College of Letters & Science

Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/37

The College of Letters and Science, the largest center for learning, teaching and research at Montana State University, offers students an excellent liberal arts and sciences education in nearly 50 majors, 25 minors and over 25 graduate degrees within the four areas of the humanities, natural sciences, mathematics and social sciences.

Browse

Now showing 1 - 2 of 2

A dependable distance estimator to black hole low-mass X-ray binaries
(Oxford University Press, 2024-03) Abdulghani, Y.; Lohfink, A. M.; Chauhan, J.
Black Hole Low Mass X-ray Binaries (BH-LMXBs) are excellent observational laboratories for studying many open questions in accretion physics. However, determining the physical properties of BH-LMXBs necessitates knowing their distances. With the increased discovery rate of BH-LMXBs, many canonical methods cannot produce accurate distance estimates at the desired pace. In this study, we develop a versatile statistical framework to obtain robust distance estimates soon after discovery. Our framework builds on previous methods where the soft spectral state and the soft-to-hard spectral state transitions, typically present in an outbursting BH-LMXB, are used to place constraints on mass and distance. We further develop the traditional framework by incorporating general relativistic corrections, accounting for spectral/physical parameter uncertainties, and employing assumptions grounded in current theoretical and observational knowledge. We tested our framework by analyzing a sample of 50 BH-LMXB sources using X-ray spectral data from the Swift/XRT, MAXI/GSC, and RXTE/PCA missions. By modeling their spectra, we applied our framework to 26 sources from the 50. Comparison of our estimated distances to previous distance estimates indicates that our findings are dependable and in agreement with the accurate estimates obtained through parallax and H i absorption methods. Investigating the accuracy of our constraints, we have found that estimates obtained using both the soft and transition spectral information have a median uncertainty (1σ) of 20%, while estimates obtained using only the soft spectral state spectrum have a median uncertainty (1σ) of around 50%. Furthermore, we have found no instrument-specific biases.
The Sloan Digital Sky Survey Reverberation Mapping Project: UV–Optical Accretion Disk Measurements with the Hubble Space Telescope
(American Astronomical Society, 2022-02) Homayouni, Y.; Sturm, Megan R.; Trump, Jonathan R.; Horne, Keith; Grier, C. J.; Shen, Yue; Brandt, W. N.; Alvarez, Gloria Fonseca; Hall, P. B.; Ho, Luis C.; I-Hsiu Li, Jennifer; Sun, Mouyuan; Schneider, D. P.
We present accretion-disk structure measurements from UV–optical reverberation mapping (RM) observations of a sample of eight quasars at 0.24 < z < 0.85. Ultraviolet photometry comes from two cycles of Hubble Space Telescope monitoring, accompanied by multiband optical monitoring by the Las Cumbres Observatory network and Liverpool Telescopes. The targets were selected from the Sloan Digital Sky Survey Reverberation Mapping project sample with reliable black hole mass measurements from Hβ RM results. We measure significant lags between the UV and various optical griz bands using JAVELIN and CREAM methods. We use the significant lag results from both methods to fit the accretion-disk structure using a Markov Chain Monte Carlo approach. We study the accretion disk as a function of disk normalization, temperature scaling, and efficiency. We find direct evidence for diffuse nebular emission from Balmer and Fe ii lines over discrete wavelength ranges. We also find that our best-fit disk color profile is broadly consistent with the Shakura & Sunyaev disk model. We compare our UV–optical lags to the disk sizes inferred from optical–optical lags of the same quasars and find that our results are consistent with these quasars being drawn from a limited high-lag subset of the broader population. Our results are therefore broadly consistent with models that suggest longer disk lags in a subset of quasars, for example, due to a nonzero size of the ionizing corona and/or magnetic heating contributing to the disk response.