Broad-band spectral evolution and temporal variability of IGR J17091-3624 during its 2016 outburst: <Emphasis Type="Italic">SWIFT</Emphasis> and <Emphasis Type="Italic">NuSTAR</Emphasis> results

We report on the 2016 outburst of the transient Galactic Black Hole candidate IGR J17091-3624 based on the observation campaign carried out with SWIFT and NuSTAR. The outburst profile, as observed with SWIFT-XRT, shows a typical ‘q’-shape in the Hardness Intensity Diagram (HID). Based on the spectral and temporal evolution of the different parameters, we are able to identify all the spectral states in the q-profile of HID and the Hardness-RMS diagram (HRD). Both XRT and NuSTAR observations show an evolution of low frequency Quasi periodic oscillations (QPOs) during the low hard and hard intermediate states of the outburst rising phase. We also find mHz QPOs along-with distinct coherent class variabilities (heartbeat oscillations) with different timescales, similar to the \(\rho \)-class (observed in GRS 1915+105). Phenomenological modelling of the broad-band XRT and NuSTAR spectra also reveals the evolution of high energy cut-off and presence of reflection from ionized material during the rising phase of the outburst. Further, we conduct the modelling of X-ray spectra of SWIFT and NuSTAR in 0.5–79 keV to understand the accretion flow dynamics based on two component flow model. From this modelling, we constrain the mass of the source to be in the range of \(10.62\mbox{--}12.33~\mbox{M}_{\odot }\) with 90% confidence, which is consistent with earlier findings.     

Plane Symmetric Dark Energy Models in the Form of Wet Dark Fluid in <Emphasis Type="Italic">f</Emphasis> (<Emphasis Type="Italic">R</Emphasis>,<Emphasis Type="Italic">T</Emphasis>) Gravity

In this paper, we have investigated the plane symmetric space-time with wet dark fluid (WDF), which is a candidate for dark energy, in the framework of f (R,T) gravity Harko et al. 2011, Phys. Rev. D, 84, 024020), where R and T denote the Ricci scalar and the trace of the energy–momentum tensor respectively. We have used the equation of state in the form of WDF for the dark energy component of the Universe. It is modeled on the equation of state p = ω(ρ ? ρ ^?). The exact solutions to the corresponding field equations are obtained for power-law and exponential volumetric expansion. The geometrical and physical parameters for both the models are studied. Also, we have discussed the well-known astrophysical phenomena, namely the look-back time, proper distance, the luminosity distance and angular diameter distance with red shift.     

Thermonuclear X-ray burst of MXB 1658-298 with <Emphasis Type="Italic">NuSTAR</Emphasis>

MXB 1658-298 is a transient Low-Mass X-ray Binary (LMXB), which shows eclipses, dips and bursts in its light curve. This source has undergone three active periods separated by long quiescent phases. The latest phase of enhanced X-ray emission was observed during 2015–2016. We have analysed broadband data from Swift/XRT and NuSTAR observations carried out in 2015. During NuSTAR observation, one thermonuclear X-ray burst took place. The X-ray emission during the burst was brighter by a factor of \(\sim 200\), compared to the pre-burst emission. This work focuses on the spectral analysis of MXB 1658-298 during the persistent and the burst phases using NuSTAR observation of 2015. We have also determined the temperature and radius evolution during the burst using the time-resolved spectroscopy. The burst phase shows mild Photospheric Radius Expansion (PRE).     

Plane Symmetric Cosmological Model with Quark and Strange Quark Matter in <Emphasis Type="Italic">f</Emphasis> (<Emphasis Type="Italic">R</Emphasis>, <Emphasis Type="Italic">T</Emphasis>) Theory of Gravity

We studied plane symmetric cosmological model in the presence of quark and strange quark matter with the help of f(R, T) theory. To decipher solutions of plane symmetric space-time, we used power law relation between scale factor and deceleration parameter. We considered the special law of variation of Hubble’s parameter proposed by Berman (Nuovo Cimento B74, 182, 1983) which yields constant deceleration parameter. We also discussed the physical behavior of the solutions by using some physical parameters.     

Synchronous <Emphasis Type="Italic">UBVR</Emphasis> photometry and spectroscopy of DI Cephei

We present our synchronous spectroscopy and photometry of DI Cep, a classical T Tauri star. The equivalent widths and radial velocities of the individual components and Hα, Hβ, D1 and D2 Na I, and HeI λ5876 Å emission line profiles exhibit variability. We have found a clear positive correlation between the brightness and equivalent width for the Hα and Hβ emission lines. The photometric and spectroscopic data are satisfactorily described in phases of a 9-day period. The expected magnetic field of the star has been estimated using existing magnetospheric models to be 655–1000 G. The star is suspected to be a binary.     

