Sandip Kumar Chakrabarti

• DSc (UGB), PhD (U Chicago)
• Managing Director at Indian Centre for Space Physics

We study viscous transonic accretion flows in vertical equilibrium in Kerr geometry. We employ the pseudo-Kerr formalism that accurately describes transonic flows around Kerr black holes and is applicable for modeling observational data. We study the effects of viscosity on the nature of sonic points and the parameter space that allows an accretion...

In this paper, we derive the exact form of effective potential in Kerr geometry from the general relativistic radial momentum equation. The effective potential accurately mimics the general relativistic features, over the entire range of the spin parameter −1<a<1. We obtain the exact expression of the rate of dragging of inertial frames that can be...

We study viscous transonic accretion flows in vertical equilibrium in Kerr geometry. We employ the pseudo-Kerr formalism which accurately describes transonic flows around Kerr black holes and is applicable for modelling observational data. We study the effects of viscosity on the nature of sonic points and the parameter space that allows an accreti...

We derive the exact form of effective potential in Kerr geometry from the general relativistic radial momentum equation. The effective potential accurately mimics the general relativistic features, over the entire range of the spin parameter $-1<a<1$. We obtain the exact expression of the rate of dragging of inertial frames that can be used to stud...

We present a comprehensive analysis of approximately 15 years (2006–2021) of X-ray observations of UGC 6728, a low-mass bare AGN, for the first time. Our study encompasses both spectral and temporal aspects of this source. The spectral properties of this source are studied using various phenomenological and physical models. We conclude that (a) the...

We study the recent outburst of the black hole candidate EXO 1846-031, which went into an outburst in 2019 after almost 34 yr in quiescence. We use archival data from the Swift/XRT, MAXI/GSC, NICER/XTI, and NuSTAR/FPM satellites/instruments to study the evolution of the spectral and temporal properties of the source during the outburst. The low-ene...

We analyze a sample of 21 “bare” Seyfert 1 active galactic nuclei, a subclass of Seyfert 1 galaxies, with intrinsic absorption N H ∼ 10 ²⁰ cm ⁻² , in the local Universe ( z < 0.2) using XMM-Newton and Swift/XRT observations. The luminosities of the primary continuum, the X-ray emission in the 3–10 keV energy range, and the soft excess—the excess em...

Astronomical objects, such as the Sun, accreting matter around black holes, neutron stars, white dwarfs, etc. are known to emit X-rays and gamma-rays. Some of these sources, such as highly magnetized neutron stars, show periodic pulsations. Even accreting matter around black holes and neutron stars shows timing properties including quasi-periodic o...

We analyse a sample of 21 `bare' Seyfert~1 Active Galactic Nuclei (AGNs), a sub-class of Seyfert~1s, with intrinsic absorption $\mathrm{N_{H}} \sim 10^{20}~ \mathrm{cm}^{-2}$, in the local universe (z $<$ 0.2) using {\it XMM-Newton} and {\it Swift}/XRT observations. The luminosities of the primary continuum, the X-ray emission in the 3 to 10 keV en...

Secondary cosmic rays are produced from the interaction of primary cosmic rays, which are high-energy (\(\sim \)GeV) particles originating from outer space, primarily, protons (\(\sim \)89%) and alpha particles (\(\sim \)10%) with atoms (mainly nitrogen and hydrogen) present in our Earth’s atmosphere. Such rays are dependent on solar activity and g...

We study the recent outburst of the black hole candidate EXO 1846-031 which went into an outburst in 2019 after almost 34 years in quiescence. We use archival data from Swift/XRT, MAXI/GSC, NICER/XTI and NuSTAR/FPM satellites/instruments to study the evolution of the spectral and temporal properties of the source during the outburst. Low energy X-r...

Solar flare intensity is strongly dependent on the phase in the solar cycle, the structure and dynamics of the magnetic field near sunspots, and also on occasional solar coronal mass ejections. In this paper we study some of the solar flares detected by the stratospheric balloon borne experiments of Indian Centre for Space Physics. We also observe...

During a solar eclipse, the temporary blockage of daytime solar illumination resembles a nighttime situation up to a certain degree. This effectively modulates the lower ionosphere by reducing the ionization rate and hence electron–ion density and the VLF signal responds accordingly. This study investigates the lower ionospheric response to the Ann...

