A5018721296- Astrophysical Phenomena and Observations
- Gamma-ray bursts and supernovae
- Pulsars and Gravitational Waves Research
- Mechanics and Biomechanics Studies
- Astrophysics and Cosmic Phenomena
- Astronomical Observations and Instrumentation
- Particle Detector Development and Performance
- High-pressure geophysics and materials
- Solar and Space Plasma Dynamics
- Stellar, planetary, and galactic studies
- Astrophysics and Star Formation Studies
- Astronomy and Astrophysical Research
- Astro and Planetary Science
- Nuclear Physics and Applications
- Streptococcal Infections and Treatments
- Multidisciplinary Science and Engineering Research
- Geophysics and Gravity Measurements
- Calibration and Measurement Techniques
Tata Institute of Fundamental Research
2014-2024
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...
ABSTRACT We report the first detection of evolving low-frequency quasi-periodic oscillation (LFQPO) frequencies in hard X-rays upto 100 keV with AstroSat/LAXPC during ‘unusual’ outburst phase Swift J1727.8−1613 intermediate state (HIMS). The observed LFQPO 20–100 has a centroid $\nu _{_{\rm QPO}}=1.43$ Hz, coherence factor Q = 7.14 and an amplitude ${\rm rms_{_{\rm QPO}}} 10.95{{\ \rm per\ cent}}$ significance σ 5.46. Type-C QPOs (1.09–2.6 Hz) are found to evolve monotonically HIMS clear...
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 present the results of Target Opportunity (ToO) observations made with AstroSat newly discovered black hole binary MAXI J1535-571. detect prominent C-type Quasi-periodic Oscillations (QPOs) frequencies varying from 1.85 Hz to 2.88 Hz, along distinct harmonics in all observations. note that while fundamental QPO is seen 3 - 50 keV energy band, harmonic not significant above ~ 35 keV. The were hard intermediate state, as state transitions observed by and Swift. attempt spectral modelling...
We have carried out the first spectro-polarimetric study of bright NS-LMXB GX 9+9 using IXPE and AstroSat observations. report a significant detection polarization $1.7\pm 0.4\%$ over $2-8$ keV energy band, with angle $63^{\circ}\pm 7^{\circ}$. The is found to be energy-dependent, $3\sigma$ degree consistent null in $2-4$ keV, $3.2\%$ $4-8$ keV. Typical spectra seen NS-LMXBs, we find that combination soft thermal emission from accretion disc Comptonized component optically thick corona...
ABSTRACT We report the results of AstroSat observations GRS 1915+105 obtained using 100 ks Guaranteed Time during soft state. The colour–colour diagram indicates a variability class δ with detection high-frequency quasi-periodic oscillation (HFQPO) in power density spectra. HFQPO is seen to vary frequency range 67.96–70.62 Hz percentage rms ∼0.83–1.90 per cent and significance varying from 1.63 7.75. energy dependent spectra show that features are dominant only 6–25 keV band. broad-band...
We present an in-depth spectral and timing analysis of the Black Hole binary 4U 1630-472 during 2016 2018 outbursts as observed by \textit{AstroSat} \textit{MAXI}. The extensive coverage with \textit{MAXI} is used to obtain Hardness Intensity Diagram (HID). source follows a `c'-shaped profile in agreement earlier findings. Based on HIDs previous outbursts, we attempt track evolution `super'-outburst `mini'-outbursts. model broadband energy spectra ($0.7-20.0$ keV) observations both using...
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...
We present a comprehensive temporal and spectral analysis of the 'softer' variability classes ($i.e.$, $\theta$, $\beta$, $\delta$, $\rho$, $\kappa$, $\omega$ $\gamma$) source GRS 1915+105 observed by AstroSat during $2016-2021$ campaign. Wide-band ($3-60$ keV) timing studies reveal detection High Frequency Quasi-periodic Oscillations (HFQPOs) with frequency $68.14-72.32$ Hz, significance $2.75-11 \sigma$, rms amplitude $1.48-2.66\%$ in $\gamma$ classes. Energy dependent power spectra impart...
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...
We study the spectral and temporal properties of MAXI J0637-430 during its 2019-2020 outburst using \textit{NICER}, \textit{AstroSat} \textit{Swift-XRT} data. The source was in a disc dominant state within day detection traces out `c' shaped profile HID, similar to `mini'-outbursts recurrent BHB 4U 1630-472. Energy spectrum is obtained $0.5-10$ keV band with \textit{NICER} \textit{Swift-XRT}, $0.5-25$ \textit{AstroSat}. spectra can be modelled multicolour emission (\textit{diskbb}) convolved...
