Search Publications
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
An Optical Study of Stellar and Interstellar Environments of Seven Luminous and Ultraluminous X-Ray Sources
Chu, You-Hua; Wang, Q. Daniel; Gruendl, Robert A. +3 more
We have studied the stellar and interstellar environments of two luminous X-ray sources and five ultraluminous X-ray sources (ULXs) in order to gain insight into their nature. Archival Hubble Space Telescope images were used to identify the optical counterparts of the ULXs Ho IX X-1 and NGC 1313 X-2, and to make photometric measurements of the loc…
Petschek-Type Reconnection Exhausts in the Solar Wind Well beyond 1 AU: Ulysses
McComas, D. J.; Forsyth, R. J.; Gosling, J. T. +2 more
We have identified 91 Petschek-type exhausts associated with local, quasi-stationary magnetic reconnection in the solar wind in plasma and magnetic field data from the Ulysses spacecraft obtained over a wide range of heliocentric distances (1.4-5.4 AU) and latitudes (S79°-N65°). The characteristic signature of an exhaust was a brief (minutes) inte…
Multiplicity and Optical Excess across the Substellar Boundary in Taurus
Kraus, Adam L.; Hillenbrand, Lynne A.; White, Russel J.
We present the results of a high-resolution imaging survey of 22 brown dwarfs and very low mass stars in the nearby (~145 pc) young (~1-2 Myr) low-density star-forming region Taurus-Auriga. We obtained images with the Advanced Camera for Surveys High Resolution Channel on HST through the F555W (V), F775W (i'), and F850LP (z') filters. This survey …
Comparing Dynamical and Photometric Mass Estimates of Low- and High-Redshift Galaxies: Random and Systematic Uncertainties
Wuyts, S.; Rix, H. -W.; van der Wel, A. +4 more
We determine the importance of redshift-dependent systematic effects in the determination of stellar masses from broadband spectral energy distributions (SEDs), using high-quality kinematic and photometric data of early-type galaxies at z~1 and z~0. We find that photometric masses of z~1 galaxies can be systematically different, by up to a factor …
A Sample of Low-Redshift BL Lacertae Objects. II. EVN and MERLIN Data and Multiwavelength Analysis
Falomo, R.; Giroletti, M.; Giovannini, G. +1 more
We present new radio observations of 9 members of a sample of 29 nearby (z<0.2) BL Lac objects. The new data have been obtained with the European VLBI Network and/or MERLIN at 1.6 and 5 GHz and complement previous observations. For one object, the TeV source Mrk 421, we also present deep multiepoch VLBA and global VLBI data, which reveal a reso…
The Faint Afterglow and Host Galaxy of the Short-Hard GRB 060121
Bremer, M.; Fruchter, A. S.; Rol, E. +14 more
We present optical and X-ray observations of the afterglow and host galaxy of the short-hard GRB 060121. The faint R-band afterglow is seen to decline as t-0.66+/-0.09 while the X-ray falls as t-1.18+/-0.04, indicating the presence of the cooling break between the two frequencies. However, the R-band afterglow is very faint c…
X-Rays from the Globular Cluster G1: Intermediate-Mass Black Hole or Low-Mass X-Ray Binary?
Pooley, David; Rappaport, Saul
The globular cluster G1 (Mayall II) in M31 is the most massive (~107 Msolar) stellar cluster in the Local Group, and it has the highest central velocity dispersion (~28 km s-1). It has been claimed to host a central ~20,000 Msolar black hole, but these claims have been controversial. We investigate here …