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SSM onboard AstroSat is designed to monitor X-ray sky in the energy range 2.5–10 keV to detect and locate X-ray sources in outburst. SSM with its three almost identical 1D-proportional counters mounted on a rotating platform, scans the sky in step and stare mode of operation. It observes the X-ray sky and generates light curves for X-ray sources detected. Here, we discuss the positional calibration to carry out imaging with SSM. Onboard calibration of SSM has been carried out with Crab, the standard X-ray source. SSM observations of Crab are compared with that of MAXI on ISS for cross calibration of the instrument.

The data pipeline at the Payload Operation Centre (POC) of the Scanning Sky Monitor (SSM) onboard AstroSat involves: (i) fetching the Level-0 data from the Indian Space Science Data Centre (ISSDC), (ii) Level-0 to Level-1 data processing followed by Level-2 data generation, and (iii) transfer of the Level-1 and Level-2 data back to ISSDC for dissemination of the re-packaged Level-2 data products. The major tasks involved in the generation of Level-1 and Level-2 data products are: (a) quality checks; time, alignment corrections, (b) temporal-HK plots generation, and, (c) image processing; light curve generation. The typical turn around time for this fully automated pipeline is about 25 min for one orbit data. In this paper, details of all the stages of this data pipeline are discussed.

We present a comprehensive study of GRS 1915+105 in wide energy band ($0.5-60$ keV) using AstroSat observations during the period of $2016-2019$. The MAXI X-ray lightcurve of the source shows rise and decay profiles similar to canonical outbursting black holes. However, the source does not follow the exemplary 'q'-diagram in the Hardness-Intensity Diagram (HID). Model independent analysis of lightcurves suggests that GRS 1915+105 displays various types of variability classes ($\delta,\chi,\rho,\kappa,\omega$ and $\gamma$). We also report possible transitions from one class to another ($\chi\rightarrow\rho,\rho\rightarrow\kappa$ via an 'unknown' class and $\omega\rightarrow\gamma\rightarrow\omega+\gamma$) within a few hours duration. Broadband energy spectra are well modeled with multi-coloured disc blackbody and Comptonised components. We explore the 'spectro-temporal' features of the source in the different variability classes, transitions between classes, and evolution during $2016-2019$. Detailed analysis indicates a gradual increase in the photon index ($\Gamma$) from $1.83$ to $3.8$, disc temperature ($kT_{in}$) from $1.33$ to $2.67$ keV, and Quasi-periodic Oscillation (QPO) frequency ($\nu$) from $4$ to $5.64$ Hz during the rise, while the parameters decrease to $\Gamma$ ~$1.18$, $kT_{in}$ ~$1.18$ keV, and $\nu$ ~$1.38$ Hz respectively in the decline phase. The source shows maximum bolometric luminosity (L$_{bol}$) during the peak at ~$36$% of Eddington luminosity (L$_{EDD}$), and a minimum of ~$2.4$% L$_{EDD}$ during the decay phase. Further evolution of the source towards an obscured low-luminosity (L$_{bol}$ of ~ 1% L$_{EDD}$) phase, with a decrease in the intrinsic bolometric luminosity of the source due to obscuration, has also been indicated from our analysis. The implication of our results are discussed in the context of accretion disc dynamics around the black hole., Comment: Accepted for publication in MNRAS, 20 pages, 19 figures, 4 tables

Scanning Sky Monitor (SSM) onboard AstroSat is an Xray sky monitor in the soft X-ray band designed with a large field of view to detect and locate transient X-ray sources and alert the astronomical community about interesting phenomena in the X-ray sky. SSM comprises position sensitive proportional counters with 1D coded mask for imaging. There are three detector units mounted on a platform capable of rotation which helps covering about 50% of the sky in one full rotation. This paper discusses the elaborate details of the instrument and few immediate results from the instrument after launch.

