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AstroSat observation of the Be/X-ray binary Pulsar 3A 0726–260(4U 0728–25)

Research in Astronomy and Astrophysics 2020年第9期20卷 349-357页

作者： Jayashree Roy prahlad c.agrawal Baibhav Singari Ranjeev Misra UM-DAE centre for Excellence in Basic Sciences University of MumbaiVidyanagari CampusMumbai400098MaharashtraIndia Inter-University center for Astronomy and Astrophysics Post Bag 4Pune411007MaharashtraIndia School of Physical Sciences National Institute of Science Education and Research BhubaneswarKhurda752050OdishaIndia

Results on timing and spectral properties of the Be/X-ray binary pulsar 3A 0726-260(4U 0728-25)are *** binary was observed on 2016 May 6-7 with the Large Area X-ray Proportional counter(LAXPc)and Soft X-ray Telescope(SXT)instruments onboard the AstroSat *** this observation,the source was in non-flaring persistent state at a flux level of^8.6±0.3×10^-11 erg cm^-2 s^-1in 0.4-20 *** X-ray pulsations with a period of 103.144±0.001 s are detected in 0.3-7 keV with the SXT and in 3-40 keV with the *** pulse profile is energy dependent,and there is an indication that the pulse shape changes from a broad single pulse to a double pulse at higher *** energies above20 keV,we report the first time detection of pulsation period 103.145±0.001 s and the double peaked pulse profile from the *** energy spectrum of the source is derived from the combined analysis of the SXT and LAXPc spectral data in 0.4-20 *** best spectral fit is obtained by a power law model with a photon index(1.7±0.03)with high energy spectral cut-off at 12.9±0.7 keV.A broad iron line at^6.3 keV is detected in the energy *** briefly discuss the implications of these results.

关键词： Be/X ray binary pulsar 4U 0728–25

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Journey through the birth, growth and maturity of X-ray astronomy

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Research in Astronomy and Astrophysics 2019年第10期19卷 1-16页

作者： prahlad chandra agrawal MU-DAE centre of Excellence in Basic Sciences Mumbai University Campus at Vidhyanagari

In this biographical account, I recall my scientific journey that began in 1961 when I joined as a Physics Trainee in the BARc Training School and after one year course was admitted in TIFR as a Research Associate. During 1962–1967, I worked on determination of the He^3 /He^4 ratio in cosmic rays using a gas cerenkov counter and also used a scintillation + solid cerenkov detector to measure flux of protons and helium nuclei in primary cosmic rays. I also developed a large area scintillation-cerenkov detector with a spark chamber between them for measuring charge composition of primary cosmic rays. I joined the X-ray astronomy programme in 1967 initiated by Prof. B. V. Sreekantan and played a leading role in developing a balloon borne hard X-ray instrument for studying time variability and energy spectra of cosmic X-ray sources. We carried out a series of balloon experiments and studied temporal intensity variation and energy spectra of X-ray objects like Sco X-1, cyg X-1, etc. Results on rapid intensity changes and spectra appeared in a series of publications based on which I obtained a Ph.D. degree in 1972. Immediately afterwards, I joined Prof. Gordon Garmire at caltech as a Research Fellow (a post-doctoral position) to work with him on the low energy component of HEAO A-2 experiment. The instrument was developed and successfully realised. Working on this satellite experiment was a thrilling experience which exposed me to the technical complexities of space instruments. The HEAO-1 satellite was launched in 1978. During 1978–1979, Guenter Riegler and I, working at JPL, reported detection of intense soft X-rays from several classes of extragalactic and Galactic objects like new BL Lacs, a new AM Her binary, coronal X-rays from active stars, etc. After returning to TIFR, I developed a rocket experiment with K. P. Singh to map the spatial and spectral distribution of the Soft Diffuse X-ray Background. At the same time, I also designed 15 cm deep Xenon filled Proportio

关键词： TIFR-X-ray Astronomy by balloons-rockets and satellites-Indian Astronomy Satellite ASTROSAT

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Atomic Processes in Emission characteristics of a Lithium Plasma Plume Formed by Double-Pulse Laser Ablation

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Plasma Science and Technology 2013年第3期15卷 204-208页

作者： V.SIVAKUMARAN AJAI KUMAR R.K.SINGH V.prahlad H.c.JOSHI Institute for Plasma Research

High resolution spectral analysis of lithium plasma formed by single and double laser ablation has been undertaken to understand the plume-laser interaction, especially at the early stages of the plasma plume. In order to identify different atomic processes in evolving plasma, time resolved spectral emission studies at different inter-pulse delays have been performed for ionic and neutral lithium lines emitting from different levels. Along with the enhancement in emission intensity, a large line broadening and spectral shift, especially in the case of excited state transition Li I 610.3 nm have been observed in the presence of the second pulse. This broadening and shift gradually decrease with increasing time delay. Another interesting feature is the appearance of a multi-component structure in the ionic line at 548.4 nm and these components change conversely into a single structure at the later stages of the plasma. The multi-component structures are correlated with the presence of different velocity （temperature） distributions in non-LTE conditions. Atomic analyses by computing photon emissivity coefficients with an ADAS code have been used to identify the above processes.

关键词： laser ablation double pulse

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