The Moon: From Research to Exploration (To the 50th anniversary of <Emphasis Type="Italic">Luna-9</Emphasis> and <Emphasis Type="Italic">Luna-10</Emphasis> Spacecraft)

The paper describes unmanned spacecraft Luna-9, Luna-10, and similar ones designed by NPO Lavochkin. The history of their development is given, and their high importance in lunar studies is noted. Projects of Luna-Globe, Luna-Resurs, and Luna-Grunt that should be implemented in the near future are briefly described.     

Determining the Absolute Magnitudes of Galactic-Bulge Red Clump Giants in the <Emphasis Type="Italic">Z</Emphasis> and <Emphasis Type="Italic">Y</Emphasis> Filters of the Vista Sky Surveys and the <Emphasis Type="Italic">IRAC</Emphasis> Filters of the Spitzer Sky Surveys

The properties of red clump giants in the central regions of the Galactic bulge are investigated in the photometric Z and Y bands of the infrared VVV (VISTA/ESO) survey and the [3.6], [4.5], [5.8], and [8.0] μm bands of the GLIMPSE (Spitzer/IRAC) Galactic plane survey. The absolute magnitudes for objects of this class have been determined in these bands for the first time: M _Z = ?0.20 ± 0.04, M _Y = ?0.470 ± 0.045, M_[3.6] = ?1.70 ± 0.03, M_[4.5] = ?1.60 ± 0.03, M_[5.8] = ?1.67 ± 0.03, and M_[8.0] = ?1.70 ± 0.03. A comparison of the measured magnitudes with the predictions of theoretical models for the spectra of the objects under study has demonstrated good mutual agreement and has allowed some important constraints to be obtained for the properties of bulge red clump giants. In particular, a comparison with evolutionary tracks has shown that we are dealing predominantly with the high-metallicity subgroup of bulge red clump giants. Their metallicity is slightly higher than has been thought previously, [M/H] ? 0.40 (Z ? 0.038) with an error of [M/H] ? 0.1 dex, while the effective temperature is 4250± 150 K. Stars with an age of 9–10 Gyr are shown to dominate among the red clump giants, although some number of younger objects with an age of ~8 Gyr can also be present. In addition, the distances to several Galactic bulge regions have been measured, as D = 8200–8500 pc, and the extinction law in these directions is shown to differ noticeably from the standard one.     

The particle background of the <Emphasis Type="Italic">X-IFU</Emphasis> instrument

In this paper we are going to review the latest estimates for the particle background expected on the X-IFU instrument onboard of the ATHENA mission. The particle background is induced by two different particle populations: the so called “soft protons” and the Cosmic rays. The first component is composed of low energy particles (< 100s keV) that get funnelled by the mirrors towards the focal plane, losing part of their energy inside the filters and inducing background counts inside the instrument sensitivity band. The latter component is induced by high energy particles (> 100 MeV) that possess enough energy to cross the spacecraft and reach the detector from any direction, depositing a small fraction of their energy inside the instrument. Both these components are estimated using Monte Carlo simulations and the latest results are presented here.     

The <Emphasis Type="Italic">z</Emphasis> distribution of hydrogen clouds and masers with kinematic distances

Data on HII regions, molecular clouds, and methanol masers have been used to estimate the Sun’s distance from the symmetry plane z _⊙ and the vertical disk scale height h. Kinematic distance estimates are available for all objects in these samples. The Local-arm (Orion-arm) objects are shown to affect noticeably the pattern of the z distribution. The deviations from the distribution symmetry are particularly pronounced for the sample of masers with measured trigonometric parallaxes, where the fraction of Local-arm masers is large. The situation with the sample of HII regions in the solar neighborhood is similar. We have concluded that it is better to exclude the Local arm from consideration. Based on the model of a self-gravitating isothermal disk, we have obtained the following estimates from objects located in the inner region of the Galaxy (R ≤ R ₀): z _⊙ = ?5.7 ± 0.5 pc and h ₂ = 24.1 ± 0.9 pc from the sample of 639 methanol masers, z _⊙ = ?7.6±0.4 pc and h ₂ = 28.6±0.5 pc from 878HII regions, z _⊙ = ?10.1 ± 0.5 pc and h ₂ = 28.2 ± 0.6 pc from 538 giant molecular clouds.     

