Journal of Astrophysics and Astronomy最新文献

In this study, cosmic rays (CR) data from the King Abdulaziz University muon detector in Jeddah (Rc  = 14.8 GV), Saudi Arabia, were utilized to investigate the amplitude and phase components of diurnal variations in CR muons. The data covered the period from 2007 to 2012 and were fitted using a single cosine function with a 24-h period and two cosine functions with periods of 24 h and 12 h, respectively. The distributions of the phases and amplitudes resulting from these fits were analyzed across different time spans.

The findings of this analysis provided valuable insights into the diurnal characteristics of CR muons. The mean amplitude and phase obtained from the single fit were reported as −0.11 ± 0.51% and 11:00 ± 4.30 UT, respectively. Furthermore, employing the two-cosine fit revealed that the first phase had a mean occurrence time of 06:00 ± 6.90 UT, accompanied by an amplitude of −0.10 ± 0.62%. The second phase occurred at 13:00 ± 3.51 UT, with an amplitude of 0.11 ± 0.25%. The study observed diverse distributions and trends in amplitude and phase values across different time scales, including months, seasons, and years.

Additionally, the study investigated the influences of five solar activity parameters on the diurnal CR components using Pearson linear, non-parametric Spearman, and Kendall correlations. These parameters included the interplanetary magnetic field, solar wind speed, Kp index, Dst index, and solar radio flux at 10.7 cm. The results revealed that the relationships between solar activity variables and the diurnal CR parameters were not uniform. There were varying degrees of correlation, with differences in strength and magnitude depending on the specific variable and correlation coefficient being examined.

Sūryasiddhānta is an important astronomical treatise, which is very popular even now in the entire Indian sub-continent. Like other astronomical texts, Sūryasiddhānta describes the procedure to compute different astronomical parameters. However, the procedure to compute the planetary true positions for a given day (as per mid-night reckoning system) and place need to be applied independently for different planets. In this study, we are presenting a mathematical model for the computation of the true positions (nirāyana longitudes) of the planets at any given instant of time of the day for any desired place. This mathematical model is based on the algorithm presented in the Sūryasiddhānta with some modifications such as the usage of the fractional part of the ahargaṇas. The planetary positions or the longitudes of the planets are computed for the Sunrise of Mandi, Himachal Pradesh, and are compared with the Stellarium values (nirāyana – Nirāyana longitude values are obtained by applying the Precision of Equinox correction to the Stellarium Ecliptic (sāyana) longitudes.) to study the accuracy of the results obtained from the mathematical model.

Forbush decreases (Fd) are transient, short-term reductions in the intensity of galactic cosmic rays that reach the Earth’s surface. When this reduction is observed at multiple locations simultaneously, it is referred to as simultaneous Forbush decreases (SFd). Identifying Fd events in daily averaged cosmic ray (CR) raw data is always tedious, but the task has gone minimal through an algorithm (automated Fd detection). We deployed an automated Fd location algorithm on daily-averaged CR data from five neutron monitor stations covering 1998–2006. We identified 80 days with the most simultaneous events. While there exists extensive research on the subject using a case study approach, the current study is statistical. Whereas most of the previous investigations employed a small sample of Fds manually selected from a single CR station, large samples of Fds selected after disentangling the Sun’s influence on CR data from multiple neutron monitors (NMs) are used. The connection between the Fds and many solar-terrestrial variables is tested. The beautiful and consistent results obtained between the space weather variables and Fds at the five NM stations call the attention of space weather researchers to the need for rigorous, detailed, and accurate cataloging of Fds. Solar cycle oscillation significantly impacts the amplitude and timing of Fds. Its influence should be removed before Fd selection.

Active galaxies hosting radio jets can exhibit distinct active phases marked by two sets of radio lobes. Typically, these episodic radio sources have been identified through morphological observations. In addition, spectral characteristics-based methods are also employed wherever multi-frequency deep radio observations are available. However, these methods are inefficient in detecting restarted radio sources that do not exhibit a clear morphology. To address this, a method of using the spectral curvature (({{textrm{SPC}}} = alpha ^{1400~{textrm{MHz}}} _{150~{textrm{MHz}}}-alpha ^{150~{textrm{MHz}}} _{74~{textrm{MHz}}})) to identify restarted radio sources is presented. This is based on the fact that restarted radio sources with significant remnant emission are expected to have concave spectra in contrast to the convex or straight spectra observed in most radio sources. We use available wide area radio surveys in the range of frequencies from 74 MHz to 1.4 GHz to search for episodic radio sources and to shortlist 9,405 sources based on the criteria of ({textrm{SPC}} ge 0.5 ). The candidates thus identified can be followed up for detailed morphological and spectral index studies. This method will find application in the automated identification of episodic radio sources in large radio sky surveys from telescopes like LOFAR and SKA.

