In this research, the pseudo vacuum energy in the inflationary universe model, the Higgs field in the standard physical model and the dark energy in the observational cosmology are reduced to the positive energy system with strong negative pressure, and they are reduced to the repulsion (all the resistance to gravity). In the high-dimensional space-time, corresponding to the introduction of supergravity

Soft X-ray telescope (SXT) built on the principle of grazing incidence optics was launched on-board AstroSat on September 28, 2015, and made operational on October 26, 2015. The telescope optics consists of two conical sections of approximate paraboloid and hyperboloid mirror segments arranged in Wolter type-I design. It comprises a total of 320 mirror segments made from aluminum foil of 0.2 mm thickness

The peculiarities of the inverse square law of Newtonian gravity in standard big bang cosmology are discussed. It is shown that the incorporation of an additive term to Newtonian gravitation, as the inverse Yukawa-like field, allows removing the incompatibility between the flatness of the Universe and the density of matter in the Friedmann equation, provides a new approach for dark energy, and enables

A Correction to this paper has been published: 10.1007/s12036-020-09679-y

We study the dynamics of a test particle around a central mass taking into account general relativistic effects within the formalism of Lagrangian mechanics, and investigate a real astrophysical object to probe the model. We consider a generalized potential for the Lagrangian of the particle, compute the corresponding equations of motion, and present a numerical scheme to integrate them. Within this

The results presented in this paper are obtained from low-latitude ionospheric total electron content (TEC) variation during the chosen geomagnetic storm events happening during the solar cycle 24. We include the four intense geomagnetic storms that occurred on 26 September 2011, 15 July 2012, 19 February 2014 and 20 December 2015, depending upon the availability of TEC data. For this, we have used

This study investigated the geomagnetic disturbances and high-speed solar-wind streams (HSSs) during the period of solar storms emitted from coronal holes. The contemplated long-term HSS observations were taken from 1963 to 2016. On the basis of the intensity of geomagnetic activity, solar storms were divided into four groups: weak (−50 nT < Dst < −30 nT), moderate (−100 nT < Dst < −50 nT), intense

We performed the timing and spectral studies of a Z source GX 17+2 observed from Astrosat LAXPC instrument. Cross-Correlation Function (CCF) was performed using soft (3–5 keV) and hard (16–40 keV) X-ray bands across the hardness intensity diagram and found correlated/anti-correlated hard and soft lags which seems to be a common feature in these sources. We performed spectral analysis for few of these

Scattering properties of irregularly shaped interstellar composite dust analogues consisting of graphite and fayalite (Fe2SiO4) were studied using discrete dipole approximation (DDA). Two dust models were developed to calculate the scattering and extinction efficiencies, single scattering albedo, asymmetry parameter, phase functions and degree of linear polarizations. Laboratory measurements were also

The purpose of this article was to examine the behavior of the Little Rip (LR) and Pseudo rip (PR) models with two interacting ideal fluids related to dark energy and dark matter with the quadratic equation of state with time-dependent parameters \(\omega (t)\) and \(\Lambda (t)\) in flat Friedmann–Lemaitre–Robertson–Walker cosmological model. In this article, the gravitational equations of motion

The Cadmium Zinc Telluride Imager (CZTI) on AstroSat is a hard X-ray coded-aperture mask instrument with a primary field-of-view of \(4.6^\circ \times 4.6^\circ \) (FWHM). The instrument collimators become increasingly transparent at energies above \(\sim \)100 keV, making CZTI sensitive to radiation from the entire sky. While this has enabled CZTI to detect a large number of off-axis transient sources

We report the detection of quasi-periodic oscillations (QPOs) in the radio light curve of the blazar PKS 1510-089 spanning nearly 38 years, by means of the weighted wavelet Z-transform and Lomb–Scargle periodogram methods. Prominent QPOs with high confidence (>4\(\sigma \)) of \(570\pm 30\), \(800\pm 30,\) and \(1070\pm 40\) days in the 8 GHz light curve, \(430\pm 10\) and \(1080\pm 30\) days in the

We propose a set of eleven faint UV white dwarf stars as potential UV standards for the UVIT filter system on-board AstroSat mission. Synthetic photometry of these stars has been carried out using the in-orbit filter curves of UVIT, GALEX, UVOT and model spectra in the literature. The synthetic photometry of GALEX and UVOT is well correlated with their respective observations. The synthetic UVIT photometry

