Large Count Research Articles

Exploring the inner-disc region of the atoll source 4U 1705-44 using AstroSat’s SXT and LAXPC observations

ABSTRACT For the first time, simultaneous broad-band spectral and timing study of the atoll source 4U 1705-44 was performed using AstroSat Soft X-ray Telescope (SXT) and Large Area X-ray Proportional Counter (LAXPC) data (0.8–70 keV). Based on the HID, the source was in the soft banana state during these observations. Spectral modelling was performed using the full reflection framework and an inner disc radii of 14 Rg was obtained. A hard power-law tail was noticed in the soft state and hot component fluxes and varying power-law indices point towards a varying corona/sub-Keplerian flow. Based on the spectral fits, the boundary layer radius and magnetospheric radius were constrained to be ∼14–18 and ∼9–19 km, respectively. Cross-correlation function studies were performed between the 0.8–3 keV soft SXT light curve and 10–20 keV hard LAXPC light curve and correlated and anticorrelated lags were found, which was used to constrain the coronal height to 0.6–20 km (β = 0.1). Since the inner disc radius is not varying during the observations, we conclude that the detected lags are possibly caused by a varying structure of corona/boundary layer in the inner region of the accretion disc. Based on the observations, a geometrical model is proposed for explaining the detected lags in the atoll source 4U 1705-44.

Revealing Thermal Comptonization of Accretion Disk Photons in IC 4329A with AstroSat

Abstract We present five simultaneous UV/X-ray observations of IC 4329A by AstroSat performed over a 5 month period. We utilize the excellent spatial resolution of the Ultra-Violet Imaging Telescope on board AstroSat to reliably separate the intrinsic active galactic nucleus (AGN) flux from the host galaxy emission and correct for the Galactic and internal reddening, as well as the contribution from the narrow- and broad-line regions. We detect large-amplitude UV variability, which is unusual for a large black hole mass AGN like IC 4329A, over such a small period. In fact, the fractional variability amplitude is larger in the UV band than in the X-ray band. This demonstrates that the observed UV variability is intrinsic to the disk and not due to X-ray illumination. The joint X-ray spectral analyses of five sets of Soft X-ray Telescope and Large Area X-ray Proportional Counter spectral data reveal a soft X-ray excess component, a narrow iron line (with no indication of a significant Compton hump), and a steepening power law (ΔΓ ∼ 0.21) with increasing X-ray flux. The soft excess component could arise due to thermal Comptonization of the inner disk photons in a warm corona with kT e ∼ 0.26 keV. The UV emission we detect acts as the primary seed photons for the hot corona, which produces the broadband X-ray continuum. The X-ray spectral variability is well described by the cooling of this corona from kT e ∼ 42 to ∼32 keV with increasing UV flux, while the optical depth remains constant at τ ∼ 2.3.

A new measurement of the spin and orbital parameters of the high mass X-ray binary Centaurus X-3 using AstroSat

We present the timing results of out-of-eclipse observations of Centaurus X-3 spanning half a binary orbit, performed on 12-13 December, 2016 with the Large Area X-ray Proportional Counter (LAXPC) on-board AstroSat. The pulse profile was confirmed to exhibit a prominent pulse peak with a secondary inter-pulse. The systemic spin period of the pulsar was found to be $4.80188 \pm 0.000085$ s in agreement with its spin up trend. The spin up timescale seems to have increased to $7709 \pm 58$ yr that points to negative torque effects in the inner accretion disk. We also report the derived values of projected semi-major axis and orbital velocity of the neutron star.

Results from AstroSat LAXPC observations of Hercules X-1 (Her X-1)

The Large Area Proportional Counter (LAXPC) instruments onboard the AstroSat Observatory has observed the X-ray binary system Her X-1 during AstroSat observing sessions AO2, AO3 and TO2. These include observations while Her X-1 is in different stages of its 35 day cycle: Low State, Turn-on to Main High State, peak of Main High State and early decline of Main High State. These observations also include a number of dips and one egress of neutron star eclipse. Here we present light curves and softness ratio analysis for these observations and discuss new features of the spectral changes with 35-day phase and orbital phase. We find a new phenomenon for dips during Main High state: About half of the dips show constant softness ratio as count rate decreases, which has not been seen before, and could be caused by highly ionized matter or very dense cold matter. The other half of the dips show the normal decrease of softness ratio as count rate decreases. These are caused by cold matter absorption and were previously known.

