Avishek K. Basu
Visiting Fellow
National Centre for Radio Astrophysics
Tata Institute of Fundamental Research
Savitribai Phule Pune University Campus,
Pune 411 007
Maharashtra, INDIA
Tata Institute of Fundamental Research
Savitribai Phule Pune University Campus,
Pune 411 007
Maharashtra, INDIA
Status: Left
Main Research Areas: Physics of neutron stars; dense matter equation of state; pulsar timing; timing irregularities; pulsar emission process
Biography:
Avishek did his B.Sc. studies from Asutosh College, Kolkata, obtaining his degree in 2012. He then moved to the Indian Institute of Technology, Kanpur, where he obtained his M.Sc. (Physics) in 2014, carrying out work on Nano structures using a Focused Ion Beam. He completed his Ph.D. at NCRA-TIFR in 2019, carrying out his doctoral research with Bhal Chandra Joshi and Dipankar Bhattacharyya (co-supervisor, from IUCAA), and is now a Visiting Fellow at NCRA-TIFR.Research description:
My research interest lies in various aspects of pulsar astrophysics. Most of my work uses the technique of pulsar timing to infer the physical processes driving the rotational dynamics of the neutron stars, like pulsar glitches and timing-noise. In the context of emission processes, I am working on giant radio pulses from pulsars and some other aspects related to the variability of single pulses from pulsars.
Pulsar Glitches: A probe of the superfluid inside neutron stars
Pulsars are extremely compact objects. They can be as massive as ~ 2 times the mass of our sun, but the mass is compressed within a radius of ~ 10 km. Hence, they are very dense objects. The density inside theneutron stars can be more than 10 times the density of an atomic nucleus and the properties of matter inside the neutron stars are dominated by the strong interaction. The extreme density of the degenerate neutrons leads to a very high Fermi temperature, much larger than the physical temperature of the system. Therefore, neutron stars are considered to be cold objects (T ~ 0 K). Hence, the presence of superfluid of neutrons and superconductor of protons is expected inside neutron stars. The presence of this superfluid is manifested in the form of "pulsar glitches". A pulsar glitch is a sudden spin-up of a neutron star. The relative change in the rotation frequency due to pulsar glitches ranges from 1 part in a million to 1 part in ten billion. Measuring such changes provides us with information about the typical size of the superfluid reservoir. The short and the long term post-glitch evolution provides detailed information about the interaction of superfluid vortices with the defects in the stellar crust. The spin evolution of neutrons stars is measured using the technique of pulsar timing. At NCRA, I and my collaborators monitor a set of young pulsars using the GMRT and the ORT to find new glitches and measure the rotational evolution in the post-glitch phase. We constrain the models of pulsar glitches from our observations, which in turn helps us in understanding the physics of superfluids inside the neutron stars.
Pulsars are extremely compact objects. They can be as massive as ~ 2 times the mass of our sun, but the mass is compressed within a radius of ~ 10 km. Hence, they are very dense objects. The density inside theneutron stars can be more than 10 times the density of an atomic nucleus and the properties of matter inside the neutron stars are dominated by the strong interaction. The extreme density of the degenerate neutrons leads to a very high Fermi temperature, much larger than the physical temperature of the system. Therefore, neutron stars are considered to be cold objects (T ~ 0 K). Hence, the presence of superfluid of neutrons and superconductor of protons is expected inside neutron stars. The presence of this superfluid is manifested in the form of "pulsar glitches". A pulsar glitch is a sudden spin-up of a neutron star. The relative change in the rotation frequency due to pulsar glitches ranges from 1 part in a million to 1 part in ten billion. Measuring such changes provides us with information about the typical size of the superfluid reservoir. The short and the long term post-glitch evolution provides detailed information about the interaction of superfluid vortices with the defects in the stellar crust. The spin evolution of neutrons stars is measured using the technique of pulsar timing. At NCRA, I and my collaborators monitor a set of young pulsars using the GMRT and the ORT to find new glitches and measure the rotational evolution in the post-glitch phase. We constrain the models of pulsar glitches from our observations, which in turn helps us in understanding the physics of superfluids inside the neutron stars.
