Hot Component Research Articles

(Digital Presentation) Offshore Gas Turbines

Offshore gas turbines are the main power drivers for offshore production facilities; they are used for gas lifting, pumping, power generation and compression due to their high power to weight ratio and size. It is therefore imperative to minimize their downtime to prevent production losses. The need to examine the how deposits formed on the blade surface limits the life and performance of the engine cannot be overemphasized.In this study the Rolls Royce RB211, an aero derivative engine commonly used offshore was selected and its performance data obtained from PYTHIA engine simulation and diagnostic software. These values were used to calculate the rate of mass deposition of potassium sulphate (K2SO4), a potential corrosive salt.In order to determine rate of mass deposition, contaminant levels for a clean gas and good filter were obtained from General Electric’s fuel specification while a higher contaminant level was assumed.It was found that at high temperature corrosive salt tend to deposits on the blade surface when concentration of contaminants was calculated for both low and high impurity levels. It was also observed that the rate of mass deposition was high at the first stage of the turbine section where high gas temperature and pressure is usually experienced and drops as hot gas travel along the turbine and leaves as exhaust gas at very low temperature and pressure.In order to minimize the risk of damage to turbine hot section components like nozzle guide vanes and blades, fuel purity specifications and an appropriate inlet air filtration system must be used. This keeps contaminants in the combusted gas below allowable contaminant levels as recommended by original equipment manufacturers.

Research and Development of Trinary Power Cycles

The most effective and environmentally safe fossil fuel power production facilities are the combined cycle gas turbine (CCGT) ones. Electric efficiency of advanced facilities is up to 58% in Russia and up to 64% abroad. The further improvement of thermal efficiency by increase of the gas turbine inlet temperature (TIT) is limited by performance of heat resistance alloys that are used for the hot gas path components and the cooling system efficiency. An alternative method for the CCGT efficiency improvement is utilization of low potential heat of the heat recovery steam generator (HRSG) exhaust gas in an additional cycle operating on a low-boiling heat carrier. This paper describes a thermodynamic analysis of the transition from binary cycles to trinary ones by integration of the organic Rankine cycle (ORC). A mathematical model of a cooled gas turbine plant (GT) has been developed to carry out calculations of high-temperature energy complexes. Based on the results of mathematical modeling, recommendations were made for the choice of the structure and parameters of the steam turbine cycle, as well as the ORC, to ensure the achievement of the maximum thermal efficiency of trinary plants. It is shown that the transition from a single pressure CCGT to a trinary plant allows the electric power increase from 213.4 MW to 222.7 MW and the net efficiency increase of 2.14%. The trinary power facility has 0.45% higher efficiency than the dual pressure CCGT.

Study of Time Evolution of Thermal and Nonthermal Emission from an M-class Solar Flare

We conduct a wide-band X-ray spectral analysis in the energy range of 1.5–100 keV to study the time evolution of the M7.6-class flare of 2016 July 23, with the Miniature X-ray Solar Spectrometer (MinXSS) CubeSat and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft. With the combination of MinXSS for soft X-rays and RHESSI for hard X-rays, a nonthermal component and three-temperature multithermal component—“cool” (T ≈ 3 MK), “hot” (T ≈ 15 MK), and “superhot” (T ≈ 30 MK)—were measured simultaneously. In addition, we successfully obtained the spectral evolution of the multithermal and nonthermal components with a 10 s cadence, which corresponds to the Alfvén timescale in the solar corona. We find that the emission measures of the cool and hot thermal components are drastically increasing more than hundreds of times and the superhot thermal component is gradually appearing after the peak of the nonthermal emission. We also study the microwave spectra obtained by the Nobeyama Radio Polarimeters, and we find that there is continuous gyrosynchrotron emission from mildly relativistic nonthermal electrons. In addition, we conducted a differential emission measure (DEM) analysis by using Atmospheric Imaging Assembly on board the Solar Dynamics Observatory and determined that the DEM of cool plasma increases within the flaring loop. We find that the cool and hot plasma components are associated with chromospheric evaporation. The superhot plasma component could be explained by the thermalization of the nonthermal electrons trapped in the flaring loop.