We present results from an observation of the Low Mass X-ray Binary 4U 1636-536 obtained with LAXPC instrument aboard AstroSat. The observations made during performance verification phase AstroSat showed seven thermonuclear bursts in a total exposure ~ 65 ks over period about two consecutive days. Moreover, light curve revealed presence rare triplet bursts, having wait time 5.5 minutes between second and third bursts. also time-resolved spectroscopy performed these In addition, we have...
In this work, we present a $\sim$90 ks continuous monitoring of the Galactic micro-quasar GRS 1915+105 with AstroSat when source undergoes major transition from non-variable, $\chi$ class (similar to radio-quiet class) structured, large amplitude, periodic heartbeat state $\rho$ class). We show that such takes place via an intermediate large-amplitude, irregular variability order hundreds seconds in soft X-ray band turned into 100-150 sec regular, nearly flares. The properties strong...
Abstract We present results from AstroSat observations of the recent outburst GRO J2058+42, an X-ray pulsar in a Be-binary system. The source was observed by LAXPC and SXT instruments on 2019 April 10 during declining phase its latest giant outburst. Light curves showed strong pulsation with period 194.2201 ± 0.0016 s spin-up rate (1.65 0.06) × −11 Hz −1 . Intermittent flaring detected light between 3 80 keV energy bands, increase intensity up to 1.8 times average intensity. Pulse profiles...
The Be X-ray Binary 4U 0115+63 was observed by Large Area Proportional Counter (LAXPC) instrument on AstroSat 2015 October 24 during the peak of a giant Type II outburst. Prominent intensity oscillations at ~ 1 and 2 mHz frequency were detected Nuclear Spectroscopic Telescope Array (NuSTAR) observations made same outburst also show quasi periodic (QPOs). Details their characteristics deduced from LAXPC/AstroSat NuSTAR are reported in this paper. Analysis archival Rossi Timing Explorer...
IGR J17091--3624 is a transient galactic black hole which has distinct quasi-periodic variability known as `heartbeat', similar to the one observed in GRS 1915+105. In this paper, we report results of $\sim 125$ ks \textit{AstroSat} observations source during 2016 outburst. For first time double peaked QPO (DPQ) detected few segments with difference $\delta f ~\sim12$ mHz between two peaks. The nature DPQ was studied based on hardness ratios and using static well dynamic power spectrum....
ABSTRACT We present a comprehensive spectrotemporal analyses of recurrent outbursting black hole sources GX 339$-$4 and H 1743$-$322 using available AstroSat NuSTAR archival observations during 2016–2024. The nature the outburst profiles both are examined long-term MAXI/GSC Swift/BAT light curves, failed as well successful outbursts classified. Wide-band (0.5–60 keV) spectral modelling with disc (diskbb) Comptonized (Nthcomp) components indicates that transits from hard ($kT_{\rm...
ABSTRACT IGR J17591–2342, a transient accretion-powered millisecond X-ray pulsar, was discovered during its 2018 outburst. Here, we present timing and spectral analysis of the source using AstroSat data same From analysis, obtain updated values binary orbital parameters, which reveal an average pulsar spin frequency 527.425 6984(8) Hz. The pulse profiles can be fit well with four harmonically related sinusoidal components fractional amplitudes fundamental second, third, fourth harmonics as...
We present here results from the X-ray timing and spectral analysis of binary Cyg X-3 using observations Large Area proportional Counter on board AstroSat. Consecutive light curves observed over a period one year show orbital 17253.56 ± 0.19 s. Another low-amplitude, slow periodicity order 35.8 1.4 days is observed, which may be due to precession as suggested earlier by Molteni et al. During rising phase, power density spectra different during flaring hard state quasi-periodic oscillations...
We present an improved background model for the Large Area X-ray Proportional Counter (LAXPC) detectors on-board AstroSat. Because of large collecting area and high pressure, LAXPC instrument has a count rate, which varies during orbit. Apart from variation with latitude longitude orbit there is prominent quasi-diurnal not been modelled earlier. Using over 5 years observations, we determined period to be 84495 s using this period, it possible account also identify time intervals where fit...
The Galactic microquasar GRS 1915+105 shows rich variability which is categorized into different classes. In this paper, we report temporal and spectral analysis of to study the properties accretion flow when light curve showing $\theta$ class variability. For purpose, use LAXPC data from Target Opportunity observations India's first multi-wavelength astronomy satellite AstroSat. marked by recurrent appearance U-shaped regions in curve, where photon count rate decreases rapidly then...
Abstract It has recently been shown that the persistent emission of a neutron star low-mass X-ray binary (LMXB) evolves during thermonuclear (type-I) burst. The reason this evolution, however, is not fully known. This uncertainty can introduce significant systematics in radius measurement using burst spectra, particularly if an unknown but fraction emission, which reprocessed, contributes to changes Here, by analyzing individual data AstroSat/LAXPC from LMXB 4U 1728–34 soft state, we show...