Soft proton flux on <Emphasis Type="Italic">ATHENA</Emphasis> focal plane and its impact on the magnetic diverter design

The experience gained with the current generation of X-ray telescopes like Chandra and XMM-Newton has shown that low energy “soft” protons can pose a severe threat to the possibility to exploit scientific data, reducing the available exposure times by up to 50% and introducing a poorly reproducible background component. These soft protons are present in orbits outside the radiation belts and enter the mirrors, being concentrated towards the focal plane instruments, losing energy along their path and finally depositing their remaining energy in the detectors. Their contribution to the residual background will be even higher for ATHENA with respect to previous missions, given the much higher collecting area of the mirrors, even if the instruments will likely suffer no significant radiation damage from this particles flux. As a consequence this soft proton flux shall be damped with the use of a magnetic diverter to avoid excess background loading on the WFI or X-IFU instruments. We present here a first complete evaluation of this background component for the two focal plane instruments of the ATHENA mission in absence of a magnetic diverter, and derive the requirements for such device to reduce the soft protons induced background below the level required to enable the mission science. We estimate the soft proton flux expected in L2 for the interplanetary component and for the component generated locally by acceleration processes in the magnetotail. We produce a proton response matrix for each of the two instruments of ATHENA focal plane, exploiting two independent Monte Carlo simulations to estimate the optics concentration efficiency, and Geant4 simulations to evaluate the energy loss inside the radiation filters and deposited in the detector. With this modular approach we derive the expected fluxes and spectra for the soft protons component of the background. Finally, we calculate the specifics of a magnetic diverter able to reduce such flux below the required level for both X-IFU and WFI.     

<Emphasis Type="Italic">GALEX</Emphasis> and star formation

Wide-field far-UV (FUV, 1344–1786 Å) and near-UV (NUV, 1771–2831 Å) imaging from GALEX provides a deep, comprehensive view of the young stellar populations in hundreds of nearby galaxies, shedding new light on the process of star formation (SF) in different environments, and on the interplay between dust and SF. GALEX’s FUV-NUV color is extremely sensitive to stellar populations of ages up to a few hundred Myrs, unambiguously probing their presence and enabling age-dating and stellar mass estimate, together with the characterization of interstellar dust extinction. The deep sensitivity, combined with the wide field-of-view, made possible in particular the discovery and characterization of star formation in extremely low-density, diffuse gas environments such as outer galaxy disks, tidal tails, low-surface-brightness galaxies (LSB) and dwarf Irregular galaxies, and of rejuvenation episodes in early-type galaxies. Such results provide several missing links for interpreting galaxy classes in an evolutionary context, extend our knowledge of the star-formation process to previously unexplored conditions, constrain models of galaxy disk formation, and clarify the mutual role of dust and star formation. We review a variety of star-forming environments studied by GALEX, and provide some model analysis tools useful for interpretation of GALEX measurements, and potentially as basic science planning tools for next-generation UV instruments.     

Dynamics of Large-Scale Solar-Wind Streams Obtained by the Double Superposed Epoch Analysis: 2. Comparisons of CIRs <Emphasis Type="Italic">vs</Emphasis>. Sheaths and MCs <Emphasis Type="Italic">vs</Emphasis>. Ejecta

This work is a continuation of our previous article (Yermolaev et al. in J. Geophys. Res. 120, 7094, 2015), which describes the average temporal profiles of interplanetary plasma and field parameters in large-scale solar-wind (SW) streams: corotating interaction regions (CIRs), interplanetary coronal mass ejections (ICMEs including both magnetic clouds (MCs) and ejecta), and sheaths as well as interplanetary shocks (ISs). As in the previous article, we use the data of the OMNI database, our catalog of large-scale solar-wind phenomena during 1976?–?2000 (Yermolaev et al. in Cosmic Res., 47, 2, 81, 2009) and the method of double superposed epoch analysis (Yermolaev et al. in Ann. Geophys., 28, 2177, 2010a). We rescale the duration of all types of structures in such a way that the beginnings and endings for all of them coincide. We present new detailed results comparing pair phenomena: 1) both types of compression regions (i.e. CIRs vs. sheaths) and 2) both types of ICMEs (MCs vs. ejecta). The obtained data allow us to suggest that the formation of the two types of compression regions responds to the same physical mechanism, regardless of the type of piston (high-speed stream (HSS) or ICME); the differences are connected to the geometry (i.e. the angle between the speed gradient in front of the piston and the satellite trajectory) and the jumps in speed at the edges of the compression regions. In our opinion, one of the possible reasons behind the observed differences in the parameters in MCs and ejecta is that when ejecta are observed, the satellite passes farther from the nose of the area of ICME than when MCs are observed.     