Solar eclipse is a unique phenomenon that produces an orderly disturbance in the ionosphere within a specific time frame. It provides us an opportunity to understand the ionospheric response due to its systematic variation during an eclipse. The amplitude and phase of a Very Low Frequency (VLF) signal carry the response of lower ionospheric perturb...

We present a statistical study of global lightning activity and correlate this activity with ionospheric fluctuations in the Total Electron Content (TEC). Thunderstorms play a significant role in modulating the ionosphere's plasma distribution. Using the well‐known World Wide Lightning Location Network (WWLLN) system, we investigate the diurnal, mo...

We study the spectral properties and accretion flow behavior of an ultraluminous X-ray source M82 X-1 using NuSTAR observations. We use the physical two-component advective flow (TCAF) model to fit the data and to derive the accretion flow properties of the source. From the model fitted parameters, we found that M82 X-1 is harboring an intermediate...

We study the spectral properties and accretion flow behavior of an ultraluminous X-ray source M82\,X-1 using {\it NuSTAR} observations. We use the physical two component advective flow (TCAF) model to fit the data and to derive the accretion flow properties of the source. From the model fitted parameters, we found that M82\,X-1 is harboring an inte...

We performed a diagnostic study of geomagnetic storm-induced disturbances that are coupled to the mid-latitude D region by quantifying the propagation characteristics of very low-frequency (VLF) radio signals from transmitters located in Cumbria, UK (call sign GQD), and Rhauderfehn, Germany (DHO), and received in southern France (A118). We characte...

Electromagnetic emissions (EMEs) associated with earthquake (EQ) epicenters are found to be one of the most reliable phenomena for the short-term pre-seismic mechanism of earthquakes. The detection mechanism of such emissions can have both direct and indirect techniques. In this manuscript, we attempted to present the signature of such emissions be...

Context. The X-ray emission in BL Lac objects is believed to be dominated by synchrotron emission from their relativistic jets. However, when the jet emission is not strong, one could expect signatures of X-ray emission from inverse Compton scattering of accretion disc photons by hot and energetic electrons in the corona. Moreover, the observed X-r...

The X-ray emission in BL Lac objects is believed to be dominated by synchrotron emission from their relativistic jets. However, when the jet emission is not strong, one could expect signatures of X-ray emission from inverse Compton scattering of accretion disc photons by the corona. Moreover, the observed X-ray variability can also originate in the...

We perform a comparative spectro-temporal analysis on the variability classes of GRS 1915+105 and IGR J17091-3624 to draw inferences regarding the underlying accretion flow mechanism. The ν, as well as C2 class Rossi X-Ray Timing Explorer observation, have been considered for analysis. We investigate the intensity variation of the source in differe...

Spectral and timing properties of accretion flows on a black hole depend on their density and temperature distributions, which in turn come from the underlying dynamics. Thus, an accurate description of the flow which includes hydrodynamics and radiative transfer is a must to interpret the observational results. In the case of non-rotating black ho...

Atmospheric disturbances caused by seismic activity are a complex phenomenon. The Lithosphere–Atmosphere–Ionosphere Coupling (LAIC) (LAIC) mechanism gives a detailed idea to understand these processes to study the possible impacts of a forthcoming earthquake. The atmospheric gravity wave (AGW) is one of the most accurate parameters for explaining s...

We focus on the possible thermal channel of the well-known Lithosphere–Atmosphere–Ionosphere Coupling (LAIC) mechanism to identify the behavior of thermal anomalies during and prior to strong seismic events. For this, we investigate the variation of Surface Latent Heat Flux (SLHF) as resulting from satellite observables. We demonstrate a spatio-tem...

It is speculated that there might be some linkage between interstellar aldehydes and their corresponding alcohols. Here an observational study and astrochemical modeling are coupled together to illustrate the connection between them. The ALMA cycle 4 data of a hot molecular core, G10.47+0.03, are utilized for this study. Various aldehydes (acetalde...

Outflows are common in many astrophysical systems. In the Two Component Advective Flow ( TCAF ) paradigm, which is essentially a generalized Bondi flow including rotation, viscosity, and cooling effects, the outflow originates in the hot, puffed up, post-shock region at the inner edge of the accretion disk. We consider this region to be the base of...

Phosphorus-related species are not known to be as omnipresent in space as hydrogen, carbon, nitrogen, oxygen, and sulfur-bearing species. Astronomers spotted very few P-bearing molecules in the interstellar medium and circumstellar envelopes. Limited discovery of the P-bearing species imposes severe constraints in modeling the P-chemistry. In this...

