Integral Flux Research Articles

H.E.S.S. Follow-up Observations of GRB 221009A

GRB 221009A is the brightest gamma-ray burst (GRB) ever detected. To probe the very-high-energy (VHE; >100 GeV) emission, the High Energy Stereoscopic System (H.E.S.S.) began observations 53 hr after the triggering event, when the brightness of the moonlight no longer precluded observations. We derive differential and integral upper limits using H.E.S.S. data from the third, fourth, and ninth nights after the initial GRB detection, after applying atmospheric corrections. The combined observations yield an integral energy flux upper limit of above E thr = 650 GeV. The constraints derived from the H.E.S.S. observations complement the available multiwavelength data. The radio to X-ray data are consistent with synchrotron emission from a single electron population, with the peak in the spectral energy distribution occurring above the X-ray band. Compared to the VHE-bright GRB 190829A, the upper limits for GRB 221009A imply a smaller gamma-ray to X-ray flux ratio in the afterglow. Even in the absence of a detection, the H.E.S.S. upper limits thus contribute to the multiwavelength picture of GRB 221009A, effectively ruling out an IC-dominated scenario.

Zone of flow: A new finding on the characteristics of airflow within the zone of influence during air sparging in aquifers

Air sparging (AS) is a popular technology for the in-situ remediation of groundwater contaminated by volatile organic compounds. The scope of the zone within which injected air exists, i.e., zone of influence (ZOI) and the airflow characteristics within ZOI are of great interest. However, few studies have shed light on the scope of the zone within which air flows, namely, the zone of flow (ZOF) and its relation with the scope of ZOI. This study focuses on the ZOF characteristics and its relation with ZOI based on quantitative observations of ZOF and ZOI using a quasi-2D transparent flow chamber. The relative transmission intensity obtained by the light transmission method presents a rapid and continuous increasing near the ZOI boundary, providing a criterion for the quantitative determination of ZOI. An integral airflow flux approach is proposed to determine the scope of ZOF based on the airflow flux distributions through aquifers. The ZOF radius decreases with the growth of particle sizes of aquifers; while it increases first and then keeps constant with the increase of sparging pressure. The ZOF radius is around 0.55– 0.82 times of the ZOI radius, which depends on air flow patterns related to particle diameters dp, that is, 0.55– 0.62 for channel flow (dp < 1– 2 mm), while 0.75– 0.82 for bubble flow (dp > 2– 3 mm). The experimental results show that the sparged air is entrapped with little flowing inside ZOI regions that are outside the ZOF, which should be considered carefully in the design of AS.

Solar wind H+ fluxes at 1 AU for solar cycles 23 and 24

The solar wind consists of electrons and ion species having kinetic energy ≲10 keVs. Ion stream is mainly composed of protons. Their flux magnitude is especially important for radiation hardness assurance scientists who qualify materials for future space missions. Materials irreversibly degrade as soon as are exposed to solar radiation. Hence, proton differential and integral flux spectra play a crucial role in properly estimating radiation loads deposited within satellite functional components. Up to now, the wind fluxes were read out, e.g., from figures made for specific periods of a solar cycle. This method is not effective and is a source of a flux, and further on, a fluence uncertainty. The objective of this work was to calculate and tabulate the solar wind differential and integral proton fluxes, which can be used further on to evaluatespace mission proton fluence spectra. Solar wind proton bulk velocity and number density from four space solar observatories (SOHO, ACE, WIND, and DSCOVR) were numerically processed to achieve that goal. Fluxes were tabulated and represented in calendar year periods.Now, the radiation hardness assurance community can quickly access, compute and compare SW proton fluxes from different energy ranges, calendar years, and satellite data sources. Proton fluxes presented here indicate magnitude variations along with the solar cycle period. A correlation between the number of sunspots and the proton average flux was found, i.e., the larger the number of spots, the larger the flux magnitude. More importantly, it was discovered that proton fluxes indicate huge variations in magnitude for a selected year based on different satellite data sources. For some years, the difference reaches 240%. This value is reported for the first time and shows that to have a complete picture of the SW proton stream population, one must compare data from all four satellites. Also, it is reported that satellites, for a given calendar year, record different ranges of proton velocity and number density values. This finding, even stronger, suggests a necessity of comparing SW data from as many solar observatories as possible. The spread in the proton flux magnitude (240%) has a direct implication for planning and executing satellite material on-ground radiation test campaigns. Not carefully choosing a proton flux may result in a false impression of how examined material would degrade under an interplanetary space radiation environment. In this article, recommendations for selecting proper proton spectra are given.

