC Online Service, provided by the NASA-GSFC, in support of the NASA High Energy Astrophysics Programs. S.B.P. thankfully acknowledges inclusion of the photometric calibration data of GRB 201015A taken with the 4K × 4K CCD Imager acquired as a part of the present analysis and extends sincere thanks to the observing and support staff of the 3.6 m DOT for maintaining and running the observational facilities at Devasthal Nainital., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001131-S).

Following the detection of a long GRB 190919B by INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory), we obtained an optical photometric sequence of its optical counterpart. The light curve of the optical emission exhibits an unusually steep rise ∼100 s after the initial trigger. This behaviour is not expected from a ‘canonical’ GRB optical afterglow. As an explanation, we propose a scenario consisting of two superimposed flares: an optical flare originating from the inner engine activity followed by the hydrodynamic peak of an external shock. The inner-engine nature of the first pulse is supported by a marginal detection of flux in hard X-rays. The second pulse eventually concludes in a slow constant decay, which, as we show, follows the closure relations for a slow cooling plasma expanding into the constant interstellar medium and can be seen as an optical afterglow sensu stricto. © ESO 2022., The operation of the robotic telescope FRAM is supported by the grant of the Ministry of Education of the Czech Republic LM2018102. The data calibration and analysis related to the FRAM telescope is supported by the Ministry of Education of the Czech Republic MSMT-CR LTT18004, MSMT/EU funds CZ.02.1.01/0.0/0.0/16_013/0001402 and CZ.02.1.01/0.0/0.0/18_046/0016010. SK and MP acknowledge support from the European Structural and Investment Fund and the Czech Ministry of Education, Youth and Sports (Project CoGraDS – CZ.02.1.01/0.0/0.0/15_003/0000437). MT and MR acknowledge support from the Ministry of Education and Research of Italy via project PRIN-MIUR 2017 UnIAM (Unifying Isolated and Accreting Magnetars). YDH acknowledges support under the additional funding from the RYC2019-026465-I. AJCT acknowledges support from the Spanish Ministry Project PID2020-118491GB-I00 and the “Center of Excellence Severo Ochoa” award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709) as well as technical support from both NIWA Lauder and San Pedro Mártir Astronomical Observatory staff.

Long gamma-ray bursts (GRBs) are produced by the dissipation of ultra-relativistic jets launched by newly-born black holes after the collapse of massive stars. Right after the luminous and highly variable gamma-ray emission, the multi-wavelength afterglow is released by the external dissipation of the jet in circumburst medium. We report the discovery of a very bright (10 mag) optical emission 28 s after the explosion of the extremely luminous and energetic GRB 210619B located at redshift 1.937. Early multi-filter observations allowed us to witness the end of the shock wave propagation into the GRB ejecta. We observed the spectral transition from a bright reverse to the forward shock emission, demonstrating that the early and late GRB multi-wavelength emission is originated from a very narrow jet propagating into an unusually rarefied interstellar medium. We also find evidence of an additional component of radiation, coming from the jet wings which is able explain the uncorrelated optical/X-ray emission.

One of the primary observational objectives of the 0.5 m robotic telescope of Ondřejov observatory is the ground-based follow-up of gamma-ray burst triggers. This independent robotic observatory has been in operation since 2008 and has followed up more than a hundred events localized by the Swift or INTEGRAL satellites. We describe the use of the weighted coaddition of astronomical images while applying this method to observations of GRB optical afterglows. We present optical photometric observations of the detected optical afterglows. The collection contains several faint optical afterglows, in some cases a lightcurve is available, in some cases only a single point detection has been achieved. A brief collection of available information is presented for each of the events together with our fitting and analysis. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

For space-born astronomical X-ray telescopes, iridium-based reflective layer systems are known as highly effective mirrors coatings. During the recent years, Aschaffenburg University of Applied Sciences and the Czech Technical University in Prague jointly developed stress compensated chromium-iridium coatings for this application. To overcome the disturbing reflectivity reduction of the iridium absorption edge around 2 keV photon energy, thin overcoat layers of chromium were applied in addition. Now a prototype of a wide-field, imaging X-ray telescope of Lobster Eye type is assembled at the company RIGAKU. For this purpose a small series of 34 mirrors based on 100 x 50 mm semiconductor grade silicon substrates has been coated at Aschaffenburg University. The applied tri-layer system consists of a stack of 40 nm chromium, which act as adhesive layer and compensates layer stress, a 30 nm iridium thick reflective layer, and an additional overcoat layer of 6 nm chromium. This layer system have been analysed by AFM and TEM images. The mirrors are assembled into an aluminium frame to build a 2D Lobster Eye type telescope. The designed focal length of this wide field X-ray telescope is two meter. To study the performance of the tri-layer coating system, a twin LE telescope with convenient gold coatings was manufactured also. Performance measurements of both telescopes and under same conditions are planned at the PANTER test facility at the Max-Planck Institute for Extraterrestrial Physics. First experimental results, their comparison with theoretical simulations and the comparison between both models will be presented in this contribution.

