Pulsars, transients and relativistic astrophysics

Abstract:

We propose the development of X-ray interferometry (XRI), to reveal the Universe at high energies with ultra-high spatial resolution. With baselines which can be accommodated on a single spacecraft, XRI can reach 100 μ as resolution at 10 Å (1.2 keV) and 20 μ as at 2 Å (6 keV), enabling imaging and imaging-spectroscopy of (for example) X-ray coronae of nearby accreting supermassive black holes (SMBH) and the SMBH ‘shadow’; SMBH accretion flows and outflows; X-ray binary winds and orbits; stellar coronae within ∼ 100 pc and many exoplanets which transit across them. For sufficiently luminous sources XRI will resolve sub-pc scales across the entire observable Universe, revealing accreting binary SMBHs and enabling trigonometric measurements of the Hubble constant with X-ray light echoes from quasars or explosive transients. A multi-spacecraft ‘constellation’ interferometer would resolve well below 1 μ as, enabling SMBH event horizons to be resolved in many active galaxies and the detailed study of the effects of strong field gravity on the dynamics and emission from accreting gas close to the black hole.

Abstract:

We describe the scientific potential of a Soft X-ray Imager (SXI) onboard the ESA–CAS satellite SMILE to study the activity of cosmic X-ray sources in the soft X-ray region and located in the fields planned to be observed by SXI. We used the 2–3 keV band flux of the monitor MAXI/ISS, covering at least part of the expected band of the SXI/SMILE telescope. We discuss how SXI can contribute to this branch and how combining the SXI/SMILE data with those obtained by other satellites on the same days can be helpful if the light curves of the 1-day means are used. We show these possibilities on several examples of cosmic X-ray sources (Vela X-1 and GROJ1008-57 containing neutron stars accreting matter from their companions) in the field of view of SXI. Including observations from MAXI/ISS and BAT/Swift will enable extending the coverage to the energy of 50 keV

Abstract:

AbstractX-ray polarimetry has long been considered the ‘holy grail’ of X-ray astronomy. Fortunately, after a silence of more than 40 years, the field is now rejuvenating. In fact, an X-ray polarimeter onboard a Cube-sat nano-satellite has been recently successfully operated. IXPE, the Imaging X-ray Polarimetry Explorer, will be launched in 2021 while eXTP, containing a larger version of IXPE, is expected to be launched in 2027. Although at present it is difficult to predict the discoveries that, given their exploratory nature, IXPE and eXTP will obtain, the path for a follow-up mission can already be envisaged. In this paper we describe the scientific goals of such a follow-up mission, and present a medium-size mission profile that can accomplish this task.