Browsing by Author "Torres, M. A.P."

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An arcsecond view at 1-2 GHz into the Galactic Bulge
(2024) Pattie, E. C. (TTU); Maccarone, T. J. (TTU); Britt, C. T.; Heinke, C. O.; Jonker, P. G.; Lorimer, D. R.; Sivakoff, G. R.; Steeghs, D.; Strader, J.; Torres, M. A.P.; Wijnands, R.
We present the results of a high angular resolution (1.1 arcsec) and sensitivity (maximum of ∼0.1 mJy) radio survey at 1-2 GHz in the Galactic Bulge. This complements the X-ray Chandra Galactic Bulge Survey, and investigates the full radio source population in this dense Galactic region. Radio counterparts to sources at other wavelengths can aid in classification, as there are relatively few types of objects that are reasonably detectable in radio at kiloparsec distances, and even fewer that are detected in both X-rays and radio. This survey covers about 3 sq deg of the Galactic Bulge Survey area (spanning the Galactic coordinate range of -3° < l < +3° and +1.6° < b < +2.1°) as a first look into this region of the Galaxy with this combination of frequency, resolution, and sensitivity. Spectral indices within the observed band of 1-2 GHz were calculated for each source to assist in determining its emission mechanism. We find 1617 unique sources in the survey, 25 of which are radio counterparts to X-ray sources, and about 100 of which are steep-spectrum (α ≲ -1.4) point sources that are viable pulsar candidates. Four radio sources are of particular interest: a compact binary; an infrared transient with an inverted radio spectrum; a potential transitional millisecond pulsar candidate; and a very steep spectrum radio source with an X-ray and bright infrared counterpart. We discuss other notable sources, including possible radio transients, potential new planetary nebulae, and active galactic nuclei.
An infrared FWHM K 2 correlation to uncover highly reddened quiescent black holes
(2023) Cúneo, V. A.; Casares, J.; Armas Padilla, M.; Sánchez-Sierras, J.; Corral-Santana, J. M.; MacCarone, T. J. (TTU); Mata Sánchez, D.; Muñoz-Darias, T.; Torres, M. A.P.; Vincentelli, F.
Among the sample of Galactic transient X-ray binaries (SXTs) discovered to date, about 70 have been proposed as likely candidates to host a black hole. Yet, only 19 have been dynamically confirmed. Such a reliable confirmation requires phase-resolved spectroscopy of their companion stars, which is generally feasible when the system is in a quiescent state. However, since most of the SXT population lies in the galactic plane, which is strongly affected by interstellar extinction, their optical brightness during quiescence usually falls beyond the capabilities of the current instrumentation (R ³ 22). To overcome these limitations and thereby increase the number of confirmed Galactic black holes, a correlation between the full-width at half maximum (FWHM) of the Hα line and the semi-amplitude of the donor's radial velocity curve (K2) was presented in the past. Here, we extend the FWHM K2 correlation to the near-infrared (NIR), exploiting disc lines such as HeIλ10830, Paγ, and Brγ, in a sample of dynamically confirmed black-hole SXTs. We obtain K2 = 0.22(3) FWHM, in good agreement with the optical correlation derived using Hα. The similarity of the two correlations seems to imply that the widths of Hα and the NIR lines are consistent in quiescence. When combined with information on orbital periods, the NIR correlation allows us to constrain the mass of the compact object of systems in quiescence by using single-epoch spectroscopy. We anticipate that this new correlation will give access to highly reddened black hole SXTs, which cannot be otherwise studied at optical wavelengths.