Large Area X-ray Proportional Counter (LAXPC) in orbit performance: Calibration, background, analysis software

The Large Area X-ray Proportional Counter (LAXPC) instrument on-board AstroSat has three nominally identical detectors for timing and spectral studies in the energy range of 3--80 keV. The performance of these detectors during the five years after the launch of AstroSat is described. Currently, only one of the detector is working nominally. The variation in pressure, energy resolution, gain and background with time are discussed. The capabilities and limitations of the instrument are described. A brief account of available analysis software is also provided.

Detection of X-ray pulsations at the lowest observed luminosity of Be/X-ray binary pulsar EXO 2030+375 with AstroSat

We present the results obtained from timing and spectral studies of Be/X-ray binary pulsar EXO 2030+375 using observations with the Large Area Xenon Proportional Counters and Soft X-ray Telescope of AstroSat, at various phases of its Type-I outbursts in 2016, 2018, and 2020. The pulsar was faint during these observations as compared to earlier observations with other observatories. At the lowest luminosity of 2.5\(\times \)10\(^{35}\) erg s\(^{-1}\) in 0.5–30 keV energy range, \(\approx \)41.3 s pulsations were clearly detected in the X-ray light curves. This finding establishes the first firm detection of pulsations in EXO 2030+375 at an extremely low mass accretion rate to date. The shape of the pulse profiles is complex due to the presence of several narrow dips. Though pulsations were detected up to \(\sim \)80 keV when the source was brighter, pulsations were limited up to \(\sim \)25 keV during the third AstroSat observation at lowest source luminosity. A search for quasi-periodic oscillations in \(2\times 10^{-4}\) Hz to 10 Hz yielded a negative result. Spectral analysis of the AstroSat data showed that the spectrum of the pulsar was steep with a power-law index of \(\sim \)2. The values of photon-indices at observed low luminosities follow the known pattern in sub-critical regime of the pulsar.

Flow investigation of circular cylinder having different cavities in shallow water

The control of the unsteady flow structure formed behind a cylinder placed horizontally in shallow water was analyzed experimentally using bare cylinder and cylinders with cavities having square and rectangular geometries, respectively. Reynolds number, Froude number and water height had been chosen as 5000, 0.27 and 90 mm, respectively and also these parameters were kept constant for all experiments. To consider the influence of height (h), the cylinder level was located at various heights from h: 0 mm to 60 mm. Furthermore, cavity angle (a) had been selected from 0°, 80°, 85°, 90° and 95° to consider influence of cavity angle on flow. With the help of Particle Image Velocimetry (PIV), average velocity vectors were measured in two dimensions at many points simultaneously in a planar flow area. The results uncovered that large negative counter was observed at h: 37.5 mm in bare cylinder as well as cylinders having square and rectangular cavities at h: 45 mm. Also, no negative counter was observed for cylinders having rectangular cavity at h: 0 mm and a: 90° and 95° due to the bottom effect. Due to surface effects, a foci point was formed in all cylinders where close to the surface and close to the base. Two foci points and a saddle point were seen as they moved away from the surface for all cylinders. Also, the smallest vortex region was observed for cylinders having rectangular cavity at h: 37.5 mm and a: 90° and 95° in whole cylinders. Also, the highest drag coefficient (Cd) value was obtained for cylinder having square cavity at h: 52.5 mm and a: 80° while the highest drag coefficient value was obtained for cylinder having rectangular cavity at h: 37.5 mm and a: 95°.

AstroSat observation of the HBL 1ES 1959+650 during its October 2017 flaring

ABSTRACT We present the results of the X-ray flaring activity of 1ES 1959+650 during 2017 October 25–26 using AstroSat observations. The source was variable in the X-ray. We investigated the evolution of the X-ray spectral properties of the source by dividing the total observation period (∼130 ks) into time segments of 5 ks, and fitting the Soft X-ray focusing Telescope and Large Area X-ray Proportional Counter spectra for each segment. Synchrotron emission of a broken power-law particle density model provided a better fit than the log-parabola one. The X-ray flux and the normalized particle density at an energy less than the break one were found to anticorrelate with the index before the break. However, a stronger correlation between the density and index was obtained when a delay of ∼60 ks was introduced. The amplitude of the normalized particle density variation |Δnγ/nγ| ∼ 0.1 was found to be less than that of the index ΔΓ ∼ 0.5. We model the amplitudes and the time delay in a scenario where the particle acceleration time-scale varies on a time-scale comparable to itself. In this framework, the rest-frame acceleration time-scale is estimated to be ∼1.97 × 105 s and the emission region size to be ∼6.73 × 1015 cm.

