Journal of Astrophysics and Astronomy最新文献

We report the measurement of X-ray polarization in the high synchrotron peaked blazar 1ES 1959(+)650. Of the four epochs of observations from the Imaging X-ray Polarimetry Explorer, we detected polarization in the 2–8 keV band on two epochs. From the model-independent analysis of the observations on 28 October 2022, in the 2–8 keV band, we found the degree of polarization of (Pi _X = 9.0 pm 1.6)% and an electric vector position angle of (Psi _X = 53 pm 5) deg. Similarly, from the observations on 14 August 2023, we found (Pi _X) and (psi _X) values as (12.5 pm 0.7)% and (20 pm 2) deg, respectively. These values are also in agreement with the values obtained from spectro-polarimetric analysis of the I, Q, and U spectra. The measured X-ray polarization is larger than the reported optical values, ranging between 2.5% and 9% when observed from 2008 to 2018. Broadband spectral energy distribution constructed for the two epochs is well described by the one-zone leptonic emission model with the bulk Lorentz factor ((Gamma )) of the jet larger on 14 August 2023 compared to 28 October 2022. Our results favor the shock acceleration of the particles in the jet, with the difference in (Pi _X) between the two epochs being influenced by a change in the (Gamma ) of the jet.

Pulsating variables play a significant role in shaping modern astronomy. Presently it is an exciting era in observational study of variable stars owing to surveys like OGLE and TESS. The vast number of sources being discovered by these surveys is also creating opportunities for 1–2-m class telescopes to provide follow-up observations to characterize these. We present some initial observations of type-II cepheids from the Mt. Abu observatory and highlight the need for dedicated observing runs of pulsating variables. We also present optical designs for several suggested instruments for the Mt. Abu observatory that will contribute towards this goal. We present designs that are fairly simple and yet take due benefit of the unique telescopes and facilities present at the observatory.

Torsional Alfvén waves (TAWs) play a significant role in the dynamics of the solar atmosphere. A detailed study of the TAWs can provide valuable insights into various aspects of the internal structure of the solar atmosphere, and the coronal heating problem. In this paper, the effect of longitudinal structuring (such as gravitational stratification, temperature inhomogeneity, radiative cooling, and background plasma flow) on the characteristics of the standing TAWs in coronal plasma loops, which can be exploited in both temporal and spatial coronal seismology applications, is investigated. The governing equation for TAWs in a dynamic and stratified coronal plasma is reduced to a time-dependent partial differential equation. Analytical dispersion relations of the differential equation are extracted and solved numerically under various scenarios by imposing the necessary and sufficient boundary conditions. The numerical results indicate that the fundamental and first overtone mode frequencies and their ratios and the spatial anti-node shift of the first overtone mode are sensitive functions of gravitational stratification and scaled time of radiative cooling. The magnitude values of these quantities are strongly influenced by the magnitude of the temperature inhomogeneity parameter and are slightly affected by the scaled background plasma flow speed. Tuning the parameters that affect the oscillatory properties of the standing TAWs and matching them with observations can enhance our understanding of the coronal structures and their evolution and serve as a diagnostic tool in coronal seismology.

Several powerful flare events have been recorded because of long-term monitoring on the RT-22 radio telescope (Simeiz) of the galactic source G25.65(+)1.05 from 2000 to 2024. The amplitude of the most powerful flare increased rapidly and reached a record level for this source of 130 kJy. The orbital (7.5 years) and precessional (60 years) periods in the binary system of massive O5 class stars responsible for the occurrence of flares based on monitoring data have been presumably determined. Individual short flares, lasting no more than a month, presumably belonged to a maser in an unsaturated state. The shape of the central part of the maser line, near the maximum phase, suggests a single-component source responsible for the bulk of the increase in flux density. Thus, the most powerful kilomaser G25.65(+)1.05 in the water vapor line at frequency 22.2 GHz has been registered in the Galaxy. The possibility of detecting gravitational waves (GWs) coming from the massive stellar binary system is considered.

