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      Volume 36, Issue 3

      September 2015,   pages  335-419

    • Hard X-ray Emission along the Z Track in GX 17+2

      G. Q. Ding C. P. Huang

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      Using the data from the Proportional Counter Array (PCA) and the High-Energy X-ray Timing Experiment (HEXTE) on board Rossi X-Ray Timing Explorer for Z source GX 17+2, we investigate the evolution of its PCA spectra and HEXTE spectra along a `Z’ track on its hardness-intensity diagram. A hard X-ray tail is detected in the HEXTE spectra. The detected hard X-ray tails are discontinuously scattered throughout the Z track. The found hard X-ray tail hardens from the horizontal branch, through the normal branch, to the flaring branch in principle and it contributes ∼ (20–50)% of the total flux in 20–200 keV. Our joint fitting results of the PCA+HEXTE spectra in 3–200 keV show that the portion of Comptonization in the Bulk-Motion Comptonization (BMC) model accounts for the hard X-ray tail, which indicates that the BMC process could be responsible for the detected hard tail. The temperature of the seed photons for BMC is ∼ 2.7 keV, implying that these seed photons might be emitted from the surface of the neutron star (NS) or the boundary layer between the NS and the disk and, therefore, this process could take place around the NS or in the boundary layer.

    • Solar Wind Associated with Near Equatorial Coronal Hole

      M. Hegde K. M. Hiremath Vijayakumar H. Doddamani Shashanka R. Gurumath

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      Present study probes temporal changes in the area and radiative flux of near equatorial coronal hole associated with solar wind parameters such as wind speed, density, magnetic field and temperature. Using high temporal resolution data from SDO/AIA for the two wave-lengths 193 Å and 211 Å, area and radiative flux of coronal holes are extracted and are examined for the association with high speed solar wind parameters. We find a strong association between different parameters of coronal hole and solar wind. For both the wavelength bands, we also compute coronal hole radiative energy near the earth and it is found to be of similar order as that of solar wind energy. However, for the wavelength 193 Å, owing to almost similar magnitudes of energy emitted by coronal hole and energy due to solar wind, it is conjectured that solar wind might have originated around the same height where 193 Å line is formed in the corona.

    • A Comparative Study on SN II Progenitors for the Synthesis of Li7 and B11 with the help of Neutrinos

      N. Lahkar S. Kalita H. L. Duorah K. Duorah

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      The synthesis of Li7 and B11 confronts astrophysicists. Type II (SN II) and Type Ic (SN Ic) supernovae are supposed to be the producers of these two elements. In this study we calculate the yields of these two elements for SN II progenitors with 8, 10 and 20 solar masses. The process considered here is the neutral current interaction of heavy flavour neutrinos (𝜈𝜇 or 𝜈𝜏) with He4 nuclei of the helium zone. The low mass progenitors are considered because the helium zone lies much closer to the core and hence experiences large neutrino flux. The starting point of the helium zone depends on detail stellar model. However, the shell radius at which it begins is available for these stars. 20 solar mass is considered for comparison of our production ratio Li/B with that of an earlier work. It is contrasted with the shock heating yields in the hydrogen envelope. The Li/B ratio has been found to be about 0.96. In the three model stars, the Li7 and B11 yields are found to be in the range 6.61×10−6 −2.63×10−6 𝑀Sun and 6.92×10−6 −2.75×10−6 𝑀Sun respectively as we go from 8 to 20 𝑀Sun. Some equivalence is found with shock induced nucleosynthesis model for SN II. The SN II yield is found to be compatible with that of hypernovae produced by C–O core collapse but higher than the yields obtained by neutrino processes in SNIc.

    • Fisher Matrix Predictions for Detecting the Cosmological 21-cm Signal with the Ooty Wide Field Array (OWFA)

      S. Bharadwaj A. K. Sarkar Sk. Saiyad Ali

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      We have used the Fisher matrix formalism to quantify the prospects of detecting the 𝑧 = 3.35 redshifted 21-cm HI power spectrum with the upcoming radio-imterferometric array OWFA. OWFA’s frequency and baseline coverage spans comoving Fourier modes in the range 1.8 × 10−2 ≤ k ≤ 2.7 Mpc−1. The OWFA HI signal, however, is predominantly from the range 𝑘 ≤ 0.2 Mpc−1. The larger modes, though abundant, do not contribute much to the HI signal. In this work, we have focused on combining the entire signal to achieve a detection. We find that a 5 - 𝜎 detection of 𝐴HI is possible with ∼ 150 h of observations, here $A^{2}_{\text{HI}}$ is the amplitude of the HI power spectrum. We have also carried out a joint analysis for 𝐴HI and 𝛽 the redshift space distortion parameter. Our study shows that OWFA is very sensitive to the amplitude of the HI power spectrum. However, the anisotropic distribution of the k modes does not make it very suitable for measuring 𝛽.

    • Discovery of a Faint Eclipsing Binary GSC 02265-01456

      D. F. Guo K. Li S. M. Hu Y. G. Jiang D. Y. Gao X. Chen

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      When observing the transiting extrasolar planets, we found a new eclipsing binary named GSC 02265-01456. The 𝑉 and 𝑅c observations were carried out for this binary. The photometric light curves of the two bands were simultaneously analyzed using the W–D code. The solutions show that GSC 02265-01456 is an extremely low mass ratio (𝑞 = 0.087) overcontact binary system with a contact degree of 𝑓 = 82.5%. The difference between the two maxima of the light curve can be explained by a dark spot on the primary component.

    • Nano-metric Dust Particles as a Hardly Detectable Component of the Interplanetary Dust Cloud

      I. Simonia Sh. Nabiyev

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      The present work introduces the hypothesis of existence of a hardly detectable component of the interplanetary dust cloud and demonstrates that such a component is a dust formation consisting of the dust particles of nano-metric dimensions. This work describes the main physical properties of such a kind of nano-dust, and its possible chemical and mineralogical peculiarities proposes new explanations related to reddening of the dynamically cold transneptunian objects on account of scattering their light by nano-dust of the hardly detectable component of the interplanetary dust cloud. We propose the relation for the coefficient of absorption by the nano-dust and provide results of the statistical analysis of the TNO color index–orbital inclinations. We also present a critical assessment of the proposed hypothesis.

  • Journal of Astrophysics and Astronomy | News

    • Continuous Article Publication

      Posted on January 27, 2016

      Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.

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