An X-Ray Study of Coronally Connected Active Eclipsing Binaries

We present a detailed X-ray analysis and imaging of stellar coronae of five coronally connected eclipsing binaries, namely, 44 Boo, DV Psc, ER Vul, XY UMa, and TX Cnc. Both components of these binaries are found to be active. The X-ray light curves of detached and semidetached type systems show eclipsed-like features, whereas no evidence for coronal eclipsing is shown by the contact type systems. The X-ray light curve of DV Psc shows the O’Connell-like effect where the first maximum is found to be brighter than that of the second. Results of the coronal imaging using three-dimensional deconvolution of X-ray light curves show the coronae of all these binaries are either in the contact or over-contact configuration, with the primary being 1.7–4 times X-ray brighter than its companion. In the current sample, a minimum of 30%–50% of total UV emission is found to originate from the photosphere and positively correlated with the X-ray emission. X-ray spectra of these systems are well explained by two-temperature plasma models. The temperature corresponding to cool and hot components of plasma are found to be in the ranges of 0.25–0.64 and 0.9–1.1 keV, respectively. For the majority of binaries in the sample, the phase-resolved X-ray spectral analysis shows the orbital modulation in X-ray luminosity and emission measure corresponding to the hot component. A total of seven flaring events are also detected in the four systems with the flare energy in the range of (1.95–27.0) × 1033 erg and loop length of the order of 109–11 cm.

Global Characteristics of Cold Protons Around Midnight in the Magnetotail: Implication for Efficient Heating and Origin

AbstractWe investigate plasma transport to and plasma heating in the plasma sheet in the noon‐midnight meridian, characterizing protons with temperature colder than the core plasma sheet protons (<700 eV). We extract the density and temperature of the cold protons from velocity distribution functions measured by the Hot Plasma Composition Analyzer instrument on board the Magnetospheric Multiscale spacecraft in the radial distance (r) of 6–25 Re, performing two‐component Maxwellian fits. We selected time intervals with no fast flow observed, to examine the characteristics of magnetotail plasma not directly affected by magnetic reconnection and associated phenomena. In the region of r > ∼10 Re, the two‐component populations are identified more frequently near the plasma sheet boundary than the central plasma sheet. The cold component density peaks near the boundary, in contrast to the hot components which display high density near the central plasma sheet. These characteristics suggest that cold protons are convected from the lobe by the open field lines and then heated and mixed with the plasma sheet hot plasma near the lobe‐plasma sheet boundary. The statistical features of the extracted cold components indicate that, in the tailward regions (r > ∼20 Re), temperature increases with decreasing vertical distance from the plasma sheet (represented by plasma β) in a similar trend to the hot components. In the near‐Earth plasma sheet (r < ∼15 Re), cold proton temperature is lower at higher‐β regions; the density decreases as increasing r. These features suggest that cold protons in the near‐Earth plasma sheet are of ionospheric origin, transported to the plasma sheet in the closed magnetic field configuration.

Solitons’ behavior of waves by the effect of linearity and velocity of the results of a model in magnetized plasma field

The nonlinear three-dimensional modified Korteweg-de Vries-Zakharov-Kuznetsov model plays the behavior of weakly nonlinear ion-acoustic waves in a magnetized electron-positron plasma, containing the same capacity of cool and hot components of each species. In this article, we have investigated the mathematical model namely, (3 + 1)-dimensional modified KdV-Zakharov-Kuznetsov equation through the new auxiliary equation method for locating the closed-form travelling and solitary wave solutions. We have constructed a well-built 3D wave profile that signifies the variations in the same solution for particular values of the associated parameters. The novel point of this article is that, the generic values of the velocity parameter (λ) of the obtained solutions represent in the wave profile which thoroughly explains the reasons for the change in the variation of solitons. Besides, the type of wave profile subject to different values ​​of all other parameters that are related to the linearity of the stated model is also discussed. We have obtained numerous new wave solutions that establish the effectiveness of the implemented method in solving evolution equation which is nonlinear in nature and has higher dimension (HNEEs).These discussions may be useful or helpful in further research on this model. Besides, the implemented method is reliable for exploring important nonlinear waves that improve a variety of dynamic models arising in nonlinear science, mathematical physics, and engineering fields.

Coherent microwave emission as an indicator of non-thermal energy release at a coronal X-ray point

A response has been found in a narrow band 5–7 GHz of microwave emission to the appearance of a coronal X-ray point. The emission source is a short X-ray loop located in the tail part of an active region and occurring when magnetic fields are reconnected near the footpoints of high and low loops rooted in nearby magnetic pores of the opposite polarity. The power of energy release is low and no response of the hot plasma component was observed in hard X-rays. Analysis of images in soft X-ray and extreme UV radiation shows that microwave emission has a coherent nature and is generated at a frequency of about twice the plasma frequency by electrons with energies above several tens of keV. The result indicates a high diagnostic potential of microwave observations to detect acceleration processes in weak transitory events and can be useful for observation planning with new generation radioheliographs currently under development.