We present a comprehensive analysis of pre-seismic anomalies as computed from the ground and space-based techniques during the recent Samos earthquake in Greece on 30 October 2020, with a magnitude M = 6.9. We proceed with a multi-parametric approach where pre-seismic irregularities are investigated in the stratosphere, ionosphere, and magnetospher...

It is speculated that there might be some linkage between interstellar aldehydes and their corresponding alcohols. Here, an observational study and astrochemical modeling are coupled together to illustrate the connection between them. The ALMA Cycle 4 data of a hot molecular core, G10.47+0.03 is utilized for this study. Various aldehydes (acetaldeh...

We performed a diagnostic study of geomagnetic storm-induced disturbances that are coupled to the lower ionosphere in mid-latitude D-region using propagation characteristics of VLF radio signals. We characterised the diurnal VLF amplitude (from two propagation paths) into five metrics, namely the mean amplitude before sunrise (MBSR), midday amplitu...

Lightning is a sudden release of electrostatic energy that plays a significant role in the ionospheric-magnetospheric coupling process. A short-term increase in the particle count rates (CR) in the Van Allen Radiation Belt (VAB) is known as the particle bursts. Due to lightning events, the increase in the number of high-energy particles in the inne...

Galactic transient black hole candidate (BHC) MAXI J1535-571 was discovered on 2017 September 02 simultaneously by MAXI/GSC and Swift/BAT instruments. It has also been observed by India’s first multi-wavelength astronomy-mission satellite AstroSat, during the rising phase of its 2017-18 outburst. We make both the spectral and the temporal analysis...

An inverse P-Cygni profile of H13CO+ (1-0) in G31.41+0.31 was recently observed, which indicates the presence of an infalling gas envelope. Also, an outflow tracer, SiO, was observed. Here, exclusive radiative transfer modelings have been implemented to generate synthetic spectra of some key species (H13 CO+, HCN, SiO, NH3, CH3 CN, CH3OH, CH3SH, an...

In 2016 − 17, the Galactic transient black hole candidate GRS 1716-249 exhibited an outburst event after a long qui-escence period of almost 23 years. The source remained in the outbursting phase for almost 9 months. We study the spectral and temporal properties of the source during this outburst using archival data from four astronomy satellites,...

An inverse P-Cygni profile of H¹³CO⁺ (1 → 0) in G31.41+0.31 was recently observed, which indicates the presence of an infalling gas envelope. Also, an outflow tracer, SiO, was observed. Here, exclusive radiative transfer modelings have been implemented to generate synthetic spectra of some key species (H¹³CO⁺, HCN, SiO, NH3, CH3CN, CH3OH, CH3SH, an...

We present the long-term X-ray spectral and temporal analysis of a ‘bare-type AGN’ Ark 120. We consider the observations from XMM-Newton, Suzaku, Swift, and NuSTAR from 2003 to 2018. The spectral properties of this source are studied using various phenomenological and physical models present in the literature. We report (a) the variations of severa...

Phosphorus related species are not known to be as omnipresent in space as hydrogen, carbon, nitrogen, oxygen, and sulfur-bearing species. Astronomers spotted very few P-bearing molecules in the interstellar medium and circumstellar envelopes. Limited discovery of the P-bearing species imposes severe constraints in modeling the P-chemistry. In this...

The abundance of interstellar ice constituents is usually expressed with respect to the water ice because, in denser regions, a significant portion of the interstellar grain surface would be covered by water ice. The binding energy (BE), or adsorption energy of the interstellar species regulates the chemical complexity of the interstellar grain man...

The 2015 Outburst of V404 Cygni is an unusual one with several X-ray and radio flares and rapid variation in the spectral and timing properties. The outburst occurred after 26 years of inactivity of the black hole. We study the accretion flow properties of the source during its initial phase of the outburst using Swift/XRT and Swift/BAT data in the...

In this work, we simulated the atmospheric drag effect on two model SmallSats (small satellites) in low Earth orbit (LEO) with different ballistic coefficients during 1-month intervals of solar–geomagnetic quiet and perturbed conditions. The goal of this effort was to quantify how solar–geomagnetic activity influences atmospheric drag and perturbs...

We performed a detailed modelling of the background counts observed in a phoswich scintillator X-ray detector at balloon altitude, used for astronomical observations, on board small scientific balloon. We used Monte Carlo simulation technique in Geant4 simulation environment, to estimate the detector background from various plausible sources. High...