The active galactic nucleus S 0528(+)134 was discovered in a search survey at a frequency of 8550 MHz in 1969 using the radio telescope RT-22 (Simeiz) at the Crimean Astrophysical Observatory—the study aimed to search for new active galactic nuclei (AGN). In this article, the goal was to determine the physical characteristics of the close binary system S 0528(+)134 for the subsequent assessment of the level of gravitational radiation coming from it. During long-term monitoring of the object at a frequency of 8 GHz, some powerful flares of flux density occurred, which made it possible to consider the source the most powerful emitter in the Universe. The presence of selected harmonic components in the flux density variations of S 0528(+)134 allowed obtaining the main physical characteristics of a binary system of supermassive black holes (SMBHs), which placed S 0528(+)134 in the rank of one of the most massive SMBHs. This AGN can also be considered the most powerful source for detecting GWs by using International Pulsar Timing Array gravitational wave detectors.

In the planetary atmosphere, hydrogen cyanide (HCN) is an important nitrogen (N)-bearing molecule that plays a key role in the formation of several biomolecules via chain reactions. The presence of HCN characterizes the stratospheric composition of the solar gas planets and exoplanets. For several years, many observations have failed to identify the rotational and vibrational emission lines of HCN from the atmosphere of Saturn using ground- and space-based radio telescopes. We present the successful detection of the rotational emission line of HCN from the atmosphere of Saturn using the Atacama Large Millimeter/Submillimeter Array (ALMA) band 7. We detected the (textrm{J} = 4)–3 transition line of the HCN from the eastern and western limbs of Saturn with ({ge }5sigma ) statistical significance. The derived abundances of HCN in the western and eastern limbs are 6.19 and 2.90 ppb, respectively. We claim that HCN is formed in the atmosphere of Saturn via the photolysis of methane ((hbox {CH}_{4})) and ammonia ((hbox {NH}_{3})).

We report a detailed spectro-temporal analysis of the black hole low mass X-ray binary 4U 1543−475 during its 2021 outburst using the data from the Large Area X-ray Proportional Counter and the Soft X-ray Telescope instruments on board AstroSat. We studied the energy and frequency dependency of the source variability to probe the origin of the disc/coronal fluctuations. Following the state transition (from soft to intermediate state), the emergence of a band-limited noise component is observed along with the power law noise when the disk is recovering from a sudden decrease in the inner disk radius. A possible correlation between the low-frequency root mean square (RMS) variability amplitude and the covering fraction of the non-thermal component is detected. During the final AstroSat observation, a flip-flop phenomenon is reported, where rapid variation in RMS occurs in concurrence with sudden flux transition. An indication of the evolution of inner disk temperature along with a significant change in thermal flux was observed during the flip-flop phase, arguing for a disk instability-driven origin for this phenomenon. Our results suggest that the long-term variability evolution is primarily affected by the coronal changes, whereas the disk behavior governs the short-term variability evolution.

This work presents the first-ever broadband (0.7–25.0 keV) timing and spectral analysis of Be-HMXB 2S 1417–624 during its 2021 outburst. Using AstroSat observations, coherent pulsations at (sim )17.36633 s (MJD 59239.082) were detected in 0.7–7.0 keV SXT and 3.0–25.0 keV LAXPC data. The pulse profile was dual peaked at all energies, with the relative intensity of the main peak increasing with energy. The peaks in the SXT profiles were broad and comprised of several mini-structures. The LAXPC profiles were relatively smooth and had higher pulsed fractions, which increased with energy. The SXT(+)LAXPC simultaneous energy spectrum is well described by an absorbed power-law with exponential cut-off, a (sim )1.6 keV black body component, and a 6.47 keV emission line. A model comprising of an absorbed power law with high energy cut-off plus a partial covering absorber and Gaussian emission line fits the spectrum quite well. These results have been compared with timing and spectral features during the previous outbursts of this transient pulsar.

