Subjects -> PHYSICS (Total: 857 journals)     - ELECTRICITY AND MAGNETISM (10 journals)    - MECHANICS (22 journals)    - NUCLEAR PHYSICS (53 journals)    - OPTICS (92 journals)    - PHYSICS (625 journals)    - SOUND (25 journals)    - THERMODYNAMICS (30 journals) PHYSICS (625 journals)            First | 1 2 3 4 | Last

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 Journal of Astrophysics and AstronomyJournal Prestige (SJR): 0.266 Number of Followers: 58     Open Access journal ISSN (Print) 0973-7758 - ISSN (Online) 0250-6335 Published by Springer-Verlag  [2469 journals]
• Photometric calibrations and characterization of the 4K $$\times$$ × 4K
CCD imager, the first-light axial port instrument for the 3.6m DOT

• Abstract: Abstract In the present work, recent characterization results of the 4K $$\times$$ 4K CCD imager (a first light instrument of the 3.6m devasthal optical telescope; DOT) and photometric calibrations are discussed along with measurements of the extinction coefficients and sky brightness values at the location of the 3.6m DOT site based on the imaging data taken between 2016 and 2021. For the 4K $$\times$$ 4K CCD imager, all given combinations of gains (1, 2, 3, 5 and 10 e $$^-$$ /ADU) and readout noise values for the three readout speeds (100 kHz, 500 kHz and 1 MHz) are verified using the sky flats and bias frames taken during early 2021; measured values resemble well with the theoretical ones. Using color–color and color–magnitude transformation equations, color coefficients ( $$\alpha$$ ) and zero-points ( $$\beta$$ ) are determined to constrain and examine their long-term consistencies and any possible evolution based on UBVRI observations of several Landolt standard fields observed during 2016–2021. Our present analysis exhibits consistency among estimated $$\alpha$$ values within the 1 $$\sigma$$ and does not show any noticeable trend with time. We also found that the photometric errors and limiting magnitudes computed using the data taken using the CCD imager follow the simulated ones published earlier. The average extinction coefficients, their seasonal variations and zenith night-sky brightness values for the moon-less nights for all ten Bessell and SDSS filters are also estimated and found comparable to those reported for other good astronomical sites.
PubDate: 2022-05-19

• Intra-night optical variability study of a non-jetted narrow-line Seyfert
1 galaxy: SDSS J163401.94+480940.1

• Abstract: Abstract SDSS J163401.94 $$+$$ 480940.1 is a non-jetted radio-loud narrow-line Seyfert 1 (NLSy1) galaxy. Optical monitoring of this object was carried out in two intra-night sessions each $$\ge$$ 3 h with 3.6-m DOT. Intra-night optical variability characterization is presented for the first time for this source. We have detected an unexpected remarkable flare in one of two monitoring sessions of SDSS J163401.94 $$+$$ 480940.1, whose rapid brightening phase implied a minute like doubling time of $$\sim$$ 22 min, thereby approaching the extremely fast minute like variability, observed from FSRQ PKS 1222 $$+$$ 21 at 400 GeV. The detection of a minute-like variability suggests the existence of relativistic jets with a small viewing angle. We briefly discuss the possible mechanisms for the non-detection of relativistic jets in its very long baseline array observations.
PubDate: 2022-05-17

• A comprehensive photometric and kinematical characteristic of the newly
discovered QCs clusters with Gaia EDR3

