Search

Herbig Ae/Be (HAeBe) stars are intermediate-mass pre-main-sequence stars, characterized by infrared (IR) excess and emission lines. They are observed to emit X-rays, whose origin is a matter of discussion and not settled yet. X-ray emission is not expected in HAeBe stars, as they lack the subsurface convective zone. In this study, we retrieved observations from the Chandra archive for 62 HAeBe stars, among which 44 sources (detection fraction ∼71  per cent) were detected in X-rays, with 7 being new detections. We use this sample as a test bed to conduct a comparative analysis of the X-ray properties of HAeBe stars and their low-mass counterparts, T Tauri stars (TTSs). Further, we compare the X-ray properties of HAeBe stars and TTSs with optical and IR properties to constrain the X-ray emission mechanism in HAeBe stars. We found no correlation between X-ray emission and disc properties of HAeBe stars, confirming that X-rays are not related to accretion shocks. About 56  per cent of HAeBe stars without any known subarcsec companions have lower plasma temperatures (kT ≤ 2 keV). We observe flaring/variability in HAeBe stars with confirmed low-mass companions. These stars show plasma temperatures > 2 keV, similar to TTSs. Guided by this information, we discuss the role of a T Tauri companion for X-ray emission seen in our sample of HAeBe stars. From the results obtained in this paper, we suggest that X-ray emission from HAeBe stars may not be related to accretion shocks or hidden TTS, but rather can be due to magnetically driven coronal emission. [ABSTRACT FROM AUTHOR]

In eclipsing X-ray binary systems, the direct X-ray emission is blocked by the companion star during the eclipse. We observe only reprocessed emission that contains clues about the environment of the compact object and its chemical composition, ionization levels, etc. We have found flares in some X-ray binaries during their eclipses. The study of eclipse flares provides additional clues regarding the size of the reprocessing region and helps distinguish between different components of the X-ray spectrum observed during the eclipse. In the archival data, we searched for flares during eclipses of high-mass X-ray binaries and found flares in three sources: Vela X-1, LMC X-4, and 4U 1700−37. Comparing spectral properties of the eclipse flare and non-flare data, we found changes in the power-law photon index in all three sources and multiple emission lines in Vela X-1 and 4U 1700-37. The fluxes of prominent emission lines showed a similar increase as the overall X-ray flux during the eclipse flare, suggesting the lines originate in the binary environment and not in the interstellar medium. We also observed a soft excess in 4U 1700-37 that remains unchanged during both eclipse flare and non-flare states. Our analysis suggests that this emission originates from the extremely thin shell of the stellar wind surrounding the photosphere of its companion star. The detection of short (100–200 s) count-rate doubling time-scale in 4U 1700−37 and LMC X-4 indicates that the eclipse reprocessing occurs in a region larger than, but comparable to the size of the companion star. [ABSTRACT FROM AUTHOR]

We present the X-ray spectral and temporal analysis of the black hole X-ray transient Swift  J1658.2–4242 observed by AstroSat. Three epochs of data have been analysed using the JeTCAF model to estimate the mass accretion rates and to understand the geometry of the flow. The best-fitting disc mass accretion rate (⁠|$\dot{m}_{\rm d}$|⁠) varies between |$0.90^{+0.02}_{-0.01}$| and |$1.09^{+0.04}_{-0.03}$| |$\dot{M}_{\rm Edd}$| in these observations, while the halo mass accretion rate changes from |$0.15^{+0.01}_{-0.01}$| to |$0.25^{+0.02}_{-0.01}$| |$\dot{M}_{\rm Edd}$|⁠. We estimate the size of the dynamic corona that varies substantially from |$64.9^{+3.9}_{-3.1}$| to |$34.5^{+2.0}_{-1.5}$|   r g and a moderately high jet/outflow collimation factor stipulates isotropic outflow. The inferred high disc mass accretion rate and bigger corona size indicate that the source might be in the intermediate to soft spectral state of black hole X-ray binaries. The mass of the black hole estimated from different model combinations is ∼14 M⊙. In addition, we compute the quasi-periodic oscillation (QPO) frequencies from the model-fitted parameters, which match the observed QPOs. We further calculate the binary parameters of the system from the decay profile of the light curve and the spectral parameters. The estimated orbital period of the system is 4.0 ± 0.4 h by assuming the companion as a mid or late K-type star. Our analysis using the JeTCAF model sheds light on the physical origin of the spectrotemporal behaviour of the source, and the observed properties are mainly due to the change in both the mass accretion rates and absorbing column density. [ABSTRACT FROM AUTHOR]