The abundance of interstellar ice constituents is usually expressed with respect to the water ice because, in denser regions, a significant portion of the interstellar grain surface would be covered by water ice. The binding energy (BE) or adsorption energy of the interstellar species regulates the chemical complexity of the interstellar grain mant...

We present the results obtained from a detailed timing and spectral studies of a black hole candidate MAXI J1813-095 using Swift, NICER, and NuSTAR observations during its 2018 outburst. The timing behaviour of the source is mainly studied by using NICER light curves in a 0.5 − 10 keV range. We did not find any signature of quasi-periodic oscillati...

We present the results obtained from detailed timing and spectral studies of a black hole candidate MAXI~J1813-095 using {\it Swift}, {\it NICER}, and {\it NuSTAR} observations during its 2018 outburst. The timing behaviour of the source is mainly studied by using {\it NICER} light curves in a $0.5-10$ keV range. We did not find any signature of qu...

Galactic short orbital period black hole candidate (BHC) XTE J1752-223 was discovered on 2009 Oct 21 by the Rossi X-ray Timing Explorer (RXTE). We study the spectral properties of this outburst using transonic flow solution based two component advective flow (TCAF) model. TCAF model fitted spectrum gives an estimation of the physical flow parameter...

Galactic short orbital period black hole candidate (BHC) XTE~J1752-223 was discovered on 2009 Oct 21 by the Rossi X-ray Timing Explorer (RXTE). We study the spectral properties of this outburst using transonic flow solution based two component advective flow (TCAF) model. TCAF model fitted spectrum gives an estimation of the physical flow parameter...

We study the properties of the faint X-ray activity of Galactic transient black hole candidate XTE J1908+094 during its 2019 outburst. Here, we report the results of detailed spectral and temporal analysis during this outburst using observations from Nuclear Spectroscopic Telescope Array (NuSTAR). We have not observed any quasi-periodic-oscillation...

We study the properties of the faint X-ray activity of Galactic transient black hole candidate XTE~J1908+094 during its 2019 outburst. Here, we report the results of detailed spectral and temporal analysis during this outburst using observations from {\it Nuclear Spectroscopic Telescope Array (NuSTAR)}. We have not observed any quasi-periodic-oscil...

In $2016-17$, the Galactic transient black hole candidate GRS 1716-249 exhibited an outburst event after a long period of quiescence of almost 23 years. The source remained in the outbursting phase for $\sim 9$ months. We study the spectral and temporal properties of the source during this outburst using archival data from four astronomy satellites...

G31.41+0.31 is a well known chemically rich hot molecular core (HMC). Using Band 3 observations from the Atacama Large Millimeter Array (ALMA), we have analyzed the chemical and physical properties of the source. We have identified methyl isocyanate (CH 3 NCO), a precursor of prebiotic molecules, toward the source. In addition to this, we have repo...

We perform a comparative spectro-temporal analysis on the variability classes of GRS 1915+105 and IGR J17091-3624 to draw inferences regarding the underlying accretion flow mechanism. The $\nu$, as well as C2 class Rossi X-Ray Timing Explorer observation, have been considered for analysis. We investigate the intensity variation of the source in dif...

We present the long-term X-ray spectral and temporal analysis of a 'bare-type AGN' Ark 120. We consider the observations from XMM-Newton, Suzaku, Swift, and NuSTAR from 2003 to 2018. The spectral properties of this source are studied using various phenomenological and physical models present in the literature. We report (a) the variations of severa...

The fundamental difference between accretion around black holes and neutron stars is the inner boundary condition, which affects the behavior of matter very close to the compact objects. This leads to formation of additional shocks and boundary layers for neutron stars. Previous studies on the formation of such boundary layers focused on Keplerian...

Very Low Frequency (VLF) remote sensing technique is used to probe the D-layer modeling for which we use a very conventional model known as Wait s 2-component iono-spheric model. This model is characterized by two iono-spheric parameters which are 'steepness parameter' (β) and 'effective reflection height' (h). International Reference Ionosphere (I...

Sub-Ionospheric Very Low Frequency (VLF) radio wave propagation characteristics are the major tool to study the lower ionospheric heights mainly D-region. Wait’s 2-component exponential model is a well-known mechanism to understand the basic characteristics of this layer based on VLF remote sensing. This model deals with two major ionospheric param...

