X-ray Data analysis
I am first year Post Doctoral Fellow in the department of Physics, under Prof. Varun Bhalerao. Previous to this, I was a Marie Skodowska-Curie Action Fellow in the project called GraWIToN (an Initial Training Network), which received funding from the European Union’s Seventh Framework. I worked as a data analyst in University of Rome, la “Sapienza”, to develop a robust and efficient methodology for detecting continuous gravitational waves from rapidly spinning neutron star in a binary system. Currently I am working on X-ray data analysis for upcoming ISRO funded satellite mission.
Detectors used in measuring high energy photons, have by design poor spatial resolution, with which it becomes very difficult to pin point the location of their sources in the sky. However, historically lunar and earth occultation techniques have been used to resolve sky position. The idea is that, if while observing the source, the moon obstructs the line of sight (called occultation), we would see a drop in our measurement. By carefully measuring the time of the drop and knowing the position of the moon at time allows us to narrow down the source’s position. Similar technique can be used for the satellites, when Earth obstructs, which is a useful technique for orbiting X-ray and gamma ray instruments to study high energy source. This change in flux can be used for direct measurement of point-source emission. We are investigating and implementing Earth Occultation Technique (previously used by BATSE and Fermi satellite missions) on AstroSat's collimated Cadmium Zinc Telluride Imager (CZTI). AstroSat is an Indian multi-wavelength satellite launched in September 2015. For the first time we use CZTI as a device for all-sky bright hard X-ray source monitor, which is not what it was initially designed for. In an uncollimated detector, these occultation features can be used to locate and monitor astrophysical sources provided their signals can be individually separated from the detector background. The sensitivity of the technique is derived as a function of incident photon energy and also as a function of angle between the source and the normal to the detector entrance window. The method is an alternative to more sophisticated photon imaging devices for astronomy and can serve well as a cost effective science capability for monitoring the high-energy sky. These methods will also help us calibrate the instruments of upcoming satellite which will be looking for X-ray counterparts of gravitational wave sources.
Parallel to this study, we also prepared deepest all sky images for archives and references purpose to enhance our search of optical counter parts for gravitational wave sources. A number of synoptic sky surveys are underway or being planned. They are usually done with smaller telescopes, and allowing relatively short exposure times. Searching for sudden change in the brightness of the source (transients) or variable sources involves comparison with deeper baseline images, ideally obtained through the same telescope and camera. Considering this we have processed images from the 68 cm Schmidt telescope on Mt. Bigelow taken over ten years as part of the Catalina Sky Survey. In order to generate deep reference images for the Catalina Real-time Transient Survey, close to 0.8 million images over 8000 pre-defined regions on the sky, which covered roughly 27000 square degree (approximately 2/3 of the entire sky), have gone into this deep stack that goes up to 3 magnitudes deeper, i.e. it includes ~15 times fainter sources than the individual images. This included carefully comparing results of various state-of-the-art software packages for processing astronomical images as well. The stacked images are available through a server at IUCAA.