We present a photometric and kinematical analysis of two poorly studied open clusters, Koposov 12 (FSR 802) and Koposov 43 (FSR 848), by using cross-matched data from PPMXL and Gaia DR2 catalogs. We used astrometric parameters to identify 285 and 310 cluster members for Koposov 12 and Koposov 43, respectively. Using the extracted member candidates and isochrone fitting to near-infrared (J, H, and Ks)

King 2, one of the oldest clusters in the Milky Way, with an age of \(\sim \)6 Gyr and distance of \(\sim \)5700 pc, has been observed with UVIT payload on the AstroSat. With membership information derived from Gaia EDR3, the cluster is found to have 39 blue straggler stars (BSSs). We created multi-wavelength spectra-energy distributions (SED) of all the BSSs. Out of 10 UV detected BSSs, 6 bright ones

The paper discusses four processes that may be responsible for shaping the relief of the comet landscape. The considerations take into account the following phenomena: intense sublimation of cometary ice, emission of dust from the surface comet and through jets, migration of dust on the cometary surface, and destruction of fragment the nucleus surface in the context of a change in cometary brightness

Magnetars are highly magnetized neutron stars. For a slowly rotating magnetar, the strong magnetic field deforms the star, making it axisymmetric with respect to the magnetic axis (the body symmetry axis). In magnetars, the rotation axis is tilted to the magnetic axis, and we have an oblique rotator. General relativistic treatment of the obliquely rotating magnetar gives rise to frame-dragging velocities

We present the far ultraviolet (FUV) imaging of the nearest Jellyfish or Fireball galaxy IC3418/VCC 1217, in the Virgo cluster of galaxies, using Ultraviolet Imaging Telescope (UVIT) onboard the AstroSat satellite. The young star formation observed here in the 17 kpc long turbulent wake of IC3418, due to ram pressure stripping of cold gas surrounded by hot intra-cluster medium, is a unique laboratory

The Andromeda galaxy (M31) has been observed with the UltraViolet Imaging Telescope (UVIT) instrument onboard the AstroSat Observatory. The M31 sky area was covered with 19 fields, in multiple UV filters per field, over the period of 2017 to 2019. The entire galaxy was observed in the FUV F148W filter, and more than half observed in the NUV filters. A new calibration and data processing is described

We present our AstroSat soft X-ray observations of a compact binary system, AR Sco, and analysis of its X-ray observations with Chandra that were taken only about a week before the AstroSat observations. An analysis of the soft X-ray (0.3–2.0 keV) data limits the modulation of the spin, orbital, or beat periods to less than 0.03 counts s\(^{-1}\) or <10% of the average count rate. The X-ray flux obtained

We present a UV study of 3 extended UV (XUV) galaxies that we have observed with the UVIT and the GMRT. XUV galaxies show filamentary or diffuse star formation well beyond their optical disks, in regions where the disk surface density lies below the threshold for star formation. GALEX observations found that surprisingly 30% of all the nearby spiral galaxies have XUV disks. The XUV galaxies can be

Cadmium–Zinc–Telluride Imager (CZTI) onboard AstroSat has been a prolific Gamma-Ray Burst (GRB) monitor. While the 2-pixel Compton scattered events (100–300 keV) are used to extract sensitive spectroscopic information, the inclusion of the low-gain pixels (\(\sim \)20\(\%\) of the detector plane) after careful calibration extends the energy range of Compton energy spectra to 600 keV. The new feature

We present a detailed timing and spectral study of an extremely variable narrow-line Seyfert 1 galaxy NGC 4748 using observations in the year 2017 and 2014 performed with AstroSat and XMM-Newton, respectively. Both observations show extremely variable soft and hard X-ray emission that are correlated with each other. In the 2014 data set, the source retains its general behaviour of “softer when brighter”

We present observations of four bright stars observed with the AstroSat Soft X-ray Telescope (SXT). Visible light from bright stars like these can leak through the very thin filter in front of the CCD in the focal plane CCD camera of the SXT and thus making the extraction of X-ray events difficult. Here, we show how to extract the X-ray events without contamination by the visible light. The procedure