Context: Coronavirus disease 2019 (COVID-19) mortality trends can help discern the pattern of outbreak evolution and systemic responses. Aim: This study aimed to explore patterns of COVID-19 deaths in Thiruvananthapuram district from 31 March 2020 to 31 December 2021. Setting and Design: Secondary data analysis of COVID-19 deaths in Thiruvananthapuram district was performed. Materials and Methods: Mortality data were obtained from the district COVID-19 control room, and deaths in the first and second waves of COVID-19 were compared. Statistical Analysis: We summarised data as proportions and medians with the inter-quartile range (IQR) and performed Chi-square tests to make comparisons wherever applicable. Results: As on 31 December 2021, 4587 COVID-19 deaths were reported in Thiruvananthapuram district, with a case fatality rate of 0.91%. We observed high mortality among older persons (66.7%) and men (56.6%). The leading cause of death was bronchopneumonia (60.6%). The majority (88.5%) had co-morbidities, commonly diabetes mellitus (54.9%). The median interval from diagnosis to hospitalisation was 4 days (IQR 2-7), and that from hospitalisation to death was 2 days (IQR 0--6). The deaths reported during the second wave were four times higher than those of the first wave with a higher proportion of deaths in the absence of co-morbidities (p < 0.001). The majority of the deceased were unvaccinated. Ecological analysis with vaccine coverage data indicated 5.4 times higher mortality among unvaccinated than those who received two vaccine doses. Conclusions: The presence of co-morbidities, an unvaccinated status, and delay in hospitalisation were important reasons for COVID-19 deaths. Primary level health providers can potentially help sustaining vaccination, expeditious referral, and monitoring of COVID-19 patients. [ABSTRACT FROM AUTHOR]

Förster resonance energy transfer (FRET) microscopy is frequently used to study protein interactions and conformational changes in living cells. The utility of FRET is limited by false positive and negative signals. To overcome these limitations we have developed Fluorescence Polarization and Fluctuation Analysis (FPFA), a hybrid single-molecule based method combining time-resolved fluorescence anisotropy (homo-FRET) and fluorescence correlation spectroscopy. Using FPFA, homo-FRET (a 1-10 nm proximity gauge), brightness (a measure of the number of fluorescent subunits in a complex), and correlation time (an attribute sensitive to the mass and shape of a protein complex) can be simultaneously measured. These measurements together rigorously constrain the interpretation of FRET signals. Venus based control-constructs were used to validate FPFA. The utility of FPFA was demonstrated by measuring in living cells the number of subunits in the α-isoform of Venus-tagged calcium-calmodulin dependent protein kinase-II (CaMKIIα) holoenzyme. Brightness analysis revealed that the holoenzyme has, on average, 11.9 ± 1.2 subunit, but values ranged from 10-14 in individual cells. Homo-FRET analysis simultaneously detected that catalytic domains were arranged as dimers in the dodecameric holoenzyme, and this paired organization was confirmed by quantitative hetero-FRET analysis. In freshly prepared cell homogenates FPFA detected only 10.2 ± 1.3 subunits in the holoenzyme with values ranging from 9-12. Despite the reduction in subunit number, catalytic domains were still arranged as pairs in homogenates. Thus, FPFA suggests that while the absolute number of subunits in an auto-inhibited holoenzyme might vary from cell to cell, the organization of catalytic domains into pairs is preserved.