Recent studies show that accretion flows around weakly magnetic Neutron Stars undergo multiple shocks, before reaching the surface of the star, which contribute to the spectral and timing variabilities observed in the X-Rays. Here, we report, for the first time, the spectral properties of a unified model of shocked accretion flows around Neutron St...

We performed a detailed modelling of the background counts observed in a phoswich scintillator X-ray detector at balloon altitude, used for astronomical observations, on board small scientific balloon. We used Monte Carlo simulation technique in Geant4 simulation environment, to estimate the detector background from various plausible sources. High...

The class variable source GRS 1915+105 exhibits a wide range of time variabilities on timescales of a few seconds to a few days. Depending on the count rates in different energy bands and the nature of the conventional color-color diagram, the variabilities were classified into sixteen classes that were later sequenced in ascending order of Compton...

Study of seismo-ionospheric coupling mechanism demands the quiet geomagnetic condition to eliminate any kind of contamination in the lower atmospheric and ionospheric parameters. In this manuscript, we present the effect of back to back two geomagnetic storms before a strong earthquake happened in Imphal, India on January 4, 2016 (M = 6.7). We stud...

G31.41+0.31 is a well known chemically rich hot molecular core (HMC). Using Band 3 observations of Atacama Large Millimeter Array (ALMA), we have analyzed the chemical and physical properties of the source. We have identified methyl isocyanate (CH3NCO), a precursor of prebiotic molecules, towards the source. In addition to this, we have reported co...

We study spectral and temporal properties of Galactic short orbital period transient black hole XTE J1118+480 during its 2005 outburst using archival data of RXTE PCA and HEXTE instruments in the combined energy range of 3 – 100 keV. Spectral analysis with the physical two component advective flow (TCAF) model allows us to understand the accretion...

The first identification of the argonium ion ( ) toward the Crab Nebula supernova remnant was proclaimed by Herschel in the submillimeter and far-infrared domains. Very recently, the discovery of the hydro-helium cation ( ) in the planetary nebula (NGC 7027) by SOFIA has been reported. The elemental abundance of neon is much higher than that of arg...

The first identification of the argonium ion (ArH+) towards the Crab Nebula supernova remnant was proclaimed by the Herschel in the sub-millimeter and far-infrared domain. Very recently the discovery of the hydro-helium cation (HeH+) in the planetary nebula (NGC 7027) has been reported by using the SOFIA. The elemental abundance of neon is much hig...

Evolution of variability properties of Galactic transient sources is a diagnostic tool to under stand various regimes of the accretion flow and its dynamics close to the central black hole. In this paper, we concentrate on the variability properties of the X-ray transient XTE J1650-500 and investigate the evolution of viscous delay, time lag, QPO f...

The Galactic microquasar GRS 1915+105 shows rich variability which is categorized into different classes. In this paper, we report temporal and spectral analysis of GRS 1915+105 to study the properties of the accretion flow when the light curve is showing $\theta$ class variability. For this purpose, we use the LAXPC data from the Target of Opportu...

In this work we simulated the effects of atmospheric drag on two model SmallSats in Low Earth Orbit (LEO) with different ballistic coefficients during 1-month intervals of solar-geomagnetic quiet and perturbed conditions. The goal of this effort was to quantify how solar-geomagnetic activity influences atmospheric drag and perturbs satellite orbits...

Evolution of variability properties of Galactic transient sources is a diagnostic tool to understand various regimes of the accretion flow and its dynamics close to the central black hole. In this paper, we concentrate on the variability properties of the X-ray transient XTE J1650-500 and investigate the evolution of viscous delay, time lag, QPO fr...

Galactic black hole candidate MAXI J1348-630 was recently discovered by MAXI and Swift/BAT satellites during its first outburst in 2019 January which continued for ∼ 4 months. We study the spectral and timing properties of the source in detail. The combined 1−150 keV Swift/XRT, Swift/BAT and MAXI/GSC spectra are investigated with the two component...

Galactic transient black hole candidate (BHC) MAXI~J1535-571 was discovered on 2017 September 02 simultaneously by {\it MAXI}/GSC and {\it Swift}/BAT instruments. It has also been observed by India's first multi-wavelength astronomy-mission satellite {\it AstroSat}, during the rising phase of its 2017-18 outburst. We make both the spectral and the...