• Abstract: Abstract This study reports the first comprehensive astrometric, photometric, and kinematical analysis of four newly discovered open clusters; namely QC1, QC2, QC3, and QC4, using astrometric and photometric data from the most recent Gaia EDR3 for $$G <17$$ mag. Utilizing the ASteCA code, we identified the most probable ( $$P \ge 50$$ %) star candidates and found the numbers of star members (N) to be 118 (QC1), 142 (QC2), 210 (QC3), and 110 (QC4). By fitting King’s density profile to the cluster’s RDPs, we found the internal structural parameters of each cluster such as the cluster radii that are in the range 7.00–11.00 arc-min. For each cluster, we constructed the CMD and by fitting them with suitable isochrones we found that the metallicity range is (0.0152–0.0199) which is in line with the Solar value, the logarithmic age (in yrs) range between 6.987 and 8.858. The distances derived from CMD are $$1674\pm 41$$ , $$1927\pm 44$$ , $$1889\pm 43$$ , and $$1611\pm 40$$ (pc) for QC1, QC2, QC3, and QC4, respectively, and they are in good agreement up to 85% with the values obtained from the astrometric data. In addition, from the MLR of the clusters, we obtained a total mass, $$M_C$$ in Solar units, of 158, 177, 232, and 182 and an absolute magnitude $$M_G$$ (mag) of 4.33, 3.80, 4.25, and 4.10 for QC1, QC2, QC3, and QC4, respectively. The dynamical analysis and evolution parameters of the cluster members indicated that all the four clusters are dynamically relaxed; except QC1 which has an evolution parameter $$\tau \sim 0.82$$ that indicates a dynamical activity within the cluster. From the kinematical analysis of the cluster data, we computed the space velocity, the coordinates of the apex point (A, D) using the AD—diagram method, as well as the Solar elements ( $$S_{\odot }$$ , $$l_{A}$$ , $$b_{A}$$ , $$\alpha _{A}$$ , $$\delta _{A}$$ ).
PubDate: 2022-05-17

• New evidence and analysis of cosmological-scale asymmetry in galaxy spin
directions

• Abstract: In the past several decades, multiple cosmological theories that are based on the contention that the Universe has a major axis have been proposed. Such theories can be based on the geometry of the Universe, or multiverse theories such as black hole cosmology. The contention of a cosmological-scale axis is supported by certain evidence such as the dipole axis formed by the CMB distribution. Here I study another form of the cosmological-scale axis, based on the distribution of the spin direction of spiral galaxies. Data from four different telescopes are analyzed, showing nearly identical axis profiles when the distribution of the redshifts of the galaxies is similar.
PubDate: 2022-05-11

• Properties of the accretion disc, jet and disc-wind around Kerr black hole

• Abstract: Abstract Relativistic jets and disc-winds are energetic phenomena exhibited by various sources, including Active Galactic Nuclei (AGNs) and black hole X-ray binaries (BH-XRBs). Despite recent observational advances in unraveling the region close to the black hole, many aspects of jet launching and particularly the jet-disc connection in these sources are not fully understood. This study investigates the role of the aspect ratio (H/r) of the underlying accretion disc on the jet launching. In this regard, we use an axisymmetric GRMHD framework with adaptive mesh refinement and initialize our simulations with a thin accretion disc in hydro-static equilibrium. In our simulations, we observe Blandford & Znajek (BZ) jet, Blandford & Payne (BP) disc-wind and $$B_{\mathrm{tor}}$$ dominated disc-wind. We find that the aspect ratio of the underlying accretion disc plays a crucial role in the dynamical properties of jet and disc-winds. For an accretion disc with a low aspect ratio, we observe the BZ-jet be thinner and the $$B_{\mathrm{tor}}$$ dominated disc-wind component of the disc-wind to be broader. Further, the BP disc-wind launching radius is closer for an accretion disc with a low aspect ratio. Such a variable launching area of BP disc-wind with an aspect ratio of the underlying disc can have potential implications on understanding the origin of jet dichotomy. Additionally, from the temporal evolution of magnetic flux, we also find the discs with higher aspect ratios are more susceptible to transform into a magnetically arrested disc (MAD) and result in more intermittent wind and jet properties.
PubDate: 2022-04-28

• A multiresolution approach to enhance small telescope data under non-ideal
conditions

