Search Publications
Spectral State Transitions of the Ultraluminous X-Ray Sources X-1 and X-2 in NGC 1313
Feng, Hua; Kaaret, Philip
X-ray spectral state transitions are a key signature of black hole X-ray binaries and follow a well-defined pattern. We examined 12 XMM-Newton observations of the nearby spiral galaxy NGC 1313, which harbors two compact ultraluminous X-ray sources (ULXs), X-1 and X-2, in order to determine if the state transitions in ULXs follow the same pattern. …
C II Abundances in Early-Type Stars: Solution to a Notorious Non-LTE Problem
Przybilla, N.; Nieva, M. F.
We address a long-standing discrepancy between non-LTE analyses of the prominent C II 4267 and 6578/82 Å multiplets in early-type stars. A comprehensive non-LTE model atom of C II is constructed based on critically selected atomic data. This model atom is used for an abundance study of six apparently slow-rotating main-sequence and giant early B-t…
Chandra ACIS Spectroscopy of N157B: A Young Composite Supernova Remnant in a Superbubble
Gotthelf, E. V.; Chu, You-Hua; Wang, Q. Daniel +3 more
We present a Chandra ACIS observations of N157B, a young supernova remnant (SNR) located in the 30 Doradus star formation region of the Large Magellanic Cloud. This remnant contains the most energetic pulsar known (PSR J053747.39-691020.2 E˙=4.8×1038 ergs s-1), which is surrounded by a X-ray-bright nonthermal nebula that like…
The Fundamental Plane for z = 0.8-0.9 Cluster Galaxies
Jørgensen, Inger; Chiboucas, Kristin; Barr, Jordi +3 more
We present the fundamental plane (FP) for 38 early-type galaxies in the two rich galaxy clusters RX J0152.7-1357 (z=0.83) and RX J1226.9+3332 (z=0.89), reaching a limiting magnitude of MB=-19.8 in the rest frame of the clusters. While the zero-point offset of the FP for these high-redshift clusters relative to our low-redshift sample is…
The Low-z Intergalactic Medium. II. Lyβ, O VI, and C III Forest
Shull, J. Michael; Danforth, Charles W.; Stocke, John T. +1 more
We present the results of a large survey of H I, O VI, and C III absorption lines in the low-redshift (z<0.3) intergalactic medium (IGM). We begin with 171 strong Lyα absorption lines (Wλ>=80 mÅ) in 31 AGN sight lines studied with the Hubble Space Telescope and measure corresponding absorption from higher order Lyman lines with FU…
Measuring M Dwarf Winds with DAZ White Dwarfs
Debes, John H.
Hydrogen atmosphere white dwarfs with metal lines, so-called DAZs, show evidence for ongoing accretion of material onto their surfaces. Some DAZs are known to have unresolved M dwarf companions, which could account for the observed accretion through a stellar wind. I combine observed Ca abundances of the DAZs with information on the orbital separa…
The Araucaria Project: The Distance to the Local Group Galaxy IC 1613 from Near-Infrared Photometry of Cepheid Variables
Soszyński, Igor; Dall'Ora, Massimo; Bono, Giuseppe +5 more
We have measured accurate near-infrared magnitudes in the J and K bands of 39 Cepheid variables in the irregular Local Group galaxy IC 1613 with well-determined periods and optical VI light curves. Using the template light curve approach of Soszyński, Gieren, & Pietrzyński, accurate mean magnitudes were obtained from these data, which allowed …
Annihilation Emission from the Galactic Black Hole
Cheng, K. S.; Chernyshov, D. O.; Dogiel, V. A.
Both diffuse high-energy gamma rays and an extended electron-positron annihilation line emission have been observed in the Galactic Center (GC) region. Although X-ray observations indicate that the Galactic black hole Sgr A* is inactive now, we suggest that Sgr A* can become active when a captured star is tidally disrupted and matter is accreted i…
The Absence of Adiabatic Contraction of the Radial Dark Matter Profile in the Galaxy Cluster A2589
Humphrey, Philip J.; Buote, David A.; Brighenti, Fabrizio +4 more
We present an X-ray analysis of the radial mass profile of the radio-quiet galaxy cluster A2589 between 0.015 and 0.25rvir, using an XMM-Newton observation. Except for a ~16 kpc shift of the X-ray center of the R=45-60 kpc annulus, A2589 possesses a remarkably symmetrical X-ray image and is therefore an exceptional candidate for precisi…
GRB 060121: Implications of a Short-/Intermediate-Duration γ-Ray Burst at High Redshift
Sakamoto, T.; McBreen, S.; Pandey, S. B. +23 more
Since the discovery of the first short-population γ-ray burst (GRB) afterglows in 2005, the handful of observed events have been found to be embedded in nearby (z < 1), bright underlying galaxies. We present multiwavelength observations of GRB 060121, the first short burst observed to clearly outshine its host galaxy (by a factor >102