Broadband X-ray Polarization of Compact Objects

Background and Motivation :
In last 40 years, X-ray spectroscopy, timing and imaging studies carried out with world class X-ray space observatories such as ASCA, RXTE, Chandra, XMM, NuSTAR, AstroSat, Nicer etc. have provided detailed understanding of compact objects. However, in recent years there is enough
interest in the investiagtion of phyiscs of strong gravity and magnetism at the vicinity of the compact objects through X-ray polarization.

Since 1960, the spectral and timing studies have enhanced our understanding of different astrophysical processes around compact objects. Worldwide many coordinated attempts have been made for simultaneous multi-wavelength and long term temporal and spectral observations. Our understanding have greatly improved with numerous data available with advanced techniques of data analysis. New theoretical models as well as various techniques of analyzing data have been developed. Considering that many models are degenerate with respect to the spectroscopy and timing information, bridging this information with broadband polarimetry in X-rays will greatly enhance the understanding of the physics in strong gravity regime and reduce the degeneracy in the models significantly.

In addition to the above, with AstroSat/CZTI we have gained expertise in polarization studies of GRBs and select X-ray sources. We also have XpoSat, a medium energy polarimetry mission due for launch in the coming year. There are few instruments proposed for near-future X-ray astronomy mission for X-ray polarimetry studies for various compact objects by several institutes across India. Few other international missons for X-ray polarimetry are also been planned in the upcoming years. With all these missions aimed for X-ray polarimetric studies, it is high time to gear up our expertise and interests to involve in various aspects of X-ray Polarimetry and work towards bringing the best out of these opportunities.

With the above motivation, we would like to propose a one day workshop to bring together active researchers working in the field of broadband spectroscopy and polarimetry of compact objects for intense discussions to focus on the future directions for X-ray astronomical research including science and instrumentation.

Goal of the workshop:
Compact objects are considered to be the 'ideal' astrophysical laboratories to test the physics of extreme gravity and magnetism. In view of the motivation, the one day workshop will address the details mentioned here below:

  • Spectro-polarimetry information of the radiation coming from the region of extreme gravity of black hole helps to constrain the mass and spin of black hole.
  • Polarization will provide powerful tool to probe the geometry of accretion flow and effect of strong gravity such light bending, frame-dragging relativistic beaming on radiation and matter close to blackhole.
  • Polarization shows extreme features around vacuum resonance energy and helps understanding QED effects in highly magnetized neutron star systems.
  • Diagnostics of magnetic field geometry in accretion powered pulsars would be easily carried out with spectro-polarimetry in X-rays.
  • Understanding of jet emission mechanism and collimation of jets from stellar mass and supermassive black holes is expected to be greatly improved with X-ray polarimetry and broadband spectroscopic observations.

In view of the above points, we propose to have the one-day workshop towards intense discussions
on X-ray spectropolarimetry of compact objects.

Tentative number of Participants: ~50

Probable list of speakers:

  1. Biswajit Paul, RRI
  2. Santosh Vadawale, PRL
  3. Vivek Kumar Agrawal, SAG
  4. Ankur Kushwaha, SAG
  5. Vikram Rana, RRI
  6. Sachindra Naik, PRL
  7. Anuj Nandi, SAG
  8. M.C. Ramadevi, SAG
  9. Gulab Dewangan, IUCAA
  10. Sudip Bhattacharya, TIFR
  11. Ranjeev Misra, IUCAA
  12. Sameer Mandal, IIST
  13. Mithun, PRL
  14. Mohammad Hasan, ISRO HQ

Proposers:Space Astronomy Group, URSC, Bangalore