• Abstract: Abstract Astronomical imaging of a star cluster is one of the paramount ways to learn about stellar evolution, stellar dynamics. A large telescope is not generally accessible to all observers. In that context, small telescope observations with a proper denoising scheme can be an excellent alternative. This paper proposes a technique to denoise star cluster data using an undecimated wavelet transform, with a modified thresholding process. Our work aims to prove the effectiveness of such a wavelet-based technique on real-time data. We present drastically noise-infested observational data of the NGC 2301 star cluster, captured over five nights from Fr. Eugene Lafont Observatory, Kolkata. We observe that for highly noise-polluted data, the conventional methods of dark frame subtraction and flat frame division are inadequate to produce the desired quality of images due to functioning exclusively in the spatial domain. Thus, we take the wavelet-based multiresolution approach to ameliorate those raw images. We also introduce a modified thresholding function to modulate the image at different resolution levels. A standard star detecting software Daophot II quantifies the increment in the number of detected stars from raw images to the images processed by our proposed method as: for red filter 397–903, for green filter 663–945, for blue filter 362–896. On the contrary, Daophot II can’t detect any star in the highly noise-polluted images processed by the conventional methods. Therefore, we hope our proposed processing methodology will motivate others to initiate small telescope observations from any site restrained by its geographical location.
PubDate: 2022-04-20

• Editorial

• PubDate: 2022-04-07

• Editorial

• PubDate: 2022-04-07

• Impact of disc-outflows in accreting neutron stars

• Abstract: Abstract In this paper, we propose a model for accreting neutron stars in which the mass outflow driven from the disc plays an important role. We assume a geometrically thin accretion disc surrounding a magnetic neutron star and apply a power-law dependence of radius for the accretion rate due to mass loss rate, $$\dot{M}_w\propto r^{\lambda }$$ . We suppose that the outflows driven from accretion discs extract the mass from the inflow, and the angular momentum of the outflows can be deposited into or taken away from the inflow. We consider the present model in situations that the inner radius of the disc is larger than the neutron star radius and lies within the corotation radius. In such situations, the solutions imply that the disc rotation in the inner transition zone outstandingly changes in the presence of the outflow. The rotation of the inner disc increases (or decreases) and the width of the inner transition zone become narrow (or wide) when the angular momentum of outflow is deposited into (or taken away from) the inflow. In this paper, we also investigate the influences of the disc-outflow on the time rate of the pulsation period of the star ( $$\dot{P}_*$$ ). The solutions imply that the spin period rate of the star increases in the presence of the outflows driven from the disc.
PubDate: 2022-04-07

• Swift J1753.5-0127: understanding the accretion geometry through
frequency-resolved spectroscopy

• Abstract: Abstract The black hole binary source Swift J1753.5−0127 remained in outburst for $$\sim$$ 12 years from May 2005 to April 2017. For the most part of the outburst, the source remained in the low hard state (LHS) displaying transitions to softer states only towards the end of the outburst for short periods of time. Quasi-periodic oscillations (QPOs) were observed in the power density spectrum (PDS) only during the decay. A soft thermal component was required to model the spectrum in LHS, which does not conform to the generally accepted disc truncation theory. In this work, we attempt to obtain a clearer picture of the accretion disc geometry by studying the QPO variability using frequency-resolved spectroscopy (FRS). We obtain the QPO rms spectrum of the source during the bright-hard state and model it with physical components. We find that the QPO rms spectrum can be described only by a Comptonization component with no contribution from the thermal disc. This indicates that the variability observed in the PDS originates in the Comptonization component and the evolution of the QPOs is likely to be a result of localization of the variabilities to different radii of the hot inner flow rather than disc truncation. The minimal variation in disc parameters also points to the existence of a stable disc throughout the outburst.
PubDate: 2022-04-01

• TIFR treasures for astronomy from ground to space

• Abstract: Abstract The infrared astronomy group of the Department of Astronomy and Astrophysics at Tata Institute of Fundamental Research has been pursuing astronomical instrumentation activities since its inception. The group has been routinely involved in a balloon-borne astronomy program from field station at Hyderabad with indigenously developed payloads. Ground-based astronomical activities began with a single element infrared detector. Later, over time, larger format array detectors are being used in the cameras. These astronomy cameras have been routinely used at observatories across India. Recently, the group has also developed a laboratory model of the infrared spectroscopic imaging survey payload, targeted for the small satellite mission of the Indian Space Research Organisation, which will carry out spectroscopic measurements in the wavelength range 1.7–6.4  $$\mu \hbox {m}$$ seamlessly.
PubDate: 2022-03-19

