Bhaswati Bhattacharyya

Reader
Email: bhaswati [at] ncra.tifr.res.in
Phone: +91 - 20 - 25719234
Extn: 9253
Office: F211
National Centre for Radio Astrophysics
Tata Institute of Fundamental Research
Savitribai Phule Pune University Campus,
Pune 411 007
Maharashtra, INDIA


Main Research Areas: Pulsar searching, Population synthesis, Timing, Astrometry, Transient searching, Fast Radio Bursts, Rotating Radio Transients, Multi wavelength study of millisecond pulsars, Giant pulses from Crab pulsar, Emission properties: sub-pulse drifting, nulling.

Biography:

Bhaswati Bhattacharyya did her B.Sc. Hons. (Physics) from New Alipur college, University of Calcutta, and her M.Sc. (Physics) from the University of Calcutta. She joined the Joint Astronomy Programme (JAP) run by the Indian Institute of Science, Bangalore, for her Ph.D. in 2002. In 2003, she moved to the National Centre for Radio Astrophysics to pursue her doctoral research on observational studies of radio pulsars to probe their emission mechanism. She finished her Ph.D. in 2009 and then moved to the Inter-University Centre for Astronomy and Astrophysics, Pune, as a postdoctoral fellow. She returned to the National Centre for Radio Astrophysics in February 2013 as a Visiting Fellow, before moving to the University of Manchester as a Marie Curie Fellow over 2013-2015 and later, an SKA Research Associate over 2015-2017. Bhaswati joined the National Centre for Radio Astrophysics as a Reader in March 2017.

Research description:

My main research interests comprise of: (1) Surveys for pulsars and transients, (2) Timing of newly discovered pulsars, (3) Study of neutron star population, and (4) Emission properties of pulsars.
Survey of pulsars and transients:
Neutron stars (ultra compact objects formed after the supernova explosion of a massive star and supported by neutron degeneracy pressure) are accessible to observations as pulsars (rapidly rotating strongly magnetized neutron stars that can be used as extremely precise celestial clocks) and thus provide a valuable means for probing the most extreme states of matter. In an attempt to understand the distribution of sources within the limits of the known population and to probe the limits themselves there are many on going surveys that are discovering pulsars at an encouraging rate, we are conducting a survey for pulsars and transients using the Giant Metrewave Radio Telescope (GMRT). GHRSS survey discovery rate is 13 pulsars in 1710 deg2, i.e. 0.007 pulsars per deg2. Our discoveries include a millisecond pulsar and mildly-recycled pulsars. In addition to the regular emission from pulsars, a wide variety of transient phenomena are known at faster time scales (micro-seconds to seconds). The discoveries of giant pulses from pulsars, quasi-periodic emission from rotating radio transients (RRATs), bursts of periodic pulsations from magnetars and highly dispersed fast radio bursts (FRBs) of possible extragalactic origin are a few examples. The FRBs have been discovered in radio pulsar surveys at Parkes and Arecibo in the last decade. All FRBs discovered to date have been single radio events of millisecond duration with DM values generally higher than the possible Galactic contribution. We are in the process of searching for FRBs and RRATs from the GHRSS survey data. More details on GHRSS survey can be found here. [http://www.ncra.tifr.res.in/ncra/research/research-at-ncra-tifr/research-areas/pulsarSurveys/GHRSS]
Timing studies of the newly discovered pulsars:
Finding pulsars is only half the job, but to understand their nature, rotational properties, spectral indices and relation to the pulsar population, follow up timing study is needed. Detection of gravitational waves facilitated by the incredible stability of spin period of millisecond pulsars can constrain the viability of theories of gravity leading to quantitative tests of general theory of relativity in the strong-field regime. The pulsar timing array (PTA) project is designed to detect low-frequency (a few nanohertz) gravitational waves using an array of spatially distributed millisecond pulsars. We are carrying out timing studies of 9 millisecond pulsars which are discovered from our surveys. This timing program uses observations from the GMRT, Parkes, GBT and Arecibo. Our timing study revealed that one of the millisecond pulsars discovered by us is in a binary system where the pulsar wind evaporates the companion and eclipses the pulsar radiation for long time. Such systems called black-widow systems, are one way to form isolated millisecond pulsar. One of the other millisecond pulsar is a transitioning system from low-mass X-ray binary to radio millisecond pulsar and can act as a probe of millisecond pulsar formation mechanism. Two other millisecond pulsars discovered by us are good candidates for inclusion in the International Pulsar Timing Array (IPTA). It is predicted that the planned surveys described above will discover many millisecond pulsars.
Study of the neutron star population:
a) Long term timing study of rotating radio transients: Rotating Radio Transients (RRATs) emit occasional flashes of dispersed radio bursts of typically a few milliseconds duration. Giant pulses from weak pulsars, manifestation of nulling of radio pulsar, presence of a circumstellar asteroid belt are the few proposed explanation for the sporadic RRAT emission. However, the connection of RRATs to other neutron star population is yet to be established, which can only be achieved through long term timing. We are carrying out a long term timing study (longer span than any existing study of the RRATs) for RRATs with Lovell, Parkes and the GBT. We have developed a pipeline for performing single pulse timing and are ready to perform timing study of the new RRATs that will be getting discovered in ongoing surveys. (b) Study of Fermi gamma-ray millisecond pulsars: We discovered seven millisecond pulsars from our Fermi directed survey with the GMRT, which are pushing the boundaries of the known parameter space of the millisecond pulsars. Long-term radio timing studies have enabled us to discover the gamma-ray pulsations for the associated millisecond pulsars. The current models predict that the high energy emission originates at higher altitudes in the magnetosphere, near the light cylinder, in contrast to the radio emission coming from near stellar surface. This leads to significant phase lags between radio and gamma-ray light curve of Fermi millisecond pulsars. However, for a subclass of gamma-ray millisecond pulsars nearly non-zero phase lag between radio and gamma-ray light curve is observed which indicates (partial)co-location of the radio and the gamma-ray emission region.
Emission properties of pulsars:
a) Simultaneous multi-wavelength study of giant radio pulses from the Crab pulsar: Although "normal" pulsar activity results in regular repeating periodic radio pulses, giant pulses occur at random intervals and have energies up to many thousand times than the mean energy. Giant radio pulses are sporadic, large amplitude, short duration bursts and can provide clues for pinning down the origin of pulsar radio emission. We are starting the deepest simultaneous radio-optical study of giant pulsars from Crab pulsar in optical wavelength with the WHT and in radio wavelength with the GMRT. In addition to deeper study of radio-optical correlation we aim to measure the time resolved optical circular polarization for Crab pulsar. (b) Single pulse and polarimetric study of pulsars: Discovery of remarkable drift patterns with phase relation between simultaneous multiple drift regions observed for PSR B0818-41 and B0826-34 and the follow up interpretations of polar cap configuration (Bhattacharyya et al. 2007, 2008, and in my Ph.D. thesis), brings out the fact that the pulsar emission mechanism is a pan magnetospheric phenomenon and exemplify the fact that constraints provided by the drifting pulsars can have far reaching implications on the theoretical models. We are in the process of detailed investigation of phase related drift regions discovered by us in PSR B1039-19.