Background A suture material producing least tissue reaction is considered as ideal. Other characteristics like tensile strength, capacity to sustain sterilization process enhance its acceptability. In the present situation there is a need to reascertain the relevance and utility of these materials. Among the suture materials mentioned by Sushrutacharya, Moorva ( Sansevieria roxburghiana ) and Shana ( Crotalaria pallida ) have been showed insignificant tissue reaction in operated cases of inguinal hernia. An experimental study to confirm the extent of tissue reaction in deeper planes is needed before extending the use of materials in the deep tissues. Objective The objective of the study was to analyze deep tissue reaction and tensile strengths of plant fibres extracted from Crotalaria pallida and Sansevieria roxburghiana . Materials and methods The study was conducted on 18 albino rats, 3 groups of 6 rats each for a period of 21 days inserting the suture materials in deeper tissue, studying histopathology changes of the deeper connective tissues, hydroxyproline content and blood parameters on 7th, 14th, 21st days of the study. The tensile strength of the two materials was also assessed on 7th day in three different conditions. Statistical analysis was carried out using paired and unpaired t tests. Results S. roxburghiana had least tissue reaction. C. pallida showed greater tensile strength in comparison to Moorva . Conclusion C. pallida can be used for deep tissue approximation because of its moderate tissue reaction and tensile strength, successive increase in hydroxyproline content and its capacity to sustain sterilization.

We present the results of Target of Opportunity (ToO) observations made with AstroSat of the newly discovered black hole binary MAXI J1535-571. We detect prominent C-type Quasi-periodic Oscillations (QPOs) of frequencies varying from 1.85 Hz to 2.88 Hz, along with distinct harmonics in all the AstroSat observations. We note that while the fundamental QPO is seen in the 3 - 50 keV energy band, the harmonic is not significant above ~ 35 keV. The AstroSat observations were made in the hard intermediate state, as seen from state transitions observed by MAXI and Swift. We attempt spectral modelling of the broadband data (0.7-80 keV) provided by AstroSat using phenomenological and physical models. The spectral modelling using nthComp gives a photon index in the range between 2.18-2.37 and electron temperature ranging from 21 to 63 keV. The seed photon temperature is within 0.19 to 0.29 keV. The high flux in 0.3 - 80 keV band corresponds to a luminosity varying from 0.7 to 1.07 L_Edd assuming the source to be at a distance of 8 kpc and hosting a black hole with a mass of 6 M$_{\odot}$. The physical model based on the two-component accretion flow gives disc accretion rates as high as ~ 1 $\dot{m}_{Edd}$ and halo rate ~ 0.2 $\dot{m}_{Edd}$ respectively. The near Eddington accretion rate seems to be the main reason for the unprecedented high flux observed from this source. The two-component spectral fitting of AstroSat data also provides an estimate of a black hole mass between 5.14 to 7.83 M$_{\odot}$., 15 pages, 9 figures, MNRAS (Accepted on 2019 May 10)

Scanning Sky Monitor (SSM) onboard AstroSat is an X-ray sky monitor in the energy range 2.5–10 keV. SSM scans the sky for X-ray transient sources in this energy range of interest. If an X-ray transient source is detected in outburst by SSM, the information will be provided to the astronomical community for follow-up observations to do a detailed study of the source in various other bands. SSM instrument, since its power-ON in orbit, has observed a number of X-ray sources. This paper discusses observations of few X-ray transients by SSM. The flux reported by SSM for few sources during its Performance Verification phase (PV phase) is studied and the results are discussed.

We report the in-orbit performance of Scanning Sky Monitor (SSM) onboard AstroSat. The SSM operates in the energy range 2.5 to 10 keV and scans the sky to detect and locate transient X-ray sources. This information of any interesting phenomenon in the X-ray sky as observed by SSM is provided to the astronomical community for follow-up observations. Following the launch of AstroSat on 28th September, 2015, SSM was commissioned on October 12th, 2015. The first power ON of the instrument was with the standard X-ray source, Crab in the field-of-view. The first orbit data revealed the basic expected performance of one of the detectors of SSM, SSM1. Following this in the subsequent orbits, the other detectors were also powered ON to find them perform in good health. Quick checks of the data from the first few orbits revealed that the instrument performed with the expected angular resolution of 12’ $$\times $$ 2.5 $$^\circ $$ and effective area in the energy range of interest. This paper discusses the instrument aspects along with few on-board results immediately after power ON.

Scanning Sky Monitor (SSM) on ASTROSAT is an X-ray sky monitor which has a large Field of View (FOV) and scans the sky to detect and locate X-ray transient sources in the energy range 2 to 10 keV. Experiments are carried out to calibrate SSM detectors for position response and to verify the calibration constants derived. In this paper we discuss the methodology of position calibration of proportional counters for SSM and results from various experiments.