Contributions from the Indian gravity community have played a significant role in shaping several branches of astronomy and astrophysics. This document reviews some of the most important contributions and presents a vision for gravity research in the context of astronomy and astrophysics in India. This is an expanded version of one of the chapters in the recently released Vision Document of the Astronomical Society of India.

Accurately determining the origin of radio emissions is essential for numerous scientific experiments, particularly in radio astronomy. Conventional techniques, such as antenna arrays, encounter significant challenges, especially at very low frequencies, due to factors like the substantial size of the antennas and ionospheric interference. To address these challenges, we employ a space-based single-telescope that utilizes co-located antennas complemented by goniopolarimetric techniques for precise source localization. This study explores a novel and elementary machine learning technique to improve and estimate direction of arrival (DoA), leveraging a tri-axial antenna arrangement for radio source localization. Employing a simplistic emission and receiving antenna model, our study involves training an artificial neural network (ANN) using synthetic radio signals. These synthetic signals can originate from any location in the sky and cover an incoherent frequency range of 0.3–30 MHz, with a signal-to-noise ratio between 0 and 60 dB. A large synthetic data set was generated to train the ANN model catering to the possible signal configurations and variations. After training, the developed ANN model demonstrated exceptional performance, achieving loss levels in the training (({sim }0.02)), validation (({sim }0.23%)), and testing (({sim }0.21%)) phases. The machine learning-based approach, remarkably, exhibits substantially quicker inference times (({sim }5) ms) in contrast to analytically derived DoA methods, which typically range from 100 ms to a few seconds. This underscores its practicality for real-time applications in radio source localization, particularly in scenarios with a limited number of sensors.

There are different categories of Indian astronomical texts ranging from theoretically complex ones to simple practical manuals. The texts pertaining to vākya system are the ones which provide simplified algorithms to compute different astronomical quantities using vākyas. Vākyas (or mnemonics) are simple phrases/sentences in which numerical values—associated with an astronomical parameter–are encoded. Since these are meaningful phrases, it is very easy to memorize them and reproduce the numerical values quickly–without any errors. In this paper, by taking an example of Bhūpajñādi-vākyas, we shall demonstrate that the system is very efficient in terms of practical utility without compromising the accuracy.

Although the star-formation process has been studied for decades, many important aspects of the physics involved remain unsolved. Recent advancements in instrumentation in the infrared, far-infrared, and sub-millimeter-wavelength regimes have contributed to a significantly improved understanding of processes in the interstellar medium (ISM) leading to star formation. The future of research on the ISM and star formation looks exciting with instruments like the JWST, ALMA, etc., already contributing to the topic by gathering high-resolution high-sensitivity data and with several larger ground- and space-bound facilities either being planned or constructed. India has a sizable number of astronomers engaged in research on topics related to the ISM and star formation. In this white paper invited by the Astronomical Society of India to prepare a vision document for Indian astronomy, we review the Indian contributions to the global understanding of the star-formation process and suggest areas that require focused efforts both in creating observing facilities and in the theoretical front in India, to improve the impact of our research in the coming decades.

Since recent years, mass segregation driven by two-body relaxation in star clusters has been proposed to be measured by the so-called dynamical clock, (A^+), a measure of the area enclosed between the cumulative radial distribution of blue straggler stars and that of a reference population. Since star clusters spend their lifetime immersed in the gravitational potential of their host galaxy, they are also subject to the effects of galactic tides. In this work, I show that the (A^+) index of a star cluster depends on both its internal dynamics in isolation and the effects of galactic tides. Mainly, I focused on the largest sample of open clusters harboring blue straggler stars with robust cluster membership. I found that these open clusters exhibit an overall dispersion of the (A^+) index in diagnostic diagrams, whereas Milky Way globular clusters show a clear linear trend. However, as also experienced by globular clusters, (A^+) values of open clusters show some dependence on their galactocentric distances, in the sense that clusters located closer or farther than (sim )11 kpc from the Galactic center have larger and smaller (A^+) values, respectively. This different response to two-body relaxation and galactic tides in globular and open clusters, which happen concurrently, can be due to their different masses. More massive clusters can protect their innermost regions from galactic tides more effectively.

The mega-parsec scale radio relics at the galaxy cluster periphery are intriguing structures. While textbook examples of relics posit arc-like elongated structures at the clusters’ peripheries, several relics display more complex structures deviating from the conventional type. Abell 115 is a galaxy cluster hosting an atypical radio relic at its northern periphery. Despite the multi-wavelength study of the cluster over the last decades, the origin of the radio relic is still unclear. In this paper, we present a multi-frequency radio study of the cluster to infer the possible mechanism behind the formation of the radio relic. We used new 400 MHz observations with the uGMRT, archival VLA 1.5 GHz observations, and archival LOFAR 144 MHz observations. Our analysis supports the previous theory on the relic’s origin from the passage of a shock front due to an off-axis merger, where the old population of particles from the radio galaxies at the relic location has been re-energized to illuminate the 2 Mpc radio relic.