Grinding method of noncircular glass ornaments based on successive approximation and discrete cross-coupling iterative learning control

In order to solve the problem of complicated calculation and large counter error of curve fitting method in industrial processing of noncircular glass ornaments, this paper proposes a grinding point searching algorithm. The successive approximation is used to find the grinding point of the workpiece contour and the grinding wheel. The proposed algorithm does not require complicated formula derivation and calculation and has good counter accuracy. According to the discrete characteristics of point-cloud data, a discrete cross-coupling iterative learning control algorithm is proposed to suppress the contour processing control error. Based on the norm theory, the convergence analysis and convergence conditions of the algorithm are presented. The effectiveness of the proposed algorithms is verified by experiments.

Broad-band ‘spectro-temporal’ features of extragalactic black hole binaries LMC X-1 and LMC X-3: an AstroSat perspective

ABSTRACT We present the first results of extragalactic black hole (BH) X-ray binaries LMC X-1 and LMC X-3 using all the archival and legacy observations by AstroSat during the period of 2016–2020. Broad-band energy spectra (0.5–20 keV) of both sources obtained from the Soft X-ray Telescope and Large Area X-ray Proportional Counter on-board AstroSat are characterized by strong thermal disc blackbody component (kTin ∼ 1keV, $f_{\mathrm{ disc}}\gt 79{{\ \rm per\ cent}}$) along with a steep power-law (Γ ∼ 2.4–3.2). Bolometric luminosity of LMC X-1 varies from $7{\,\mathrm{ to}\,}10{{\ \rm per\ cent}}$ of Eddington luminosity (LEdd) and for LMC X-3 is in the range $7{-}13{{\ \rm per\ cent}}$ of LEdd. We study the long-term variation of light curve using MAXI data and find the fractional variance to be ${\sim}25{{\ \rm per\ cent}}$ for LMC X-1 and ${\sim}53{{\ \rm per\ cent}}$ for LMC X-3. We examine the temporal properties of both sources and obtain fractional rms variability of power density spectrum in the frequency range 0.002–10 Hz to be ${\sim}9{}-17{{\ \rm per\ cent}}$ for LMC X-1, and ${\sim}7{}-11{{\ \rm per\ cent}}$ for LMC X-3. The ‘spectro-temporal’ properties indicate both sources are in thermally dominated soft state. By modelling the spectra with relativistic accretion disc model, we determine the mass of LMC X-1 and LMC X-3 in the range $7.64{-}10.00$ and $5.35{-}6.22\, \mathrm{ M}_{\odot }$, respectively. We also constrain the spin of LMC X-1 to be in the range 0.82–0.92 and that of LMC X-3 in 0.22–0.41 with 90 per cent confidence. We discuss the implications of our results in the context of accretion dynamics around the BH binaries and compare it with the previous findings of both sources.

OUP accepted manuscript

We present results from timing and spectral analysis of the HMXB X-ray pulsar IGR J19294+1816 observed using \asr during its recent Type-I outburst in October, 2019. AstroSat observations sampled the outburst at the decline phase right after the outburst peak. We carried out timing analysis on the light curves obtained using the Large Area X-ray Proportional Counter (LAXPC) instrument on board AstroSat and measured a spin period of 12.485065$\pm$0.000015 s. The peak in the power density spectrum (PDS) corresponding to the spin period of 12.48 s also shows a broadened base. We also detected a Quasi Periodic Oscillation (QPO) feature at 0.032$\pm$0.002 Hz with an RMS fractional amplitude of $\sim$18% in the PDS. We further carried out a joint spectral analysis using both the Soft X-ray Telescope (SXT) and the LAXPC instruments and detected a Cyclotron Resonant Scattering Feature (CRSF) at 42.7$\pm$0.9 keV and an Fe emission line at 6.4$\pm$0.1 keV. IGR J19294+1816, being an intermediate spin pulsar, has exhibited a plethora of spectral and timing features during its most recent 2019 outburst, adding it to the list of transients that exhibit both a QPO as well as a CRSF.

AstroSat view of IGR J17091−3624 and GRS 1915 + 105: decoding the ‘pulse’ in the ‘Heartbeat State’

