X-Ray Scaling for SMBH Mass of NGC4151

In the case of heavily obscured or inclined AGN, direct dynamical methods fail and a new measurement technique must be used. Employment of x-ray wavelength spectral modelling yield highly accurate replication of observed continuum. These models can be either physically or phenomenologically motivated and both can produce equally accurate products. Fitting parameters that are certain (i.e., cosmological element abundance) are fixed within the model, and uncertain variables are allowed to “walk” as a function of the Monte Carlo Markov Chain simulation to provide insight into the specific AGN structure. The walking variables settle into values that most closely resemble required values to approximate the observed spectrum. Once the high-fidelity model is attained, the black hole mass can be directly computed from the continuum model. For the target NGC 4151 this method yielded values within 2-3times M☉ which is consistent with values attained in literature via primary methods. From comparison with dynamical methods, our independent reproduction of a similar mass indicates the x-ray scaling method could be employed to more secluded or poorly studied AGN. Ideally more targets that have existing dynamically calculated black hole masses will be used to further corroborate these findings.

Title slide – Hello, My name is Kyle Bockwoldt and I am a Senior Undergraduate Physics Major with Astrophysics Concentration at George Mason University. This is my spring 2022 OSCAR URSP research project involving Xray Scaling to determine Supermassive black hole mass in AGN NGC4151. Working alongside my mentor Dr Mario Gliozzi and group member James Williams. Slide 2 – So Active Galactic Nuclei, or AGN, are structures at the centers of galaxies. They have supermassive black holes in their centers which gravitationally bind the galaxy together. Constraining the mass of a black hole is imperative because it alone can tell you crucial details about the black hole system like its gravitational radius, or how strong its pull is. Interactions between the black hole and its surroundings produce astrophysically distinct and highly penetrating X-rays that we can reproducibly see from far distances. In the case of AGN that are far away or visually obscured, we can’t determine the mass with traditional methods, or primary methods as they’re known motivating us to further develop the X-ray scaling method which works in cases where primary methods fail. Slide 3 – In order to do this, we need X-rays! So we used archival observations from the Nuclear Spectroscopic Telescope Array, or NuSTAR, from the NASA HEASARC database. We chose 3 observation ID’s of an AGN called NGC4151, and processed the data on a GMU computer server called BGC01. Slide 4 – This is an example of what those observations actually look like, where there are 2 images per observation due to NuSTAR’s 2 parallel instrument panels. Slide 6 – And here on top we have a visual representation of our observed data overlayed with the model. Here in the higher energies, you can see the model line is so close to the data that its entirely consumed by the data points. Below that we have another representation of how close our model and data are, with commensurately large errors in the upper regime due to the high energy photon’s intrinsically larger propagated errors. The tighter these points are to a ratio of 1, the better our model performed. Slide 7 – Here we have the same data on top as before but also we have a visual display of the individual model components and their corresponding energies. Slide 5 – Here is an example of one of the two models we implemented to explain the X-ray Spectra we observed. At the top here we can see the model and its parameters and boxed in here at the bottom we see our reduced chi squared of 1.02 for this particular fit, which is pretty close to that of the other observations and indicates our model closely represents the observation. Slide 8 – So once we have our X-ray spectra fitted, we save the BMC normalization and a quantity called the Photon Index, which is this capital symbol Gamma here, which indicates how much the AGN is accreting at a given time, and we plug it into these equations along with those same parameters of a reference black hole to get our calculated mass. These equations precipitate out of assumed symmetries between all black holes, that is if they have a certain mass, they should behave in the same ways proportionate to how much larger the target is relative to the reference in X-ray production. Slide 9 – As a validation of the fidelity of the scaling method, here we compare our masses on the right to that of previous works using primary methods on the left. A good sign is that these are close enough to agree within a factor of 2-3 to that of the primary methods. This shows that our method is in agreement with prior calculations for this target. Slide 10 – Of course I would like to thank my Mentor Dr Mario Gliozzi, our group member James Williams, GMU OSCAR for funding the project, as well as Justin Brown from the GMU Physics IT Department for his support as well as Dr Karen Lee. Thanks so much, I hope you enjoyed!