Когерентное микроволновое излучение как индикатор нетеплового энерговыделения в рентгеновской корональной точке

A response has been found in a narrow band 5–7 GHz of microwave emission to the appearance of a coronal X-ray point. The emission source is a short X-ray loop located in the tail part of an active region and occurring when magnetic fields are reconnected near the footpoints of high and low loops rooted in nearby magnetic pores of the opposite polarity. The power of energy release is low and no response of the hot plasma component was observed in hard X-rays. Analysis of images in soft X-ray and extreme UV radiation shows that microwave emission has a coherent nature and is generated at a frequency of about twice the plasma frequency by electrons with energies above several tens of keV. The result indicates a high diagnostic potential of microwave observations to detect acceleration processes in weak transitory events and can be useful for observation planning with new generation radioheliographs currently under development.

Investigation of evaluated temperature oxidation for IN-738 LC superalloy turbine blade thermally coated by AL2O3 using slurry coating process

The study aims to investigate the effect of Al2O3 and Al additions to Nickel-base superalloys as a coating layer on oxidation resistance, and structural behavior of nickel superalloys such as IN 738 LC. Nickel-base superalloys are popular as base materials for hot components in industrial gas turbines such as blades due to their superior mechanical performance and high-temperature oxidation resistance, but the combustion gases' existence generates hot oxidation at high temperatures for long durations of time, resulting in corrosion of turbine blades which lead to massive economic losses. Turbine blades used in Iraqi electrical gas power stations require costly maintenance using traditional processes regularly. These blades are made of nickel superalloys such as IN 738 LC(Inconel 738). Few scientists investigated the impact of Al2O3 or Al additions to Nickel-base superalloys as coating layer by using the slurry coating method on oxidation resistance to enhance the Nickel-base superalloy's oxidation resistance. In this study, IN 738 LC is coated with two different coating percentages, the first being (10 Al+90 Al2O3) and the second being (40 Al+60 Al2O3). Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD) were performed on all samples before and after oxidation. According to the results, SEM images of the surface revealed that the layer of the surface has a relatively moderated porosity value and that some of the coating layers contain micro-cracks. The best surface roughness of specimens coated with 60 % alumina+40 % aluminum was 5.752 nm. Whereas, the surface roughness of specimens coated with 90 % alumina+10 % aluminum was 6.367 nm.Results reveal that alloys with both Al2O3 and Al additions have reported a positive synergistic effect of the Al2O3and Al additions on oxidation resistance. Moreover,the NiCrAl2O3 thermal coating has good oxidation resistance and the effective temperature of anti-oxidation is raised to 1100 °C in turn reducing the maintenance period of turbine blades

Interaction of crack-tip constraint and welding residual stresses on the fracture behavior of Ni-based alloy

The present paper aims to study the effect of crack-tip geometrical constraints and welding residual stresses (WRS), as well as their interaction on fracture behavior of IN939 superalloy, which is widely used in gas turbine hot section components, such as turbine vanes. For the thermal–mechanical simulation of welding processes, a finite element (FE) model was developed, and the predicted WRS was verified through experiments. Two welding paths and two mechanical boundary conditions were considered to develop four different WRS distributions within the same geometry. These results were mapped to the validated fracture finite element models. By varying the loading conditions, two sets of specimens with high and low geometrical constraints were achieved in the same geometry. Two-parameter fracture mechanics analyses were then used to examine the effects of four WRS profiles and geometrical constraints on the fracture behavior of each set. Generally, the impact of WRS is more evident in specimens with lower geometrical constraints. The fracture behavior might be unexpectedly affected if the WRS changes from tensile to compressive near the crack tip. Using the maximum stress triaxiality factor, it was shown that the fracture behavior as a function of WRS is better demonstrated than that of the Q-constraint parameter.