Action-minimizing solutions of the one-dimensional <Emphasis Type="Italic">N</Emphasis>-body problem

We supplement the following result of C. Marchal on the Newtonian N-body problem: A path minimizing the Lagrangian action functional between two given configurations is always a true (collision-free) solution when the dimension d of the physical space \({\mathbb {R}}^d\) satisfies \(d\ge 2\). The focus of this paper is on the fixed-ends problem for the one-dimensional Newtonian N-body problem. We prove that a path minimizing the action functional in the set of paths joining two given configurations and having all the time the same order is always a true (collision-free) solution. Considering the one-dimensional N-body problem with equal masses, we prove that (i) collision instants are isolated for a path minimizing the action functional between two given configurations, (ii) if the particles at two endpoints have the same order, then the path minimizing the action functional is always a true (collision-free) solution and (iii) when the particles at two endpoints have different order, although there must be collisions for any path, we can prove that there are at most \(N! - 1\) collisions for any action-minimizing path.     

A New Inner Heliosphere Proton Parameter Dataset from the <Emphasis Type="Italic">Helios</Emphasis> Mission

In the near future, Parker Solar Probe and Solar Orbiter will provide the first comprehensive in-situ measurements of the solar wind in the inner heliosphere since the Helios mission in the 1970s. We describe a reprocessing of the original Helios ion distribution functions to provide reliable and reproducible data to characterise the proton core population of the solar wind in the inner heliosphere. A systematic fitting of bi-Maxwellian distribution functions was performed to the raw Helios ion distribution function data to extract the proton core number density, velocity, and temperatures parallel and perpendicular to the magnetic field. We present radial trends of these derived proton parameters, forming a benchmark to which new measurements in the inner heliosphere will be compared. The new dataset has been made openly available for other researchers to use, along with the source code used to generate it.     

Optical spectroscopy of candidates for quasars at 3 &lt; <Emphasis Type="Italic">z</Emphasis> &lt; 5.5 from the XMM-newton X-ray survey. A distant X-ray quasar at <Emphasis Type="Italic">z</Emphasis> = 5.08

We present the results of optical spectroscopy for 19 quasar candidates at photometric redshifts z _phot ? 3, 18 of which enter into the Khorunzhev et al. (2016) catalog (K16). This is a catalog of quasar candidates and known type 1 quasars selected among the X-ray sources of the 3XMM-DR4 catalog of the XMM-Newton serendipitous survey. We have performed spectroscopy for a quasi-random sample of new candidates at the 1.6-m AZT-33IK telescope of the Sayan Solar Observatory and the 6-m BTA telescope of the Special Astrophysical Observatory. The spectra at AZT-33IK were taken with the new low- and medium-resolution ADAM spectrograph that was produced and installed on the telescope in 2015. Fourteen of the 18 candidates actually have turned out to be quasars; 10 of them are at spectroscopic redshifts z _spec > 3. The high purity of the sample of new candidates suggests that the purity of the entire K16 catalog of quasars is probably 70–80%. One of the most distant (z _spec = 5.08) optically bright (i′ ? 21) quasars ever detected in X-ray surveys has been discovered.     

Catalog of candidates for quasars at 3 &lt; <Emphasis Type="Italic">z</Emphasis> &lt; 5.5 selected among X-Ray sources from the 3XMM-DR4 survey of the XMM-Newton observatory

We have compiled a catalog of 903 candidates for type 1 quasars at redshifts 3 < z < 5.5 selected among the X-ray sources of the “serendipitous” XMM-Newton survey presented in the 3XMMDR4 catalog (the median X-ray flux is ≈5 × 10^?15 erg s^?1 cm^?2 in the 0.5–2 keV energy band) and located at high Galactic latitudes |b| > 20° in Sloan Digital Sky Survey (SDSS) fields with a total area of about 300 deg². Photometric SDSS data as well infrared 2MASS and WISE data were used to select the objects. We selected the point sources from the photometric SDSS catalog with a magnitude error δ _mz′ < 0.2 and a color i′ ? z′ < 0.6 (to first eliminate the M-type stars). For the selected sources, we have calculated the dependences χ²(z) for various spectral templates from the library that we compiled for these purposes using the EAZY software. Based on these data, we have rejected the objects whose spectral energy distributions are better described by the templates of stars at z = 0 and obtained a sample of quasars with photometric redshift estimates 2.75 < z _phot < 5.5. The selection completeness of known quasars at z _spec > 3 in the investigated fields is shown to be about 80%. The normalized median absolute deviation (Δz = |z _spec ? z _phot|) is σ _Δz /(1+z _spec) = 0.07, while the outlier fraction is η = 9% when Δz/(1 + z _спек.) > 0.2. The number of objects per unit area in our sample exceeds the number of quasars in the spectroscopic SDSS sample at the same redshifts approximately by a factor of 1.5. The subsequent spectroscopic testing of the redshifts of our selected candidates for quasars at 3 < z < 5.5 will allow the purity of this sample to be estimated more accurately.     