ABSTRACT IGR J17091−3624 is a transient galactic black hole which has a distinct quasi-periodic variability known as ‘heartbeat’, similar to the one observed in GRS 1915 + 105. In this paper, we report the results of ∼125 ks AstroSat observations of this source during the 2016 outburst. For the first time, a double-peaked QPO (DPQ) is detected in a few time segments of this source with a difference of δf ∼ 12 mHz between the two peaks. The nature of the DPQ was studied based on hardness ratios and using the static as well as the dynamic power spectrum. Additionally, a low-frequency (25–48 mHz) ‘heartbeat’ single-peak QPO (SPQ) was observed at different intervals of time along with harmonics (50–95 mHz). Broad-band spectra in the range 0.7–23 keV, obtained with Soft X-ray Telescope and Large Area X-ray Proportional Counter, could be fitted well with combination of a thermal Comptonization and a multicolour disc component model. During AstroSat observation, the source was in the soft-intermediate state (SIMS) as observed with Swift/XRT. We present a comparative study of the ‘heartbeat’ state variability in IGR J17091−3624 with GRS 1915 + 105. Significant difference in the timing properties is observed although spectral parameters (Γ ∼ 2.1–2.4 and Tmax ∼ 0.6–0.8 keV) in the broad energy band remain similar. Spectral properties of segments exhibiting SPQ and DPQ are further studied using simple phase-resolved spectroscopy which does not show a significant difference. Based on the model parameters, we obtain the maximum ratio of mass accretion rate in GRS 1915 + 105 to that in IGR J17091−3624 as ∼25: 1. We discuss the implications of our findings and comment on the physical origin of these exotic variabilities.

Improving the Precision of Calibrating a Large Low-background Proportional Counter

The study of low-yield effects requires not only good quality of the original data but also puts high requirements for their processing procedures to increase the efficiency of the selection of useful events. The exploiting of the large cylindrical proportional counter’s electrostatic topology allows improving the extrapolation of information about the primary ionization of a multipoint event. Long-term calibration measurements with an external 109Cd-source allowed the development of a new method for analyzing the pulse shape from a sizeable proportional counter. Optimized analysis of the current’s pulse shape from the electron cloud of primary ionization in the counter improved the resolution and energy calibration. As a result, the efficiency of selecting useful events was increased by 25%.

Numerical studies on the hydraulic and thermal performances of trapezoidal microchannel heat sink

The present work numerically studies the hydraulic and thermal performances of trapezoidal microchannel heat sink (TMCHS) with rectangular cross-sectional shape under the constant total channel volume. Considering the flow direction, channel arrangement direction and inlet location, TMCHSs with six different configurations are proposed to compare their hydraulic and thermal performances. The results demonstrate that the pressure drop of the six THCHSs always increases with the decreasing small-to-large end width ratio. For the thermal performance, only the two TMCHSs with Parallel Channel Parallel Flow Large Inlet (PCPFLI) and Reverse Channel Counter Flow Large Inlet (RCCFLI) configurations have improved thermal performances with the decreasing small-to-large end width ratio, including decreasing maximum temperature, decreasing thermal resistance and decreasing center zone temperature difference. On the basis of these, the effects of the channel height and inlet flowrate on the thermal performances of TMCHSs with PCPFLI and PCPFLI configurations are further studied. It is found that PCPFLI and RCCFLI configurations have lower thermal resistance and more uniform temperature distribution with increasing channel height and inlet flowrate. The TMCHS with RCCFLI configuration has the best thermal performances among the six TMCHSs. The findings reported in present work provide a simple method to improve the thermal performances of MCHS by changing the channel shape and configurations.

KARAKTERISTIK ATRIBUT TERHADAP PERILAKU PENGGUNA PADA PUSAT KULINER DI KOPLAKAN BLORA

Renovation will not succeed if the designer does not consider user attributes, so the results of the design will be changed according to the needs of user attributes. This happened in Koplakan Blora, which was more spacious and modern, but they complained about the lack of visitors after the renovation. This study aims to determine the characteristics of post-occupant users, interests, responses, and expectations of Koplakan users. Using descriptive qualitative research methods with instrument attributes (comfort, sociality, visibility, legibility) of the user, knowing the relationship between perceptions and user attributes, and knowing the comfortable space settings for the user. The results of the study are based on the required attributes, the user needs a large counter, the location of the sign that is easily visible to visitors, the size of a low counter barrier to be able to socialize with other traders, the shape of the building that is in accordance with the local culinary center

AstroSat view of GRS 1915+105 during the soft state: detection of HFQPOs and estimation of mass and spin