TiB₂/SiCN Thin-Film Strain Gauges Fabricated by Direct Writing for High-Temperature Application

The in situ strain/stress monitoring of hot components in harsh environments remains a challenging task. In this study, TiB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /SiCN thin-film strain gauges were fabricated on nickel base alloy substrates via direct writing. The static and dynamic strain responses were investigated from 25 °C up to 800 °C. The results show that this thin-film strain gauge fabricated by ceramic-based materials exhibits excellent thermal stability and strain response. Without any anti-oxidative protective layer deposited, its operating temperature is as high as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$700^{\circ }\text{C}$ </tex-math></inline-formula> , which is 200 °C higher than that of the high-temperature piezoresistive thin-film strain gauges that have been developed and comparable to thin-film strain gauges with protective layers. The gauge factor of theTiB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /SiCN high-temperature thin-film strain gauge is 7.12, which is higher than that of most high-temperature thin-film strain gauges. In addition, the strain gauge exhibits excellent resistance stability with a mechanical hysteresis of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3~\mu \varepsilon $ </tex-math></inline-formula> and a resistance drift of 0.0008/h at room temperature. Therefore, TiB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /SiCN thin-film strain gauges provide an effective approach for the measurement of in-situ static and dynamic strain of hot components in harsh environments.

Electromagnetic Electron-Cyclotron Wave for Ring Distribution with Alternating Current (AC) Electric Field in Saturn Magnetosphere

During their respective missions, the spacecraft Voyager and Cassini measured several Saturn magnetosphere parameters at different radial distances. As a result of information gathered throughout the journey, Voyager 1 discovered hot and cold electron distribution components, number density, and energy in the 6–18 Rs range. Observations made by Voyager of intensity fluctuations in the 20–30 keV range show electrons are situated in the resonance spectrum’s high energy tail. Plasma waves in the magnetosphere can be used to locate Saturn’s inner magnetosphere’s plasma clusters, which are controlled by Saturn’s spin. Electromagnetic electron cyclotron (EMEC) wave ring distribution function has been investigated. Kinetic and linear approaches have been used to study electromagnetic cyclotron (EMEC) wave propagation. EMEC waves’ stability can be assessed by analyzing the dispersion relation’s effect on the ring distribution function. The primary goal of this study is to determine the impact of the magnetosphere parameters which is observed by Cassini. The magnetosphere of Saturn has also been observed. When the plasma parameters are increased as the distribution index, the growth/damping rate increases until the magnetic field model affects the magnetic field at equator, as can be seen in the graphs. We discuss the outputs of our model in the context of measurements made in situ by the Cassini spacecraft.

Spectral Properties and Hybrid Jet Model Constraints of Fermi GRB 210610B

The jet composition of gamma-ray bursts (GRBs) is still an open question and the energy spectrum characteristics can provide us with evidence. GRB 210610B is a special burst with low-energy indices that are all greater than the synchrotron cutoff. We first use two empirical models, Band and CPL, and one physics model, a blackbody, to perform time-resolved spectral analysis on GRB 210610B and find that about 76.47% of the spectra need an addition thermal component to obtain a better fit. Moreover, these spectra could be well fitted by a multicolor blackbody (mBB) and the synchrotron model. We then adopt the hybrid jet model proposed by Gao & Zhang to perform a “top-down” approach to diagnose the photospheric properties (η and σ 0) of the central engine from observational data. We find both the dimensionless entropy η and the magnetization parameters (1 + σ 0) are greater than 1, indicating that the Poynting flux component may play an important role in addition to the hot fireball component. Our analysis also shows that most of the spectra have a magnetization parameter (1 + σ 15) ≃ 1 at ∼1015 cm, suggesting that nonthermal emission may originate from internal shocks. Furthermore, we find that α and E p show different time evolution behaviors: α exhibits a “hard-to-soft” behavior and moderately correlates with flux, while E p exhibits a “tracking” behavior. The magnetic field strength B and the mBB parameter kT max also show a “tracking” behavior. Our results suggest that the empirical model CPL may be interpreted by an mBB.

Investigating Biochar-Derived Dissolved Organic Carbon (DOC) Components Extracted Using a Sequential Extraction Protocol