India has an expanding program in using space as a platform for research. Astrophysics research from satellites increasingly complement ground-based observations with unique wavelength coverage, more frequent temporal coverage and diffraction-limited observations. India’s first dedicated space astronomy mission, AstroSat has completed five years in orbit and continues to generate important results

To answer the question posed in the title, we consider a novel diagnostic, viz., the difference in the time of arrival (TOA) at the observer of two light rays that simultaneously emanate from a source behind a spinning lens and pass by either side of the lens to reach the observer. This is completely different from the usual Shapiro gravitational time delay, where only one onward light ray is reflected

We study the multi-wavelength variability of the blazar Mrk 421 at minutes to days timescales using simultaneous data at \(\gamma \)-rays from Fermi, 0.7–20 keV energies from AstroSat, and optical and near infrared (NIR) wavelengths from ground based observatories. We compute the shortest variability timescales at all of the above wave bands and find its value to be \(\sim \)1.1 ks at the hard X-ray

AstroSat is India’s first space-based astronomical observatory, launched on September 28, 2015. One of the payloads aboard AstroSat is the Cadmium Zinc Telluride Imager (CZTI), operating at hard X-rays. CZTI employs a two-dimensional coded aperture mask for the purpose of imaging. In this paper, we discuss various image reconstruction algorithms adopted for the test and calibration of the imaging capability

It is necessary to better understand the dynamic process of solar differential rotation. Here the hand-drawing sunspot group records from 1958 to 2015 of Yunnan Observatories (YNAO) are used to study the solar rotation profile. Firstly, the rotation profile in each solar cycle 19-23 is calculated. Secondly, the rotation parameters (equatorial rotation velocity A and differential gradient B) of YNAO

A new model of an anisotropic compact star is obtained in our present paper by assuming the pressure anisotropy. The proposed model is singularity free. The model is obtained by considering a physically reasonable choice for the metric potential \(g_{rr}\), which depends on a dimensionless parameter n. The effect of n is discussed numerically, analytically, and through plotting. We have concentrated

The Cadmium–Zinc–Telluride Imager on AstroSat has proven to be a very effective All-Sky monitor in the hard X-ray regime, detecting over three hundred GRBs and putting highly competitive upper limits on X-ray emissions from gravitational wave sources and fast radio bursts. We present the algorithms used for searching for such transient sources in CZTI data, and for calculating upper limits in case

The Cadmium Zinc Telluride (CZT) Imager onboard AstroSat consists of pixelated CZT detectors, which are sensitive to hard X-rays above 20 keV. The individual pixels are triggered by ionising events occurring in them, and the detectors operate in a self-triggered mode, recording each event separately with information about its time of incidence, detector co-ordinates, and channel that scales with the

We present the results obtained from analysis of two AstroSat observations of the high mass X-ray binary pulsar OAO 1657-415. The observations covered 0.681–0.818 and 0.808–0.968 phases of the \(\sim \)10.4 day orbital period of the system, in March and July 2019, respectively. Despite being outside the eclipsing regime, the power density spectrum from the first observation lacks any signature of pulsation

SSM onboard AstroSat is designed to monitor X-ray sky in the energy range 2.5–10 keV to detect and locate X-ray sources in outburst. SSM with its three almost identical 1D-proportional counters mounted on a rotating platform, scans the sky in step and stare mode of operation. It observes the X-ray sky and generates light curves for X-ray sources detected. Here, we discuss the positional calibration

The Cadmium–Zinc–Telluride Imager (CZTI) onboard AstroSat is designed for hard X-ray imaging and spectroscopy in the energy range of 20–100 keV. The CZT detectors are of 5-mm thickness and hence have good efficiency for Compton interactions beyond 100 keV. The polarisation analysis using CZTI relies on such Compton events and have been verified experimentally. The same Compton events can also be used

A considerable fraction of incident high energy photons from astrophysical transients such as Gamma Ray Bursts (GRBs) is Compton scattered by the Earth’s atmosphere. These photons, sometimes referred to as the “reflection component”, contribute to the signal detected by space-borne X-ray/γ-ray instruments. The effectiveness and reliability of source parameters such as position, flux, spectra and polarization