Pulsar emission physics:
In general, single pulses from pulsars are faint and hard to detect. However, there are a few exceptions where every single pulse is visible like Vela, B0329+54 and others. The energy distribution of these pulses follows either a normal or a log-normal distribution. In general, these are referred to as normal pulses. However, there exist another category of pulses along with these normal pulses observed in a few pulsars like Crab, J1823-3021A, B1937+21 and a few more, where the energy distribution is observed with a power-law tail, called as giant pulses. They are bursty in nature and can be a million times brighter than the normal radio pulses. Giant pulses are thought to originate from the region far away from the stellar surface closer to the radius of the light cylinder, where the magnetosphere rotates with the speed of light, unlike the normal radio pulses, where the emission height is ~ 100 - 500 km above the stellar surface. Evidence for enhancement of photon count at the optical wavelength at the phase of giant radio pulses implies the emission region of giant radio pulses and high-energy are closely spaced. However, despite multiple attempts to find such correlations at the X-rays and gamma-rays, no positive result has been found. Studying giant pulses can help us understand the radio emission at the comparatively weaker magnetic field, it also helps us probing the pair-cascade process at the outer acceleration zone in the pulsar magnetosphere. To probe the pair-cascade process at the outer acceleration zone, it is essential to search for clear emission changes at radio and at high energies like X-rays and gamma-rays at the phase of giant radio pulses. Since pulsars are steep spectrum source, it is essential to use sensitive telescopes to detect the larger number of photons, for significant detection of emission changes. Here at NCRA, we use the GMRT, ORT and AstoSat to observe the Crab pulsar simultaneously at different bands to probe such emission changes. To put a better constraint, it is important to have polarimetric observations of giant pulses, for which we use other single-dish telescopes.
In general, single pulses from pulsars are faint and hard to detect. However, there are a few exceptions where every single pulse is visible like Vela, B0329+54 and others. The energy distribution of these pulses follows either a normal or a log-normal distribution. In general, these are referred to as normal pulses. However, there exist another category of pulses along with these normal pulses observed in a few pulsars like Crab, J1823-3021A, B1937+21 and a few more, where the energy distribution is observed with a power-law tail, called as giant pulses. They are bursty in nature and can be a million times brighter than the normal radio pulses. Giant pulses are thought to originate from the region far away from the stellar surface closer to the radius of the light cylinder, where the magnetosphere rotates with the speed of light, unlike the normal radio pulses, where the emission height is ~ 100 - 500 km above the stellar surface. Evidence for enhancement of photon count at the optical wavelength at the phase of giant radio pulses implies the emission region of giant radio pulses and high-energy are closely spaced. However, despite multiple attempts to find such correlations at the X-rays and gamma-rays, no positive result has been found. Studying giant pulses can help us understand the radio emission at the comparatively weaker magnetic field, it also helps us probing the pair-cascade process at the outer acceleration zone in the pulsar magnetosphere. To probe the pair-cascade process at the outer acceleration zone, it is essential to search for clear emission changes at radio and at high energies like X-rays and gamma-rays at the phase of giant radio pulses. Since pulsars are steep spectrum source, it is essential to use sensitive telescopes to detect the larger number of photons, for significant detection of emission changes. Here at NCRA, we use the GMRT, ORT and AstoSat to observe the Crab pulsar simultaneously at different bands to probe such emission changes. To put a better constraint, it is important to have polarimetric observations of giant pulses, for which we use other single-dish telescopes.
Selected publications:
1. A. Basu et al., Observed glitches in eight young pulsars, MNRAS, 491, 3182 2. A. Basu et al., Glitch Behavior of Pulsars and Contribution from Neutron Star Crust, 2018, ApJ, 866, 94. 3. A. Basu et al., Timing Offset Calibration of CZTI instrument aboard ASTROSAT, 2018, A&A, 617, A22, 4. S. V. Vadawale, T. Chattopadhyay, N. P. S. Mithun, A. R. Rao, D. Bhattacharya, A. Vibhute, V. B. Bhalerao, G. C. Dewangan, R. Misra, B. Paul, A. Basu, B. C. Joshi, S. Sreekumar, E. Samuel, P. Priya, P. Vinod & S. Seetha, Phase-resolved X-ray polarimetry of the Crab pulsar with the AstroSat CZT Imager, 2018, Nature Astronomy, 2, 50 5. B. C. Joshi, P. Arumugasamy, M. Bagchi, D. Bandyopadhyay, A. Basu, N. D. Batra, S. Bethapudi, A. Choudhary, K. De, L. Dey, A. Gopakumar, Y. Gupta, M.A. Krishnakumar, Y. Maan, P.K. Manoharan, A. Naidu, R. Nandi, D. Pathak, M. Surnis & A. Susobhanan, Precision pulsar timing with the ORT and the GMRT and its applications in pulsar astrophysics, Journal of Astrophysics and Astronomy, 2018, 39, 51
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