• Development of a new type of metallic mirrors for 21m MACE
γ-ray telescope

• Abstract: Abstract Major atmospheric Cherenkov experiment (MACE) is a ground-based imaging atmospheric Cherenkov telescope installed at Hanle (~4.3 km above sea level), Ladakh in the northern region of India. With a large parabolic reflector of 21 m diameter and 25 m focal length, MACE telescope is expected to explore the γ-ray Universe above 20 GeV. The tesselated light collector of MACE telescope employs 356 mirror panels each of size ~1m × 1m. The individual panel comprises of 4 metallic mirror facets each of size ~0.5m × 0.5m with a similar focal length. All 1424 mirror facets (356 × 4) are aligned in such a way that the whole reflector functions approximately as a single quasi-parabolic mirror of area ~339 m2 with a focal length varying from 25 m in the central region to 26.16 m on the periphery. Here, we describe the methodology for developing the metallic mirrors using the diamond turning technique. We also present the results from the testing and characterization of ~1500 mirror facets, which qualify all the optical requirements of the MACE reflector. The testing of mirrors includes dimensionality, water ingress and environmental tests. The optical characterization of individual mirror facets is based on the measurements of focal length, spot size and reflectance.
PubDate: 2022-03-19

• Multi-wavelength characterization of Fermi blazars of uncertain type

• Abstract: Abstract One of the major challenges in the research of jetted active galactic nuclei (AGN) is the completeness of the source catalogs released using the $$\gamma$$ -ray data taken from the Fermi-large area telescope (LAT). There are about $$\sim$$ 30% of the Fermi-LAT detected blazars whose classification is yet to be ascertained, so-called blazars candidates of uncertain (BCU) type, thereby hampering the attempts made to explore the problems associated with relativistic jets. Using the results obtained in a recent study focused on the optical spectroscopic and multi-band properties of a large sample of Fermi blazars, this work classifies 57 BCUs presents in the fourth catalog of the Fermi-LAT detected AGN as flat-spectrum radio quasars (FSRQs) and 96 as BL Lac type sources. In the $$\gamma$$ -ray luminosity versus $$\gamma$$ -ray photon index plane, these newly classified blazars occupy regions populated by their known counterparts. The Compton dominance and accretion luminosity normalized by the Eddington one, for BCUs appear to follow the positive correlation already identified for known blazars. These observations suggest that Compton dominance can be used as a proxy for the accretion rate, thus supporting the Compton dominance-based blazar classification scheme.
PubDate: 2022-03-12

• New parameterizations of generalized Chaplygin gas model constrained at
background and perturbation levels

• Abstract: Abstract We study the main cosmological properties of the generalized Chaplygin gas (GCG) dark energy model at the background and perturbation levels. By using the latest cosmological data in both the background and perturbation levels, we implement a joint likelihood analysis to constrain the cosmological parameters of the model. Using the available expansion and growth rate data, we place constraints on the free parameters of the GCG model based on the statistical Markov chain Monte Carlo method. Then, the best-fit values of cosmological parameters and those of confidence regions are found. We obtain the best-fit value of the current expansion rate of the Universe in the GCG model and show that it is in good agreement with the $$\Lambda$$ CDM model. Moreover, the growth rate of matter perturbations is investigated in the context of a unified GCG model. It is shown that in this model, the dark energy component, like the $$\Lambda$$ sector in the $$\Lambda$$ CDM model, can suppress the amplitude of matter perturbations. We show that the growth rate of perturbations in GCG parametrization is consistent with cluster-scale observations similar to the case of the concordance $$\Lambda$$ CDM model. Our results show that the tension on $$\sigma _{8}$$ appeared in the concordance model can be alleviated in GCG cosmology.
PubDate: 2022-03-03
DOI: 10.1007/s12036-022-09797-9