Biochar-derived dissolved organic carbon (DOC), as the most important component of biochar, can be released on farmland, improving fertility and playing a role in soil amendment and remediation. The complexity of molecular structures and diversity of DOC compounds have influenced these functions to some extent. A sequential extract protocol consisting of water (25 °C), hot water (80 °C), and NaOH solution (0.05 M) was used to fully extract DOC compounds and gain a thorough understanding of the possible DOC components released from biochar. Rape straw (RS), apple tree branches (ATB), and pine sawdust (PS) were pyrolyzed at 300, 500, and 700 °C, respectively, to make nine distinct biochars. A TOC analyser, ultraviolet-visible spectroscopy (UV–vis), and excitation–emission fluorescence (EEM) spectrophotometer were used in conjunction with parallel factor analysis (PARAFAC) to determine the distribution of DOC content, the diversity of aromaticity, molecular weight characteristics and components of biochar-derived DOC. The results show that the relative distribution of water-extractable fractions ranged from 3.21 to 35.57%, with a low-aromaticity and extremely hydrophilic fulvic-acid-like compounds being found in the highest amounts (C2 and C3). The smallest amount of hot water-extractable components was produced from the release of small-molecule aliphatic compounds adsorbed on biochar and susceptible to migration loss once in a soil solution. More than half of the biochar-derived DOC was released in a NaOH solution, which primarily consisted of humic-acid-like compounds (C1), with higher molecular weights, more aromaticity, and lower bioavailability, according to the distribution of DOC in various extractants. In addition, the pyrolysis temperature and biomass type had a significant impact on the DOC properties released by biochar. As a result, the findings of this study showed that using a sequential extract protocol of water, hot water, and NaOH solution in combination with spectroscopic methods could successfully reveal the diversity of biochar-derived components, which could lead to new insights for the accurate assessment of potential environmental impacts and new directions for biochar applications.

Non-Destruction Evaluation Method for Long-Term Oxidation Behavior of SiC/SiC Composites with Different Preforms in Wet Oxygen.

The implementation of SiC fiber reinforced SiC/SiC composites to aero-engine hot components has attracted wide attention, due to their many excellent properties. Along these lines, in order to predict the oxidation behavior of the material in extreme environments and to explore the effect of different preforms on the oxidative behavior of the composites, four SiC/SiC composites, with different preforms, were oxidized under environmental conditions of pressure of 12 kPa H2O:8 kPa O2:80 kPa Ar, at 1400 °C temperature. Moreover, the morphology and defect distribution of the samples were characterized by carrying out scanning electron microscopy, and micro-computed X-ray tomography measurements. Furthermore, the relation between the micro- and macro-scales was established, so as to be able to predict the oxidation behavior of the composites; not only the quantitative relationship between the mass change rate and the defect volume change rate, but also the combination of micro-computed X-ray images.

Wear and Corrosion Characterization of a Ti–6Al–4V Component for Automotive Applications: Forging versus Selective Laser Melting Technologies

Selective laser melting (SLM) is applied to manufacture a Ti–6Al–4V conrod, an engine component, in order to reduce the weight respect to the original version produced by forging with the same alloy. The weight reduction is achieved through a topological optimization and is about 15%. The article focuses on an experimental study of titanium SLM and hot forging components based on evaluation and comparison of properties relevant for automotive applications: metallurgy, corrosion behavior, and wear resistance. The microstructure is duplex, composed of equiaxial α and β grains for both the technologies analyzed; different morphology and distribution of α and β phases are observed as expected. The analysis on corrosion and wear resistance against 100Cr6 highlights very similar properties for the two technologies. Finally, this study confirms that Ti–6Al–4V made by SLM can substitute the traditional forging technologies in the transport field for the properties here studied.

TiB2‐Modified Polymer‐Derived Ceramic SiCN Double‐Layer Thin Films Fabricated by Direct Writing for High‐Temperature Application

The thermal stability at high temperatures is the first design principle of high‐temperature thin‐film sensors. To improve the thermal stability of the thin‐film sensor, a TiB2‐modified SiCN double‐layer thin‐film resistor grid with a thickness of 18 μm is fabricated on an alumina substrate via direct writing. Owing to their in situ–generated SiO2–B2O3–TiO2 thermally grown oxide protective layer on the surface and TiB2 percolation paths inside, the produced films exhibit large high‐temperature oxidation resistance, electrical conductivity and high‐temperature‐resistance stability. In the thermal cycling test up to 800 °C, the TiB2‐modified SiCN films exhibit a negative‐temperature coefficient of resistance and excellent repeatability and stability. The resistance change rate at 800 °C for 1 h is only 1.1%. With the flexible manufacturing and high‐temperature stability of such ceramic films, this work on double‐layer ceramic films can be applied to in situ monitoring of hot components at high temperature.

