Journal of Astrophysics and Astronomy最新文献

A recent study announced the detection of three bands in the ultraviolet emission spectra of more than a dozen comets, assigning two of them to pentacene (C(_{22})H(_{14})) and the third one to toluene (C(_7)H(_8)). The comparison of the spectra with the results of exploitable laboratory measurements on rare-gas-matrix-isolated pentacene and jet-cooled toluene does not reveal any elements that justify the assignment, which is therefore unsubstantiated. The study also claimed the detection of an Fe ii line in the gas of all but one comet. Yet, spectroscopic data on Fe(^+) do not corroborate the attribution. Because spectroscopic measurements on the ultraviolet emission of pentacene in the gas phase are not available, this work also presents a synthetic spectrum of the S(_5rightarrow textrm{S}_0) transition relevant to the wavelength range of the observations. Calculated using density functional theory and its time-dependent extension, the synthetic spectrum may facilitate the search for pentacene fluorescence in cometary spectra until laboratory measurements are accessible.

Understanding thermal and turbulence properties of interplanetary coronal mass ejections (ICMEs) is essential for analysing their evolution and interactions with the surrounding medium. This study explores these characteristics across different regions of two distinct ICMEs observed at 1 AU, utilizing in situ measurements from the Wind spacecraft. Polytropic indices ((Gamma _e) for electrons and (Gamma _p) for protons) reveal significant deviations from adiabatic expansion, suggesting sustained heating mechanisms within the ICMEs even at 1 AU. Effective polytropic index ((Gamma _{text {eff}})) of the magnetic ejecta (ME) in both ICME1 and ICME2 is found to be near-isothermal ((Gamma _{text {eff}} = 0.88) and 0.76), aligning with measurements near the Sun, highlighting consistent heating across heliospheric distances. Spectral analysis at the inertial scale reveals Kolmogorov-like turbulence in the fast ICME1’s ME, while ME of the slower ICME2 exhibits less-developed turbulence with a shallower spectral index ((alpha _B)). Turbulence analysis in the dissipation scale indicates that the ME of slower ICME2 is less affected by the ambient medium than the faster ICME2. The MEs of both ICMEs show magnetic compressibility much smaller than unity ((C_B<1)), suggesting dominant Alfvénic fluctuations in the MEs. Notably, the partial variance of increments (PVI) method identifies more intermittent structures, such as current sheets and reconnection sites, in sheath and post-ICME regions. Higher PVI values correlate with regions of increased electron and proton temperatures (for the sheath region) as well as higher (C_B) values, highlighting their role in local energy dissipation. These results enchance the importance of ongoing heating and turbulence processes in shaping the evolution of ICMEs.

Fermi Large Area Telescope (Fermi-LAT) observations reveal a significant population of blazars, and recent astrophysical research has focused on exploring flux variations in blazars. Up to now, Fermi-LAT has discovered a significant number of blazars, displaying quasi-periodic behaviour. In this study, Fermi-LAT data is utilized to construct the (gamma )-ray light curve for blazar J0811.4(+)0146 spanning from August 2008 to November 2024, covering 16 years of observations. Four distinct methods, namely, Lomb–Scargle periodogram (LSP), Weighted wavelet Z-transform (WWZ), discrete correlation function (DCF) and Jurkevich (JV), are employed to investigate (gamma )-ray emissions from this blazar in detail. The analysis reveals quasi-periodic oscillation (QPO) behaviour with a period of (4.35 pm 0.34) years. Significance of this QPO is assessed using Monte Carlo simulations, which indicate a significance level of 4.5(sigma ). This study suggests that the detected QPO can be plausibly explained by Newtonian-driven jet precession associated with a supermassive black hole binary system (SMBHB). Utilizing this model, we estimate, mass of the primary black hole to be (7.3 times 10^9 textrm{M}_{odot }), mass of the secondary black hole to be (2.1 times 10^9 textrm{M}_{odot }) and (frac{R_{1}}{R_{2}}) to be 0.27, resulting in an orbital period of the secondary black hole ((P_{M_2})) of 1.15 years and a precession period of the jet of (sim )42.49 years.