Selected publications:

p1. The GMRT High Resolution Southern Sky Survey for pulsars and transients -I. Survey description and initial discoveries (Bhattacharyya, B. et al. 2016, ApJ, 817, 130)

2. Discovery of PSR J1227-4853: A Transition from a Low-mass X-Ray Binary to a Redback Millisecond Pulsar (em>Roy, J. et al. (including Bhattacharyya, B.), 2015, ApJL, 800, L12)

3. A 24-Hr Global Campaign to Assess Precision Timing of the Millisecond Pulsar J1713+0747 (Dolch, T. et al. (including Bhattacharyya, B.), 2014, ApJ, 794, 21)

4. Discovery of an eclipsing Black Widow PSR J1544+4937 in a Fermi source with the GMRT (Bhattacharyya, B. et al., 2013, ApJL, 772, L12)

5. Coherently dedispersed gated imaging of millisecond pulsars (Roy, J., Bhattacharyya, B. 2013, ApJL, 765, 45) /p>

6. Investigation of the unique nulling properties of PSR B0818-41 (Bhattacharyya, B., Gupta, Y. & Gil, J. 2010,MNRAS, 407, 408)

7. Exploring remarkable subpulse drift pattern and polarization properties of PSR B0818-41 (Bhattacharyya, B., Gupta, Y. & Gil, J., 2009, MNRAS, 398, 1435)

8. Results from multi-frequency observations of PSR B0826-34 (Bhattacharyya, B., Gupta, Y. & Gil, J., 2008, MNRAS, 383, 1538)

9. Determination of orbital parameters of Binary pulsars (Bhattacharyya, B. & Nityananda, R. 2008, MNRAS, 387, 273)

10. Discovery of a remarkable subpulse drift pattern in PSR B0818-41 (Bhattacharyya, B. et al. 2007, MNRAS, 377, L10)




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