The Aditya-L1 is the first space-based solar observatory of the Indian Space Research Organization (ISRO). The spacecraft will carry seven payloads providing uninterrupted observations of the Sun from the first Lagrangian point. Aditya-L1 comprises four remote sensing instruments, viz. a coronagraph observing in visible and infrared, a full disk imager in Near Ultra-Violet (NUV), and two full-sun integrated spectrometers in soft X-ray and hard X-ray. In addition, there are three instruments for in-situ measurements, including a magnetometer, to study the magnetic field variations during energetic events. Aditya-L1 is truly a mission for multi-messenger solar astronomy from space that will provide comprehensive observations of the Sun across the electromagnetic spectrum and in-situ measurements in a broad range of energy, including magnetic field measurements at L1.

Solar rotation is still one of the unresolved concern of solar physics. We performed time series analysis on the bins formed on equally separated latitude regions on the soft X-ray images. These images are observed with the X-ray telescope (XRT) on board the Hinode satellite. The flux modulation method traces the passage of X-ray feature over the solar disc and statistical analysis of the time series data of the SXR images (one per day) for the period extends from year 2015 to 2017 gives the coronal rotation period as a function of latitude. The investigation provided quite systematic information of the solar rotation and its variability.

A characteristic pattern of solar hard X-ray emission, first identified in SOL1969-03-30 by Frost & Dennis (1971), turns out to have a close association with the prolonged high-energy gamma-ray emission originally observed by Forrest et al. (1985). This identification has become clear via the observations of long-duration γ-ray flares by the Fermi/LAT experiment, for example in the event SOL2014-09-01. The distinctive features of these events include flat hard X-ray spectra extending well above 100 keV, a characteristic pattern of time development, low-frequency gyrosynchrotron peaks, CME association, and gamma-rays identifiable with pion decay originating in GeV ions. The identification of these events with otherwise known solar structures nevertheless remains elusive, in spite of the wealth of EUV imagery available from SDO/AIA. The quandary is that these events have a clear association with SEPs in the high corona, and yet the gamma-ray production implicates the photosphere itself, despite the strong mirror force that should focus the particles away from the Sun We discuss the morphology of these phenomena and propose a solution to this problem.

Solar hard X-ray and gamma-ray emission was measured by BDRG instrument, the part of set of instruments operated on board the Russian satellite Lomonosov from April 2016 until now (solar-synchronous orbit with altitude 490 km, inclination of 97.6 degrees). Lomonosov measurements (11 flares with the X-ray energy more than 10 keV, and more than half of them have class in soft X-rays less than C2) were compared to the data obtained by RHESSI and Fermi space observatories as well as the Nobeyama Radioheliograph operating at the same time. The quasi-periodicity with different periods were found in some of them.

A M2.5 solar flare observed by RHESSI in the 6-100 keV range on July 6, 2006 led to a Coronal Mass Ejection (CME). Two compact sources at 12-100 keV are seen at the beginning of the flare, whose further evolution fits well in a loop. Also, time-profiles of the flare at radio wavelengths are compared. The X-ray light-curves at different bands in the 6-100 keV range and radio time profiles show some peaks superimposed on smooth variations. The aim of this work is to compare the X-ray light-curves, of fluxes integrated over the whole source, with the physical parameters of the sources of the flare. Yashiro and Gopalswamy (2009) have found that the fraction of flares that produce CME increases with the flare energy. Here, we look for the characteristics of an M2.5 flare that could make it a generator of a CME. The idea is, in future works, to look in the light-curves of similar flares at other stars for these features. It is found that the CME onset takes place around the time when an X-ray source at 12-25 keV of Chromospheric evaporation stagnates at the loop apex, before the main peak at the light-curve at 25-50 keV and at the radio emission curves. Probably, the amount of evaporated plasma could play some role in triggering the CME.

The assumption of an equilibrium (Maxwellian) distribution of electron energies cannot explain observed high intensities of the Si XIId satellite lines relative to the Si XIII allowed lines during the flares. However, the presence of n-distribution with a higher and narrower shape than the Maxwellian one is able to explain this behavior. We calculated the ionization equilibrium for the non-thermal n-distributions using the latest atomic data for each element up to the proton number of 30. Significant changes in the shape and maxima of the ion abundance peak occur and can strongly influence the temperature diagnostics.

During late October 2014, active region NOAA 2192 caused an unusual high level of solar activity, within an otherwise weak solar cycle. While crossing the solar disk, during a period of 11 days, it was the source of 114 flares of GOES class C1.0 and larger, including 29 M- and 6 X-flares. Surprisingly, none of the major flares (GOES class M5.0 and larger) was accompanied by a coronal mass ejection, contrary to statistical tendencies found in the past. From modeling the coronal magnetic field of NOAA 2192 and its surrounding, we suspect that the cause of the confined character of the flares is the strong surrounding and overlying large-scale magnetic field. Furthermore, we find evidence for multiple magnetic reconnection processes within a single flare, during which electrons were accelerated to unusual high energies.

