Instruments of RT-2 experiment onboard CORONAS-PHOTON and their test and evaluation IV: background simulations using GEANT-4 toolkit     

Ritabrata Sarkar  Samir Mandal  Dipak Debnath  Tilak B. Kotoch  Anuj Nandi  A. R. Rao  Sandip K. Chakrabarti 《Experimental Astronomy》2011,29(1-2):85-107

Hard X-ray detectors in space are prone to background signals due to the ubiquitous cosmic rays and cosmic diffuse background radiation that continuously bombards the satellites which carry the detectors. In general, the background intensity depends on the space environment as well as the material surrounding the detectors. Understanding the behavior of the background noise in the detector is very important to extract the precise source information from the detector data. In this paper, we carry out Monte Carlo simulations using the GEANT-4 toolkit to estimate the prompt background noise measured with the detectors of the RT-2 Experiment onboard the CORONAS-PHOTON satellite.  相似文献   

Feasibility of spectro-photometry in X-rays (SPHINX) from the moon     

Ritabrata Sarkar  Sandip Kumar Chakrabarti 《Experimental Astronomy》2010,28(1):61-77

Doing space Astronomy on lunar surface has several advantages. We present here feasibility of an All Sky Monitoring Payload for Spectro-photometry in X-rays (SPHINX) which can be placed on a lander on the moon or in a space craft orbiting around the moon. The Si–PIN photo-diodes and CdTe crystals are used to detect solar flares, bright gamma bursts, soft gamma-ray repeaters from space and also X-ray fluorescence (XRF) from lunar surface. We present the complete Geant4 simulation to study the feasibility of such an instrument in presence of Cosmic Diffused X-Ray Background (CDXRB). We find that the signal to noise ratio is sufficient for moderate to bright GRBs (above 5 keV), for the quiet sun (up to 100 keV), solar flares, soft gamma-ray repeaters, X-ray Fluorescence (XRF) of lunar surface etc. This is a low-cost system which is capable of performing multiple tasks while stationed at the natural satellite of our planet.  相似文献   

Did Tsunami tremor jolt microbial biomass and their activities in soils? A case study in Andaman Island,India     

Pradip Bhattacharyya  Tanmoy Karak  Kalyan Chakrabarti  Asish Chakraborty  Ranjit Kumar Paul  Sudipta Tripathi 《Environmental Earth Sciences》2014,72(5):1443-1452

The nature of selected soil-chemical and microbial properties influenced by tsunami affected and non-affected areas along the border areas of the alluvial Andaman Island in India were investigated. Soils of these areas have turned saline and saline-sodic due to the ingression of sea water. The electrical conductivity of the saturation extract of the surface soil varied from 11.2 to 23.8 dS m^?1 in 2005, and it was decreased to 0.8–10.3 dS m^?1 in 2006 due to the heavy rain in the following year after the tsunami. Soil quality indicators, like microbial biomass C, microbial metabolic quotient, microbial respiration quotient and fluorescein diacetate hydrolyzing activity, decreased in the tsunami affected soil in 2005, but slightly increased in 2006. All microbial parameters were significantly negatively correlated with the electrical conductivity, sodium absorption ratio and exchangeable sodium percentage. Suppression of microbial biomass and their activities in the soils due to the increased-salinity is of great agronomic significance and needs suitable intervention for sustainable crop production. Significant differences were found in soil-chemical and microbial characteristics between tsunami affected and non-affected areas. Hierarchical clustering algorithm on the basis of different soil-chemical and microbial characteristics revealed that there is significant difference in grouping between tsunami affected and non-affected zones. From this study, it can be concluded that the sea water ingression detrimentally influenced the microbial properties of tsunami affected soil.  相似文献   

Standing shocks around black holes and estimation of outflow rates     

Santabrata Das  Sandip K. Chakrabarti 《Journal of Astrophysics and Astronomy》2002,23(1-2):143-147

We self-consistently obtain shock locations in an accretion flow by using an analytical method. One can obtain the spectral properties, quasi-periodic oscillation frequencies and the outflow rates when the inflow parameters are known. Since temperature of the CENBOL decides the spectral states of the black hole, and also the outflow rate, the outflow rate is directly related to the spectral states.  相似文献   

Radiatively driven winds from effective boundary layer around black holes     

Indranil Chattopadhyay  Sandip K. Chakrabarti 《Journal of Astrophysics and Astronomy》2002,23(1-2):149-153

Matter accreting onto black holes suffers a standing or oscillating shock wave in much of the parameter space. The post-shock region is hot, puffed up and reprocesses soft photons from a Keplerian disc to produce the characteristic hard tail of the spectrum of accretion discs. The post-shock torus is also the base of the bipolar jets. We study the interaction of these jets with the hard photons emitted from the disc. We show that radiative force can accelerate outflows but the drag can limit the terminal speed. We introduce an equilibrium speed υ_eq as a function of distance, above which the flow will experience radiative deceleration.  相似文献   

Molecular hydrogen formation during dense interstellar cloud collapse     

Kinsuk Acharyya  Sandip K. Chakrabarti  Sonali Chakrabarti 《Monthly notices of the Royal Astronomical Society》2005,361(2):550-558

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Erratum to: Spherical collapse in vacuum f ( R ) gravity     

Soumya Chakrabarti  Narayan Banerjee 《Astrophysics and Space Science》2015,357(1):1-1

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Spectral signatures of dissipative standing shocks and mass outflow in presence of Comptonization around a black hole     

Santanu Mondal  Sandip K. Chakrabarti  Dipak Debnath 《Astrophysics and Space Science》2014,353(1):223-231

Accretion flows having positive specific energy are known to produce outflows and winds which escape to a large distance. According to Two Component Advective Flow (TCAF) model, centrifugal pressure dominated region of the flow just outside the black hole horizon, with or without shocks, acts as the base of this outflow. Electrons from this region are depleted due to the wind and consequently, energy transfer rate due to inverse Comptonization of low energy photons are affected. Specifically, it becomes easier to cool this region and emerging spectrum is softened. Our main goal is to show spectral softening due to mass outflow in presence of Compton cooling. To achieve this, we modify Rankine-Hugoniot relationships at the shock front when post-shock region suffers mass loss due to winds and energy loss due to inverse Comptonization. We solve two-temperature equations governing an accretion flow around a black hole which include Coulomb exchange between protons and electrons and other major radiative processes such as bremsstrahlung and thermal Comptonization. We then compute emitted spectrum from this post-shock flow. We also show how location of standing shock which forms outer boundary of centrifugal barrier changes with cooling. With an increase in disc accretion rate \((\dot{m}_{d})\) , cooling is enhanced and we find that the shock moves in towards the black hole. With cooling, thermal pressure is reduced, and as a result, outflow rate is decreased. We thus directly correlate outflow rate with spectral state of the disc.  相似文献   

Properties of accretion shock waves in viscous flows around black holes     

Sandip K. Chakrabarti  Santabrata Das 《Monthly notices of the Royal Astronomical Society》2004,349(2):649-664

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Thermoelastic waves in non-simple media     

S. Chakrabarti 《Pure and Applied Geophysics》1973,109(1):1682-1692

Summary The present paper is an attempt to investigate the propagation of thermoelastic waves propagated in non-simple media and study the distinction between propagation in simple and nonsimple media. Plane progressive waves and Rayleigh waves have been discussed.  相似文献