A5081245939- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- SAS software applications and methods
- Astronomical Observations and Instrumentation
- Astrophysics and Cosmic Phenomena
- Astronomy and Astrophysical Research
- Particle Detector Development and Performance
- Nuclear Physics and Applications
- Pulsars and Gravitational Waves Research
- Astro and Planetary Science
- High-pressure geophysics and materials
- X-ray Spectroscopy and Fluorescence Analysis
- Atmospheric Ozone and Climate
- Particle Accelerators and Free-Electron Lasers
- Advanced X-ray Imaging Techniques
- Atmospheric aerosols and clouds
- Stellar, planetary, and galactic studies
- Radiation Detection and Scintillator Technologies
- Atmospheric chemistry and aerosols
- Medical Imaging Techniques and Applications
- Solar and Space Plasma Dynamics
- Superconducting Materials and Applications
- Advanced X-ray and CT Imaging
- Atomic and Subatomic Physics Research
- Mechanics and Biomechanics Studies
ExxonMobil (Germany)
2023
University of Mumbai
2014-2022
University of Southern Queensland
2021-2022
Ministry of AYUSH
2019
Government of India
2019
Tata Institute of Fundamental Research
2005-2016
Electronics Corporation of India
2006-2016
The University of Texas at Austin
2012
TIFR Centre for Interdisciplinary Sciences
2011
University of Delhi
2010
We describe and discuss the global properties of 45 gamma-ray bursts (GRBs) observed by HETE-2 during first 3 years its mission, focusing on X-ray flashes (XRFs) X-ray-rich GRBs (XRRs). find that numbers XRFs, XRRs, are comparable, durations sky distributions XRFs XRRs similar to those GRBs. also spectral GRBs, except values peak energy E burst spectrum in νFν, flux Fpeak, fluence SE much smaller (and smaller) than Finally, we all three kinds form a continuum [SE(2-30 keV), SE(30-400) keV]...
ASTROSAT is India's first astronomy satellite that will carry an array of instruments capable simultaneous observations in a broad range wavelengths: from the visible, near ultraviolet (NUV), far-UV (FUV), soft X-rays to hard X-rays. There be five principal scientific payloads aboard satellite: (i) Soft X-ray Telescope (SXT), (ii) three Large Area Xenon Proportional Counters (LAXPCs), (iii) Cadmium-Zinc-Telluride Imager (CZTI), (iv) two Ultra-Violet Imaging Telescopes (UVITs) one for visible...
[1] First ever in-situ measurements of black carbon (BC) aerosols in the troposphere (up to 9 km) made over central India and resulting atmospheric impact as revealed by environment lapse rate are presented. The altitude distribution BC showed multiple peaks; two surprisingly large peaks, one at ∼4.5 km, another above 8 km. Associated with these, rapid decrease environmental a sharp increase atmosphere stability were observed, probably caused warming layers. This important observation calls...
We describe and discuss the global properties of 45 gamma-ray bursts (GRBs) observed by HETE-2 during first three years its mission, focusing on X-Ray Flashes (XRFs) X-ray-rich GRBs (XRRs). find that numbers XRFs, XRRs, are comparable. durations sky distributions XRFs XRRs similar to those GRBs. also spectral GRBs, except values peak energy $E^{\rm obs}_{\rm peak}$ burst spectrum in $νF_ν$, flux $\Fp$, fluence $S_E$ much smaller -- than Finally, we all kinds form a continuum [$S_E$(2-30...
ASTROSAT, India's first dedicated astronomy space mission was launched on September 28, 2015. The Large Area X-ray Proportional Counter (LAXPC) is one of the major payloads ASTROSAT. A cluster three co-aligned identical LAXPC detectors provide large area collection .The detection volume (15 cm depth) filled with mixture xenon gas (90(%) and methane (10%) at ~ 2 atmospheres pressure, results in efficiency greater than 50%, above 30 keV. instrument best suited for timing spectral studies. It...
ABSTRACT We present the first quick look analysis of data from nine AstroSat 's Large Area X-ray Proportional Counter (LAXPC) observations GRS 1915+105 during 2016 March when source had characteristics being in Radio-quiet χ class. find that a simple empirical model disk blackbody emission, with Comptonization and broad Gaussian Iron line can fit time-averaged 3–80 keV spectrum systematic uncertainty 1.5% background flux 4%. A dead time corrected Poisson noise level matches well observed...
