Special Talk

• Special Talks

  Speaker: Chris Nagele (JHU)
  Title: Predicting X-ray Spectra of Accreting Black Holes from Simulation​​​​​​​
  Abstract: In recent decades, extensive observing campaigns have targeted X-ray sources believed to be stellar mass or supermassive black holes accreting material in the radiatively efficient regime. In parallel, GRMHD simulations of ever increasing sophistication have been developed in order to model this process of black hole accretion. To date, however, relatively few attempts have been made to compare these two campaigns given that many simulations lack radiative cooling, and those that include it have mostly grey opacity, which is of limited use for comparison to X-ray spectra. We have developed a post-processing scheme which can relate simulation to observation by outputting optical to X-ray spectra of simulation snapshots. We have recently extended this technique from stellar masses up to the supermassive, and we present spectra spanning seven orders of magnitude in black hole mass. We discuss the hard Compton power law and reflection features such as Fe-Kalpha and the 'soft X-ray excess'. We also show preliminary results related to accreting SMBH binaries, systems which are targets of current and future gravitational wave observatories.

  Speaker: Francesco Iacovelli (JHU)​​​​​​​
  Title: Prospects of Bright-Siren Cosmology at Third-Generation Gravitational-Wave Detectors​​​​​​​
  Abstract: The direct detection of gravitational waves in 2015, thanks to the LIGO and Virgo interferometers, opened a new window on our Universe. The discoveries during the first three observing runs already had an extraordinary impact on astrophysics, cosmology, and fundamental physics, and the fourth run is ongoing. The gravitational-wave community is now looking at the next long-prepared step: 'third-generation' detectors. Thanks to an increase of more than one order of magnitude in sensitivity and a larger bandwidth, Einstein Telescope and Cosmic Explorer will have an outstanding potential, capable of triggering fundamental discoveries. I will focus on the most direct technique to exploit gravitational-wave detectors to learn about the evolution of our Universe: 'bright sirens'. I will review the basics of the bright siren method, which exploits gravitational-wave detections with an associated electromagnetic counterpart, and discuss some of its subtleties. I will then present recent forecasts on the prospects of observing such multi-messenger events with different kinds of counterparts at future instruments, and how they will allow us to reconstruct cosmological parameters and modified gravity to exquisite accuracy.