At peak, long-duration gamma-ray bursts are the most luminous sources of electromagnetic radiation known. Since their progenitors are massive stars, they provide a tracer of star formation and star-forming galaxies over the whole of cosmic history. Their bright power-law afterglows provide ideal backlights for absorption studies of the interstellar and intergalactic medium back to the reionization era. The proposed THESEUS mission is designed to detect large samples of GRBs at $z>6$ in the 2030s, at a time when supporting observations with major next generation facilities will be possible, thus enabling a range of transformative science. THESEUS will allow us to explore the faint end of the luminosity function of galaxies and the star formation rate density to high redshifts; constrain the progress of re-ionisation beyond $z\gtrsim6$; study in detail early chemical enrichment from stellar explosions, including signatures of Population III stars; and potentially characterize the dark energy equation of state at the highest redshifts., Submitted to Experimental Astronomy

Multi-messenger astrophysics is becoming a major avenue to explore the Universe, with the potential to span a vast range of redshifts. The growing synergies between different probes is opening new frontiers, which promise profound insights into several aspects of fundamental physics and cosmology. In this context, THESEUS will play a central role during the 2030s in detecting and localizing the electromagnetic counterparts of gravitational wave and neutrino sources that the unprecedented sensitivity of next generation detectors will discover at much higher rates than the present. Here, we review the most important target signals from multi-messenger sources that THESEUS will be able to detect and characterize, discussing detection rate expectations and scientific impact., Submitted to Experimental Astronomy

The 2nd generation of the X-ray Multi-Foil Optical (MFO) system for rocket experiment is presented Theoretical study of the multi-foil wide-field X-ray “Lobster eye” based optics addresses the X-ray monitoring for astrophysical applications. Previous Developments and Tests of Small X-ray Optical Systems for Space Applications in collaboration with Pennsylvania State University, Department of Astronomy and Astrophysics (REX I) were continued. A novel approach (REX II) based on the use of MFO optics in combination with quad Timepix X-ray detector and X-ray spectrometer is proposed and studied. MFO X-ray telescope is designed especially for the Water Recovery REX II sub-orbital rocket experiment. A designed optical system combined with Timepix X-ray detectors is described.

This paper contains the printed version of the concluding remarks I gave at the Conference XIII Multi-frequency Behaviour of High Energy Cosmic Sources Workshop, 3–8 June, 2019 in Palermo, Italy.

In the upcoming generation of small satellites there is a great potential for testing new sensors, processes and technologies for space and also for the creation of large in situ sensor networks. It plays a significant role in the more detailed examination, modelling and evaluation of the orbital environment. Scientific payloads based on the CubeSat technology are also feasible and the miniature X-ray telescope described in this paper may serve as an example. One of these small satellites from CubeSat family is a Czech CubeSat VZLUSAT-1, which is going to be launched during QB50 mission in 2017. This satellite has dimensions of 100 mm × 100 mm × 230 mm. The VZLUSAT-1 has three main payloads. The tested Radiation Hardened Composites Housing (RHCH) has ambitions to be used as a structural and shielding material to protect electronic devices in space or for constructions of future manned and unmanned spacecraft as well as Moon or Martian habitats. The novel miniaturized X-ray telescope with a Lobster Eye (LE) optics represents an example of CubeSat's scientific payload. The telescope has a wide field of view and such systems may be essential in detecting the X-ray sources of various physical origin. VZLUSAT-1 also carries the FIPEX payload which measures the molecular and atomic oxygen density among part of the satellite group in QB50 mission. The VZLUSAT-1 is one of the constellation in the QB50 mission that create a measuring network around the Earth and provide multipoint, in-situ measurements of the atmosphere.

