2021, Predehl, P., Andritschke, R., Arefiev, V., Babyshkin, V., Batanov, O., Becker, W., Böhringer, H., Bogomolov, A., Boller, T., Borm, K., Bornemann, W., Bräuninger, H., Brüggen, M., Brunner, H., Brusa, M., Bulbul, E., Buntov, M., Burwitz, V., Burkert, W., Clerc, N., Churazov, E., Coutinho, D., Dauser, T., Dennerl, K., Doroshenko, V., Eder, J., Emberger, V., Eraerds, T., Finoguenov, A., Freyberg, M., Friedrich, P., Friedrich, S., Fürmetz, M., Georgakakis, A., Gilfanov, M., Granato, S., Grossberger, C., Gueguen, A., Gureev, P., Haberl, F., Hälker, O., Hartner, G., Hasinger, G., Huber, H., Ji, L., Kienlin, A. v., Kink, W., Korotkov, F., Kreykenbohm, I., Lamer, G., Lomakin, I., Lapshov, I., Liu, T., Maitra, C., Meidinger, N., Menz, B., Merloni, A., Mernik, T., Mican, B., Mohr, J., Müller, S., Nandra, K., Nazarov, V., Pacaud, F., Pavlinsky, M., Perinati, E., Pfeffermann, E., Pietschner, D., Ramos-Ceja, M. E., Rau, A., Reiffers, J., Reiprich, T. H., Robrade, J., Salvato, M., Sanders, J., Santangelo, A., Sasaki, M., Scheuerle, H., Schmid, C., Schmitt, J., Schwope, A., Shirshakov, A., Steinmetz, M., Stewart, I., Strüder, L., Sunyaev, R., Tenzer, C., Tiedemann, L., Trümper, J., Voron, V., Weber, P., Wilms, J., Yaroshenko, V.

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the primary instrument on the Spectrum-Roentgen-Gamma (SRG) mission, which was successfully launched on July 13, 2019, from the Baikonour cosmodrome. After the commissioning of the instrument and a subsequent calibration and performance verification phase, eROSITA started a survey of the entire sky on December 13, 2019. By the end of 2023, eight complete scans of the celestial sphere will have been performed, each lasting six months. At the end of this program, the eROSITA all-sky survey in the soft X-ray band (0.2-2.3 keV) will be about 25 times more sensitive than the ROSAT All-Sky Survey, while in the hard band (2.3-8 keV) it will provide the first ever true imaging survey of the sky. The eROSITA design driving science is the detection of large samples of galaxy clusters up to redshifts z > 1 in order to study the large-scale structure of the universe and test cosmological models including Dark Energy. In addition, eROSITA is expected to yield a sample of a few million AGNs, including obscured objects, revolutionizing our view of the evolution of supermassive black holes. The survey will also provide new insights into a wide range of astrophysical phenomena, including X-ray binaries, active stars, and diffuse emission within the Galaxy. Results from early observations, some of which are presented here, confirm that the performance of the instrument is able to fulfil its scientific promise. With this paper, we aim to give a concise description of the instrument, its performance as measured on ground, its operation in space, and also the first results from in-orbit measurements.

2020, Gazibegović-Busuladžić, A., Busuladžić, M., Čerkić, A., Hasović, E., Becker, W., Milošević, D.B.

We investigate strong-field ionization of linear molecules by a two-color laser field of frequencies rω and sω having coplanar counterrotating or corotating elliptically polarized components (ω is the fundamental laser field frequency and r and s are integers). Using the improved molecular strong-field approximation we analyze direct above-threshold ionization (ATI) and high-order ATI (HATI) spectra. More precisely, reflection and rotational symmetries of these spectra for linear molecules aligned in the laser-field polarization plane are considered. The reflection symmetries for particular molecular orientations, known to be valid for a bicircular field (this is the field with circularly polarized counterrotating components), are valid also for arbitrary component ellipticities. However, specific rotational symmetries that are satisfied for HATI by a bicircular field, are violated for an arbitrary elliptically polarized field with counterrotating components. For the corotating case and the N2 molecule we analyze molecular-orientation-dependent interferences and plateau structures for various ellipticities.

2020, Milošević, D.B., Becker, W.

High-order harmonic generation by orthogonally polarized two-color (OTC) laser fields is analysed using strong-field approximation and quantum-orbit theory. Results for the field components frequency ratio of 2:1 and 3:1 are presented and compared. We have shown that, depending on the relative phase between the field components, the shape of the high-harmonic spectrum can be very different from that obtained by a monochromatic linearly polarized laser field. It is also shown that it is possible to generate elliptically polarized high-order harmonics with very high photon energies using OTC laser field with the frequency ratio of 3:1 and a long fundamental wavelength. An effective relative phase control of the harmonic emission is demonstrated. The obtained results are explained using the quantum-orbit theory. © Published under licence by IOP Publishing Ltd.