Schedule

Saturday, 27th January, 2024.
10:15 PM IST

About Speaker

Dr. Debnandini Mukherjee is a postdoctoral researcher at the Center of Space Plasma and Aeronomic Research (CSPAR). She works in NASA's Marshall Space Flight Center in Huntsville Alabama, with Tyson Littenberg's group. She works in the area of gravitational wave data analysis and astrophysics. Her work involves looking for gravitational waves from inspiralling compact object binaries comprising neutron stars, black holes or both. She has been working with the LIGO-VIrgo-KAGRA (LVK) Collaboration and using data collected by the same to look for signatures of gravitational waves and gleaning astrophysical implications of such observations. Her focus has been on the search for intermediate-mass black-hole (IMBH) binaries which is an interesting astrophysical source for the LISA mission as well. She is also involved in developing searches for gravitational waves for the LISA mission. In particular, she is interested in developing early warning (pre-merger) searches, aimed at sending out early alerts for gravitational waves. Debnandini completed her PhD from the University of Wisconsin Milwaukee in 2018. Before joining CSPAR, she was a postdoctoral scholar at the Pennsylvania State University.

Abstract

The discovery of gravitational waves in 2015, added a new channel for multi-messenger observations of powerful astrophysical phenomena. Besides telescope observations using the pre-existing electromagnetic channels like X-rays, Gamma rays and Optical light, many such observations can also be supplemented and corroborated using gravitational waves. On the more massive end of the mass spectrum of compact objects, the intermediate mass black holes (IMBHs) are expected to have masses in the range of 100 to 100,000 solar masses, making up the mass space between the stellar mass and the supermassive black holes. GW190521, the heaviest black hole binary coalescence seen by the end of the last observation run in data from LIGO-Virgo, with its total mass being about 150 solar masses, has been the first clear observation of an IMBH. The rates of observation of gravitational wave sources with at least one IMBH component, to which the detectors are currently sensitive, would help constrain their formation channel, which so far remains uncertain. Their observations could also point to a missing link between stellar mass and super massive black holes. On the other end of the mass spectrum, GW170817 was not only the first observed binary neutron star (BNS) event in gravitational waves but it also started a new-era in multi-messenger astronomy through its observation and detection in other channels. Such multi-channel observations can lead to a more robust understanding of the physics that can be gleaned from BNS mergers. Such BNSs are expected to spend several minutes before merging in LIGO-Virgo's sensitive band, at design sensitivity. This can be leveraged to send out early alerts to multi-messenger partners, to enable observation of such events in multiple bands.

The space based laser interferometer LISA, expected to be operational in the next decades, will be able to probe the millihertz frequency band. This will make it sensitive to a vast array of compact object mergers, including the massive black holes or MBHs. These black holes, straddling the intermediate and supermassive types of black holes, have masses extending above a minimum of 1000 M_ⵙ. They are expected to be observable within the LISA band for several weeks to months before they merge. This makes them excellent candidates for low latency, pre-merger observations. Also, some mergers of MBHs are expected to have electromagnetic counterparts due to the presence of gas or disks. Pre-merger alerts with sky location information from LISA data analysis sent out to the astronomy community, would enable early detections of such mergers in electromagnetic bands. Such multi-messenger observations stand to further our knowledge of astrophysics, including that of black hole formation and evolution. 

In my talk I will discuss the search for the presently observable gravitational wave sources in LIGO-Virgo data and the possibility of future observations of more massive sources using LISA and explore the possibility of sending out pre-merger alerts for electromagnetically observable sources, to enable multi-messenger observations.

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Bahata Anshumali Mukhapadhyay

This presentation seeks to demonstrate how multi-disciplinary approaches are indispensable for understanding the semantic role of the Indus valley inscriptions, one of the most enigmatic aspects of the most expansive Bronze Age civilization of the world (c. 2600 BC to 1900 BC).

Interrogating Indus inscriptions to unravel their mechanisms of
meaning conveyance

https://www.nature.com/articles/s41599-019-0274-1

Ancestral Dravidian languages in Indus Civilization: ultraconserved Dravidian tooth-word reveals deep
linguistic ancestry and supports genetics

https://www.nature.com/articles/s41599-021-00868-w

Bahata Ansumali Mukhopadhyay is a software technologist and an independent researcher originally from Bengal, presently settled in Bangalore. She researches the structural and semantic aspects of Indus script inscriptions and explores the linguistic identities of the people of the Indus Valley civilization. Her first paper, titled “Interrogating Indus inscriptions to unravel their mechanisms of meaning conveyance” (https://www.nature.com/articles/s41599-019-0274-1), problematizes more than 90% of existing decipherment effort, as it claims that Indus script inscriptions were mostly written using logographic and/or semasiographic signs, and thus any attempt to read them by treating those signs as phonological units must be flawed. Her second article, titled “Ancestral Dravidian languages in Indus Civilization: ultraconserved Dravidian tooth-word reveals deep linguistic ancestry and supports genetics” (https://www.nature.com/articles/s41599-021-00868-w), published in the Nature group journal Humanities and Social Sciences Communications, seeks to partly resolve one of the most debated questions of South Asian prehistory, the linguistic identities of the Indus valley population. Ms. Mukhopadhyay continues to research the semantic aspects of Indus script inscriptions and her latest research paper, that claims to have decoded certain signs of Indus script, is under peer review. Bahata A. Mukhopadhyay is also a prolific and widely published Bengali poet, whose first book of poetry, ‘Ṭhung Śobdo Holei Kobitā’, came out at the 44th International Kolkata Book Fair 2020.

This presentation seeks to demonstrate how multi-disciplinary approaches are indispensable for understanding the semantic role of the Indus valley inscriptions, one of the most enigmatic aspects of the most expansive Bronze Age civilization of the world (c. 2600 BC to 1900 BC). Traditionally, study of inscriptions, i.e. epigraphy, was known to mostly demand a thorough knowledge of linguistics, ancient languages, numismatics, palaeography, and history. However, much like how the Linear B script of ancient Greece was finally deciphered based on the grid-based statistical analyses done by Michael Ventris, the yet undeciphered Indus valley inscriptions too have immensely benefited from the researches of various mathematicians, physicists, computer professionals, etc. who have employed their skills, building on various incisive analyses done by linguists, archaeologists, and historians. The methods used by them encompass a broad spectrum of scientific tools and techniques ranging from the use of n-gram Markov model for exploring the correlation between co-occurring signs; calculating conditional entropy of the sign-sequences to predict their linguistic nature; and clustering Indus signs based on their frequency distributions; to applying different linguistic rules to tease out the underlying language used in the inscriptions. The author of this paper has applied the role of aerodynamic factors on the phonetic basis of phonological structures used in natural languages, the distinction between phonological and semantic co-occurrence restriction patterns, as well as comparison between various formalized data carriers and coexistence of document specific and linguistic syntaxes in their mechanisms of meaning conveyance, to understand certain aspects of the Indus script and its nature. This presentation would also very briefly discuss a few points from another upcoming paper, currently going through peer review, where the author explores the semantics of certain Indus inscriptions using various archaeological, linguistic, and historical evidences. A theoretical payoff from this presentation would be demonstration of the extent to which fluid movements between different branches of science can aid in the understanding of inscriptions that have obstinately defied and resisted traditional decipherment methods for 150 years since their discovery.