Journal of Astrophysics and Astronomy

Đề xuất rằng GLEAM-X $$\hbox {J162759.5}{-}523504.3$$, dạng biến thiên vô tuyến mới được phát hiện với chu kỳ quay bất thường dài ($$P_s = 1091$$.1690 giây), có thể được xác định là một magnetar vô tuyến, có từ trường bề mặt lưỡng cực là $$2.5 \times 10^{16}$$ G. Kết quả cho thấy: (a) có thể neo giữ một trường mạnh như vậy tại ranh giới lõi-vỏ của một sao neutron và (b) năng lượng từ sự phân rã của trường có thể giải thích độ sáng quan sát được (vô tuyến và X-quang) của nguồn này.

A review of observational properties of the Vela pulsar across a wide energy spectrum is given. Then current approaches to the modelling of pulsars and their wind zones are briefly presented. The challenges posed to the models by the diversity of Vela’s light curves in different energy ranges are discussed.

An examination of the existing period searches for 2CG195 + 4 leads to the conclusion that the 59 second periodicity is highly significant only for the 1981 March 17–18 detection of Bignami, Caraveo & Paul (1984). The statistical significance is increased substantially if the pulsation period is half the previously reported value. The period derivative is not well determined. Here we propose that 2CG 195 + 4 is a neutron star powered by accretion from a low (≲ 1M ⊙) mass main-sequence companion. A distance of a few hundred pc would imply that the neutron star is a fast rotator and is spinning down.

This article briefly overviews the physics of the Sun’s hot atmosphere, using observations from recent solar spacecrafts: Yohkoh, SOHO, TRACE and RHESSI.

Blazars are the most powerful class of persistent $$\gamma $$ -ray sources in the extragalactic Universe. Study of high redshift blazars is important to understand their cosmological evolution and formation of the supermassive black holes in the early phases of the Universe. The distant blazars are expected to be faint in the $$\gamma $$ -ray energy band since the high-energy $$\gamma $$ -ray photons traveling over cosmological distances are absorbed by the low-energy extragalactic background light photons via $$\gamma $$ – $$\gamma $$ pair production. Therefore, detection of high-energy $$\gamma $$ -ray emission from the blazars at high redshifts using ground-based telescopes is a very challenging task. In this paper, we report the feasibility of observing high redshift blazars with the MACE gamma-ray telescope which has recently become operational at Hanle, Ladakh. We have prepared a catalog of 94 high redshift blazars from the Fourth Fermi-LAT catalog of $$\gamma $$ -ray sources for their plausible observation with the MACE telescope. We have calculated the integral flux for these sources by extrapolating their Fermi-LAT spectra in the energy range from 30 GeV to 5 TeV. Using the MACE sensitivity information, we have estimated the total time required for the MACE telescope to detect the high-energy $$\gamma $$ -ray emission from these high redshift blazars at 5 $$\sigma $$ statistical significance level.

A volume-limited sample of F-dwarfs is chosen from Knude (1989) with low radial velocity as well as distance from the sun and compared with the expected model metallicity [Fe/H] distributions, taking the possible chemical inhomogeneity into account. There is found to be an agreement between the two within the error limits of small sampling.

The recent results on CNO in dwarfs and subdwarfs are discussed. The value of [O/Fe] ≃ 0.0 at solar abundances but gradually increases with decreasing [Fe/H]. The value of [C/Fe] is constant at ≃ 0.0 −2 +1 as [Fe/H] declines from + 0.5 to −2.0; for [Fe/H] < − 2.0, [C/Fe] increases somewhat reaching a mean value near + 0.2 or + 0.3 dex. All the investigations agree that N has a strong primary component.

The effect of intense magnetic field on the cosmic quark-hadron phase transition and also on the baryon number inhomogeneity has been investigated using phenomenological MIT bag model for the quark sector. For the sake of simplicity an ideal gas equation of state has been considered for the hadronic phase.