Blazar OJ287 exhibits large thermal flares at least twice every 12 years. The times of these flares have been predicted successfully using the model of a quasi-Keplerian eccentric black hole binary where the secondary impacts the accretion disk of the primary, creating the thermal flares. New measurements of the historical light curve have been combined with the observations of the 2015 November/December flare to identify the impact record since year 1886, and to constrain the orbit of the binary. The orbit solution shows that the binary period, now 12.062 year, is decreasing at the rate of 36 days per century. This corresponds to an energy loss to gravitational waves that is 6.5 +- 4 % less than the rate predicted by the standard quadrupolar gravitational wave (GW) emission. We show that the difference is due to higher order gravitational radiation reaction terms that include the dominant order tail contributions., to appear in the Proceedings of Gravitational Wave Astrophysics: Early Results from Gravitational Wave Searches and Electromagnetic Counterparts. eds. Gabriela Gonzales and Robert Hynes

In the binary black hole model of OJ 287 the secondary black hole orbits a much more massive primary, and impacts on the primary accretion disk at predictable times. We update the parameters of the disk, the viscosity $\alpha$ and the mass accretion rate $\dot m$. We find $\alpha=0.26 \pm 0.1$ and $\dot m = 0.08 \pm 0.04$ in Eddington units. The former value is consistent with Coroniti (1981) and the latter with Marscher and Jorstad (2011). Predictions are made for the 2019 July 30 superflare in OJ 287. We expect that it will take place simultaneously at the Spitzer infrared channels as well as in the optical and that therefore the timing of the flare in optical can be accurately determined from Spitzer observations. We also discuss in detail the light curve of the 2015 flare and find that the radiating volume has regions where bremsstrahlung dominates as well as regions that radiate primarily in synchrotron radiation. The former region produces the unpolarised first flare while the latter region gives rise to a highly polarized second flare., Comment: 12 pages, 4 figures, to appear in ApJ

The paper presents the X-ray Multi-Foil Optical (MFO) system proposed for the CubeSat demonstrator. The Lobster Eye (LE) design represents wide field of view (FOV) X-ray optics. This feature is unique in comparison with classical Wolter types of X-ray optics that reaches a field of view of typically 1 degree or less. LE optics can theoretically achieve an unlimited field of view, but for practical reasons, modules with, for example, 6 deg x 6 deg large FOV can be designed, developed, and constructed. Presented theoretical study of the Multi-Foil wide-field X-ray “Lobster eye” based optics shows effects of focal length, foil spacing and reflective surface (Au versus Ir). The main parameters that have been compared are effective area, gain, FWHM and/or transmission. The system can be used as an all‐sky monitor in future projects.

Focusing optics for hard x-/soft gamma-rays (above 100 keV) are in a development phase. One promising method is represented by the Laue lens technology that has already been validated through on-ground prototypes and balloon tests. Laue lens optics will be an outstanding tool for observing weak sources in a notably short integration time thanks to the excellent sensitivity they can provide. Such performances has been further increased with the employ of cylindrical bent crystals that are capable to dramatically narrow the Laue lens Point Spread Function (PSF). One aspect that is under investigation is the image aberrations for off-axis sources. This fact limits the Field of View (FoV) of a Laue lens to few arcmin. The employ of bent crystals in double diffraction configuration would reduce the mentioned aberration, increasing the FoV of the resulting Laue lens. Double diffraction crystals would represent an extension to hundreds of keV of the Lobster Eye (LE) principles that is well tested for focusing < 10 keV photons. We investigate pros and cons of the double diffraction configuration with respect to the single diffraction through Monte Carlo simulations and we compare their performances in terms of efficiency, PSF, pass-band and effective area. We also present preliminary tests performed at the LARIX facility to evaluate the technical feasibility of crystals with the aforementioned characteristics.

The picosatellites, recently in development at many institutes and universities worldwide (e.g.Schmidt et al. 2009 and Schilling 2006), represent, apart from growing commercial applications,a challenge for space astronomy and astrophysics, as they can act as complementary tools formodern space astrophysics.

We report here on the progress in digitization of astronomical plate archives and tests of the scanning devices for digitization of archival astronomical plates. These archives represent large database of stellar, solar, and planetary astronomical data, astrometric, photometric, and spectroscopic, with numerous applications in modern astrophysics

A novel design of x-ray optical system wide field telescope for astrophysical rocket experiments is investigated and tested in real space flight experiment. The proposed system is based on 1D and 2D modules with Schmidt Lobster Eye (LE) configuration allowing usage of multi-foil mirrors arranged to Schmidt profile.

