A5108038189- Astrophysics and Cosmic Phenomena
- Astrophysical Phenomena and Observations
- Radio Astronomy Observations and Technology
- Stellar, planetary, and galactic studies
- Pulsars and Gravitational Waves Research
- Astrophysics and Star Formation Studies
- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- High-pressure geophysics and materials
- Astronomy and Astrophysical Research
- Calibration and Measurement Techniques
- Neutrino Physics Research
- Astro and Planetary Science
- Dark Matter and Cosmic Phenomena
- Galaxies: Formation, Evolution, Phenomena
- Advanced Glycation End Products research
- Laser-Plasma Interactions and Diagnostics
- Geomagnetism and Paleomagnetism Studies
- Planetary Science and Exploration
- Nuclear Physics and Applications
- Advanced X-ray and CT Imaging
Tata Institute of Fundamental Research
2006-2017
Abstract We present a statistical characterization of the γ -ray emission from four Fermi -LAT sources: FR I radio galaxy NGC 1275, BL Lac Mrk 421, FSRQs B2 1520+31, and PKS 1510-089 detected almost continuously over time integration three days between 2008 August 2015 October. The observed flux variation is large, spanning <?CDATA $\gtrsim 2$?> orders magnitude extremes, except for 421. compute distributions compare with Gaussian lognormal ones. find that blazars have consistent lognormal,...
We present a detailed investigation of the flaring activity observed from BL Lac object, S5 0716+714 , during its brightest ever optical state in second half 2015 January. Observed almost simultaneously optical, X-rays, and γ-rays, significant change degree polarization (PD) swing position angle (PA) were recorded. A TeV (VHE) detection was also reported by MAGIC consortium this episode. Two prominent sub-flares, peaking about five days apart, seen all energy bands. The multi-wavelength...
ABSTRACT We present a systematic characterization of multi-wavelength emission from blazar PKS 1510-089 using well-sampled data at near-infrared (NIR), optical, X-ray, and γ -ray energies. The resulting flux distributions, except X-rays, show two distinct lognormal profiles corresponding to high low level. dispersions exhibit energy-dependent behavior in the LAT optical B-band. During level states, it is higher toward peak spectral energy distribution, with being intrinsically more variable...
We present a high time resolution study of the two brightest $\gamma$-ray outbursts from blazar PKS 1222+216 observed by \textit{Fermi} Large Area Telescope (LAT) in 2010. The light-curves obtained four different energy bands: 0.1--3, 0.1--0.3, 0.3--1 and 1--3 GeV, with bin 6 hr, show asymmetric profiles similar rise all bands but rapid decline during April flare gradual one June. $\sim 2$ days long plateau 0.1--0.3 GeV emission, erratic variations daily recurring feature emission until...
We present analyses of archival X-ray data obtained from the XMM-Newton satellite and optical photometric 1 m class telescopes ARIES, Nainital a magnetic cataclysmic variable (MCV) Paloma. Two persistent periods at 156 $\pm$ minutes 130 are in data, which we interpret as orbital spin periods, respectively. These similar to those previous well new observations. The soft-X-ray excess seen spectrum Paloma averaged spectra fitted by two-temperature plasma models with temperatures...
Results from a study of Fe Kα emission lines for sample six nonmagnetic cataclysmic variables (CVs) using high-resolution X-ray data the Chandra High Energy Transmission Grating (HETG) are presented. Two sources, SS Cyg and U Gem, observed in both quiescent outburst states, whereas V603 Aql, V426 Oph, WX Hyi, SU UMa only quiescence. The fluorescent line is prominent during quiescence, indicating presence conspicuous reflection component these sources. equivalent width consistent with white...
We present X-ray light curves of Cygnus X-3 as measured by the recently launched AstroSat satellite. The curve folded over binary period 4.8 hours shows a remarkable stability past 45 years and we find that can use this information to measure zero point better than 100 s. revisit historical phase measurements examine years. new ephemeris with derivative determined an accuracy much previously reported. do not any evidence for second in variation. precise measurements, however, indicate hint...
We summarize the results of a line-by-line fitting analysis available spectra obtained using Chandra High-Energy Transmission Grating. confirm existence broad ionization and electron temperature ranges high number densities in cataclysmic variables (CVs) all subtypes. Temperatures range from ∼0.4 keV to ∼5–10 or more with detected any given CV. In other words, single-temperature models do not describe line emission. Number also cover range, 1012 >1016 cm−3. demonstrate that much plasma is...
Stellar activity can produce large amounts of high-energy radiation, which is absorbed by the planetary atmosphere leading to irradiation-driven mass loss. We present detection and an investigation emission in a transiting super-Earth host system, GJ 1214, based on XMM-Newton observations. derive X-ray luminosity LX = 7.4 × 1025 erg s−1 corresponding level log (LX/Lbol) ∼ −5.3. Further, we determine coronal temperature about ∼3.5 MK, typical for moderately active low-mass stars. estimate...
We present an analysis of the high-resolution Chandra observation multiple system, HD 155555 (an RS Canum Venaticorum; CVn type binary AB, and its spatially resolved low-mass companion C). This is intriguing system that shows properties both active pre-main-sequence star a synchronized (main sequence) binary. obtain emission measure distribution, temperature structures, plasma densities, abundances this compare them with coronal other young/active stars. AB C produce copious X-ray log 30.54...
Our study focuses on analysing the coronal, transition and chromospheric activity of four rapidly rotating stars located within 50 pc in solar neighbourhood. We have used multi-wavelength capabilities AstroSat, to investigate outer atmospheres AB Dor, BO Mic, DG CVn GJ 3331. These stars, classified as M K type active are known for their short rotation periods, leading increased surface magnetic activity. soft X-ray observations provide coronal properties such emission measures, temperatures...