Free–free absorption parameters of Cassiopeia A from low-frequency interferometric observations

Context. Cassiopeia A is one of the most extensively studied supernova remnants (SNRs) in our Galaxy. The analysis of its continuum spectrum through low-frequency observations plays an important role for understanding the evolution of the radio source and the propagation of synchrotron emission to observers through the SNR environment and the ionized interstellar medium. Aims. In this paper we present measurements of the integrated spectrum of Cas A to characterize the properties of free–free absorption toward this SNR. We also add new measurements to track its slowly evolving and decreasing integrated flux density. Methods. We used the Giant Ukrainian Radio Telescope (GURT) to measure the continuum spectrum of Cassiopeia A within the frequency range of 16–72 MHz. The radio flux density of Cassiopeia A relative to the reference source of the radio galaxy Cygnus A was measured in May–October 2019 with two subarrays of the GURT, used as a two-element correlation interferometer. Results. We determine magnitudes of emission measure, electron temperature, and an average number of charges of the ions for both internal and external absorbing ionized gas toward Cassiopeia A. Generally, their values are comparable, albeit with slight differences, to recently presented values. In the absence of clumping, we find that the unshocked ejecta of M = 2.61 M⊙ at the electron density of 15.3 cm−3 has a gas temperature of T ≈ 100 K. If the clumping factor is 0.67, then the unshocked ejecta of 0.96 M⊙ has an electron density of 18.7 cm−3. Conclusions. The integrated flux density spectrum of Cassiopeia A obtained with the GURT interferometric observations is consistent with the theoretical model within measurement errors and also reasonably consistent with other recent results in the literature.

Search for Pulsars in an Area with Coordinates 3h &lt; α &lt; 4h and +21° &lt; δ &lt; +42°

The search for pulsars outside the plane of the galaxy in an area of 300 sq. deg. was carried out with the LPA LPI antenna at 111 MHz, with a sensitivity 5 to 10 times better than that of previous surveys. The search was performed in the summed power spectra. With an accumulation time equivalent to 100 hours of continuous observations for each point of the area, 5 known pulsars were found with a signal-to-noise ratio (S/N) from 20 to 1300 in the first harmonic of the spectrum. Average profiles are obtained for the detected pulsars. Estimates are given for the peak and integrated flux densities of the found pulsars for individual sessions and for power spectra summed over 5.5 years, using the developed method based on measurements of harmonic heights in the power spectrum. No new pulsars were found in the area. Apparently, when searching for pulsars in the area, we approached the lower limit of the luminosity of second pulsars. The survey completeness is at the level of 0.5 mJy.

Search for Pulsars in an Area with Coordinates 3h &lt; α &lt; 4h and +21° &lt; δ &lt; +42°

On the Large Phased Array (LPA) of Lebedev Physics Institute (LPI), a search for pulsars outside the Galaxy plane was carried out in a 300 sq. deg area. The search with a sensitivity 5-10 times better than that of previously conducted surveys was at a frequency of 111 MHz. The search was carried out in the summed power spectra. With an accumulation equivalent to 100 hours of continuous observations for each point of the area, 5 known pulsars were detected with a signal-to-noise ratio (S/N) from 20 to 1300 in the first harmonic of the spectrum. Average profiles were obtained for the detected pulsars. Estimates of the peak and integral flux densities of the found pulsars are given for individual sessions and for the power spectra summarized over 5.5 years, obtained using the developed method based on measurements of the height of harmonics in the power spectrum. No new pulsars have been detected in the area. Apparently, when searching for pulsars in the area, we have approached the lower limit of the luminosity of the second pulsars. The completeness of the survey is at the level of 0.5 mJy.

