Tanmoy Chattopadhyay

Physical Science Research Scientist
Department: Kavli Institute for Particle Astrophysics and Cosmology
PhD, Physical Research Laboratory, Astrophysics (2016)
M.Sc., BHU (India), Physics (2010)
B.Sc., Burdwan University (India), Physics (2008)
Research Group
Tanmoy Chattopadhyay
In order to cope up with the large photon flux at the focal plane of the next generation large area telescopes (e.g. X-ray mission concepts like Lynx), the focal plane detectors need to be extremely fast (order of magnitude faster compared to the Chandra CCDs) and low noise to avail <1 keV measurements along with small pixel sizes in order to fully utilize the high angular resolution of the next generation X-ray mirrors. One approach towards achieving these goals is to use active pixel sensors. As part of the collaboration between the Penn State University and the Teledyne Imaging Sensors to develop Silicon based X-ray Hybrid CMOS detectors (an active pixel sensor), I was involved in characterizing these X- ray HCDs with Cryogenic SIDECAR ASICs. The other approach is to build upon the success of Chandra by developing faster and low noise X-ray CCDs and readout electronics. As a part of the collaboration between the Stanford University, MIT and MIT Lincoln Laboratory, I have been working on the development of fast low noise readout electronics and characterization of these new generation X-ray CCDs. While the X-ray CCDs are based on traditional source follower voltage readout, a potential solution to this could be by utilizing current readout from these detectors (like in DEPFETs) which can be fast along with extremely low noise yield. I am currently working on one such novel technology called SiSeRO or Single electron sensitive readout manufactured by MITLL. Moreover, SiSeROs are supposed to provide sub-electron read noise by utilizing repetitive non-destructive readout (RNDR) of the charge packets. We are currently working on the readout circuitry to enable this feature and developing a suitable set up to test these aspects. If successful, it might also be possible to develop a matrix of these current readout amplifiers to develop an active pixel sensor.

I am interested in the hard X-ray polarimetric studies of X-ray sources. With the advent of hard X-ray mirrors (e.g. NuSTAR), it is now possible to conceive hard X-ray polarimeters at the focal plane of hard X-ray telescopes. I have been working on the performance study and development of one such instrument which consisted of a central plastic scatterer (viewed by a PMT) surrounded by an array of CsI(Tl) scintillators (read out by Si photo-multipliers). We are also exploring the possibility of replacing the plastic scatterer by a fast Silicon imager (a fast X-ray CCD / SiSeRO matrix / X-ray HCD) to enable simultaneous X-ray spectroscopy, imaging, timing and polarimetry.

I am involved in the X-ray spectro-polarimetric studies with CdZnTe Imager (CZTI) onboard Indian astronomy mission – AstroSat for various bright X-ray sources. We verified polarimetric capabilities of CZTI by measuring polarization of Crab pulsar and nebula. Currently, I am leading the spectro-polarimetry studies of Gamma-ray Bursts and the high mass black hole X-ray binary, Cygnus X-1 using AstroSat-CZTI data.