We present broad-band X-ray spectral-timing analysis of the new Galactic X-ray transient MAXI J1348–630 using five simultaneous AstroSat and NICER observations. Spectral analysis using AstroSat data identify the source to be in the soft state for the first three observations and in a faint and bright hard state for the next two. Quasi-periodic oscillations at ∼0.9 and ∼6.9 Hz, belonging to the type-C and type-A class are detected. In the soft state, the power density spectra are substantially lower (by a factor >5) for the NICER (0.5–12 keV) band compared to the AstroSat /LAXPC (3–80 keV) one, confirming that the disc is significantly less variable than the Comptonization component. For the first time, energy-dependent fractional rms and time lag in the 0.5–80 keV energy band was measured at different Fourier frequencies, using the bright hard state observation. Hard time lag is detected for the bright hard state, while the faint one shows evidence for soft lag. A single-zone propagation model fits the LAXPC results in the energy band 3–80 keV with parameters similar to those obtained for Cygnus X–1 and MAXI J1820+070. Extending the model to lower energies, reveals qualitative similarities but having quantitative differences with the NICER results. These discrepancies could be because the NICER and AstroSat data are not strictly simultaneous and because the simple propagation model does not take into account disc emission. The results highlight the need for more joint coordinated observations of such systems by NICER and AstroSat. [ABSTRACT FROM AUTHOR]

We carried a detailed spectral and temporal study of blazar PKS 0903-57 using the Fermi -LAT and Swift -XRT/UVOT observations, during its brightest flaring period MJD 58931–58970. During this period, the maximum daily averaged γ-ray flux (⁠|$\rm F_{0.1-500\, GeV}$|⁠) of |$\rm 9.42\times 10^{-6}\, ph\, cm^{-2}\, s^{-1}$| is observed on MJD 58951.5, the highest γ-ray flux detected from PKS 0903-57 till now. Several high-energy (HE) photons (⁠|$\gt 10$|  GeV) consistent with the source location at high probability (>99 per cent) are detected, and the γ-ray light curve in the active state shows multiple substructures with asymmetric profile. In order to understand the possible physical scenario responsible for the flux enhancement, we carried a detailed broad-band spectral study of PKS 0903-57 by choosing different flux states from its active period. Neglecting the multiband variability in each of the selected time intervals, we could reproduce their averaged broad-band SEDs with a one-zone leptonic model whose parameters were derived with a χ2-fit. We found that the broad-band SED during different flux states can be reproduced by the synchrotron, synchrotron-self-Compton (SSC), and external-Compton (EC) processes. The seed photons for EC process from BLR or IR torus provide acceptable fits to the GeV spectrum in all the flux states; however, the detection of HE photons together with the equipartition condition suggests that the EC/IR process is a more likely scenario. Further, a detailed comparison between the fit parameters shows that the flux enhancement from quiescent-state to the flaring-state is mostly related to increase in the bulk Lorentz factor of the emission region and change in the break energy of the source spectrum. [ABSTRACT FROM AUTHOR]

Ultraluminous X-ray sources (ULXs) are a class of extragalactic, point-like, off-nuclear X-ray sources with X-ray luminosity from ∼1039 to 1041 erg s−1. We investigated the temporal and broadband X-ray spectral properties of the ULX M81 X–6 using simultaneous Suzaku and NuSTAR observations. To understand the nature of the source, we searched for pulsating signals from the source using the NuSTAR observation. However, we failed to identify any strong pulsating signals from the source. Alternatively, the broadband spectral modelling with accreting magnetic neutron star continuum model provides a statistically acceptable fit, and the inferred spectral parameters, and X-ray colours are consistent with other pulsating ULXs. Thus, our analysis suggests that M81 X–6 is another candidate ULX pulsar. [ABSTRACT FROM AUTHOR]