• Filters for NIR astronomical photometry: comparison of commercial IRWG
filters and designs using OpenFilters

• Abstract: Abstract The photometric accuracy in the near-infrared (NIR) wavelength range (0.9–2.6 $$\mu$$ m) is strongly affected by the variability of atmospheric transmission. The Infrared Working Group (IRWG) has recommended filters that help alleviate this issue and provide a common standard of NIR filtersets across different observatories. However, accurate implementation of these filters are yet to be available to astronomers. In the meantime, InGaAs based detectors have emerged as a viable option for small and medium telescopes. The present work explores the combination of IRWG filtersets with InGaAs detectors. A few commercially available filtersets that approximate the IRWG profile are compared. Design of more accurate IRWG filtersets suitable for the InGaAs sensitivity range is undertaken using an open-source filter design software – OpenFilters. Along with the photometric filters iZ, iJ and iH, design of a few useful narrow band filters is also presented. These filters present opportunities for small and medium telescopes for dedicated long-term observation of interesting infrared sources.
PubDate: 2022-02-26
DOI: 10.1007/s12036-021-09788-2

• Effects of the moonlight on the operating parameters of the MACE
$$\gamma$$ γ -ray telescope: a feasibility study

• Abstract: Abstract Major atmospheric Cherenkov experiment (MACE) is a very high-energy $$\gamma$$ -ray telescope based on imaging atmospheric Cherenkov technique. The telescope has recently been installed at Hanle, Ladakh and results from its first light are expected very soon. The imaging atmospheric Cherenkov telescopes like MACE are usually operated during dark, clear and moonless nights and hence their duty cycle is limited to $$\sim$$ 10% (1000 hours per year). Increasing the duty cycle of these telescopes is a challenging task in the field of ground-based very high-energy $$\gamma$$ -ray astronomy. In this work, we study the feasibility of operating the MACE telescope under moderate moonlight to monitor the variable $$\gamma$$ -ray sources in the sky as long as possible. We have developed a detailed methodology for estimating the contribution of moonlight as a function of its phase to the night sky background at the MACE site using the model of the brightness of moonlight proposed by Krisciunas & Shaefer (1991). The effect of additional background due to moonlight is examined on the various operational parameters such as anode current of the photomultiplier tubes in the camera, discriminator threshold, threshold energy and sensitivity of the MACE telescope. For the safe operation of the photomultiplier tubes under partial moonlight conditions, we estimate the gain in observation time or duty cycle of the telescope. It is found that if the strict requirements of the imaging atmospheric Cherenkov telescopes are relaxed by operating the photomultiplier tubes in the MACE camera at a lower gain or higher anode current and hence at a relatively higher energy threshold under moderate moonlight, a significant increase of $$\sim$$ 20% in the effective observation time is expected every year for observations with the MACE telescope.
PubDate: 2022-02-23
DOI: 10.1007/s12036-021-09792-6

• Upcoming 4m ILMT facility and data reduction pipeline testing

• Abstract: Abstract The 4m international liquid mirror telescope (ILMT) installation activities have recently been completed at the Devasthal observatory (Uttarakhand, India). The ILMT will perform continuous observation of a narrow strip of the sky ( $$\sim$$ 27 $$'$$ ) passing over the zenith in the SDSS $$g'$$ , $$r'$$ and $$i'$$ bands. In combination with a highly efficient $$4{\rm k}\times 4{\rm k}$$ CCD camera and an optical corrector, the images will be secured at the prime focus of the telescope using the time delayed integration technique. The ILMT will reach $$\sim$$ 22.5 mag ( $$g'$$ -band) in a single scan and this limiting magnitude can be further improved by co-adding the nightly images. The uniqueness of the one-day cadence and deeper imaging with the ILMT will make it possible to discover and study various galactic and extra-galactic sources, specially variable ones. Here, we present the latest updates of the ILMT facility and discuss the preparation for the first light, which is expected during early 2022. We also briefly explain different steps involved in the ILMT data reduction pipeline.
PubDate: 2022-02-22
DOI: 10.1007/s12036-021-09795-3