The coordinated radio and infrared survey for high-mass star formation – V. The CORNISH-South survey and catalogue

ABSTRACT We present the first high spatial resolution radio continuum survey of the southern Galactic plane. The CORNISH project has mapped the region defined by 295° &amp;lt; l &amp;lt; 350°; |b| &amp;lt; 1° at 5.5 GHz, with a resolution of 2.5 arcsec (FWHM). As with the CORNISH-North survey, this is designed to primarily provide matching radio data to the Spitzer GLIMPSE survey region. The CORNISH-South survey achieved a root mean square noise level of ∼0.11 mJy beam−1, using the 6A configuration of the Australia Telescope Compact Array (ATCA). In this paper, we discuss the observations, data processing and measurements of the source properties. Above a 7σ detection limit, 4701 sources were detected, and their ensemble properties show similar distributions with their northern counterparts. The catalogue is highly reliable and is complete to 90 per cent at a flux density level of 1.1 mJy. We developed a new way of measuring the integrated flux densities and angular sizes of non-Gaussian sources. The catalogue primarily provides positions, flux density measurements, and angular sizes. All sources with IR counterparts at 8 μm have been visually classified, utilizing additional imaging data from optical, near-IR, mid-IR, far-IR, and sub-millimetre galactic plane surveys. This has resulted in the detection of 524 H ii regions of which 255 are ultra-compact H ii regions, 287 planetary nebulae, 79 radio stars, and 6 massive young stellar objects. The rest of the sources are likely to be extragalactic. These data are particularly important in the characterization and population studies of compact ionized sources such as UCHII regions and PNe towards the Galactic mid-plane.

DEVELOPMENT AND STUDY OF A MICROSPECTROMETER LAYOUT

The photoelectronic processes occurring in a vertically located double-barrier photode-tector under the influence of an external bias voltage are simulated depending on the char-acteristics of the penetrating waves. Under conditions of vertical illumination, to obtain the spectral dependence of the intensity of absorbed radiation, an algorithm was developed for selecting individual waves from the integral flux of the optical signal under conditions of changing the external bias voltage in steps of 1 mV. The algorithm takes into account the main cause-and-effect relationships between the absorption coefficient and design and technological parameters. It makes it possible to obtain the intensities of individual waves from the integral radiation flux in the optical range, where there is a change in the sign of the spectral characteristics and a linear dependence of the point of sign change on the ap-plied voltage. A general architecture, functional structure and remote control scheme for the monitor-ing system for hazardous substances have been developed, as well as corresponding pro-grams with the help of which the algorithm was operated in the LabVIEW environment. To run the algorithm, a prototype of a spectral analysis device was developed and prepared, in which an Arduino Mega board controlled by a microcontroller was used to analyze the output signal of the photodetector. The layout was tested using multi-colored LEDs. The spectral dependence of the inten-sity and its numerical data are obtained on the screen using a new principle. This method is novel and opens up prospects for further development of the field of micro-sized spectro-photometers. To identify mixtures by spectral analysis and estimate their quantity, the RDP (Remote Desktop) protocol of the remote system and the LABVIEW graphical programming envi-ronment were used. RDP was created by Microsoft to provide remote access to Windows servers and workstations.