The hard X-ray spectral index of some active galactic nuclei (AGN) has been observed to steepen with the source flux. This has been interpreted in a Comptonization scenario, where an increase in the soft flux decreases the temperature of the corona, leading to steepening of the photon index. However, the variation of the coronal temperature with flux has been difficult to measure due to the presence of complex reflection component in the hard X-rays and the lack of high-quality data at that energy band. Recently, a 200 ks Nuclear Spectroscopic Telescope Array (NuSTAR) observation of Ark 564 in 3–50 keV band revealed the presence of one of the coolest coronae with temperature kT e ∼ 15 keV in the time-averaged spectrum. Here, we reanalyse the data and examined the spectra in four flux levels. Our analysis shows that the coronal temperature decreased from ∼17 to ∼14 keV as the flux increased. The high energy photon index Γ ∼ 2.3 varied by less than 0.1, implying that the optical depth of the corona increased by about 10 per cent as the flux increased. This first reporting of coronal temperature variation with flux shows that further long observation by NuSTAR of this and other sources would shed light on the geometry and dynamics of the inner regions of the accretion flow. [ABSTRACT FROM AUTHOR]

We present a detailed temporal and spectral study of the blazar 3C 279 using multiwavelength observations from Swift -XRT, Swift -UVOT, and Fermi -LAT during a flare in 2018 January. The temporal analysis of γ-ray light curve indicates a lag of ∼1 d between the 0.1–3 GeV and 3–500 GeV emission. Additionally, the γ-ray light curve shows asymmetry with slow rise–fast decay in energy band 0.1–3 GeV and fast rise–slow decay in the 3–500 GeV band. We interpret this asymmetry as a result of shift in the Compton spectral peak. This inference is further supported by the correlation studies between the flux and the parameters of the log-parabola fit to the source spectra in the energy range 0.1–500 GeV. We found that the flux correlates well with the peak spectral energy and the log-parabola fit parameters show a hard index with large curvature at high flux states. Interestingly, the hardest index with large curvature was synchronous with a very high energy flare detected by H.E.S.S. Our study of the spectral behaviour of the source suggests that γ-ray emission is most likely to be associated with the Compton upscattering of IR photons from the dusty environment. Moreover, the fit parameters indicate the increase in bulk Lorentz factor of emission region to be a dominant cause for the flux enhancement. [ABSTRACT FROM AUTHOR]

Context: Although Intensive Care Units (ICUs) only account for 10% of the hospital beds, they consume nearly 22% of the hospital resources. Few definitive costing studies have been conducted in Indian settings that would help determine appropriate resource allocation. Aim: The aim of this study was to evaluate and compare the cost of intensive care delivery between multispecialty and neurosurgery ICUs at an apex trauma care facility in India. Materials and Methods: The study was conducted in a polytrauma and neurosurgery ICU at a 203-bedded Level IV trauma care facility in New Delhi, India, from May 1, 2012 to June 30, 2012. The study was cross-sectional, retrospective, and record-based. Traditional costing was used to arrive at the cost for both direct and indirect cost estimates. The cost centers included in the study were building cost, equipment cost, human resources, materials and supplies, clinical and nonclinical support services, engineering maintenance cost, and biomedical waste management. Statistical Analysis: Statistical analysis was performed by Fisher's two tailed t-test. Results: Total cost/bed/day for the multispecialty ICU was Rs. 14,976.9/- and for the neurosurgery ICU, it was Rs. 14,306.7/-, workforce constituting nearly half of the expenditure in both ICUs. The cost center wise and overall difference in the cost among the ICUs were statistically significant. Conclusions: Quantification of expenditure in running an ICU in a trauma center would assist health-care decision makers in better allocation of resources. Although multispecialty ICUs are more cost-effective, other factors will also play a role in defining the kind of ICU that needs to be designed. [ABSTRACT FROM AUTHOR]

