Search for traversable wormholes in active galactic nuclei using x-ray data

In a previous paper, one of us calculated iron $\mathrm{K}\alpha$ line profiles emitted from possible accretion disks around traversable wormholes as a first step to use x-ray reflection spectroscopy to search for astrophysical wormholes in active galactic nuclei. In the present paper, we extend that work and construct an XSPEC model for the whole relativistic reflection spectrum. We apply our model to XMM-Newton and NuSTAR observations of the supermassive object in MCG-6-30-15 and we check whether these observations prefer the hypothesis that the central body is a Kerr black hole or a traversable wormhole. We find that the two models provide equally good fits, so with the available data we cannot distinguish the black hole and wormhole scenarios.

Figure 1

Grid points in the FITS file of the wormhole model for the spin parameter $a_{*}$ and the parameter $\gamma$. See the text for more details.

Figure 2

Iron line profiles in wormhole spacetime. The viewing angle of the observer is $i=20°$ (left panel) and $i=60°$ (right panel). The value of the spin parameter is $a_{*}=0$ (black line), 0.01 (red line), 0.1 (green line), 0.3 (blue line), and 0.8 (magenta line). The emissivity index of the intensity profile is always $q=3$.

Figure 3

Iron line profiles in Kerr spacetime. The viewing angle of the observer is $i=20°$ (left panel) and $i=60°$ (right panel). The value of the spin parameter is $a_{*}=0.4$ (black line), 0.8 (red line), 0.9 (green line), 0.95 (blue line), and 0.998 (magenta line). The emissivity index of the intensity profile is always $q=3$.

Figure 4

Constraints on the spin parameter $a_{*}$ and the parameter $\gamma$ from the fit of the wormhole model. The red, green, and blue curves correspond, respectively, to the 68%, 90%, and 99% confidence level limits for two relevant parameters ($\mathrm{\Delta }{\chi }^2=2.30$, 4.61, and 9.21, respectively).

Figure 5

Light curves and flux states for XMM-Newton/EPIC-Pn (0.5–10 keV), and NuSTAR/FPMA and NuSTAR/FPMB (3–80 keV). The three dashed horizontal lines separate the four different flux states.

Figure 6

Black hole model: Spectra of the best-fit models and ratios between the data and the best-fit model for the low-flux state (top left panel), medium-flux state (top right panel), high-flux state (bottom left panel), and very high-flux state (bottom right panel). In the spectra, the black curve is for the total spectrum, the blue curve is for the coronal component (cutoffpl), the red curve is for the relativistic reflection component (relxill), the green curve is for the nonrelativistic reflection component (xillver), and the magenta curve is for narrow emission lines (zgauss). In the ratio plots, the red crosses are used for XMM-Newton, the green crosses for NuSTAR/FPMA, and the blue crosses for NuSTAR/FPMB.

Figure 7

Wormhole model: Spectra of the best-fit models and ratios between the data and the best-fit model for the low-flux state (top left panel), medium-flux state (top right panel), high-flux state (bottom left panel), and very high-flux state (bottom right panel). In the spectra, the black curve is for the total spectrum, the blue curve is for the coronal component (cutoffpl), the red curve is for the relativistic reflection component (see Sec. 2), the green curve is for the nonrelativistic reflection component (xillver), and the magenta curve is for narrow emission lines (zgauss). In the ratio plots, the red crosses are used for XMM-Newton, the green crosses for NuSTAR/FPMA, and the blue crosses for NuSTAR/FPMB.