We present the calibration and background model for Large Area X-ray Proportional Counter (LAXPC) detectors on board AstroSat. The LAXPC instrument has three nominally identical to achieve a large collecting area. These are independent of each other, in event analysis mode they record arrival time energy photon that is detected. have resolution 10 μs dead-time about 42 μs. This makes ideal timing studies. peak channel-to-energy mapping were obtained from ground using radioactive sources...
We report High Energy Transient Explorer 2 (HETE-2) Wide Field X-Ray Monitor/French Gamma Telescope observations of the X-ray flash XRF 020903. This event was extremely soft: ratio log(SX/Sγ) = 0.7, where SX and Sγ are fluences in 2-30 30-400 keV energy bands, is most extreme value observed so far by HETE-2. In addition, spectrum has an peak E < 5.0 (99.7% probability upper limit), no photons were detected above ~10 keV. The burst shorter at higher energies, which similar to behavior long...
One year measurement of vertical profiles volume backscatter and extinction coefficient, aerosol optical depth (AOD), mass concentration black carbon (BC) composite along with thermodynamic structure the atmosphere has been carried out over an urban tropical location Hyderabad(17.47°N, 78.58°E), India, during April 2009 to March 2010. The mean mixing layer height (MLH) exhibits large seasonality exceeding 4 km in pre‐monsoon period whereas winter it comes down ~1.5 annual value 2.35 ± 1.02...
Abstract Regular measurements of spectral Aerosol Optical Depth (AOD) at ten wavelengths, obtained from multi‐wavelength radiometer (MWR) under cloudless conditions in the outskirts tropical urban region Hyderabad, India for period January 2008 to December 2009, are examined. In general, high AOD with a coarse‐mode abundance is seen during pre‐monsoon (March May) and summer monsoon (June September) flat spectra low Ångström wavelength exponent ( α ), while post‐monsoon (October–November)...
Abstract. The present study focuses on analyzing the seasonal changes in aerosol characteristics using a classification scheme proposed by Gobbi et al. (2007). This is based correlation between Ångström exponent (α) 440–870 nm range and difference α values [dα = (440–675 − α(675–870)] including size of fine-mode particles (Rf) fraction (η). can therefore provide information their modification transit. Spectral measurements Microtops-II sun photometer (MT-II) have systematically been...
We report the first analysis of data from AstroSat/LAXPC observations Cygnus X-1 in January 2016. LAXPC spectra reveals that source was canonical hard state, represented by a prominent thermal Comptonization component having photon index 1.8 and high temperature kT electron > 60 keV along with weak reflection possible disk emission. The power spectrum can be characterized two broad lorentzian functions centered at 0.4 3 Hz. r.m.s low frequency decreases 15% around 4 to 10% 50 keV, while one...
An exceptionally intense gamma-ray burst, GRB 030329, was detected and localized by the instruments on board High Energy Transient Explorer satellite (HETE) at 11:37:14 UT 2003 March 29. The burst consisted of two ~10 s pulses roughly equal brightness an X-ray tail lasting more than 100 s. energy fluence in 30-400 keV band Sγ = 1.2 × 10-4 ergs cm-2, making 030329 one brightest GRBs ever detected. Communication a 2' error box 73 minutes after allowed rapid detection counterpart optical,...
Abstract The vertical distribution of aerosols in the lower troposphere is critically important for assessing their impact on Earth's radiation budget and modulation cloud microphysics. This study analyzed cloud‐free aerosol extinction coefficient ( β ext ), subtypes, particulate depolarization ratios obtained from CALIOP (Cloud‐Aerosol Lidar with Orthogonal Polarization) over six regions India during 2008–2018. We investigated unprecedented climatology physical optical characteristics...
The low mass X-ray binary 4U 1728-24 was observed with AstroSat/LAXPC on 8th March 2016. Data from a randomly chosen one orbit of over 3 ks analyzed for detection rapid intensity variations. We found that the source nearly steady but towards end observation typical Type-1 burst detected. Dynamical power spectrum data in to 20 keV band, reveals presence kHz Quasi-Periodic Oscillation (QPO) whose frequency drifted around 815 Hz at beginning about 850 just before burst. QPO is also detected 10...
A bright, X-ray-rich gamma-ray burst (GRB) was detected by the French Gamma Telescope (FREGATE) and localized with Wide-field X-ray Monitor (WXM) Soft Camera (SXC) instruments on High Energy Transient Explorer 2 satellite (HETE-2) at 11:18:34.03UT (40714.03SOD) 11 December 2002.The WXM flight software to a 14 ′ radius; this relayed astronomical community 22 seconds after start of burst.