The Fermi Large Area Telescope (LAT) is the most sensitive instrument ever deployed in space for observing gamma-ray emission >100 MeV. This has also been demonstrated by its detection of quiescent gamma-ray emission from pions produced by cosmic-ray protons interacting in the solar atmosphere, and from cosmic-ray electron interactions with solar optical photons. The Fermi-LAT has also detected high-energy gamma-ray emission associated with GOES M-class and X-class solar flares, each accompanied by a coronal mass ejection and a solar energetic particle event, increasing the number of detected solar flares by almost a factor of 10 with respect to previous space observations. During the impulsive phase, gamma rays with energies up to several hundreds of MeV have been recorded by the LAT. Emission up to GeV energies lasting several hours after the flare has also been detected by the LAT. Of particular interest are the recent detections of three solar flares whose position behind the limb was confirmed by the STEREO satellites. While gamma-ray emission up to tens of MeV resulting from proton interactions has been detected before from occulted solar flares, the significance of these particular events lies in the fact that these are the first detections of >100 MeV gamma-ray emission from footpoint-occulted flares. We will present the Fermi-LAT, RHESSI and STEREO observations of these flares and discuss the various emission scenarios for these sources.

ChemiX is a Bragg crystal spectrometer that will fly on the two Interhelioprobe spacecraft due for launch in 2025 and 2026. The spacecraft perihelion will be only 0.3 a.u. and the orbit inclination up to 30°, and so instruments on board will have a close view of solar active regions and flares and regions near each solar pole. The ChemiX X-ray spectrometer, built by a consortium of groups led by the Space Research Centre, Polish Academy of Sciences, will fly on each of the spacecraft, and observe X-ray spectra in the 1.5 - 9 Å range. Spectral lines in this range include resonance lines of helium-like and hydrogen-like ions of elements such as Fe, Ca, Ar, S, and Si, with less abundant elements such as K and Cl represented by weaker lines which the high sensitivity of ChemiX should be able to detect. The free–free and free–bound continua should also be detected since instrumental background will be eliminated. Three of the seven channels of ChemiX will be in a “dopplerometer” arrangement by which spatial and spectral shifts present in flare impulsive stages can be disentangled.

Solar flare X-ray loop top sources (LTSs) are known since early observations from Skylab.They are always present accompanying long duration events (LDE), but their nature remains unclear. One of the main unknowns is spatial structure of LTSs. Observations indicate that LTSs are large and diffuse, but several authors suggested that there is present a fine, internal structure within them which should be resolved even using present space instrumentation.We present an example for the solar flare well observed by SDO/AIA and RHESSI. The LTS was dynamic with an episode of splitting into two sources. We performed detailed analysis of X-ray sources morphology using restored RHESSI images. Moreover, we conducted a number of simulations taking into account various possible spatial distributions of X-ray emission. We have found that in case of the flare investigated RHESSI should be capable to detect the fine structure if present. However it is not visible on the restored images. Some of our simulations suggest that we can also miss large, diffuse sources in the X-ray observations which may eventually lead to misinterpretation of the observed X-ray features.

We present results of analysis of the spectra collected with Polish instrument RESIK flown on CORONAS-F satellite. RESIK was the bent crystal spectrometer, measuring spectra in the spectral range 3.3 - 6.1 Å with a high cadence during flares. The emission lines as well as the continuum observed by RESIK are formed in hotter (T > 3 MK) plasmas of active regions and flares. RESIK observed various types of flares: from X-ray class B and C up to strongest flares of X-class, for both, short and long duration events. The analysis of absolute and relative spectral intensities of the lines and continuum observed for 33 events allowed for determining the plasma elemental composition with subsequent detailed study of time changes of the temperature structure of the sources described in terms of the differential emission measure (DEM). As an example we present the typical DEM evolutionary patterns for the C1.9 flare (SOL2002-12-26T08:35) and discuss its thermodynamics.

We explore the temporal evolution of flare plasma parameters including temperature (T) - differential emission measure (DEM) relationship by analyzing high spectral and temporal cadence of X-ray emission in 1.6-8.0 keV energy band, recorded by SphinX (Polish) and Solar X-ray Spectrometer (SOXS; Indian) instruments, during a B8.3 flare which occurred on July 04, 2009. SphinX records X-ray emission in 1.2-15.0 keV energy band with the temporal and spectral cadence as good as 6 μs and 0.4 keV, respectively. On the other hand, SOXS provides X-ray observations in 4-25 keV energy band with the temporal and spectral resolution of 3 s and 0.7 keV, respectively. We derive the thermal plasma parameters during impulsive phase of the flare employing well-established Withbroe-Sylwester DEM inversion algorithm.

