Testing the Kerr black hole hypothesis with GRS 1716-249 by combining the continuum-fitting and the iron-line methods

Abstract

The continuum-fitting and the iron-line methods are currently the two leading techniques for measuring the spins of accreting black holes. In the past few years, these two methods have been developed for testing fundamental physics. In the present work, we employ state-of-the-art models to test black holes through the continuum-fitting and the iron-line methods and we analyze three NuSTAR observations of the black hole binary GRS 1716-249 during its outburst in 2016-2017. In these three observations, the source was in a hard-intermediate state and the spectra show both a strong thermal component and prominent relativistic reflection features. Our analysis confirms the Kerr nature of the black hole in GRS 1716-249 and provides quite stringent constraints on possible deviations from the predictions of general relativity.

Testing the Kerr black hole hypothesis with the continuum-fitting and the iron line methods: the case of GRS 1915+105

“…Our goal is to test the Kerr hypothesis by combining the study of the thermal component and the reflection features. We note that similar studies were reported in Tripathi et al (2021a) and in Zhang et al (2021). Tripathi et al (2021a) analyzed a NuSTAR observation of GX 339-4 in which spectrum simultaneously shows a strong thermal component and prominent reflection features.…”

“…This constraint is somewhat weaker than the typical constraints obtained from the analysis of the reflection features with relxill nk; see, e.g., Tab. 5 in Zhang et al (2021). However, it is stronger than the constraint on α 13 inferred by the study of the thermal spectrum of LMC X-1 with nkbb in Tripathi et al (2020b).…”

“…However, the BH mass and the distance of the source are not known for GX 339-4, so they were inferred in the fit and we cannot really speak of the continuum-fitting method. Zhang et al (2021) analyzed three NuSTAR observations of the BH in GRS 1716-249 in the hard-intermediate state where, again, we simultaneously see a strong thermal spectrum and prominent reflection features. For GRS 1716-249, the distance is known, while for the BH mass we only -Constraints on the BH spin parameter a * and the deformation parameter α 13 from the individual fits of the five RXTE observations of GRS 1915+105 (R1, R2, R3, R4, and R5) and from the fit of all observations together (R1-R5, bottom-right panel).…”

Constraining the Konoplya-Rezzolla-Zhidenko deformation parameters II: limits from stellar-mass black hole X-ray data

“…The constraints inferred from the 2019 NuSTAR observation of EXO 1846-031 are among the most stringent ones. Slightly stronger constraints can be obtained from three sources in which it is possible to combine the analysis of the reflection features with that of the thermal spectrum: GRS 1716-249 [49], GRS 1915+105 [48], and GX 339-4 [22]. As discussed in Ref.…”

Constraining the Konoplya-Rezzolla-Zhidenko deformation parameters III: limits from stellar-mass black holes using gravitational-wave observations

“…To test GR as a theory of gravity, one of the approaches is to use a parametrized metric and measure possible deviations from the solution of Einstein equations such as the Kerr solution [5][6][7][8]. In the past few years, there have been a number of studies testing the Kerr hypothesis [9] by using X-ray data from NuSTAR, RXTE, Suzaku, and XMM-Newton [10][11][12][13][14][15], GW data from LIGO and Virgo [16][17][18], and radio data from the Event Horizon Telescope (EHT) experiment [18][19][20][21].…”