Термомагнитная конвекция в гидродинамическом контуре: роль капельных агрегатов

In order to clarify the effect of drop-like aggregates on the thermomagnetic convection of a fer-rofluid in a vertical hydrodynamic circuit (convective loop), two series of experiments were carried out, which differ in the dispersed composition of single-domain particles in the fluid. This particular geometry of the cavity with the ferrofluid was chosen because in a closed hydrodynamic circuit the best conditions are created for thermomagnetic convection and the heat transfer en-hancement, provided that a magnetic field is applied to the heated section of the circuit in one of its vertical sections. In this case, the field nonuniformity in the cross section of the channel form-ing the loop is sufficiently small, and the ponderomotive force acting on the liquid is directed along the tube. The heated section of the circuit, which is affected by a nonuniform magnetic field, ‘works’ as a kind of thermomagnetic pump and a circulation flow occurs in the circuit. In the first series of experiments, we used a ferrofluid containing a coarse fraction of particles capable of causing thermodynamic instability of the ferrofluid in a magnetic field (spinodal decomposition) and the formation of drop-like aggregates. The second series of experiments was carried out with a ferrofluid that had undergone magnetic separation and was free from coarse particles. It is shown that the results of convective experiments differ qualitatively depending on the disperse composi-tion of particles and the presence of drop-like aggregates. A ferrofluid with a coarse fraction com-pletely blocks the global circulation flow, including gravitational convection, while a separated ferrofluid, purified from large particles, increases the intensity of convection in a strong magnetic field and the integral heat flux by 6–7 times.

Forecasting solar energetic proton integral fluxes with bi-directional long short-term memory neural networks

Solar energetic particles are mainly protons and originate from the Sun during solar flares or coronal shock waves. Forecasting the Solar Energetic Protons (SEP) flux is critical for several operational sectors, such as communication and navigation systems, space exploration missions, and aviation flights, as the hazardous radiation may endanger astronauts’, aviation crew, and passengers’ health, the delicate electronic components of satellites, space stations, and ground power stations. Therefore, the prediction of the SEP flux is of high importance to our lives and may help mitigate the negative impacts of one of the serious space weather transient phenomena on the near-Earth space environment. Numerous SEP prediction models are being developed with a variety of approaches, such as empirical models, probabilistic models, physics-based models, and AI-based models. In this work, we use the bidirectional long short-term memory (BiLSTM) neural network model architecture to train SEP forecasting models for three standard integral GOES channels (&gt;10 MeV, &gt;30 MeV, &gt;60 MeV) with three forecast windows (1-day, 2-day, and 3-day ahead) based on daily data obtained from the OMNIWeb database from 1976 to 2019. As the SEP variability is modulated by the solar cycle, we select input parameters that capture the short-term, typically within a span of a few hours, and long-term, typically spanning several days, fluctuations in solar activity. We take the F10.7 index, the sunspot number, the time series of the logarithm of the X-ray flux, the solar wind speed, and the average strength of the interplanetary magnetic field as input parameters to our model. The results are validated with an out-of-sample testing set and benchmarked with other types of models.

Erratum for article: “Forecasting Solar Energetic Proton Integral Fluxes with Bi-Directional Long Short-Term Memory Neural Networks”

Erratum for article: “Forecasting Solar Energetic Proton Integral Fluxes with Bi-Directional Long Short-Term Memory Neural Networks”

Experimental Performance Evaluation of an Integrated, LCPV/T Membrane Distillation System for Electricity and Seawater Desalination

In this paper, an integrated system based on low-concentrated photovoltaic/thermal (LCPV/T) technology and efficient vacuum membrane distillation (VMD) seawater desalination utilizing the energy of solar is established. Through a theoretical analysis and a series of experiments, this paper explores the temperature change of a single VMD process, and the variation trend of single-day membrane flux with solar irradiation and temperature parameters. In addition, the changes in solar irradiation, temperatures of the integrated system, membrane flux, and thermoelectric properties in different seasons are also analyzed. A mathematical model was established to calculate the relationship between membrane flux and temperature difference. The experimental results show that the membrane flux of VMD is 2.73 L/(m2·h); the simulated seawater can achieve a desalination rate of 99.9%. After economic analysis, the operating incomes of the system under sunny weather conditions in different seasons were all positive.

