ORCID Profile
0000-0001-5802-6041
Current Organisation
University of Michigan
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Publisher: Oxford University Press (OUP)
Date: 11-01-2010
Publisher: American Astronomical Society
Date: 12-11-2009
Publisher: Oxford University Press (OUP)
Date: 24-09-2014
Publisher: Oxford University Press (OUP)
Date: 26-06-2019
Abstract: We report on Atacama Large Millimeter Array (ALMA) continuum observations of the black hole X-ray binary A0620–00 at an X-ray luminosity nine orders of magnitude sub-Eddington. The system was significantly detected at 98 GHz (at 44 ± 7 $\\mu$Jy) and only marginally at 233 GHz (20 ± 8 $\\mu$Jy), about 40 d later. These results suggest either an optically thin sub-mm synchrotron spectrum, or highly variable sub-mm jet emission on month time-scales. Although the latter appears more likely, we note that, at the time of the ALMA observations, A0620–00 was in a somewhat less active optical-IR state than during all published multiwavelength c aigns when a flat-spectrum, partially self-absorbed jet has been suggested to extend from the radio to the mid-IR regime. Either interpretation is viable in the context of an internal shock model, where the jet’s spectral shape and variability are set by the power density spectrum of the shells’ Lorentz factor fluctuations. While strictly simultaneous radio–mm-IR observations are necessary to draw definitive conclusions for A0620–00, the data presented here, in combination with recent radio and sub-mm results from higher luminosity systems, demonstrate that jets from black hole X-ray binaries exhibit a high level of variability – either in flux density or intrinsic spectral shape, or both – across a wide spectrum of Eddington ratios. This is not in contrast with expectations from an internal shock model, where lower jet power systems can be expected to exhibit larger fractional variability owing to an overall decrease in synchrotron absorption.
Publisher: Oxford University Press (OUP)
Date: 06-2008
Publisher: Oxford University Press (OUP)
Date: 11-11-2011
Publisher: American Astronomical Society
Date: 04-2022
Abstract: We present ultraviolet spectroscopy covering the Ly α + N v complex of six candidate low-redshift (0.9 z 1.5) weak emission-line quasars (WLQs) based on observations with the Hubble Space Telescope. The original systematic searches for these puzzling Type 1 quasars with intrinsically weak broad emission lines revealed an N ≈ 100 WLQ population from optical spectroscopy of high-redshift ( z 3) quasars, defined by a Ly α + N v rest-frame equivalent width (EW) threshold .4 Å. Identification of lower-redshift ( z 3) WLQ candidates, however, has relied primarily on optical spectroscopy of weak broad emission lines at longer rest-frame wavelengths. With these new observations expanding existing optical coverage into the ultraviolet, we explore unifying the low- and high- z WLQ populations via EW[Ly α +N v ]. Two objects in the s le unify with high- z WLQs, three others appear consistent with the intermediate portion of the population connecting WLQs and normal quasars, and the final object is consistent with typical quasars. The expanded wavelength coverage improves the number of available line diagnostics for our in idual targets, allowing a better understanding of the shapes of their ionizing continua. The ratio of EW[Ly α +N v ] to EW[Mg ii ] in our s le is generally small but varied, favoring a soft ionizing continuum scenario for WLQs, and we find a lack of correlation between EW[Ly α +N v ] and the X-ray properties of our targets, consistent with a “slim-disk” shielding gas model. We also find indications that weak absorption may be a more significant contaminant in low- z WLQ populations than previously thought.
Publisher: American Astronomical Society
Date: 29-04-2013
Publisher: American Astronomical Society
Date: 25-01-2021
Publisher: Oxford University Press (OUP)
Date: 31-12-2015
Publisher: American Astronomical Society
Date: 14-10-2015
Publisher: Oxford University Press (OUP)
Date: 10-12-2012
DOI: 10.1093/MNRAS/STS377
Publisher: American Astronomical Society
Date: 14-05-2015
Publisher: Oxford University Press (OUP)
Date: 16-05-2012
Publisher: Oxford University Press (OUP)
Date: 22-06-2006
Publisher: American Astronomical Society
Date: 04-10-2018
Publisher: American Astronomical Society
Date: 20-11-2007
DOI: 10.1086/521524
Publisher: American Astronomical Society
Date: 05-01-2017
Publisher: Oxford University Press (OUP)
Date: 11-04-2009
Publisher: Springer Science and Business Media LLC
Date: 02-03-2020
Publisher: Oxford University Press (OUP)
Date: 21-01-2004
Publisher: American Astronomical Society
Date: 29-05-2020
Publisher: American Astronomical Society
Date: 26-03-2019
Publisher: American Astronomical Society
Date: 06-2022
Abstract: We present a detailed study of the evolution of the Galactic black hole transient GRS 1716−249 during its 2016–2017 outburst at optical (Las Cumbres Observatory), mid-infrared (Very Large Telescope), near-infrared (Rapid Eye Mount telescope), and ultraviolet (the Neil Gehrels Swift Observatory Ultraviolet/Optical Telescope) wavelengths, along with archival radio and X-ray data. We show that the optical/near-infrared and UV emission of the source mainly originates from a multi-temperature accretion disk, while the mid-infrared and radio emission are dominated by synchrotron emission from a compact jet. The optical/UV flux density is correlated with the X-ray emission when the source is in the hard state, consistent with an X-ray irradiated accretion disk with an additional contribution from the viscous disk during the outburst fade. We find evidence for a weak, but highly variable jet component at mid-infrared wavelengths. We also report the long-term optical light curve of the source and find that the quiescent i ′ -band magnitude is 21.39 ± 0.15 mag. Furthermore, we discuss how previous estimates of the system parameters of the source are based on various incorrect assumptions, and so are likely to be inaccurate. By comparing our GRS 1716−249 data set to those of other outbursting black hole X-ray binaries, we find that while GRS 1716−249 shows similar X-ray behavior, it is noticeably optically fainter, if the literature distance of 2.4 kpc is adopted. Using several lines of reasoning, we argue that the source distance is further than previously assumed in the literature, likely within 4–17 kpc, with a most likely range of ∼4–8 kpc.
Publisher: Oxford University Press (OUP)
Date: 18-05-2012
Publisher: American Astronomical Society
Date: 12-07-2016
Publisher: American Astronomical Society
Date: 15-01-2010
Publisher: Oxford University Press (OUP)
Date: 09-12-2014
Publisher: American Astronomical Society
Date: 24-01-2020
Location: United States of America
Location: United States of America
No related grants have been discovered for Elena Gallo.