Browsing by Author "Xue, Y. Q."

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    Probing a magnetar origin for the population of extragalactic fast X-ray transients detected by Chandra
    (2024) Quirola-Vasquez, J.; Bauer, F. E.; Jonker, P. G.; Brandt, W. N.; Eappachen, D.; Levan, A. J.; Lopez, E.; Luo, B.; Ravasio, M. E.; Sun, H.; Xue, Y. Q.; Yang, G.; Zheng, X. C.
    Context. Twenty-two extragalactic fast X-ray transients (FXTs) have now been discovered from two decades of Chandra data (analyzing similar to 259 Ms of data), with 17 associated with distant galaxies (greater than or similar to 100 Mpc). Different mechanisms and progenitors have been proposed to explain their properties; nevertheless, after analyzing their timing, spectral parameters, host -galaxy properties, luminosity function, and volumetric rates, their nature remains uncertain. Aims. We interpret a sub -sample of nine FXTs that show a plateau or a fast -rise light curve within the framework of a binary neutron star (BNS) merger magnetar model. Methods. We fit their light curves and derive magnetar (magnetic field and initial rotational period) and ejecta (ejecta mass and opacity) parameters. This model predicts two zones: an orientation -dependent free zone (where the magnetar spin -down X-ray photons escape freely to the observer) and a trapped zone (where the X-ray photons are initially obscured and only escape freely once the ejecta material becomes optically thin). We argue that six FXTs show properties consistent with the free zone and three FXTs with the trapped zone. Results. This sub -sample of FXTs has a similar distribution of magnetic fields and initial rotation periods to those inferred for short gamma -ray bursts, suggesting a possible association. We compare the predicted ejecta emission fed by the magnetar emission (called merger -nova) to the optical and near -infrared upper limits of two FXTs, XRT 141001 and XRT 210423 where contemporaneous optical observations are available. The non -detections place lower limits on the redshifts of XRT 141001 and XRT 210423 of z greater than or similar to 1.5 and greater than or similar to 0.1, respectively. Conclusions. If the magnetar remnants lose energy via gravitational waves (GWs), it should be possible to detect similar objects with the current advanced LIGO detectors out to a redshift z less than or similar to 0.03, while future GW detectors will be able to detect them out to z approximate to 0.5.
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    THE 4 Ms CHANDRA DEEP FIELD-SOUTH NUMBER COUNTS APPORTIONED BY SOURCE CLASS: PERVASIVE ACTIVE GALACTIC NUCLEI AND THE ASCENT OF NORMAL GALAXIES
    (2012) Lehmer, B. D.; Xue, Y. Q.; Brandt, W. N.; Alexander, D. M.; Bauer, F. E.; Brusa, M.; Comastri, A.; Gilli, R.; Hornschemeier, A. E.; Luo, B.; Paolillo, M.; Ptak, A.; Shemmer, O.; Schneider, D. P.; Tozzi, P.; Vignali, C.
    We present 0.5-2 keV, 2-8 keV, 4-8 keV, and 0.5-8 keV (hereafter soft, hard, ultra-hard, and full bands, respectively) cumulative and differential number-count (log N-log S) measurements for the recently completed approximate to 4 Ms Chandra Deep Field-South (CDF-S) survey, the deepest X-ray survey to date. We implement a new Bayesian approach, which allows reliable calculation of number counts down to flux limits that are factors of approximate to 1.9-4.3 times fainter than the previously deepest number-count investigations. In the soft band (SB), the most sensitive bandpass in our analysis, the approximate to 4 Ms CDF-S reaches a maximum source density of approximate to 27,800 deg(-2). By virtue of the exquisite X-ray and multiwavelength data available in the CDF-S, we are able to measure the number counts from a variety of source populations (active galactic nuclei (AGNs), normal galaxies, and Galactic stars) and subpopulations (as a function of redshift, AGN absorption, luminosity, and galaxy morphology) and test models that describe their evolution. We find that AGNs still dominate the X-ray number counts down to the faintest flux levels for all bands and reach a limiting SB source density of approximate to 14,900 deg(-2), the highest reliable AGN source density measured at any wavelength. We find that the normal-galaxy counts rise rapidly near the flux limits and, at the limiting SB flux, reach source densities of approximate to 12,700 deg(-2) and make up 46% +/- 5% of the total number counts. The rapid rise of the galaxy counts toward faint fluxes, as well as significant normal-galaxy contributions to the overall number counts, indicates that normal galaxies will overtake AGNs just below the approximate to 4 Ms SB flux limit and will provide a numerically significant new X-ray source population in future surveys that reach below the approximate to 4 Ms sensitivity limit. We show that a future approximate to 10 Ms CDF-S would allow for a significant increase in X-ray-detected sources, with many of the new sources being cosmologically distant (z greater than or similar to 0.6) normal galaxies.
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    THE CHANDRA DEEP FIELD-SOUTH SURVEY: 7 MS SOURCE CATALOGS
    (2017) Luo, B.; Brandt, W. N.; Xue, Y. Q.; Lehmer, B.; Alexander, D. M.; Bauer, Franz Erik; Vito, F.; Yang, G.; Basu-Zych, A. R.; Comastri, A.
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    Tracing the accretion history of supermassive black holes through X-ray variability: results from the Chandra Deep Field-South
    (2017) Paolillo, M.; Papadakis, I.; Brandt, W. N.; Luo, B.; Xue, Y. Q.; Tozzi, P.; Shemmer, O.; Allevato, V.; Bauer, Franz Erik; Comastri, A.