| Name: | UTKARSH PATHAK |
| Affiliation: | INDIAN INSTITUTE OF TECHNOLOGY BOMBAY |
| Conference ID : | ASI2024_488 |
| Title : | GRB230812B - Exploring Jet Physics and Polarization for an Extremely Bright Gamma Ray Burst |
| Authors : | Utkarsh Pathak 1, Anirudh Salgundi 1, Gaurav Waratkar 1, Vishwajeet Swain 1, Tomas Ahumada 2, Gokul Srinivasaragavan 3, Harsh Kumar 1 7, Varun Bhalerao 1, Gulab Dewangan 4, Poonam Chandra 8, G C Anupama 5, Dipanker Bhattacharya 4 6, on behalf of a larger collaboration |
| Authors Affiliation: | 1 Department of Physics, IIT Bombay, Powai, Mumbai - 400076, India
2 Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
3 Department of Astronomy, University of Maryland, College Park, MD 20742, USA
4 Inter University Centre for Astronomy & Astrophysics, Post Bag 4, Ganeshkhind, Pune, 411007, India
5 Indian Institute of Astrophysics, 2nd Block 100 Feet Rd, Koramangala Bangalore, 560 034, India
6 Ashoka University, Department of Physics, Sonepat - 131029, India
7 Center for Astrophysics, Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138-1516, USA
8 National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA, 22903, USA |
| Mode of Presentation: | Poster |
| Abstract Category : | High Energy Phenomena, Fundamental Physics and Astronomy |
| Abstract : | Gamma-ray Bursts (GRBs) are produced by highly relativistic beamed jets powered by a compact central engine. The nature of the central engine and the role of magnetic fields are open questions best answered by the measurement of jet parameters and polarization of the prompt emission. However, polarization studies are only possible for bright bursts, and need extensive broadband observations - hence the studied sample is rather small. GRB 230812B offers a unique opportunity to overcome this limitation.
GRB 230812B, first detected by Fermi-GBM, is relatively nearby compared to other GRBs with a distance of around 2 Gpc and an isotropic equivalent energy (Eiso) 10^53 erg. It is among the brightest GRBs ever detected with a fluence of 3.27 × 10^-4 erg cm-2. It had a narrow peak with T90 = 3 s, and an extended emission lasting for about 20 s after the initial burst in the Fermi data. This bright burst saturated the Cadmium Zinc Telluride Imager (CZTI) on AstroSat. However, there is clear detection of an unsaturated tail emission lasting 8s where we detected 765 Compton events, sufficient to undertake polarization analysis. We undertook extensive broadband observations of the afterglow using the Swift XRT, a director’s discretionary time proposal on Chandra, optical imaging with GROWTH-India Telescope, Zwicky Transient Facility, Himalayan Chandra Telescope, and Radio observations with uGMRT and the JVLA.
Our data allow us to put together a comprehensive picture of the GRB. We do not detect statistically significant polarization, ruling out models and scenarios making such a prediction. The long X-ray monitoring shows absence of a jet break, helping constrain the jet geometry. We use afterglow data to probe jet physics using models through afterglowpy. I will present the results of our detailed modeling and discuss them in context of current open questions in GRB physics. |