Upset bulging as a preforming operation for hot metal gas forming of 22MnB5 tubes

Hot Metal Gas Forming (HMGF) is a coupled process of gas forming and quenching of tubes. This process allows to obtain complex and accurate geometry due to the elimination of springback and high mechanical properties due to the formation of martensite, as a result, the weight of the parts can be reduced. HMGF is widely used in the aerospace and automotive industries to make critical parts from high hardenability steels such as 22MnB5. A typical hot stamped component has 1000 MPa yield stress and 1500 MPa ultimate tensile strength. The main challenge of HMGF process is a significant material thinning and cracking due to the biaxial tension stress state. The paper proposes a preforming method for increasing the forming limits of HMGF by the cold upset bulging of tubes by means of the additional volume of material in the deformation zone. This method allows to obtain one or several waves in the cross section of the tube, which helps to increase the minimum workpiece wall thickness after the forming process by more than 40% and to reduce a probability of the crack formation.

Phase-resolved X-ray spectroscopy of PSR B0656+14 with SRG/eROSITA andXMM-Newton

We present a detailed spectroscopic and timing analysis of X-ray observations of the bright pulsar PSR B0656+14. The observations were obtained simultaneously with eROSITA andXMM-Newtonduring the calibration and performance verification phase of the Spektrum-Roentgen-Gamma mission (SRG). The analysis of the 100 ks deep observation of eROSITA is supported by archival observations of the source, includingXMM-Newton, NuSTAR, and NICER. UsingXMM-Newtonand NICER, we first established an X-ray ephemeris for the time interval 2015 to 2020, which connects all X-ray observations in this period without cycle count alias and phase shifts. The mean eROSITA spectrum clearly reveals an absorption feature originating from the star at 570 eV with a Gaussianσof about 70 eV that was tentatively identified in a previous longXMM-Newtonobservation. A second previously discussed absorption feature occurs at 260–265 eV and is described here as an absorption edge. It could be of atmospheric or of instrumental origin. These absorption features are superposed on various emission components that are phenomenologically described here as the sum of hot (120 eV) and cold (65 eV) blackbody components, both of photospheric origin, and a power law with photon index Γ = 2 from the magnetosphere. We created energy-dependent light curves and phase-resolved spectra with a high signal-to-noise ratio. The phase-resolved spectroscopy reveals that the Gaussian absorption line at 570 eV is clearly present throughout ~60% of the spin cycle, but it is otherwise undetected. Likewise, its parameters were found to be dependent on phase. The visibility of the line strength coincides in phase with the maximum flux of the hot blackbody. If the line originates from the stellar surface, it nevertheless likely originates from a different location than the hot polar cap. We also present three families of model atmospheres: a magnetized atmosphere, a condensed surface, and a mixed model. They were applied to the mean observed spectrum, whose continuum fit the observed data well. The atmosphere model, however, predicts distances that are too short. For the mixed model, the Gaussian absorption may be interpreted as proton cyclotron absorption in a field as high as 1014G, which is significantly higher than the field derived from the moderate observed spin-down.

SN 1987A: Tracing the flux decline and spectral evolution through a comparison of SRG/eROSITA and XMM-Newton observations

Context. SN 1987A is the supernova closest to us observed in the past four centuries. It provides the unique opportunity of witnessing the birth and evolution of a supernova remnant. Monitoring the source in X-rays provides insights into the physics of the shock, the X-ray emitting plasma, and the interaction of the shock with the structures in the circumstellar medium. The source has been monitored by XMM-Newton EPIC-pn from 2007 to 2020. SRG/eROSITA also observed the source during its commissioning phase and first light in September and October 2019. Aims. We investigated the spectral and flux evolution of SN 1987A in X-rays in the last 14 yr up to November 2020 using XMM-Newton and eROSITA observations. Methods. We performed a detailed spectral analysis using a three-component plane-parallel shock model and analysed and modelled the EPIC-pn monitoring and eROSITA observations in a consistent manner. Results. This paper reports a complete and the most recent flux evolution of SN 1987A in the soft (0.5−2 keV) and hard (3−10 keV) X-ray band. The flux in the soft band flattened around 9424 days and then displayed a turnover between 10 142 and 10 493 days, after which it showed a continued decline. At about the same time, a break in the hard-band flux time evolution slope was detected. This implies that the blast wave has now passed beyond the dense structures of the equatorial ring and is expanding farther into more tenuous circumstellar medium. The temporal evolution of the normalisations of the three shock components match the results of hydrodynamical simulations well, which predict a blue supergiant progenitor scenario. The trend in recent epochs indicates that the emission caused by the forward shock after leaving the equatorial ring and by the reverse shock in the ejecta is now becoming more dominant. The elemental abundances in the hot plasma component are significantly higher than those in the cooler component, indicating an origin in the reverse shock that propagates into the ejecta.