• Revealing nature of GRB 210205A, ZTF21aaeyldq (AT2021any) and follow-up
observations with the 4K $$\times$$ × 4K CCD imager + 3.6m DOT

• Abstract: Abstract Optical follow-up observations of optical afterglows of gamma-ray bursts are crucial to probe the geometry of outflows, emission mechanisms, energetics and burst environments. We performed the follow-up observations of GRB 210205A and ZTF21aaeyldq (AT2021any) using the 3.6m Devasthal optical telescope (DOT) around one day after the burst to deeper limits due to the longitudinal advantage of the place. This paper presents our analysis of the two objects using data from other collaborative facilities, i.e., 2.2m Calar Alto Astronomical Observatory (CAHA) and other archival data. Our analysis suggests that GRB 210205A is a potential dark burst once compared with the X-ray afterglow data. Also, comparing results with other known and well-studied dark GRBs samples indicate that the reason for the optical darkness of GRB 210205A could either be intrinsic faintness or a high redshift event. Based on our analysis, we also found that ZTF21aaeyldq is the third known orphan afterglow with a measured redshift except for ZTF20aajnksq (AT2020blt) and ZTF19abvizsw (AT2019pim). The multiwavelength afterglow modeling of ZTF21aaeyldq using the afterglowpy package demands a forward shock model for an ISM-like ambient medium with a rather wider jet opening angle. We determine circumburst density of $$n_{0} = 0.87$$ cm $$^{-3}$$ , kinetic energy $$E_{k} = 3.80 \times 10^{52}$$ erg and the afterglow modeling also indicates that ZTF21aaeyldq is observed on-axis ( $$\theta _{\mathrm{obs}} < \theta _{\mathrm{core}}$$ ) and a gamma-ray counterpart was missed by GRBs satellites. Our results emphasize that the 3.6m DOT has a unique capability for deep follow-up observations of similar and other new transients for deeper observations as a part of time-domain astronomy in the future.
PubDate: 2022-02-22
DOI: 10.1007/s12036-021-09794-4

• Optical flux and spectral characterization of the blazar PG 1553 + 113
based on the past 15 years of data

• Abstract: Abstract We study flux and spectral variability of the high energy peaked TeV blazar PG 1553 + 113 on diverse timescales using the data collected from 2005 to 2019 which also includes the intensive intra-night monitoring of the target. Additionally, we recorded the brightest flare of the blazar PG 1553 + 113 during April 2019 when the source attained an R-band magnitude of 13.2. Analyzing the spectral evolution of the source during the flare gave a clockwise spectral hysteresis loop and a time lag with V-band variations leading to the R-band ones. Various statistical tests, fitting procedures and cross-correlation techniques are applied to search for periodicity and examine the color-magnitude relationship. We find a median period of (2.21 ± 0.04) years along with the secondary period of about 210 days. Finally, we briefly discuss various physical mechanisms which are capable of explaining our findings.
PubDate: 2022-02-15
DOI: 10.1007/s12036-021-09793-5

• Understanding emission signatures of AGN jets through numerical
simulations

• Abstract: Abstract The multi-wavelength non-thermal emission from the relativistic AGN jets exhibits flux variability ranging from a very short timescale of minutes, hours to long-timescale of months and years. These magnetically driven jets are subject to several instabilities during their propagation in space. Magneto-hydrodynamical (MHD) instabilities are the most probable candidate responsible for magnetic energy dissipation that could prompt jet radiation and particle acceleration. In this work, we have investigated the impact of the pitch profile and magnetization value on developing the current-driven (CD) kink instability in the moderately relativistic regime of Lorentz factor 5. To achieve this, we simulate a 3D plasma column, a representative section of an AGN jet. From our analysis, a stalled growth of the instability is apparent with a lower magnetization value due to the variable Alfvénic nature of the flow. In addition, we have also investigated the impact of constant pitch profile on the dynamical evolution of the plasma column and the corresponding emission features.
PubDate: 2022-02-12
DOI: 10.1007/s12036-021-09796-2

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