NuSTAR Spectral Analysis beyond 79 keV with Stray Light

Due to the structure of the NuSTAR telescope, photons at a large off axis (>1°) can reach the detectors directly (stray light), without passing through the instrument optics. At these off-axis angles NuSTAR essentially turns into a collimated instrument and the spectrum can extend to energies above the Pt K edge (79 keV) of the multilayers, which limits the effective area bandpass of the optics. We present the first scientific spectral analysis beyond 79 keV using a Cygnus X-1 observation in StrayCats: the catalog of stray light observations. This serendipitous stray light observation occurred simultaneously with an INTEGRAL observation. When the spectra are modeled together in the 30–120 keV energy band, we find that the NuSTAR stray light flux is well calibrated and constrained to be consistent with the INTEGRAL flux at the 90% confidence level. Furthermore, we explain how to treat the background of the stray light spectral analysis, which is especially important at high energies.

Universal Formulas for Calculating Emissivity and Integral Radiation Flux Densities of Black Bodies and Subwavelength Particles

Universal Formulas for Calculating Emissivity and Integral Radiation Flux Densities of Black Bodies and Subwavelength Particles

Механизм компенсации Бьеркнеса как возможный триггер низкочастотной изменчивости Арктического усиления

The causes of Arctic amplification are widely debated, and a cohesive picture has not been obtained yet. This study has investigated the role of the Atlantic meridional oceanic and atmospheric heat transport into the Arctic in the emergence of Arctic amplification. The integral advective fluxes in the layer of Atlantic waters and in the lower troposphere were considered. The results show a strong coupling between the meridional heat fluxes and regional Arctic amplification in the Eurasian Arctic on the decadal time scales (10–15 years). We argue that the low-frequency variability of Arctic amplification is regulated via the chain of oceanic heat transport — atmospheric heat transport — Arctic amplification. The atmospheric response to the ocean influence occurs with a delay of three years and is attributed to the Bjerknes compensation mechanism. In turn, the atmospheric heat and moisture transport directly affects the magnitude of Arctic amplification, with the latter lagging by one year. Thus, the variability of oceanic heat transport at the southern boundary of the Nordic Seas might be a predictor of the Arctic amplification magnitude over the Eurasian Basin of the Arctic Ocean with a lead time of four years. The results are consistent with the concept of the decadal Arctic climate variability expressed via the Arctic Ocean Oscillation index.

Helical magnetic mirror performance at up- and downstream directions of the axial force

The paper presents experimental results from the SMOLA device on the testing of the helical mirror confinement hypothesis. Helical mirror confinement is the technique of an active control of axial plasma losses from a confinement zone by multiple magnetic mirrors that move along the axis in the reference frame of the plasma that experiences $\boldsymbol{E} \times \boldsymbol{B}$ rotation due to an applied radial electric field. Theory predicts that a helical mirror will provide an axial force that modifies the plasma flow and, simultaneously, density pinching to the axis. The force direction depends on the plasma rotation direction. Experimental data on the axial plasma losses at different direction of the magnetic mirror movement are presented. If the trapped ions move in the direction opposite to the direction of the axial losses, then the particle flux reduces in the broad range of the plasma density. The confinement improves with the increase of the fraction of the trapped particles (effective mirror ratio was up to $R_{{\rm eff}}=5.8\pm 1.4$ ). If the trapped ions move in the same direction as the axial losses, then the flux depends on density. At intermediate densities, the integral flux through the transport section rises compared to the plasma flowing through the straight magnetic field. The effective mirror ratio is lower and does not significantly depend on the fraction of the trapped particles (effective mirror ratio at intermediate density was $R_{{\rm eff}}=3.3\pm 0.8$ ).

