Publications

Research articles in peer reviewed journals:

  1. ‘GRB110721A: An Extreme Peak Energy and Signatures of the Photosphere’ Axelsson, M., Baldini, L., Barbiellini, G., et al., Astrophysical Journal, 757, L31 (2012). DOI: 10.1088/2041-8205/757/2/L31

  2. ‘Variable jet properties in GRB 110721A: time resolved observations of the jet photosphere’ Iyyani, S., Ryde, F., Axelsson, M., Monthly Notices of Royal Astronomical Society, 433, 2739 (2013). DOI: 10.1093/mnras/stt863

  3. ‘Transparency Parameters from Relativistically Expanding Outflows’ Bégué, D., Iyyani, S., Astrophysical Journal, 792, 42 (2014). DOI: 10.1088/0004-637X/792/1/42

  4. ‘Extremely narrow spectrum of GRB110920A: further evidence for localised, subphotospheric dissipation.’ Iyyani, S., Ryde, F., Ahlgren, B., et al. Monthly Notices of Royal Astronomical Society, 450, 1651(2015). DOI: 10.1093/mnras/stv636

  5. ‘Synchrotron emission in GRBs observed with Fermi: Its limitations and the role of the photosphere.’ Iyyani, S., Ryde, F., Burgess J, M., et al. Monthly Notices of Royal Astronomical Society, 456, 2157 (2016). DOI:10.1093/mnras/stv2751

  6. ‘The First Pulse of the Extremely Bright GRB 130427A: A Test Lab for Synchrotron Shocks.’ Preece, R., Burgess, J. M., von Kienlin, A. et al., Science, 343, 51-54 (2014). DOI: 10.1126/science.1242302

  7. ‘Time-resolved Analysis of Fermi Gamma-Ray Bursts with Fast- and Slow-cooled Synchrotron Photon Models.’ Burgess, J. M., Preece, R. D., Connaughton, V. et al., Astrophysical Journal, 784, 17 (2014). DOI: 10.1088/0004-637X/784/1/17

  8. ‘An Observed Correlation between Thermal and Non-thermal Emission in Gamma-Ray Bursts.’ Burgess, J. M., Preece, R. D., Ryde, F. et al., Astrophysical Journal Letter, 784, L43 (2014). DOI: 10.1088/0004-637X/784/1/17

  9. ‘AstroSat CZT Imager Observations of GRB 151006A: Timing, Spectroscopy, and Polarization Study’ Rao, A. R.; Chand, Vikas; Hingar, M. K.; Iyyani, Shabnam.; Khanna, Rakesh; Kutty, A. P. K.; Malkar, J. P. et al., The Astrophysical Journal, 833, p86 (2016). DOI:10.3847/1538-4357/833/1/86

  10. ‘Explosive and Radio-Selected Transients: Transient Astronomy with Square Kilometre Array and its Precursors’ Chandra, Poonam; Anupama, G. C.; Arun, K. G.; Iyyani, Shabnam; Misra, Kuntal; Narasimha, D.; Ray, Alak; Resmi, L.; Roy, Subhashis; Sutaria, Firoza, Journal of Astrophysics and Astronomy, 37, p24 (2016). DOI:10.1007/s12036-016-9408-7

  11. 'Surprise in simplicity: an unusual spectral evolution of a single pulse GRB 151006A' Basak, R.; Iyyani. S.; Chand, V.; Chattopadhyay, T.; Bhattacharya, D.; Rao, A. R.; Vadawale, S, V., Monthly Notices of the Royal Astronomical Society, 472, p.891-903 (2017). DOI:10.1093/mnras/stx1970

  12. 'Violation of Synchrotron Line of Death by the Highly Polarized GRB 160802A' Chand, Vikas; Chattopadhyay, Tanmoy; Iyyani, S.; Basak, Rupal; Aarthy, E.; Rao, A. R.; Vadawale, Santosh V.; Bhattacharya, Dipankar; Bhalerao, V. B., The Astrophysical Journal, 862, article id. 154, 11 pp. (2018). DOI:10.3847/1538-4357/aacd12

  13. 'Observations and physics of prompt emission of gamma ray bursts' Iyyani, Shabnam, Journal of Astrophysics and Astronomy, 39, article id. 75, 29 pp (2018). DOI:10.1007/s12036-018-9567-9

14. ‘Time-varying Polarized Gamma-Rays from GRB 160821A: Evidence for Ordered Magnetic Fields’ Sharma, Vidushi; Iyyani, Shabnam; Bhattacharya, Dipankar; Chattopadhyay, Tanmoy, Rao, A R; Aarthy, E; Vadawale, Santosh V; Mithun, NPS; Bhalerao, V B; Ryde, Felix; Pe’er, Asaf, The Astrophysical Journal Letters, 882, L10, (2019). DOI: 10.3847/2041-8213/ab3a48

15. ‘Spectro-polarimetric analysis of prompt emission of GRB 160325A: jet with evolving environment of internal shocks’ Vidushi Sharma, Shabnam Iyyani, Dipankar Bhattacharya, Tanmoy Chattopadhyay, Santosh V. Vadawale, Varun. B. Bhalerao, Monthly Notices of the Royal Astronomical Society, 493, p. 5218-5232 (2020). DOI: 10.1093/mnras/staa570

