Search Publications
Novae as a Class of Transient X-Ray Sources
Mukai, K.; Della Valle, M.; Orio, M.
Motivated by the recently discovered class of faint (1034-1035 ergs s-1) X-ray transients in the Galactic center region, we investigate the 2-10 keV properties of classical and recurrent novae. Existing data are consistent with the idea that all classical novae are transient X-ray sources with durations of months t…
Limits on Hot Galactic Halo Gas from X-Ray Absorption Lines
Yao, Y.; Nowak, M. A.; Wang, Q. D. +2 more
Although the existence of large-scale hot gaseous halos around massive disk galaxies has been theorized for a long time, there is yet very little observational evidence. We report the Chandra and XMM-Newton grating spectral detection of O VII and Ne IX Kα absorption lines along the sight line of 4U 1957+11. The line absorption is consistent with t…
The ACS LCID Project: RR Lyrae Stars as Tracers of Old Population Gradients in the Isolated Dwarf Spheroidal Galaxy Tucana
Skillman, Evan D.; Cole, Andrew A.; Mateo, Mario +9 more
We present a study of the radial distribution of RR Lyrae variables, which present a range of photometric and pulsational properties, in the dwarf spheroidal galaxy Tucana. We find that the fainter RR Lyrae stars, having a shorter period, are more centrally concentrated than the more luminous, longer period RR Lyrae variables. Through comparison w…
Coronal Jet Observed by Hinode as the Source of a3He-rich Solar Energetic Particle Event
Krucker, Säm; Shibata, Kazunari; Nitta, Nariaki V. +5 more
We study the solar source of the 3He-rich solar energetic particle (SEP) event observed on 2006 November 18. The SEP event showed a clear velocity dispersion at energies below 1 MeV nucleon-1, indicating its solar origin. We associate the SEP event with a coronal jet in an active region at heliographic longitude of W50°, as o…
Weighing the Quiescent Central Black Hole in an Elliptical Galaxy with X-Ray-Emitting Gas
Gebhardt, Karl; Humphrey, Philip J.; Buote, David A. +2 more
We present a Chandra study of the hot interstellar medium (ISM) in the giant elliptical galaxy NGC 4649. In common with other group-centered ellipticals, its temperature profile rises with radius in the outer parts of the galaxy, from ~0.7 keV at 2 kpc to ~0.9 keV by 20 kpc. However, within the central ~2 kpc the trend reverses, and the temperatur…
Injection and Interplanetary Transport of Near-Relativistic Electrons: Modeling the Impulsive Event on 2000 May 1
Lario, D.; Vainio, R.; Sanahuja, B. +1 more
We present a Monte Carlo method to model the transport of solar near-relativistic electrons in the interplanetary medium, including adiabatic focusing, pitch-angle dependent scattering, and solar wind effects. By taking into account the angular response of the LEFS60 telescope of the EPAM instrument on board the ACE spacecraft, we transform the si…
Probing the Radio to X-Ray Connection of the Vela X Pulsar Wind Nebula with Fermi LAT and H.E.S.S.
LaMassa, S.; de Jager, O. C.; Slane, P. O.
Morphologically, it appears as if the Vela X pulsar wind nebula (PWN) consists of two emission regions: whereas X-ray (~1 keV) and very high energy (VHE) H.E.S.S. γ-ray observations appear to define a cocoon-type shape south of the pulsar, radio observations reveal an extended area of size 2° × 3° (including the cocoon area), also south of the Vel…
Optical Counterpart of the Ultraluminous X-Ray Source IC 342 X-1
Feng, Hua; Kaaret, Philip
We present Chandra and HST observations of the ultraluminous X-ray source (ULX) IC 342 X-1. The Chandra and HST images are aligned using two X-ray-emitting foreground stars. The astrometry-corrected position for X-1 is R .A . = 03h45m55.61s, decl . = + 68°04'55.3'' (J2000.0), with an error circle of 0.2''. One exte…
Low-Ionization Emission Regions in Quasars: Gas Properties Probed with Broad O I and Ca II Lines
Kawara, K.; Oyabu, S.; Matsuoka, Y.
We have compiled the emission-line fluxes of O I λ8446, O I λ11287, and the near-infrared (IR) Ca II triplet (λ8579) observed in 11 quasars. These lines are considered to emerge from the same gas as do the Fe II lines in the low-ionized portion of the broad emission line region (BELR). The compiled quasars are distributed over wide ranges of redsh…
The Birth Place of the Type Ic Supernova 2007gr
Stephens, Andrew W.; Smartt, Stephen J.; Mattila, Seppo +8 more
We report our attempts to locate the progenitor of the peculiar Type Ic SN 2007gr in Hubble Space Telescope (HST) preexplosion images of the host galaxy, NGC 1058. Aligning adaptive optics Altair/NIRI imaging of SN 2007gr from the Gemini (North) Telescope with the preexplosion HST WFPC2 images, we identify the supernova (SN) position on the HST fr…