The spectral region between 1250–3000 \(\AA \) contains important spectral lines to understand the morphological structures and evolution of planetary nebulae. This is the region sampled by UVIT through various filter bands both in the continuum and in emission lines (e.g.. [C iv], [He i], [Mg ii] etc.). We have mapped several planetary nebulae with different characteristics, ranging in morphology

A recent study of hot (20,000 to 30,000 K) extreme horizontal branch (EHB) stars in globular clusters (GCs) has led to the discovery of their variability. It is suggested that this variability is driven by the projected rotation of magnetic spots on the stellar surfaces and is expected to have higher amplitudes at shorter wavelengths. Here, we present the analysis of such hot stars in the massive GC

We present the first detailed X-ray study and simultaneous optical observations of the active fast rotating star FR Cnc. The X-ray spectra are found to be explained by two-temperature plasma model with temperature of cool and hot components of 0.34 and 1.1 keV, respectively. The X-ray light curve in the 0.5–2.0 keV energy band is found to be rotationally modulated with the degree of rotational modulation

All-sky monitors can measure the fluxes of astrophysical sources by measuring the changes in observed counts as the source is occulted by the Earth. Such measurements have typically been carried out by all-sky monitors like CGRO-BATSE and Fermi-GBM. We demonstrate for the first time the application of this technique to measure fluxes of sources using a collimated instrument: the Cadmium Zinc Telluride

Fundamental astrophysical parameters have been derived for Berkeley 55 (Be 55) open cluster based on the UBVI charge-coupled device (CCD) photometric data observed using a AZT-22 1.5 m telescope at Maidanak Astronomical Observatory (MAO) in Uzbekistan. The mean reddening is obtained as \(E(B-V)=1.77\pm 0.10\,\mathrm {mag}\) from early-type members. The zero-age main sequence fitting in the \(Q_{V\lambda

The AstroSat mission carries several high-energy detectors meant for fast timing studies of cosmic sources. In order to carry out high precision multi-wavelength timing studies, it is essential to calibrate the absolute time stamps of these instruments to the best possible accuracy. We present here the absolute time calibration of the AstroSat LAXPC instrument, utilising the broad-band electromagnetic

Malin 1, being a class of giant low surface galaxies, continues to surprise us even today. The HST/F814W observation has shown that the central region of Malin 1 is more like a normal SB0/a galaxy, while the rest of the disk has the characteristic of a low surface brightness system. The AstroSat/UVIT observations suggest scattered recent star formation activity all over the disk, especially along the

AstroSat is India’s first mission dedicated to space-based Astronomy and carries a complement of instruments sensitive over a wide spectral region covering visible, ultraviolet, soft X-ray and hard X-ray bands. The spacecraft platform provides the required stability, pointing, power, thermal control, and interface requirements. Among the critical functions of the Attitude and Orbit Control System (AOCS)

The Cadmium–Zinc–Telluride Imager (CZTI) is an imaging instrument onboard AstroSat. This instrument operates as a nearly open all-sky detector above 60 keV, making possible long integrations irrespective of the spacecraft pointing. We present a technique based on the AstroSat-CZTI data to explore the hard X-ray characteristics of the \(\gamma \)-ray pulsar population. We report highly significant (\(\sim

We present the timing results of out-of-eclipse observations of Centaurus X-3 spanning half a binary orbit, performed on 12–13 December, 2016 with the Large Area X-ray Proportional Counter (LAXPC) on-board AstroSat. The pulse profile was confirmed to exhibit a prominent pulse peak with a secondary inter-pulse. The systemic spin period of the pulsar was found to be \(4.80188 \pm 0.000085\) s in agreement

The data pipeline at the Payload Operation Centre (POC) of the Scanning Sky Monitor (SSM) onboard AstroSat involves: (i) fetching the Level-0 data from the Indian Space Science Data Centre (ISSDC), (ii) Level-0 to Level-1 data processing followed by Level-2 data generation, and (iii) transfer of the Level-1 and Level-2 data back to ISSDC for dissemination of the re-packaged Level-2 data products. The

We present the UV photometry of one of the Ultra-Faint Dwarf (UFD) Milky Way (MW) satellite galaxies, Reticulum II, using images acquired with the Ultra-Violet Imaging Telescope (UVIT) onboard AstroSat. Reticulum II is a dark matter dominated, one of the most metal-poor and old (13.5 Gyr) satellite galaxies. High resolution spectroscopy of red giant branch (RGB) stars in the galaxy showed that the