16. 'A machine learning approach for GRB detection in AstroSat CZTI data' Sheelu Abraham, Nikhil Mukund, Ajay Vibhute, Vidushi Sharma, Shabnam Iyyani, Dipankar Bhattacharya, AR Rao, Santosh Vadawale, Varun Bhalerao, Monthly Notices of the Royal Astronomical Society, 504, p3084-3091 (2021). DOI: 10.1093/mnras/stab1082

17. 'Identifying black hole central engines in gamma-ray bursts' Vidushi Sharma, Shabnam Iyyani, Dipankar Bhattacharya, The Astrophysical Journal Letters, 908 (1), L2 (2021) DOI: 10.3847/2041-8213/abd53f

18. 'Sub-MeV spectroscopy with AstroSat-CZT Imager for Gamma Ray Bursts' Tanmoy Chattopadhyay, Soumya Gupta, Vidushi Sharma, Shabnam Iyyani, Ajay Ratheesh, NPS Mithun, E Aarthy, Sourav Palit, Abhay Kumar, Santosh V Vadawale, AR Rao, Varun Bhalerao, Dipankar Bhattacharya, Journal of Astrophysics and Astronomy, 42, p82 (2021)

19. 'Discovery and confirmation of the shortest gamma ray burst from a collapsar', Ahumada et al., Nature Astronomy, (2021)

20. 'Prompt emission of short gamma ray bursts: a clue to the viewing angle and the post-merger remnant' Shabnam Iyyani and Vidushi Sharma, The Astrophysical Journal Supplement Series, 255 25 (2021) DOI: 10.3847/1538-4365/ac082f

Conference Proceedings:

  1. 'GRB 160821A: Time varying polarised prompt gamma ray emission - Observations and physical modelling' Shabnam Iyyani, Vidushi Sharma, Asaf Pe’er, Felix Ryde,Yokohama GRB 2019 (28th October - 1st November 2019), published, http:// yokohamagrb2019.wikidot.com/proceedings

  2. 'Probing the emission mechanism of GRBs using spectral and polarisation observations' Vidushi Sharma, Dipankar Bhattacharya, Shabnam Iyyani Yokohama GRB 2019 (28th October - 1st November 2019), published, http:// yokohamagrb2019.wikidot.com/proceedings

3. 'Diverse Manifestations of the Jet Photosphere in GRB Spectra', Acuner, Zeynep; Ryde, Felix; Iyyani, Shabnam, 41st COSPAR Scientific Assembly, http://cospar2016.tubitak.gov.tr/en/, Abstract E1.18-36-16 (2016).

4. ' Manifestation of the Jet Photosphere in GRB Spectra', Ryde, F.; Acuner, Z.; Iyyani, S.; Pe'er, A. , Eighth Huntsville Gamma-Ray Burst Symposium, Huntsville, Alabama. LPI Contribution No. 1962, id.4083 (2016).

5. 'Pasta structures in neutron stars' Neha Gupta, P Arumugam, Iyyani Shabnam, DAE Symp. Nucl. Phys., 56, 702-703

Thesis:

'Photospheric emission in gamma ray bursts: analysis and interpretations of the observations by Fermi gamma ray space telescope.'

Affiliation: University of Stockholm, Sweden; Erasmus Mundus Joint Doctorate Fellowship

Supervisor: Professor Felix Ryde, Royal Institute of Technology (KTH), Stockholm, Sweden.

Public defence: 22nd May 2015.

Opponent: Professor David Burrows, Department of Astronomy & Astrophysics, Pennsylvania State University, US.

Synopsis: Gamma ray bursts are the most energetic explosions known to occur in the universe. They are believed to be narrow beam of intense radiation coming from cosmological distances. The large flashes of radiation that are observed in GRBs are generally believed to arise in a relativistic jetted outflow. My thesis addresses the question of how and where in the jet this radiation is produced. It further explores the jet properties that can be inferred from the observations made by the Fermi GST that regularly observes GRBs in the range 8 keV - 300 GeV. In my analysis I focus on the observational effects of the emission from the jet photosphere. I show that the photosphere has an important role in shaping the observed radiation spectrum and that its manifestations can significantly vary between bursts.

✴ For bursts in which the photospheric emission component can be identified, the dynamics of the flow can be explored by determining the jet Lorentz factor and the position of the jet nozzle. I find that these outflow properties show distinct evolution over a GRB pulse such as the Lorentz factor decreases with time and the nozzle radius increases with time between the limits of the black hole event horizon radius and the core of Wolf- Rayet progenitor star.

✴ I also develop the theory of how to derive the properties of the outflow for general cases.

✴ The spectral analysis of the strong burst GRB110721A reveals a two-peaked spectrum, with the peaks evolving differently. I conclude that three main flow quantities can describe the observed spectral behaviour in bursts: the luminosity, the Lorentz factor, and the nozzle radius.

✴ While the photosphere can appear like a pure blackbody it can also be substantially broadened, due to dissipation of the jet energy below the photosphere. I show that Comptonisation of the blackbody can shape the observed spectra and describe its evolution. In particular this model can very well explain GRB110920A which has two prominent breaks in its spectra.

✴ Alternative models including synchrotron emission leads to severe physical constraints, such as the need for very high electron Lorentz factors, which are not expected in internal shocks.

Even though different manifestations of the photospheric emission can explain the data, and lead to ambiguous interpretations, I argue that dissipation below the photosphere is the most important process in shaping the observed spectral shapes and evolutions.


Summary statistics of my publication record:

Number of papers (peer reviewed): 20

H-index: 10

Number of citations: 525