The 2015 Outburst of V404 Cygni is an unusual one with several X-ray and radio flares and rapid variation in the spectral and timing properties. The outburst occurred after $26$ years of inactivity of the black hole. We study the accretion flow properties of the source during its initial phase of the outburst using {\it Swift}/XRT and {\it Swift}/B...

After hydrogen, oxygen, and carbon, nitrogen is one of the most chemically active species in the interstellar medium. Nitrogen-bearing molecules are very important as they are actively involved in the formation of biomolecules. Therefore, it is essential to look for nitrogen-bearing species in various astrophysical sources, specifically around high...

Spectroscopic studies play a key role in the identification and analysis of interstellar ices and their structure. Some molecules have been identified within the interstellar ices either as pure, mixed, or even as layered structures. Absorption band features of water ice can significantly change with the presence of different types of impurities (C...

Spectroscopic studies play a key role in the identification and analysis of interstellar ices and their structure. Some molecules have been identified within the interstellar ices either as pure, mixed, or even as layered structures. Absorption band features of water ice can significantly change with the presence of different types of impurities (C...

Galactic black hole candidate MAXI~J1348-630 was recently discovered by MAXI and Swift/BAT satellites during its first outburst in 2019 January which continued for ~4 months. We study the spectral and timing properties of the source in detail. The combined 1-150 keV Swift/XRT, Swift/BAT and MAXI/GSC spectra are investigated with the two component a...

We study spectral and temporal properties of Galactic short orbital period transient black hole XTE J1118+480 during its 2005 outburst using archival data of RXTE PCA and HEXTE instruments in the combined energy range of $3-100$ keV. Spectral analysis with the physical two-component advective flow (TCAF) model allows us to understand the accretion...

Spectral and timing properties of the stellar-mass black hole candidate XTE J1752-223 during its 2009-10 outburst are studied using RXTE PCA data in the 2.5–25 keV energy range. Low frequency quasi-periodic oscillations are seen during outburst. The spectral analysis is done using two types of models: one is the combined disc blackbody plus power-l...

After hydrogen, oxygen, and carbon, nitrogen is one of the most chemically active species in the interstellar medium (ISM). Nitrogen bearing molecules have great importance as they are actively involved in the formation of biomolecules. Therefore, it is essential to look for nitrogen-bearing species in various astrophysical sources, specifically ar...

Galactic transient black hole candidate (BHC) MAXI J1836–194 was discovered on 2011 Aug 30, by MAXI/GSC and Swift/BAT. The source activity during this outburst continued for ∼ 3 months before entering into the quiescent state. It again became active in March 2012 and continued for another ∼ 2 months. In this paper, 3 – 25 keV RXTE/PCA spectra from...

We carry out a detailed study of the spectral and the timing properties of the stellar-mass black hole candidate XTE J1752-223 during its 2009-10 outburst using RXTE PCA data in the $2.5-25$ keV energy range. Low frequency quasi-periodic oscillations (LFQPOs) are seen in the power density spectrum (PDS). The spectral analysis is done using two type...

Magnetic fields advected along with low angular momentum accretion flows predominantly become toroidal owing to the strong azimuthal velocity close to a black hole. We study self-consistently the movements of these flux tubes inside an advective disk and how they dynamically influence the flow. We find that the centrifugal barrier slows down the ra...

The nature of lag variation of Galactic black holes remains enigmatic mostly because of nonlinear and nonlocal physical mechanisms which contribute to the lag of the photons coming from the region close to the central black holes. One of the widely accepted major sources of the hard lag is the inverse Comptonization mechanism. However, the exact re...

Magnetic fields advected along with low angular momentum accretion flows predominantly become toroidal due to the strong azimuthal velocity close to a black hole. We study self-consistently the movements of these flux tubes inside an advective disc and how they dynamically influence the flow. We find that the centrifugal barrier slows down the radi...

X-ray time lags are complicated in nature. The exact reasons for complex lag spectra are yet to be known. However, the hard lags, in general, are believed to be originated due to the inverse Comptonization process. But, the origin of soft lags remained mischievous. Recent studies on "Disk-Jet Connections" revealed that the jets are also contributin...

Icy grain mantles are the principal repository of the complex organic molecules (COMs) in the interstellar medium (ISM). Such icy mantles constitute the main reservoir of volatiles in clouds, protostellar envelopes, comets, and protoplanetary disks. The condensation of atoms and molecules formed ices. Among almost 200 interstellar and/or circumstel...