Search Publications
Probing The Origins of the C IV and Fe Kα Baldwin Effects
Brandt, W. N.; Wu, Jian; Schneider, Donald P. +3 more
We use UV/optical and X-ray observations of 272 radio-quiet Type 1 active galactic nuclei and quasars to investigate the C IV Baldwin Effect (BEff). The UV/optical spectra are drawn from the Hubble Space Telescope, International Ultraviolet Explorer and Sloan Digital Sky Survey archives. The X-ray spectra are from the Chandra and XMM-Newton archiv…
Hubble Space Telescope Observations of an Extraordinary Flare in the M87 Jet
Madrid, Juan P.
HST-1, a knot along the M87 jet located 0farcs85 from the nucleus of the galaxy, has experienced dramatic and unexpected flaring activity since early 2000. We present analysis of Hubble Space Telescope near-ultraviolet (NUV) imaging of the M87 jet from 1999 May to 2006 December that reveals that the NUV intensity of HST-1 has increased 90 times ov…
A High Yield of New Sightlines for the Study of Intergalactic Helium: Far-UV-Bright Quasars from the SDSS, GALEX, AND HST
Anderson, Scott F.; Schneider, Donald P.; York, Donald G. +6 more
Investigations of He II Lyα (304 Å rest-frame) absorption toward a half-dozen quasars at z ~ 3-4 have demonstrated the great potential of helium studies of the intergalactic medium, but the current critically small sample size of clean sightlines for the He II Gunn-Peterson test limits confidence in cosmological inferences, and a larger sample is …
Imaging Observations of Quasi-Periodic Pulsatory Nonthermal Emission in Two-Ribbon Solar Flares
Zimovets, I. V.; Struminsky, A. B.
Using RHESSI and some auxiliary observations we examine possible connections between the spatial and temporal structure of nonthermal hard X-ray (HXR) emission sources from the two-ribbon flares of 29 May 2003 and 19 January 2005. In each of these events quasi-periodic pulsations (QPP) with time period of 1 - 3 minutes are evident in both hard X r…
The Correlation Between X-ray and UV Properties of BAL QSOs
Zhang, Kai; Wang, Tinggui; Wang, Junxian +4 more
We compile a large sample of broad absorption line (BAL) quasars with X-ray observations from the XMM-Newton archive data and Sloan Digital Sky Survey Data Release 5. The sample consists of 41 BAL QSOs. Among 26 BAL quasars detected in X-ray, spectral analysis is possible for 12 objects. X-ray absorption is detected in all of them. Complementary t…
Non-LTE Modeling of the Near-Ultraviolet Band of Late-Type Stars
Hauschildt, P. H.; Short, C. Ian
We investigate the ability of both LTE and non-LTE (NLTE) models to fit the near-UV band absolute flux distribution, f λ(λ), and individual spectral line profiles of three standard stars for which high-quality spectrophotometry and high-resolution spectroscopy are available: The Sun (G2 V), Arcturus (K2 III), and Procyon (F5 IV-V). We i…
The Solar Energetic Particle Event of 14 December 2006
Leske, R. A.; Wiedenbeck, M. E.; Cohen, C. M. S. +6 more
The solar energetic particle event on 14 December 2006 was observed by several near-Earth spacecraft including the Advanced Composition Explorer (ACE), STEREO A and B, SOHO and Wind. An interesting feature of this event is a series of unusual fluctuations in the particle intensity that occurred during the first few hours. These fluctuations were o…
Role of emission angular directionality in spin determination of accreting black holes with a broad iron line
Dovčiak, M.; Karas, V.; Svoboda, J. +1 more
Aims: The spin of an accreting black hole can be determined by spectroscopy of the emission and absorption features produced in the inner regions of an accretion disc. In this work, we discuss the method employing the relativistic line profiles of iron in the X-ray domain, where the emergent spectrum is blurred by general relativistic effects.
Xmm-Newton Discovery of 2.6 s Pulsations in the Soft Gamma-Ray Repeater SGR 1627-41
Tiengo, A.; Götz, D.; Mereghetti, S. +6 more
After nearly a decade of quiescence, the soft gamma-ray repeater SGR 1627-41 reactivated on 2008 May 28 with a bursting episode followed by a slowly decaying enhancement of its persistent emission. To search for the still unknown spin period of this SGR taking advantage of its high flux state, we performed on 2008 September 27-28 a 120 ks long X-r…
Icy Satellites of Saturn: Impact Cratering and Age Determination
Dones, Luke; McKinnon, William B.; Neukum, Gerhard +4 more
Saturn is the first giant planet to be visited by an orbiting spacecraft that can transmit large amounts of data to Earth. Crater counts on satellites from Phoebe inward to the regular satellites and ring moons are providing unprecedented insights into the origin and time histories of the impacting populations. Many Voyager-era scientists conclude…