Magnetic field in a fluctuating <Emphasis Type="Italic">ABC</Emphasis> flow

The standard dynamo models that explain the origin of the large-scale magnetic fields of celestial bodies are related to the view of turbulent or convective flows as a locally statistically homogeneous and isotropic, but not mirror-symmetric, random field. Using an ABC flow, which is a classical example of a flow with deterministic chaos, we ascertain the extent to which the behavior of the magnetic field in such a flow is similar to the behavior of the magnetic field in mirror-asymmetric turbulence. Such a similarity has been found to be achieved if its coefficients A, B, and C are assumed to be random processes.     

Observations of soft gamma-ray or hard X-ray bursts in the GRIF experiment on the <Emphasis Type="Italic">Mir</Emphasis> orbiting station

During the GRIF experiment onboard the Mir orbiting station, the sky was monitored with a PX-2 wide-field (～1 sr) scintillation X-ray spectrometer to detect bursts in the photon energy range 10–300 keV. Because of the comprehensive instrumentation, which, apart from the X-ray and gamma-ray instruments, also included charged-particle detectors, the imitations of astrophysical bursts by magnetospheric electron precipitations and strongly ionizing nuclei were effectively filtered out. It was also possible to separate solar and atmospheric events. Several tens of bursts interpreted as being astrophysical were detected in the experiment at sensitivity levels S～10^?7 erg cm^?2 (for bursts whose spectra were characterized by effective temperatures kT～100 keV) and S～3×10^?8 erg cm^?2 (for bursts with kT～25 keV). Some of the soft gamma-ray or hard X-ray bursts with kT～10–50 keV were identified with the bursting pulsar GRO J1744-28. Our estimate of the detection rate for cosmological soft gamma-ray or hard X-ray bursts from the entire sky suggests that the distributions of long-duration (>1 s) gamma-ray bursts (GRBs) in characteristic energy kT and duration are inconsistent with the steady-state cosmological model in which the evolution of burst sources is disregarded. Based on GRIF and BATSE/CGRO data, we conclude that most of the GRB sources originate at redshifts 1<z<5.     

Estimating the Mg <Emphasis Type="SmallCaps">ii</Emphasis> Index from 1961 Through 1981 Using Ca <Emphasis Type="SmallCaps">ii</Emphasis> K Images from the Mt Wilson Observatory

An empirical model of solar UV spectral irradiance has been developed that is based on observed spectral radiance measurements and full disk Ca ii K images. The Mg ii index is then calculated from the estimated spectra in a narrow wavelength range (180 Å) near the Mg ii doublet at 2800 Å. Our long term goal is to expand this wavelength range from 10 to 4000 Å in continuing studies based on spectral data covering this wavelength range (e.g. Skylab, UARS/SUSIM, TIMED/SEE, etc.). Our previous modeling effort produced spectra in this 180 Å range and the resulting Mg ii index values for the period from 1991 through 1995 and we have used observations during this time period to validate the model results. The current paper presents results from this model based on a 21-year portion of the recently digitized Ca ii K images from the Mt Wilson Observatory (MWO) film archive. Here we present details of the model, the required model modifications, and the resulting Mg ii index from 1961 through 1981. Since the NOAA Mg ii index did not begin until 1978, the present model results are compared to a Mg ii index estimated from the F_10.7 radio flux over this 21-year period. The NOAA Mg ii index, which is derived from measured UV spectra, is also included for comparison from late 1978 through 1981.     

Fission and the <Emphasis Type="Italic">r</Emphasis>-process: Competition between neutron-induced and beta-delayed fission

We show that for the discussed scenario of a neutron-star merger in highly neutronized ejecta (Y _e ?0.1), neutron-induced fission plays a major role in the r-process cycling and is the main obstacle to the formation of superheavy elements. At the final stage of the r-process, when the free-neutron density is already too low to maintain rapid nucleosynthesis and only beta-decay and beta-delayed fission take place, the leading role in forming the final abundances of chemical elements passes to delayed fission. The latter ultimately changes the abundances of individual isotopes in the region before the second peak and heavier than lead, which, in particular, affects the determination of the age of the Galaxy.