The paper summarizes the Rocket EXperiment (REX) Lobster Eye (LE) X-ray Telescope payload results. The experiment was performed by the PennState University with X-ray spectroscope on board a Water Recovery X-Ray Rocket (WRXR) launched on 4th April, 2018. The secondary payload was the REX LE X-ray Telescope. The REX LE X-ray telescope consists of two X-ray telescopes with one-dimensional (1D) and two-dimensional (2D) optics, a visible-light camera and an IR grid-eye. The primary structure consists of a metal housing for the optics and a carbon fiber baffle with the Timepix sensors mounted at the end. The observation data from the experiment are briefly presented and discussed.

Lobster eye X-ray optics in the one dimensional (1D) arrangement has advantages in higher reflectivity, especially for higher energies, compared to classical two dimensional (2D) Schmidt's arrangement. One dimensional optics can determine only one direction of the incoming beam. There is placed a strip in front of the optics for determining of the second direction. This strip is made of X-ray proof material which blocks the incoming beam and thus causes a gap in the line. Based on these facts, it is possible to determine the position of each point source which has enough signal to gap ratio. Unfortunately, the intensity of sources is not possible to assess by this method. Copyright © 2018 SPIE., I would like to thank all the co-authors for their help in the research. Their involvement was priceless. The work was supported by the Grant Agency of the Czech Republic under grant no. 18-10088Y, by the Grant Agency of the Czech Technical University in Prague grant No. SGS18/186/OHK3/3T/13 and by the fellowship as ’Personal Tecnico de Apoyo’ number PTA2016-13192-I.

The algorithm presented is intended mainly for lobster eye optics. This type of optics (and some similar types) allows for a simplification of the classical ray-tracing procedure that requires great many rays to simulate. The method presented performs the simulation of a only few rays; therefore it is extremely effective. Moreover, to simplify the equations, a specific mathematical formalism is used. Only a few simple equations are used, therefore the program code can be simple as well. The paper also outlines how to apply the method to some other reflective optical systems.

This article covers ten years of GRB follow-ups by the Spanish BOOTES stations: 71 follow-ups providing 23 detections. Follow-ups by BOOTES-1B from 2005 to 2008 were given in a previous article and are here reviewed and updated, and additional detection data points are included as the former article merely stated their existence. The all-sky cameras CASSANDRA have not yet detected any GRB optical afterglows, but limits are reported where available., The authors appreciate the auspices of INTA, IHSM-UMA/CSIC, and UMA as well as the financial support by the Junta de Andaluca and the Spanish Ministry of Economy and Competitiveness through the Research Projects P07-TIC-03094, P12-TIC2839, AYA2009-14000-C03-01, AYA 2010-39727-C03-01, and AYA-2015-71718-R. Martin Jelinek was supported by the postdoctoral fellowship of the Czech Academy of Sciences. This study was carried out in the framework of the Unidad Asociada IAA-CSIC at the Group of Planetary Science of ETSI-UPV/EHU. This work was supported by the Ikerbasque Foundation for Science. The Czech CVUT FEL team acknowledges the support by GA CR Grant 13-33324S.

The recent discovery of the electromagnetic counterpart of the gravitational wave source GW170817, has demonstrated the huge informative power of multi-messenger observations. During the next decade the nascent field of multi-messenger astronomy will mature significantly. Around 2030, third generation gravitational wave detectors will be roughly ten times more sensitive than the current ones. At the same time, neutrino detectors currently upgrading to multi km^3 telescopes, will include a 10 km^3 facility in the Southern hemisphere that is expected to be operational around 2030. In this review, we describe the most promising high frequency gravitational wave and neutrino sources that will be detected in the next two decades. In this context, we show the important role of the Transient High Energy Sky and Early Universe Surveyor (THESEUS), a mission concept proposed to ESA by a large international collaboration in response to the call for the Cosmic Vision Programme M5 missions. THESEUS aims at providing a substantial advancement in early Universe science as well as playing a fundamental role in multi-messenger and time-domain astrophysics, operating in strong synergy with future gravitational wave and neutrino detectors as well as major ground- and space-based telescopes. This review is an extension of the THESEUS white paper (Amati et al. 2017), also in light of the discovery of GW170817/GRB170817A that was announced on October 16th, 2017., Comment: 25 pages, 13 figures, accepted to Advances in Space Research with minor revisions. Details on the THESEUS instrumentation, science case and expected performances can also be found in Amati et al. 2017 (arXiv:1710.04638) and in the presentations of the THESEUS Workshop 2017 (http://www.isdc.unige.ch/theseus/workshop2017-programme.html). v2 few typos corrected