To investigate the cosmic future of the universe, first, we obtain the particle and event horizons, and their evolution in time for three well-known varying cosmological constant models. We investigate the implications of these varying cosmological constant models on the particle and event horizons, and their time evolution during the universe history and future. We study the behaviours around the

An alternative scheme is described to estimate the layer 1 LAXPC 20 background for faint sources where the source contribution to the 50–80 keV count rate is less than 0.25 counts/s (15 milli-crabs or \(6 \times 10^{-11}\) ergs/s/cm\(^2\)). We consider 12 blank sky observations and based on their 50–80 keV count rate in 100 second time-bins, generate four template spectra which are then used to estimate

We present the study of dynamical status of the globular cluster NGC 1851. A combination of multi-wavelength space and ground-based data sets are used for the present analysis. In order to select the genuine cluster members, we used the astro-photometric data available from HST and GAIA-DR2 catalogs. The BSS radial distribution of the cluster is plotted from the center of the cluster to the outskirts

In this work, the effects of extensive air showers (EASs) were described by estimating the lateral distribution function (LDF) at very high energies of various cosmic-ray particles. The LDF simulation was performed using the air shower extended simulation (AIRES) system version 2.8.4a. LDF was simulated for charged particles such as pair production, muons, and all charged particles at very high energies

We present the results from the multi-wavelength monitoring observations of the Narrow-Line Seyfert 1 galaxy Mrk 335 with AstroSat. We analysed both the X-ray (SXT and LAXPC) and UV (UVIT) data of the source at two epochs, separated by \(\sim\)18 days. The source was in a low flux state during the observations, and the X-ray spectra were found to be harder than usual. The presence of soft X-ray excess

We present an ultra-violet study of two nearby dwarf irregular galaxies WLM and IC 2574, using the Far-UV and Near-UV data from the Ultra-Violet Imaging Telescope (UVIT). We used the F148W band Far-UV images and identified 180 and 782 young star-forming clumps in WLM and IC 2574, respectively. The identified clumps have sizes between 7–30 pc in WLM and 26–150 pc in IC 2574. We noticed more prominent

AstroSat/UVIT carries two gratings in the FUV channel and a single grating in the NUV channel. These gratings are useful for low resolution, slitless spectroscopy in the far and near UV bands of a variety of cosmic sources such as hot stars, interacting binaries, active galactic nuclei, etc. We present calibration of these gratings using observations of UV standards NGC 40 and HZ 4. We perform wavelength

We review the basic definitions and properties of trapped surfaces and discuss them in the context of Kerr–Vaidya line element. Our study shows that the apparent horizon does not exist in general for axisymmetric space–times. The reason being the surface at which the null tangent vectors are geodesics and the surface at which the expansion of such vectors vanishes do not coincide. The calculation of

We present the UV photometry of the old open cluster NGC188 obtained using images acquired with Ultraviolet Imaging Telescope (UVIT) on board the AstroSat satellite, in two far-UV (FUV) and one near-UV (NUV) filters. UVIT data is utilised in combination with optical photometric data to construct the optical and UV colour-magnitude diagrams (CMDs). In the FUV images, we detect only hot and bright blue

We report the discovery of a bright, compact ultraviolet source at a projected separation of 1.1 kpc from the known active galactic nucleus (AGN) in Mrk 766 based on AstroSat/UVIT observations. We perform radial profile analysis and derive the UV flux almost free from the nearby contaminating sources. The new source is about 2.5 and 5.6 times fainter than the AGN in the far and near UV bands. The two

AstroSat, India’s first observatory class satellite, operates as a proposal based observatory. AstroSat carries five science payloads capable of simultaneous observations in a broad energy band. In this article, we will summarize the science operations of AstroSat, AstroSat user distribution, user support available for AstroSat users and publications related to AstroSat and AstroSat data.

Ultra Violet Imaging Telescope (UVIT) is one of the 5 instruments on AstroSat satellite, which was launched on September 28, 2015. UVIT was designed to make images with a resolution of \(< 1.8''\), simultaneously in two ultraviolet channels: Far Ultraviolet (130–180 nm) and Near Ultraviolet (200–300 nm). Images are also made in visible region (320–550 nm) for tracking drifts in pointing. The shortest