We report the outbursts from a newly discovered X-ray transient in the Magellanic-type, SB(s)m galaxy NGC 55. The transient source, XMMU J001446.81-391123.48, was undetectable in the 2001 XMM--Newton and 2004 Chandra observations, but detected in a 2010 XMM--Newton observation at a significance level of 9σ in the 0.3-8 keV energy band. The XMM--Newton spectrum is consistent with a power law with photon index Γ = 3.17-0.20+0.22, but is better fitted with a kTin = 0.70 ± 0.06 keV disc blackbody. The luminosity was ~1038 erg s-1, and the source displayed strong short-term X-ray variability. These results, combined with the hardness ratios of its emission, strongly suggest an X-ray binary nature for the source. The follow-up studies with Swift XRT (X-ray Telescope) observations revealed that the source exhibited recurrent outbursts with period about a month. The XRT spectra can be described by a power law (Γ ~ 2.5-2.9) or a disc blackbody (kTin ~ 0.8-1.0 keV), and the luminosity was in a range of 1038-1039 erg s-1, with no evidence showing any significant changes of the spectral parameters in the observations. Based on the X-ray spectral and temporal properties, we conclude that XMMU J001446.81-391123.48 is a new transient X-ray binary in NGC 55, which possibly contains a black hole primary. [ABSTRACT FROM AUTHOR]

Fö rster resonance energy transfer (FRET) microscopy is frequently used to study protein interactions and conformational changes in living cells. The utility of FRET is limited by false positive and negative signals. To overcome these limitations we have developed Fluorescence Polarization and Fluctuation Analysis (FPFA), a hybrid single-molecule based method combining time-resolved fluorescence anisotropy (homo-FRET) and fluorescence correlation spectroscopy. Using FPFA, homo-FRET (a 1-10 nm proximity gauge), brightness (a measure of the number of fluorescent subunits in a complex), and correlation time (an attribute sensitive to the mass and shape of a protein complex) can be simultaneously measured. These measurements together rigorously constrain the interpretation of FRET signals. Venus based control-constructs were used to validate FPFA. The utility of FPFA was demonstrated by measuring in living cells the number of subunits in the a-isoform of Venus-tagged calcium-calmodulin dependent protein kinase-II (CaMKIIa) holoenzyme. Brightness analysis revealed that the holoenzyme has, on average, 11.9±1.2 subunit, but values ranged from 10-14 in individual cells. Homo-FRET analysis simultaneously detected that catalytic domains were arranged as dimers in the dodecameric holoenzyme, and this paired organization was confirmed by quantitative hetero-FRET analysis. In freshly prepared cell homogenates FPFA detected only 10.2±1.3 subunits in the holoenzyme with values ranging from 9-12. Despite the reduction in subunit number, catalytic domains were still arranged as pairs in homogenates. Thus, FPFA suggests that while the absolute number of subunits in an auto-inhibited holoenzyme might vary from cell to cell, the organization of catalytic domains into pairs is preserved. [ABSTRACT FROM AUTHOR]

With increasing reports on bioterrorism, avian flu, and other bio-threats, rapid and real time detection methods are highly warranted. Studies on developing highly sensitive immunosensors aiming at the early detection and clinical diagnoses of various diseases including cancer are undertaken all over the globe. Carbon nanotubes (CNTs) have been widely discussed as materials with enormous potential for a wide range of in vivoand in vitrobioapplications, ranging from drug delivery to highly sensitive biosensors, owing to their superior electronic and mechanical properties along with nanoscale dimensions. Though a lot of attention has been drawn toward carbon nanotubes for the past 15 years in academia and to a certain extent in industry, CNT-based immunosensors and other applications are still in the nascent stage, and there are many challenges to be overcome for the successful commercialization of the concepts. This article highlights on the recent developments and the possible impacts of carbon nanotube based immunosensors. [ABSTRACT FROM AUTHOR]