Signature of black hole event horizon in X-ray binary spectra
Abstract
A black hole (BH) lacks a hard surface and is confined by an invisible boundary, an event horizon, a definitive proof of which is a holy grail of modern physics and astronomy. A signature of this horizon could be identified if the X-ray radiation from accreting stellar-mass BHs is compared with that from accreting low magnetized neutron stars (NSs), which have hard surfaces. However, it is difficult to distinguish such a difference from the observation, and hitherto no general method could be established to reliably achieve this goal. In our work, we investigated how the additional X-ray photons emanating from the surface/boundary layer of NSs can affect the Comptonization process in these objects in the hard state, and how such an interaction is manifested on the distribution of the properties of Comptonizing components: the temperature of the electron cloud surrounding the compact object, the Compton y parameter, and the Compton amplification factor A. We analyzed the hard X-ray spectra from 11 accreting black holes and 13 atoll neutron stars (∼ 850 observations) as observed with RXTE/PCA and RXTE/HEXTE instruments, and find that there exists a clear dichotomy in the distributions of these parameters between BHs and NSs. Thus, our findings establish a new method of determining the nature of the compact object in X-ray binaries through broad-band X-ray spectroscopy.
- Publication:
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44th COSPAR Scientific Assembly. Held 16-24 July
- Pub Date:
- July 2022
- Bibcode:
- 2022cosp...44.2190B