An analysis of the high-resolution ((Rsim 48000)) optical spectrum of hot (B1Ibe) post-AGB star LS 4331 (IRAS 17381−1616) is presented. The detailed identification of the observed absorption and emission features in the wavelength range 3700–9200 Å is carried out for the first time. The atmospheric parameters and chemical composition of the star are derived from the non-LTE analysis of absorption lines. We estimated (T_textrm{eff}=20900pm 500) K, (log g=2.57,pm ,0.08), (V_r=-51.7,pm ,0.8) km s(^{-1}), (xi _textrm{t}=24,pm ,4) km s(^{-1})  and (v sin i=30,pm ,5) km s(^{-1}). An abundance analysis for C, N, O, Mg, Al, S, and Si reveals that the N and O abundance is close to solar while metal underabundances relative to the solar value (i.e., ([mathrm{Mg/H}] = -1.04) dex, ([mathrm{Al/H}] = -1.20) dex, ([mathrm{Si/H}] = -0.46) dex) are found. LS 4331 is a high galactic latitude metal-poor and carbon-deficient hot post-AGB star. The underabundance of carbon (([mathrm{C/H}]=-0.64) dex) is similar to that found in other hot post-AGB stars and indicates that the star’s AGB phase of evolution was terminated before the third dredge-up. Plasma diagnostics are derived from the nebular emission lines. The presence of nebular emission lines in the spectrum of LS 4331 indicates that the photoionization of the circumstellar envelope has already started. The nebular parameters and expansion velocity of the nebula are derived. Using the Gaia DR3 distance, the absolute luminosity of the star is derived, and the star’s position on the post-AGB evolutionary tracks suggests that its initial main sequence mass is about 1.2 (M_{odot }). It is also reported that fast irregular brightness variations with an amplitude of up to 0.3 mag in the V band have been found in the star, typical of hot post-AGB objects.

The effect of finite non-zero temperature on the masses and radii of anisotropic deformed magnetized white dwarfs in the parameterized (gamma )-metric formalism is investigated. The equation of state (EoS) for a relativistic free Fermi gas of electrons surrounding a lattice of nuclei, considering the effects of finite temperature, Landau quantization, and anisotropic pressure is developed. We found stable super-Chandrasekhar masses of white dwarfs (above ({sim }5) (M_{odot })). At a fixed central density and temperature, the masses decrease monotonically as the central magnetic field increases, and equatorial radii increase monotonically. We also observed that the maximum mass and its corresponding equatorial radius decrease with the increase of the central magnetic field. Moreover, the maximum mass occurs at a higher central density as the magnetic field increases. This shows that increasing the magnetic field (hence increasing anisotropy) softens the EoS and makes the star more compact. We also found that the mass and equatorial radius increase with increasing temperature at a fixed central density and central magnetic field strength. This effect is significant for low central magnetic fields and low central densities. In essence, the finite temperature has an opposing effect to that of the magnetic field by decreasing the anisotropy of the system, thereby making the EoS stiffer and the star less compact.

Since the Fermi Large Area Telescope launch, a large sample of blazars has been detected in the (gamma )-ray band. One of the important parameters, the variability index (VI), is adopted to quantify the (gamma )-ray blazar variability. The variability of blazars can be affected by the geometric jet structure, accretions, source sizes, or evolutions of particles. In this paper, we compiled a sample of 2250 blazars (792 flat spectrum radio quasars, 1458 BL Lacertae objects) with some physical parameters to investigate the correlations between the VI and beaming effects. The VI shows positive correlations with the Doppler factors, (gamma )-ray luminosities, core dominances, and superluminal motions for both FSRQs and BL Lacs but only holds a positive correlation on polarizations for BL Lacs. The close correlations between VI and the beaming indicators reinforced the previous results that the (gamma )-ray variability is related to the jet, and the VI can be regarded as an effective indicator for the jet beaming effects of Fermi blazars.