Possible discovery of Calvera’s supernova remnant

We report the discovery of a ring of low surface brightness radio emission around the Calvera pulsar, a high Galactic latitude, isolated neutron star, in the LOFAR Two-metre Sky Survey (LoTSS). It is centered at α = 14h11m12s.6, δ = +79°23′15″, has inner and outer radii of 14′.2 and 28′.4, and has an integrated flux density at 144 MHz of 1.08 ± 0.15 Jy. The ring center is offset by 4′.9 from the location of the Calvera pulsar. Observations with the Isaac Newton Telescope in the Hα band show no coincident optical emission, but they do show a small (~20″) optical structure internal to the ring. We consider three possible interpretations for the ring: that it is an H II region, a supernova remnant (SNR), or an odd radio circle (ORC). The positional coincidence of the ring, the pulsar, and an X-ray-emitting non-equilibrium ionization plasma previously detected lead us to prefer the SNR interpretation. If the source is indeed a SNR and if its association with the Calvera pulsar is confirmed, then Calvera’s SNR, or G118.4+37.0, will be one of few SNRs in the Galactic halo.

PIK Research Reactor Put into Megawatt-Power Operation

High-flux research reactor PIK has reached megawatt power. The reactor is undergoing the commissioning process divided into several stages, and it reached the power of 7 MW in March 2022. The reactor is designed to operate on extracted neutron beams, accommodating the first five neutron stations, which have already been used in test experiments. The value of the thermal neutron flux at the output of the PIK reactor’s Horizontal Experimental Channel No.10 (HEC-10) was measured by two independent methods. During the course of the reactor reaching 7 MW power, the integral neutron flux on the extracted neutron beam was measured. The spectrum of the extracted neutron beam is measured and presented.

Totally volume integral of fluxes for discontinuous Galerkin method-two dimensional Euler equations

In this paper, the scheme of constructing high-order accurate totally volume discontinuous finite element method for the numerical solution of the 1D Euler equations is extended to 2D Euler equations on Cartesian meshes. In the present work, the boundary integral fluxes are transformed into volume integral by applying divergence theorem to the boundary integral of the Riemann fluxes. Therefore, the totally volume discontinuous finite element is independent on the boundary integral fluxes at the element boundaries as opposed to the classical discontinuous Galerkin method. The accuracy is obtained by applying high-order polynomial approximations within elements using the tensor product of Lagrange polynomial. For temporal integration, strong stability preserving Runge-Kutta method SSPRK (3, 3) is applied. The scheme is stabilized by using Streamline Upwind Petrov Galerkin (SUPG) stabilization technique. For the spatial discretization, the polynomial of order 1and 2 are used, the shape function is constructed for the master (computational) element after applying the coordinate transformation for the physical domain, the transformation for the governing equations is performed to get it in the function of computational Cartesian, then the governing equations are put in conservative form. The numerical results of applying totally volume integral discontinuous Galerkin method for two-dimensional Euler equations presented in this paper show that the scheme is very accurate, fast, and effective even with shock appearance.

High gas throughput SOLPS-ITER simulations extending the ITER database to strong detachment

SOLPS-ITER simulations performed for Q DT = 10, P SOL = 100 MW burning plasmas on ITER extend the existing database to high values of separatrix averaged neon impurity concentration (⟨c Ne⟩ ≈ 6%) and divertor neutral pressure (⟨p div⟩ > 25 Pa) in order to determine the heat flux mitigation capability of these scenarios and whether strongly detached states are accessible. In the existing database of ITER simulations, the level of detachment was limited to cases where the integral ion flux to the outer target was greater than 80% of the value at rollover, with the impurity radiation localized near the target. With the possibility of narrow heat flux channels and increased deposited power due to tile shaping, it is important to explore operation at a higher degree of detachment. Two series of simulations were explored to extend the database of SOLPS simulations. By increasing the deuterium and neon puff rates proportionally, the peak divertor energy flux (q ⊥,max) is decreased from 5 to 3 MW m−2 while ⟨p div⟩ increased from 11 to 27 Pa. By increasing only the neon puff, q ⊥, max can be reduced to <1MW m−2 while ⟨p div⟩ is maintained at Pa. As the neon puff level is increased, the position of the impurity radiation peak is shifted towards the X-point. At the highest neon puff levels with steady-state solutions, the electron temperature is reduced below 1 eV across 50 cm of each divertor target. The new cases extend previously observed tight relationships in power and momentum loss factors to low electron temperature improving their utility for highly detached regimes.