Iron Kα line of boson stars

Abstract

Abstract. The present paper is a sequel to our previous work [Y. Ni et al., JCAP 1607, 049 (2016] in which we studied the iron Kα line expected in the reflection spectrum of Kerr black holes with scalar hair. These metrics are solutions of Einstein's gravity minimally coupled to a massive, complex scalar field. They form a continuous bridge between a subset of Kerr black holes and a family of rotating boson stars depending on one extra parameter, the dimensionless scalar hair parameter q, ranging from 0 (Kerr black holes) to 1 (boson stars). Here we study the limiting case q = 1, corresponding to rotating boson stars. For comparison, spherical boson stars are also considered. We simulate observations with XIS/Suzaku. Using the fact that current observations are well fit by the Kerr solution and thus requiring that acceptable alternative compact objects must be compatible with a Kerr fit, we find that some boson star solutions are relatively easy to rule out as potential candidates to explain astrophysical black holes, while other solutions, which are neither too dilute nor too compact are more elusive and we argue that they cannot be distinguished from Kerr black holes by the analysis of the iron line with current X-ray facilities.

Testing conformal gravity with astrophysical black holes

“…A rough estimate of the maximum value of L allowed by current X-ray data can be obtained quite easily following the method already employed in Refs. [33][34][35][36]. We know that current X-ray data are consistent with the Kerr metric, in the sense that observations are fitted with theoretical Kerr model and we obtain acceptable fits.…”

Testing Einstein-dilaton-Gauss-Bonnet gravity with the reflection spectrum of accreting black holes

“…[48][49][50][51][52][53] to study the possibility of testing a number of non-Kerr metrics. We simulate an observation with a specific instrument employing the iron line calculated in the non-Kerr metric, and we fit the simulated data with the iron line of a Kerr model.…”

Iron Kα line of Proca stars

“…In this letter, we have extended previous work on Kerr BHs with scalar hair [1] and boson stars [2] to the case of the Proca star solutions found in Ref. [3].…”

“…We instead follow the strategy already employed in Refs. [1,2,31,32], which permits to get quickly a rough estimate of current constraints. The key point is that current observations are consistent with the Kerr metric, in the sense that X-ray data are normally fitted with reflection spectra computed in the Kerr metric and the result is acceptable.…”