IIA SAMPOORNA, MFull non-LTE multi-level radiative transfer: I. An atom with three bound infinitely sharp levels
The standard nonlocal thermodynamic equilibrium (non-LTE) multi-level radiative transfer problem only takes into account the deviation of the radiation field and atomic populations from their equilibrium distribution. Aims. We aim to show how to solve for the full non-LTE (FNLTE) multi-level radiative transfer problem, also accounting for deviation of the velocity distribution of the massive particles from Maxwellian. We considered, as a first step, a three-level atom with zero natural broadening. Methods. In this work, we present a new numerical scheme. Its initialisation relies on the classic, multi-level approximate Λ-iteration (MALI) method for the standard non-LTE problem. The radiative transfer equations, the kinetic equilibrium equations for atomic populations, and the Boltzmann equations for the velocity distribution functions were simultaneously iterated in order to obtain self-consistent particle distributions. During the process, the observer’s frame absorption and emission profiles were re-computed at every iterative step by convolving the atomic frame quantities with the relevant velocity distribution function. Results. We validate our numerical strategy by comparing our results with the standard non-LTE solutions in the limit of a two-level atom with Hummer’s partial redistribution in frequency, and with a three-level atom with complete redistribution. In this work, we considered the so-called cross-redistribution problem. We then show new FNLTE results for a simple three-level atom while evaluating the assumptions made for the emission and absorption profiles of the standard non-LTE problem with partial and cross-redistribution.
IIA SANTANU MONDALInterpreting the spectrotemporal properties of the black hole candidate swift J151857.0-572147 during its first outburst in 2024
The transient Galactic black hole candidate Swift J151857.0-572147 went through an outburst in 2024 March for the first time. Using publicly archived Insight-HXMT data, we have analyzed the timing and spectral properties of the source. We have extracted the properties of the quasiperiodic oscillations (QPOs) by fitting the power density spectrum, which inferred that the QPOs are of type C. We have detected QPOs up to ∼48 keV using an energy dependence study of the QPOs. A high-frequency QPO was not observed during this period. We also conclude that the oscillations of the shock in transonic advective accretion flows may be the possible reason for the origin of the QPOs. In the broad energy band of 2–100 keV, simultaneous data from the three onboard instruments of Insight-HXMT were used to perform spectral analysis. Different combinations of models, including a broken power law, a multicolor disk blackbody, interstellar absorption, nonrelativistic reflection in both neutral and ionized medium, and relativistic reflection, were used to understand the spectral properties during the outburst. We discovered that at the beginning of the analysis period, the source was in an intermediate state and later transitioning toward the soft state based on the spectral parameters. It has a high hydrogen column density, which could be due to some local absorption by the source.
IIA AMRUTHA, SA pilot method to determine the high mass end of the stellar initial mass function in galaxies using UVIT, Hα-MUSE observations and applied to NGC 628
We present a pilot method to estimate the high-mass initial mass function (IMF) across the arm, interarm, and spur regions in galaxies and apply it to NGC 628. We extracted star-forming complexes (SFCs) from the Hα Very Large Telescope/Multi Unit Spectroscopic Explorer and Ultraviolet Imaging Telescope (far-ultraviolet (FUV) and near-ultraviolet (NUV)) observations of NGC 628 and used Atacama Large Millimeter/submillimeter Array observations to define the molecular gas distribution. We find that the extinction-corrected Hα and FUV luminosities correlate well. Using the fact that O stars have a shorter lifetime (107 yr) compared to B stars (108 yr), we estimated the approximate number of O stars from Hα emission, and the number of B0 (M* > 10M⊙), and B1 (10M⊙ ≥ M* ≥ 3M⊙) stars using FUV and NUV observations. We derived the IMF index (α) for different regions using O to B0 (α1) and B0 to B1 (α2) stellar ratios. Our findings indicate that if we assume Hα arises only from O8-type stars, the resulting α1 value is consistent with the canonical IMF index. It steepens when we assume O stars with masses up to 100 M⊙ with mean α1 = 3.16 ± 0.62. However, the α2 does not change for large variations in the O-star population, and the mean α = 2.64 ± 0.14. When we include only blue SFCs (FUV − NUV ≤ 0.3), mean α2 is 2.43 ± 0.06. The IMF variation for SFCs in arms and spurs is insignificant. We also find that α2 correlates with different properties of the SFCs, the most prominent being the extinction-corrected UV color (FUV − NUV).
IIA VIVEK, MSpectroscopic quasar anomaly detection (SQuAD): I. Rest-frame UV spectra from SDSS DR16
We present the results of applying anomaly detection algorithms to a quasar spectroscopic subsample from the SDSS DR16 quasar catalog, covering the redshift range of 1.88 ≤ z ≤ 2.47. Methods. A principal component analysis (PCA) was employed for the dimensionality reduction of the quasar spectra, followed by a hierarchical k-means clustering in a 20-dimensional PCA eigenvector hyperspace. To prevent broad absorption line (BAL) quasars from being identified as the primary anomaly group, we conducted separate analyses on BAL and non-BAL quasars (a.k.a. QSOs), comparing both classes for a clearer identification of other anomalous quasar types. Results. We identified 2066 anomalous quasars, categorized into 10 broadly defined groups. The anomalous groups include: C IV peakers: quasars with extremely strong and narrow C IV emission lines; Excess Si IV emitters: quasars where the Si IV line is as strong as the C IV line; and Si IV deficient anomalies: which exhibit significantly weaker Si IV emission compared to typical quasars. The anomalous nature of these quasars is attributed to lower Eddington ratios for C IV peakers, supersolar metallicity for Excess Si IV emitters, and subsolar metallicity for Si IV deficient anomalies. Additionally, we identified four groups of BAL anomalies: blue BALs, flat BALs, reddened BALs, and FeLoBALs, distinguished primarily by the strength of reddening in these sources. Furthermore, among the non-BAL quasars, we identified three types of reddened anomaly groups classified as heavily reddened, moderately reddened, and plateau-shaped spectrum quasars, each exhibiting varying degrees of reddening. We present the detected anomalies as an accompanying value-added catalog.