ABSTRACT We report the results of AstroSat observations of GRS 1915+105 obtained using 100 ks Guaranteed Time during the soft state. The colour–colour diagram indicates a variability class of δ with the detection of high-frequency quasi-periodic oscillation (HFQPO) in the power density spectra. The HFQPO is seen to vary in the frequency range of 67.96–70.62 Hz with percentage rms ∼0.83–1.90 per cent and significance varying from 1.63 to 7.75. The energy dependent power spectra show that the HFQPO features are dominant only in 6–25 keV energy band. The broad-band energy spectra (0.7–50 keV) of Soft X-ray Telescope and Large Area X-ray Proportional Counter modelled with nthComp and powerlaw imply that the source has an extended corona in addition to a compact ‘Comptonizing corona’ that produces high-energy emission and exhibits HFQPOs. The broad-band spectral modelling indicates that the source spectra are well described by thermal Comptonization with electron temperature (kTe) of 2.07–2.43 keV and photon index (Γnth) between 1.73 and 2.45 with an additional powerlaw component of photon index (ΓPL) between 2.94 and 3.28. The norm of nthComp component is high (∼8) during the presence of strong HFQPO and low (∼3) during the absence of HFQPO. Further, we model the energy spectra with the kerrbb model to estimate the accretion rate, mass, and spin of the source. Our findings indicate that the source accretes at super-Eddington rate of $1.17\!-\!1.31~ \dot{M}_{\rm Edd}$. Moreover, we find the mass and spin of the source as 12.44–13.09 M⊙ and 0.990–0.997 with $90{{\ \rm per\ cent}}$ confidence suggesting that GRS 1915+105 is a maximally rotating stellar mass X-ray binary black hole source.

Coronal vertical structure variations in normal branch of GX 17+2: AstroSat’s SXT and LAXPC perspective

ABSTRACT We performed spectro-temporal analysis in the 0.8–50 keV energy band of the neutron star Z source GX 17+2 using AstroSat Soft X-ray Telescope (SXT) and Large Area X-ray Proportional Counter (LAXPC) data. The source was found to vary in the normal branch (NB) of the hardness–intensity diagram. Cross-correlation studies of LAXPC light curves in soft and hard X-ray band unveiled anticorrelated lags of the order of few hundred seconds. For the first time, cross-correlation studies were performed using SXT soft and LAXPC hard light curves and they exhibited correlated and anticorrelated lags of the order of a hundred seconds. Power density spectrum displayed normal branch oscillations (NBOs) of 6.7–7.8 Hz (quality factor 1.5–4.0). Spectral modelling resulted in inner disc radius of ∼12–16 km with Γ ∼ 2.31–2.44 indicating that disc is close to the innermost stable circular orbit and a similar value of disc radius was noticed based on the reflection model. Different methods were used to constrain the corona size in GX 17+2. Using the detected lags, corona size was found to be 27–46 km (β = 0.1, β = vcorona/vdisc) and 138–231 km (β = 0.5). Assuming the X-ray emission to be arising from the boundary layer (BL), its size was determined to be 57–71 km. Assuming that BL is ionizing the disc’s inner region, its size was constrained to ∼19–86 km. Using NBO frequency, the transition shell radius was found to be around 32 km. Observed lags and no movement of the inner disc front strongly indicate that the varying corona structure is causing the X-ray variation in the NB of Z source GX 17+2.

In Memoriam: Marvin A. Van Dilla: 1919-2019.

© 2020 International Society for Advancement of Cytometry.

Estimation of the black hole spin in LMC X-1 using AstroSat

ABSTRACT LMC X-1, a persistent, rapidly rotating, extra-galactic, black hole X-ray binary (BHXB) discovered in 1969, has always been observed in its high soft state. Unlike many other BHXBs, the black hole mass, source distance, and binary orbital inclination are well established. In this work, we report the results of simultaneous broad-band spectral studies of LMC X-1 carried out using the data from Soft X-ray Telescope and Large Area X-ray Proportional Counter aboard AstroSat as observed on 2016 November 26 and 2017 August 28. The combined spectrum was modelled with a multicolour blackbody emission (diskbb), a Gaussian along with a Comptonization component (simpl) in the energy range 0.7–30.0 keV. The spectral analysis revealed that the source was in its high soft state (Γ = 2.67$^{+0.24}_{-0.24}$ and Γ = 2.12$^{+0.19}_{-0.20}$) with a hot disc (kTin = 0.86$^{+0.01}_{-0.01}$ and kTin = 0.87$^{+0.02}_{-0.02}$). Thermal disc emission was fitted with a relativistic model (kerrbb) and spin of the black hole was estimated to be 0.93$^{+0.01}_{-0.01}$ and 0.93$^{+0.04}_{-0.03}$ (statistical errors) for the two Epochs through X-ray continuum-fitting, which agrees with the previous results.

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

Results on timing and spectral properties of the Be/X-ray binary pulsar 3A 0726–260 (4U 0728–25) are presented. The 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 satellite. During 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−1 in 0.4–20 keV. Strong 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 LAXPC. 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 energy. At energies above 20 keV, we report the first time detection of pulsation period 103.145±0.001 s and the double peaked pulse profile from the source. The energy spectrum of the source is derived from the combined analysis of the SXT and LAXPC spectral data in 0.4–20 keV. The 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 spectrum. We briefly discuss the implications of these results.