Constraints on the dark mass distribution surrounding Sgr A*: simple $\chi^2$ analysis for the redshift of photons from orbiting stars
Abstract
Sagittarius A* (Sgr A*) is the central supermassive black hole with the mass $\sim 4\times 10^6 M_{\odot}$ in the Milky Way and stars are orbiting around it. In May 2018, one of the nearest stars to Sgr A* named S02/S2 experienced the pericenter passage. The redshift of photons from S02 had varied from $4000\>{\rm km\>s^{1}}$ to $2000\>{\rm km\>s^{1}}$ during the pericenter passage, which is within $0.5\>{\rm yr}$. In this paper, we show that this steep variation of the redshift gives a strong constraint on a dark mass distribution inside the orbit of S02. By applying a simple $\chi^2$ analysis to the observed redshift, we can easily distinguish between the two models, the point mass model and the point mass plus an extended mass model without the bestfitting parameter search. Our redshift data during the pericenter passage in 2018 with Subaru/IRCS bound the amount of the extended mass inside the orbit of S02 less than $0.5\,\%$ ($\sim 2 \times 10^4 M_\odot$) of the mass of Sgr A*. This constraint obtained by our simple analysis is comparable to previous works with the bestfitting parameter search to the motion of S02 including the effect of the extended mass. We consider both the powerlaw and the Plummer models for the dark mass distribution model, but the significant difference between these results is not found.
 Publication:

arXiv eprints
 Pub Date:
 June 2020
 arXiv:
 arXiv:2006.06219
 Bibcode:
 2020arXiv200606219T
 Keywords:

 Astrophysics  Astrophysics of Galaxies;
 General Relativity and Quantum Cosmology
 EPrint:
 10 pages, 9 figures, 2 tables