IIA LABANYA KUMAR GUHACircumgalactic medium of quasar host galaxies at 0.4 ⩽ z ⩽ 0.8 probed by strong Mg II absorption
Using a sample of 166 projected quasar pairs, we investigate the influence of active galactic nuclei on the circumgalactic medium of the quasar host galaxies probed using strong Mg II absorption (i.e. W2796 ≥ 1 Å) at impact parameters (D) <100 kpc. The foreground quasars are restricted to the redshift range 0.4 ≤ z ≤ 0.8 and have median bolometric luminosity and stellar mass of 1045.1 erg s−1 and 1010.89M , respectively. We report detections of Mg II absorption in 29 cases towards the background quasar and in four cases along the line of sight to the foreground quasars. We do not find any difference in the distribution of W2796 and covering fraction (fc) as a function of D between quasar host galaxies and control sample of normal galaxies. These results are different from what has been reported in the literature, possibly because (i) our sample is restricted to a narrow redshift range, (ii) comparative analysis is carried out after matching the galaxy parameters, (iii) we focus mainly on strong Mg II absorption, and (iv) our sample lacks foreground quasars with high bolometric luminosity (i.e. Lbol > 1045.5 erg s−1). Future studies probing luminous foreground quasars, preferably at lower impact parameters and higher equivalent width sensitivity, are needed to consolidate our findings.
IIA ARCHANA SOAMKinematic study of molecular gas in cometary globule – LBN 437
Bright-rimmed, cometary-shaped star-forming globules, associated with H II regions, are remnants of compressed molecular shells exposed to ultraviolet radiation from central OB-type stars. The interplay between dense molecular gas and ionizing radiation, analysed through gas kinematics, provides significant insights into the nature and dynamic evolution of these globules. This study presents the results of a kinematic analysis of the cometary globule, Lynds’ Bright Nebula (LBN) 437, focusing on the first rotational transition of 12CO and C18O molecular lines observed using the Taeduk Radio Astronomy Observatory. The averaged 12CO spectrum shows a slightly skewed profile, suggesting the possibility of a contracting cloud. The molecular gas kinematics reveals signatures of infalling gas in the cometary head of LBN 437, indicating the initial stages of star formation. The mean infall velocity and mass infall rate towards the cometary head of LBN 437 are 0.25 km s−1 and 5.08 × 10−4 M yr−1, respectively, which align well with the previous studies on intermediate or high-mass star formation.
IIA WAGEESH MISHRAProton heating estimates from near-Earth observations of coronal mass ejections in solar cycle 24 Open Access
As solar coronal mass ejections (CMEs) propagate through the heliosphere, they expend energy in heating protons to compensate for the cooling that occurs due to expansion. CME propagation models usually treat energy dissipation implicitly via a polytropic index (δ). Here we calculate the power dissipation implied by a given δ and compare it with the power available in the turbulent velocity fluctuations. We make this comparison using near-Earth in-situ observations of 27 of the most geoeffective CMEs (Dst < −75 nT) in solar cycle 24. For δ = 5/3, the power in the turbulent velocity fluctuations is ≈54% smaller than what would be required to maintain the proton temperature at the observed values. If the power in the turbulent cascade is assumed to be fully expended in local proton heating, the most probable value for δ is 1.35. Our results contribute to a better understanding of CME energetics, and thereby to improved CME propagation models and estimates of Earth arrival times.
IIA SIVARAM, CIs asteroid 33 Polyhymnia a dark matter (DM) degenerate object?
Polyhymnia (33 Polyhymnia) is a main belt asteroid in our solar system with a diameter around 54 km. The density of asteroid 33 Polyhymnia, located in the main asteroid belt, is calculated to be 75 g/cc. Researchers have speculated the possibility that Polyhymnia could be composed of high-density superheavy elements near atomic number 164. Here, we propose that Polyhymnia could be an asteroid composed of degenerate dark matter (DM) and there could be many such asteroids in our solar system. (This is following our earlier work suggesting that Planet Nine could be such an object.)
IIA SAMPOORNA, MAn alternative iterative scheme to the full non-LTE transfer problem with coherent scattering in the atom’s frame
We propose an alternative scheme for the computation of the so-called ‘full non-LTE’ (non-local thermodynamic equilibrium) radiative transfer problem, assuming coherent scattering in the atom’s frame. This generalized problem should explicitly deal with the coupling between atomic velocities and the photon paths, thereby requiring the implementation of new numerical strategies to solve it. Recently, Paletou et al., presented a numerical scheme, based on the -iteration, to solve this problem; however it needs to be initialized using the standard non-LTE solution with complete redistribution to achieve convergence. Our new scheme is based on accelerated -iteration (ALI), which is robust and insensitive to the choice of the initial guess solution. After bench-marking our new iterative scheme against the previously developed -iteration method, we demonstrate its robustness by studying its convergence behaviour. This new iterative scheme has been coded in the Julia language, and its main characteristics are hereafter described with some details.