The subject of our work is the review and comparison of solar activity during the last two solar minima that occurred between recent activity cycles. We use the soft X-ray global solar corona observations covering the two nine-months long time intervals in 1997/98 and 2009. Data from RF15-I multichannel photometer are used for the penultimate minimum. For the last unusually deep and prolonged solar activity minimum in 2009 the data from SphinX spectrophotometer are used. Comparison of measurements from both minima takes place in the overlapping energy range 2–15 keV. We focus on the active region formation, evolution and flaring productivity during respective minima.

In February 2009, during recent deepest solar minimum, Polish Solar Photometer in X-rays (SphinX) begun observations of the Sun in the energy range of 1.2–15 keV. SphinX was almost 100 times more sensitive than GOES X-ray Sensors. The silicon PIN diode detectors used in the experiment were carefully calibrated on the ground using Synchrotron Radiation Source BESSY II. The SphinX energy range overlaps with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) energy range. The instrument provided us with observations of hundreds of very small flares and X-ray brightenings. We have chosen a group of solar flares observed simultaneously with GOES, SphinX and RHESSI and performed spectroscopic analysis of observations wherever possible. The analysis of thermal part of the spectra showed that SphinX is a very sensitive complementary observatory for RHESSI and GOES.

We have searched for quasi-periodic oscillations in the hard X-ray emission of solar flares. We have selected 14 flare events which were divided into two groups: a) the events with the X-ray sources located at the flare loop footpoints and b) the events with the X-ray source above the solar limb, i.e. with the loop-top X-ray source. We found that while in the case with the footpoints X-ray sources the quasi-periods of the recorded oscillations were in the interval 2–380 s, in the events with loop-top sources only the quasi-periods longer than 50 s were recognized. These results are probably connected with the MHD oscillation modes of the flaring loop. While the long periods, which are dominant in loop-top sources, are produced by acoustic oscillations along the whole long loop, in the layers close to the loop footpoints also the MHD wave modes in shorter structures with shorter periods are generated.

Recent observations of coronal loops in solar active regions show that their heating must be a truly dynamic process. Even though it seems clear that the energy source is the magnetic field that confines the coronal plasma, the details of how it dissipates are still a matter of debate. In this presentation we review the theoretical models of coronal heating, which have been traditionally clasified as DC or AC depending on the electrodynamic response of the loops to the photospheric driving motions.

Also, we show results from numerical simulations of the internal dynamics of coronal loops within the framework of the reduced MHD approximation. These simulations indicate that the application of a stationary velocity field at the photospheric boundary leads to a turbulent stationary regime after several photospheric turnover times. Once this turbulent regime is set, both DC and AC stresses dissipate at faster rates as a result of a direct energy cascade.

In this work, we investigate the possible effects produced by soft X-rays (and secondary electrons) on Titan aerosol analogs in an attempt to simulate some prebiotic photochemistry. The experiments have been performed inside a high vacuum chamber coupled to the soft X-ray spectroscopy beamline at the Brazilian Synchrotron Light Source (LNLS). In-situ sample analysis were performed by a Fourier transform infrared spectrometer. The infrared spectra have presented several organic molecules, including nitriles and aromatic CN compounds. After the irradiation, the brownish-orange organic residue was analyzed ex-situ by gas chromatographic technique revealing the presence of adenine (C5H5N5), one of the constituents of the DNA molecule.

In this paper we analyze soft and hard X-ray emission of the 2002 September 20 M1.8 GOES class solar flare observed by RHESSI and GOES satellites, where soft X-ray emission precedes the onset of the main bulk hard X-ray emission by ~5 min. This suggests that an additional heating mechanism may be at work at the early beginning of the flare. However RHESSI spectra indicate presence of the non-thermal electrons also before impulsive phase. So, we assumed that a dominant energy transport mechanism during rise phase of solar flares is electron beam-driven evaporation. We used non-thermal electron beams derived from RHESSI spectra as the heating source in a hydrodynamic model of the analyzed flare. We showed that energy delivered by non-thermal electron beams is sufficient to heat the flare loop to temperatures in which it emits soft X-ray closely following the GOES 1–8 Å light-curve.

Multi-wavelength studies of energetic solar flares with seismic emissions have revealed interesting common features that may help us to identify the correlations of flare signatures from the inner to the outer solar atmosphere and, to develop diagnostic techniques to aid in the sun quake detection. In our study, we make use the relation between the microwave and the hard X-ray emissions associated with such flares to propose a scenario for the ignition of seismic transients from flares. We explore the mechanisms of energy transport to the photosphere, such us back-warming or direct particle impacts.

We have analysed the 6 mHz egression power signatures of some accoustically active X-class solar flares. During the impulsive phase these flares produced conspicuous seismic signatures which have kernel-like structures, mostly aligned with the neutral line of the host active region. The kernel-like structures show the effect of constructive interference of the acoustic waves emanating from the complex sources, suggesting motion of the acoustic sources. The co-aligment between the seismic signatures and the hard X-ray emission observed by RHESSI from the footpoints of the coronal loops suggests a direct link between relativistic particles accelerated during the flare and the hydrodynamic response of the photosphere during flares.