The detection of gravitational waves (GW) by the LIGO-Virgo-KAGRA (LVK) network has opened up a new era in astrophysics. The identification of the electromagnetic counterparts of GW sources is crucial for multi-messenger astronomy, one way of which is to use galaxy catalogues to guide optical follow-up observations. In this paper, we test the utility of a galaxy-targeted approach with mass prioritised galaxy ranking for the ongoing LIGO O4 run. We have used the simulated results for the expected LIGO O4 events and the NED-LVS galaxy catalogue, and based our study on small field of view telescopes, specifically the GROWTH-India Telescope (GIT). With the increase in sensitivity of LIGO/Virgo in the ongoing observing run O4, the expected number of total detections have gone up, but most of these are also now poorly localised. We show that a larger volume covered in the same field-of-view (FoV) on the sky results in a large increase in the total number of galaxies in each FoV. A significant top-heaviness is observed in the mass-ranked list of galaxies, which still numbers a few thousand in most cases. At larger distances, such high numbers of deep follow-up observations are infeasible in most cases, rendering galaxy catalogues useful in limited cases. However, these are still useful at lower distances where LVK detectors are currently sensitive and where galaxy completeness is higher. We also explore the effect of mass-filling to account for galaxy catalogue incompleteness at large distances. If mass-filled probabilities are considered as the metric for ranking and coverage, we find that the conventional 2D probability search performs better than a 3D galaxy catalogue (without mass-filling) based search at distances larger than 300 Mpc (up to which NED-LVS is ({sim } 70)% complete), and using 3D mass times probability in each tile performs better for nearby events.

I explore models of the dust-scattered component of the cosmic ultraviolet background (CUVB) at the north galactic pole (NGP) to develop a framework for calculating the dust-scattered light as a function of the optical depths. As expected, I find that the dust-scattered emission scales linearly, with reddening up to (E(B-V) approx 0.1) mag and derive a parametric model for this dependence. I have applied these models to fit the far-ultraviolet (1350–1800 Å) observations from the galaxy evolution explorer (GALEX) finding that the optical constants of the interstellar dust grains—albedo (a) and phase function asymmetry factor (g)—are consistent with predictions from the Astrodust model ((a = 0.33), (g = 0.68)). I detect an isotropic offset of (267 pm 7) ph cm(^{-2}) s(^{-1}) sr(^{-1}) Å(^{-1}), half of which remains unaccounted for, by known Galactic or extragalactic sources. I will now extend my analysis to wider sky regions with the goal of generating high-resolution extinction maps.

This research focuses on parametrization of deceleration parameter within the structure of modified symmetric teleparallel gravity or (fleft(Qright)) gravity, where (Q) represents the nonmetricity scalar. To explore evolutionary timeline of the Universe, we considered the logarithmic form: (fleft(Qright)=m+n text,{rm{{ln}}}(Q)), where (m) and (n) are constants. In this context, we utilize a particular form of deceleration parameter given by (qleft(zright)=frac{1}{2}+frac{{q}_{1}z+{q}_{2}}{{(1+z)}^{2}},) where ({q}_{1}), ({q}_{2}) and redshift, (z) are the parameters. This form allows a transition from a decelerating phase to an accelerating phase. Solution for the Hubble parameter is derived using the given parametric form of (q), which is then applied to the Friedmann equations. Following this, we estimated the model parameters’ best-fit values by using 115 supernovae Ia data points and Planck Collaboration (2018). We also focus on testing energy conditions in the context of cosmological acceleration. Moreover, we analysed the evolution of density, pressure, equation of state (EoS) parameter and Om(z) diagnostics to understand accelerated expansion phase of the Universe.

