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Taufiq Hidayat Achmad Munir Budi Dermawan Anton Timur Jaelani Stéphane Léon Dading Hadi Nugroho Andriyan Bayu Suksmono Putra Mahasena Premana Wardayanti Premadi Dhani Herdiwijaya Chatief Kunjaya Zadrach Ledoufij Dupe Budi Brahmantyo Denny Mandey Muhammad Yusuf Hesti Retno Tri Wulandari Falahuddin Arief Muhammad Irfan Agus Triono Puri Jatmiko Evan Irawan Akbar Hery Leo Sianturi Jehunias Leonidas Tanesib Ali Warsito Judhistira Aria Utama 《Experimental Astronomy》2014,37(1):85-108
We report the first measurements of radio frequency spectrum occupancy performed at sites aimed to host the future radio astronomy observatory in Indonesia. The survey is intended to obtain the radio frequency interference (RFI) environment in a spectral range from low frequency 10 MHz up to 8 GHz. The measurements permit the identification of the spectral occupancy over those selected sites in reference to the allocated radio spectrum in Indonesia. The sites are in close proximity to Australia, the future host of Square Kilometre Array (SKA) at low frequency. Therefore, the survey was deliberately made to approximately adhere the SKA protocol for RFI measurements, but with lower sensitivity. The RFI environment at Bosscha Observatory in Lembang was also measured for comparison. Within the sensitivity limit of the measurement equipment, it is found that a location called Fatumonas in the surrounding of Mount Timau in West Timor has very low level of RFI, with a total spectrum occupancy in this measured frequency range being about 1 %, mostly found at low frequency below 20 MHz. More detailed measurements as well as a strategy for a radio quiet zone must be implemented in the near future. 相似文献
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Ichsan Ibrahim Hakim L.Malasan Chatief Kunjaya Anton Timur Jaelani Gerhana Puannandra Putri Mitra Djamal 《天文和天体物理学研究(英文版)》2018,(4)
In astronomy,the brightness of a source is typically expressed in terms of magnitude.Conventionally,the magnitude is defined by the logarithm of received flux.This relationship is known as the Pogson formula.For received flux with a small signal to noise ratio(S/N),however,the formula gives a large magnitude error.We investigate whether the use of Inverse Hyperbolic Sine function(hereafter referred to as the Asinh magnitude)in the modified formulae could allow for an alternative calculation of magnitudes for small S/N flux,and whether the new approach is better for representing the brightness of that region.We study the possibility of increasing the detection level of gravitational microlensing using 40 selected microlensing light curves from the 2013 and 2014 seasons and by using the Asinh magnitude.Photometric data of the selected events are obtained from the Optical Gravitational Lensing Experiment(OGLE).We found that utilization of the Asinh magnitude makes the events brighter compared to using the logarithmic magnitude,with an average of about 3.42×10~(-2)magnitude and an average in the difference of error between the logarithmic and the Asinh magnitude of about 2.21×10(-2)magnitude.The microlensing events OB140847 and OB140885 are found to have the largest difference values among the selected events.Using a Gaussian fit to find the peak for OB140847 and OB140885,we conclude statistically that the Asinh magnitude gives better mean squared values of the regression and narrower residual histograms than the Pogson magnitude.Based on these results,we also attempt to propose a limit in magnitude value for which use of the Asinh magnitude is optimal with small S/N data. 相似文献
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Active Galactic Nuclei (AGN), such as Seyfert galaxies, quasars, etc., show light variations in all wavelength bands, with
various amplitude and in many time scales. The variations usually look erratic, not periodic nor purely random. Many of these
objects also show lognormal flux distribution and RMS–flux relation and power law frequency distribution. So far, the lognormal
flux distribution of black hole objects is only observational facts without satisfactory explanation about the physical mechanism
producing such distribution in the accretion disk. One of the most promising models based on cellular automaton mechanism
has been successful in reproducing PSD (Power Spectral Density) of the observed objects but could not reproduce lognormal
flux distribution. Such distribution requires the existence of underlying multiplicative process while the existing SOC models
are based on additive processes. A modified SOC model based on cellular automaton mechanism for producing lognormal flux distribution
is presented in this paper. The idea is that the energy released in the avalanche and diffusion in the accretion disk is not
entirely emitted instantaneously as in the original cellular automaton model. Some part of the energy is kept in the disk
and thus increase its energy content so that the next avalanche will be in higher energy condition and will release more energy.
The later an avalanche occurs, the more amount of energy is emitted to the observers. This can provide multiplicative effects
to the flux and produces lognormal flux distribution. 相似文献
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Hanindyo Kuncarayakti Desima Kristyowati Chatief Kunjaya 《Astrophysics and Space Science》2008,314(1-3):209-212
We present the results of our photometric and spectroscopic observations of Nova Sco 2007 N.1 (V1280 Sco). The photometric data was represented by a single data point in the light curve since the observation was carried out only for one night. The spectra cover two different phases of the object’s evolution during the outburst, i.e. pre-maximum and post-maximum. Measurements of the P-Cygni profile on Na I ‘D’ line (5889 Å) was derived as the velocity of shell expansion, yielding 1567.43±174.14 km s?1. We conclude that V1280 Sco is a fast Fe II-type nova. 相似文献
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