Time-resolved spectro-polarimetric analysis of extremely bright GRB 230307A: Possible Evidence of evolution from photospheric to synchrotron dominated emission
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| Main Authors: | , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| author | Gupta, Soumya Gupta, Rahul Chattopadhayay, Tanmoy Sahayanathan, Sunder Frederiks, D. Svinkin, D. Bhattacharya, Dipankar Racusin, Judith Vadawale, Santosh Bhalerao, Varun Lysenko, A. Ridnaia, A. Tsvetkova, A. Ulanov, M. |
| author_facet | Gupta, Soumya Gupta, Rahul Chattopadhayay, Tanmoy Sahayanathan, Sunder Frederiks, D. Svinkin, D. Bhattacharya, Dipankar Racusin, Judith Vadawale, Santosh Bhalerao, Varun Lysenko, A. Ridnaia, A. Tsvetkova, A. Ulanov, M. |
| contents | The radiation mechanisms powering Gamma-ray bursts (GRBs) and their physical processes remain one of the unresolved questions in high-energy astrophysics. Spectro-polarimetric observations of exceptionally bright GRBs provide a powerful diagnostic tool to address these challenges. GRB 230307A, the second-brightest long-duration GRB ever detected, exhibits a rare association with a Kilonova, offering a unique and rare probe into the emission processes of GRBs originating from compact object mergers. We present a comprehensive time-averaged and time-resolved spectro-polarimetric analysis of GRB 230307A using joint observations from the $AstroSat$ Cadmium Zinc Telluride Imager (CZTI), the $Fermi$ Gamma-ray Burst Monitor (GBM) and $Konus$-Wind. Spectral analysis reveals a temporal evolution in the low-energy photon index, $α$, transitioning from a hard to a softer state over the burst duration. Time-averaged polarimetric measurements yield a low polarization fraction ($<$ 12.7 %), whereas time-resolved polarization analysis unveils a marked increase in polarization fractions ($>$ 49 %) in the later stages of the emission episode. This spectro-polarimetric evolution suggests a transition in the dominant radiative mechanism: the initial phase, possibly characterized by thermal-dominated photospheric emission (unpolarized or weakly polarized), gives way to a regime dominated by non-thermal synchrotron emission (highly polarized). This transition provides possible evidence for the evolving influence of magnetic fields in shaping the GRB emission process and jet dynamics. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_05038 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Time-resolved spectro-polarimetric analysis of extremely bright GRB 230307A: Possible Evidence of evolution from photospheric to synchrotron dominated emission Gupta, Soumya Gupta, Rahul Chattopadhayay, Tanmoy Sahayanathan, Sunder Frederiks, D. Svinkin, D. Bhattacharya, Dipankar Racusin, Judith Vadawale, Santosh Bhalerao, Varun Lysenko, A. Ridnaia, A. Tsvetkova, A. Ulanov, M. High Energy Astrophysical Phenomena The radiation mechanisms powering Gamma-ray bursts (GRBs) and their physical processes remain one of the unresolved questions in high-energy astrophysics. Spectro-polarimetric observations of exceptionally bright GRBs provide a powerful diagnostic tool to address these challenges. GRB 230307A, the second-brightest long-duration GRB ever detected, exhibits a rare association with a Kilonova, offering a unique and rare probe into the emission processes of GRBs originating from compact object mergers. We present a comprehensive time-averaged and time-resolved spectro-polarimetric analysis of GRB 230307A using joint observations from the $AstroSat$ Cadmium Zinc Telluride Imager (CZTI), the $Fermi$ Gamma-ray Burst Monitor (GBM) and $Konus$-Wind. Spectral analysis reveals a temporal evolution in the low-energy photon index, $α$, transitioning from a hard to a softer state over the burst duration. Time-averaged polarimetric measurements yield a low polarization fraction ($<$ 12.7 %), whereas time-resolved polarization analysis unveils a marked increase in polarization fractions ($>$ 49 %) in the later stages of the emission episode. This spectro-polarimetric evolution suggests a transition in the dominant radiative mechanism: the initial phase, possibly characterized by thermal-dominated photospheric emission (unpolarized or weakly polarized), gives way to a regime dominated by non-thermal synchrotron emission (highly polarized). This transition provides possible evidence for the evolving influence of magnetic fields in shaping the GRB emission process and jet dynamics. |
| title | Time-resolved spectro-polarimetric analysis of extremely bright GRB 230307A: Possible Evidence of evolution from photospheric to synchrotron dominated emission |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2504.05038 |