Talks

The association of quasi-steady persistent radio sources (PRSs) with a few repeating fast radio bursts (FRBs) offers a valuable testbed for examining the magnetar progenitor hypothesis. A widely favored interpretation attributes the PRS emission to synchrotron radiation from highly charged electron-positron pairs in a magnetar wind nebula. Observational probes—including radio imaging, scintillation studies, and equipartition analysis—consistently point to a very compact source size. This compactness strongly disfavors scenarios involving rapid expansion, such as those expected from millisecond magnetars formed in superluminous or ultra-stripped supernovae. In this talk, I will show that the observed PRS properties are naturally explained by a magnetar wind nebula powered by the decay of the internal magnetic field of a magnetar formed in a sub-energetic supernova, with an initial spin period of a few tens of milliseconds. This scenario also leads to clear observational predictions at both ends of the PRS spectrum: a synchrotron self-absorption break near 200 MHz and a cooling break around 150 GHz—features that can be tested with current radio telescopes.

Fast radio bursts (FRBs) are bright, millisecond-duration pulses, originating from unidentified sources. The dispersion measure (DM) of FRBs strongly suggests an extragalactic origin, however, the underlying emission mechanism and the nature of their sources remain elusive. Several theoretical models have been proposed to explain the origin of FRBs, with magnetars emerging as a prominent candidate.

We have studied magnetar XTE J1810-197 to understand the magnetar-FRB connection. We have used a large number of data sets, spanning a wide range of frequencies (300 to 6000 MHz) and covering more than 4 years from December 2018 to March 2023. These data sets were taken using the upgraded Giant Metrewave Radio Telescope (GMRT) and the Green Bank Telescope (GBT). In our study of bright single pulses, we have investigated different properties, including energetics, waiting time, and energy-time correlation, and compared them with FRBs. Additionally, we have examined how these properties evolve over time and with frequency. Our results suggest that the magnetar XTE J1810-197 can emit a FRB-like burst on a reasonably short timescale. The waiting-time distribution of the bursts from this magnetar also shows significant similarities with that of the repeating FRBs and could hold clues to why finding any underlying periodicity in the repeating FRB bursts might be hard. Correlation in time and energy of the bursts also shows similarities between magnetars and the FRBs and has implications for a starquake-like scenario to be responsible for the emission.. We will present our analyses and results in detail, which have significant implications for understanding the origin of FRBs as well as the likelihood of FRB-like emission from the Galactic magnetar population.

"Magnetars are highly magnetised neutron stars and are considered leading candidates for explaining Fast Radio Bursts (FRBs), at least a subset of them. Repeating FRBs, in particular, often exhibit band-limited bursts. Intriguingly, similar spectral characteristics have been observed in radio bursts from the Galactic magnetar J1809-1943. If such features are confirmed to be intrinsic to the source and not a result of propagation through the interstellar medium or instrumental effects, they would offer strong support for a direct physical connection between magnetars and repeating FRBs.
In this work, we have developed a pipeline to systematically search for such narrowband bursts. We further characterise the spectral properties of the detected bursts and provide evidence that the observed emission is intrinsic to the source. These findings contribute not only to bridging the gap between magnetars and FRBs, but also to advancing our understanding of magnetar radio emission mechanisms.

Magnetars remain the leading candidates for powering fast radio bursts (FRBs), yet their ability to reproduce the full diversity of observed behaviors is far from settled. In this talk, I will present two recent advances that sharpen the constraints on what magnetars can - and cannot - explain about FRBs. First, a population-level analysis shows that repeating and apparently non-repeating FRBs can be described by a single unified distribution of sources with a power-law distribution of activity rates. This framework explains why repeaters tend to be nearer and reproduces the wide range of inferred activity rates, the fraction of repeaters to non-repeaters and its weak dependence on survey observation time and sensitivity. Second, we model FRB emission from magnetar polar caps, showing how the orientation of the magnetic and spin axes controls observed repetition behavior, inferred energetics and polarization and spectro/temporal properties. The results imply that geometry may account for much of the apparent FRB diversity. At the same time, the small inferred emission regions and burst energetics rule out broad classes of emission scenarios, tightening the viable range of magnetar-based models. Together, these results provide stringent tests of the magnetar hypothesis. I will outline the specific observational signatures - in repetition statistics, polarization behavior, and energetics - that can confirm or refute magnetars as the dominant FRB progenitors.

Among the mysteries of Fast Radio Bursts (FRBs) is how they direct, or 'beam' their energy. Despite observations of over 1000 FRBs from unique sources, the majority of the leading theories for emission mechanisms include some form of beaming, but this is often ignored for simplicity. Interpretations of features in the energy distribution, such as bimodality and broken power-laws implicitly assume an isotropic or unphysical top hat emission cone. In this work, we approach the FRB beaming problem by simulating FRB bursts with a variety of beam shapes and their effects on different underlying intrinsic energy distributions. Under the most realistic beaming models (e.g. a Gaussian, pulsar-like beam), it is challenging to preserve bimodality and even a break in the power-law of the intrinsic energy function. We find that a large beam area with small intensity variation is the only way to reproduce bimodality. With our new approach, we are able to reproduce bimodality in simulated energy distributions, resembling that of FRB 20201124A and FRB 20121102. 
We are also able to simulate a broken power-law energy distribution from a combination of one Gaussian and one relativistic beam, affected by the same intrinsic power-law distribution,  energy distribution, showing that the effects of beaming play a significant role in interpreting the intrinsic energy distribution.

The Square Kilometre Array (SKA) is the most sensitive Radio Telescope to be deployed in the most radio-quiet parts of the world: African and Australian deserts. The first phase of the project, SKA1  will commission up to 197 dish antenna arrays in South Africa and up to 1,31,072 element aperture arrays in Western Australia. Together, these arrays will observe over an extensive frequency range from 50 MHz to about 15 GHz. These arrays will produce very high volume imaging and non-imaging data streams and support exploring a variety of radio astronomy problems. Complex hardware forms part of the digital backend, namely the Tile Processing Module(TPM). We are involved in characterizing and developing firmware features to form multiple beams for the SKA-Low telescope. We also contribute to the accelerated pulsar search associated candidate sifting using High Performance SOC FPGA. In this talk, I will provide an overview of firmware features developed for SKA-LOW beamforming especially for FRB-like transient search point of view, and provide an update on how we plan to test using Gauribidanur Observatory facilities and also present challenges involved in candidate sifting during a search and present our approaches towards solving them.

The Square Kilometre Array (SKA) project is realising a state-of-the-art and most sensitive radio telescope. The telescopes are coming up in two radio-quiet zones, the Western Australian and South African deserts. Pulsar and fast-transient search is a significant Program planned with SKA that needs enormous real-time computing to reduce about 60 petabytes of data from several hundred pulsar search beams of the telescopes. High-performance computing solutions with 10 Peta-operations per second processing capabilities are being constructed, exploiting the state-of-the-art CPU, GPUS and FPGA accelerators. This talk will provide a detailed outline of this transient search Program, highlighting the time and Fourier domain search pipelines, challenges, and current status.

Chirality is a fundamental feature of many-body physics, typically manifesting through the breaking of time-reversal symmetry. Yet a precise quantum information-theoretic characterization of chirality has remained elusive. A recent proposal defines a state as chiral if transforming it into its complex conjugate requires a circuit of large depth. Here, we rigorously establish many-body chirality for a broad family of two-dimensional stabilizer pure and mixed states. We also prove that these states are 4-partite chiral, but not 3-partite chiral.