Non-specular meteor trail echoes are radar reflections from plasma instabilities, which are caused by field-aligned irregularities (FAI). Here, we reported on characteristics of non-specular trail echoes frequently detected with 53 MHz Gadanki ((13.5^circ )N, (79.2^circ )E) MST radar. These echoes are characteristically different in size and nature, having non-specular reflections over several range-bins with several seconds of duration. We presented few representative examples of such echoes detected with Gadanki MST radar. These examples were analysed and discussed on case by case to understand their evolutionary mechanism. Based on the current understanding of meteor trail theories, we also discussed the most possible factors responsible for the evolution of such echoes.

In this paper, we presented the relationship between prominence eruptions (PEs) and coronal mass ejections (CMEs) from May 2010 to December 2019 covering most of the solar cycle 24. We used data from the atmospheric imaging assembly (AIA) for PEs and the large angle and spectrometric coronagraph (LASCO) for CMEs. We identified 1225 PEs, with 67% being radial, 32% transverse and 1% failed PEs. The radial and transverse PEs, and the combined set have average speeds of (approx )53, 9 and 38 (text {km s}^{-1}), respectively. PE association with CMEs is examined by assigning a confidence level (CL) from 0 (no association) to 3 (clear association). Out of 1225 PEs, 662 (54%) are found to be associated with CMEs including CLs 1, 2 and 3. Our study reveals that the spatial and temporal relationships between PEs and CMEs vary over the solar cycle. During solar minima, CMEs tend to deflect towards the equator, possibly due to a stronger polar field. Temporal offsets are larger during solar maxima and smaller during the minima. This implies that the PEs appear earlier in LASCO C2 FOV during the minima than the maxima. Among the 662 CMEs associated with PEs, 78% show clear bright core structures. Investigation of morphological and temporal behaviour’s of these CMEs indicate that the prominences evolve into CME cores at higher altitudes suggesting that PEs and CME cores are the same structure. Average speeds of the PEs, CME core and CME leading edge are 62, 390 and 525 (text {km s}^{-1}), respectively. The speed of CME cores is faster than the PEs because the former was observed at larger heights, where they have accelerated to higher speeds.

We are exploring the possibility of carrying out radio interferometric observations of the solar chromosphere at ({approx }) 11.2 GHz (({lambda }=2.68) cm), in both total intensity (Stokes-I) and circularly polarized intensity (Stokes-V), using low-cost commercial dish TV antennas. Here, we present our initial results on the magnetic field strength (B) estimated using data obtained with a prototype set-up, and compare them with similar observations.

Astrophysical compact objects, viz., white dwarfs, neutron stars and black holes, are the remnants of stellar deaths at the end of their life cycles. They are ideal testbeds for various fundamental physical processes under extreme conditions that are unique in nature. Observational radio astronomy with uGMRT and OORT facilities has led to several important breakthroughs in studies of different kinds of pulsars and their emission mechanisms. On the other hand, accretion processes around compact objects are at the core of Indian astronomy research. In this context, AstroSat mission revolutionized spectro-temporal observations and measurements of accretion phenomena, quasi-periodic oscillations, and jet behaviour in binary systems hosting compact objects. Moreover, recently launched XPoSat mission is set to provide an impetus to these high-energy phenomena around compact objects by enabling us to conduct polarization measurements in the X-ray band. Further, during the past decade, numerous gravitational wave signals have been observed from coalescing black holes and neutron stars in binary systems. Recent simultaneous observation of GW170817 event in both gravitational waves and electromagnetic channels has ushered in the era of multi-messenger astronomy. In the future, synergistic efforts among several world-class observational facilities, e.g., LIGO-India, SKA, TMT, etc., within the Indian astrophysics community will provide a significant boost to achieve several key science goals that have been delineated here. In general, this paper plans to highlight scientific projects being pursued across Indian institutions in this field, the scientific challenges that this community would be focusing, and the opportunities available in the coming decade. Finally, we have also mentioned the required resources, both in the form of infrastructural and human resources.