Testing general relativity with X-ray reflection spectroscopy of MCG-06-30-15 Ashutosh Tripathi Fudan University 3 rd Karl Schwarzschild Meeting , 25 th July 2017 Ashutosh Tripathi Testing general relativity with X-ray reflection spectroscopy
Introduction The theory of general relativity has been proposed by Albert Einstein in 1915 and is the standard explanation for the dynamics of spacetime. It has been tested many times in the last 60 years with experiments in Solar system and radio observations of Pulsars. Recently, there have been new methods to test this theory using electromagnetic radiation and gravitational waves. In order to test the general relativity, strong gravity region is required in which the effect can be quantified. In universe, there exist black holes which can be used to test the strong gravity. Ashutosh Tripathi Testing general relativity with X-ray reflection spectroscopy
According to the theory, an uncharged black hole is described by the Kerr solution and only two parameters (mass M and angular momentum J ) are required for complete quantification. Although within Einstein’s gravity, the Kerr metric should describe the spacetime around black hole, deviations from Kerr solutions are also possible. The electromagnetic approach analyzed the properties of electromagnetic radiation from the accretion disk close to black hole. It depends on the gas motion in strong gravity region and the photon propagation from the emission point in the disk to the faraway region where the spacetime is almost flat. Ashutosh Tripathi Testing general relativity with X-ray reflection spectroscopy
Electromagnetic Approach to Test General Relativity There are two leading techniques to probe the strong gravity region. Continuum fitting method 1 Reflection method 2 Both the techniques assume Kerr black hole and can be extended to study the deviation from Kerr metric. Reflection method involves the analysis of relativistically smeared reflection spectrum of thin accretion disk. It can be easily applied to both stellar mass black hole and supermassive black hole. It is independent of the black hole mass and distance. Ashutosh Tripathi Testing general relativity with X-ray reflection spectroscopy
Black Hole Geometry Ashutosh Tripathi Testing general relativity with X-ray reflection spectroscopy
Theoretical Models for X-ray reflection XILLVER provides the detailed treatment of K-shell atomic properties of ionized ions. RELCONV is the relativistic convolution code that gives the spectrum measured by distant observer given the local spectrum at any emission point in the disk assuming the Kerr metric. RELXILL is the combination of RELCONV and XILLVER. It describes the relativistic smearing of X-ray reflection spectrum. RELXILL NK is the extension of RELXILL to Johannsen metric of which Kerr metric is the special case. Ashutosh Tripathi Testing general relativity with X-ray reflection spectroscopy
MCG-06-30-15 MCG-06-30-15 is a narrow line Seyfert 1 (NLS1) galaxy situated at a distance of 37 Mpc ( z = 0 . 008) There has been detection of relativistic effects in the X-ray emission line (iron K α line) from ionized iron in the source. It is believed to be originated from the innermost region of the accretion disk. The relativistic broadening of the iron line can be a potential probe to study the deviation from Kerr metric. The data analyzed is one of the longest observation of this source (350 ks) by XMM-Newton during July-August 2001. Ashutosh Tripathi Testing general relativity with X-ray reflection spectroscopy
Data used (ratioed against power law) data and folded model 1 normalized counts s −1 keV −1 0.1 0.01 1.2 1 ratio 0.8 2 5 Energy (keV) Ashutosh Tripathi Testing general relativity with X-ray reflection spectroscopy
Parameters for Relxill NK Name Description emissivity index for r < Rbr , where emissivity is r − Index 1 Index 1 emissivity index for r > Rbr , where emissivity is r − Index 2 Index 2 radius where emissivity changes from Index1 to Index2 Rbr a spin of the object Incl inclination angle measured w.r.t. normal of the disk Inner radius of the disk Rin Rout Outer radius of the disk redshift of the source z Power law Index of the primary source ( E − Γ ) gamma (Γ) ionization parameter at the inner edge of the disk log ξ Afe Iron abundance in solar units Cut off energy of the input spectrum Ecut defpar deformation parameter α 13 Ashutosh Tripathi Testing general relativity with X-ray reflection spectroscopy
Warm Absorber Warm absorbers are the ionized absorbing gas within Active Galactic Nuclei. They contain a rich forest of lines and edges from various species of gas and dust. They incorporate several ”zones” of materials, distinct in their kinematic properties as well their column densities and ionizations, but maintained in pressure balance. XSTAR spectral synthesis package for photoionized gases is used to construct a grid of warm absorbers as a function of column density and ionization parameter. They are multiplicative models i.e., they are the absorber models that can be applied to any emission spectrum Ashutosh Tripathi Testing general relativity with X-ray reflection spectroscopy
Model used The model reads in xspec as follows: TBABS*WARMABS1*WARMABS2*(RELXILL NK) Relxill NK models the power law continuum and reflection component from the region near black hole and take into account the relativistic smearing of iron line. XILLVER accounts for the reflection from the disk away from the black hole where relativistic effects are not prominent. WARMABS1 and WARMABS2 are the two warm absorbers used to model the ionized gas around the source. TBABS models the galactic absorption. Emissivity index Index 2 and Iron abundance Afe is frozen. Ashutosh Tripathi Testing general relativity with X-ray reflection spectroscopy
Best fit model data and folded model normalized counts s −1 keV −1 1 0.1 0.01 1.1 1 ratio 0.9 5 sign(data−model) × ∆ χ 2 0 −5 2 5 Energy (keV) Ashutosh Tripathi Testing general relativity with X-ray reflection spectroscopy ashutoshtripathi 20−Jul−2017 11:53
( χ 2 Best Fit Parameters red = 1 . 04) Components Parameters Best fit value N H (10 22 ) TBABS 0.29 ± 0.06 N H (10 22 ) 0.24 ± 0.11 WARMABS1 log ξ 1.40 ± 0.34 N H (10 22 ) 0.40 ± 0.27 WARMABS2 log ξ 2.47 ± 0.27 Index 1 2.3 ± 0.28 76.60 ± 121.18 R br a 0.92 ± 0.12 i ( deg ) 3.6 ± 35.8 RELXILL NK Γ 1.98 ± 0.03 log ( ξ refl ) 3.34 ± 0.04 Refl frac 1.72 ± 0.57 -2.43 ± 0.07 defpar Ashutosh Tripathi Testing general relativity with X-ray reflection spectroscopy
Confidence Ellipses in spin-defpar plane 3 2 1 0 -1 13 -2 -3 -4 -5 -6 -7 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 a * Ashutosh Tripathi Testing general relativity with X-ray reflection spectroscopy
Summary and Future Work We present constraints on deformation parameter α 13 using long XMM-Newton observation of MCG-06-30-15. Other deformation parameters can also be included in the RELXILL NK and can be constrained. Other sources can be analyzed in order to have better constraints on deformation parameters. Future X-ray missions like ATHENA and LAD/eXTP can be proved useful in constraining possible deviations from the Kerr metric. Ashutosh Tripathi Testing general relativity with X-ray reflection spectroscopy
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