A maximum likelihood analysis of the NGC 4258 maser positions and velocities reveals a $2 deviation from Keplerian motion in the projected rotation curve of the high-velocity features, corresponding to a $9 km s À1 , or 0.8%, flattening of the LOS velocities with respect to Keplerian motion over the range of the high-velocity masers. While there are a number of potential explanations for this flattening, we argue for pure Keplerian rotation in an inclinationwarped disk on the basis of the ability of this model to explain a number of otherwise puzzling features of the system. A radial gradient in the disk inclination of 0.034 mas À1 is not only consistent with the observed rotation curve, but it generates a bowl along the near edge of the disk that naturally explains the otherwise puzzling narrow spread in the declinations of the systemic masers. It also explains the existence and location of an apparently recurring flare among the systemic masers. There is no significant evidence for non-Keplerian rotation in the inclination-warped disk. An additional implication of the inclination warp is that the disk rises in front of and obscures the central engine at a disk radius of about 8.3 mas, or 0.29 pc. By comparing the observed X-ray column to conditions in the disk at this radius, we argue that the disk must be atomic at 0.29 pc. Hence, we conclude that the molecular-to-atomic transition occurs just beyond the outermost maser at 0.28 pc, and from this we infer an accretion rate of $10 À4 M yr À1 , where (P1) is the standard dimensionless parameterization of the kinematic viscosity. Our model suggests that most of the observed X-ray column arises in the warped accretion disk at 0.29 pc and that the maser emission is truncated at large radii predominantly as a result of the molecular-to-atomic phase transition originally proposed by Neufeld & Maloney. The inferred accretion rate is consistent with the jet-dominated accretion models of Yuan et al.

We have conducted VLBI observations at subparsec resolution of water maser and radio continuum emission in the nucleus of the nearby active galaxy NGC 3079. The 22 GHz maser emission arises in compact (D0.01 pc at a distance of 16 Mpc) clumps, distributed over D2 pc along an axis that is approximately aligned with the major axis of the galactic disk. The Doppler velocities of the water maser clumps are consistent with their lying in the inner parsec of a molecular disk with a binding mass D106 rotating in the same sense as the edge-on kiloparsec-scale molecular disk observed in CO emission. M _ , However, the velocity Ðeld has a signiÐcant nonrotational component, which may indicate supersonic turbulence in the disk. This distribution is markedly di †erent from that of water masers in NGC 4258, which trace a nearly perfectly Keplerian rotating disk with a binding mass of 3.5 ] 107The 22 M _ . GHz radio continuum emission in NGC 3079 is dominated by a compact (\0.1 pc) source that is o †set 0.5 pc to the west of the brightest maser feature. No bright maser emission is coincident with a detected compact continuum source. This suggests that the large apparent luminosity of the maser is not caused by beamed ampliÐcation of high brightness temperature continuum emission. At 8 and 5 GHz, we conÐrm the presence of two compact continuum sources with a projected separation of 1.5 pc. Both have inverted spectra between 5 and 8 GHz and steep spectra between 8 and 22 GHz. NGC 3079 may be a nearby, low-luminosity example of the class of compact symmetric gigahertz-peaked spectrum radio sources. We detected a third continuum component that lies along the same axis as the other two, strongly suggesting that this galaxy possesses a nuclear jet. Faint maser emission was detected near this axis, which may indicate a second population of masers associated with the jet.

We present the first reported case of the simultaneous metallicity determination of a gamma-ray burst (GRB) host galaxy, from both afterglow absorption lines as well as strong emission-line diagnostics. Using spectroscopic and imaging observations of the afterglow and host of the long-duration Swift GRB 121024A at z = 2.30, we give one of the most complete views of a GRB host/environment to date. We observe a strong damped Lyα absorber (DLA) with a hydrogen column density of log N (H i) = 21.88 ± 0.10, H 2 absorption in the Lyman-Werner bands (molecular fraction of log(f ) ≈ −1.4; fourth solid detection of molecular hydrogen in a GRB-DLA), the nebular emission −1 (and 1-3 kpc) from the gas that is photoexcited by the GRB. This implies a fairly massive host, in agreement with the derived stellar mass of log(M * /M ⊙ ) = 9.9 +0.2 −0.3 . We dissect the host galaxy by characterising its molecular component, the excited gas, and the line-emitting star-forming regions. The extinction curve for the line of sight is found to be unusually flat (R V ∼ 15). We discuss the possibility of an anomalous grain size distributions. We furthermore discuss the different metallicity determinations from both absorption and emission lines, which gives consistent results for the line of sight to GRB 121024A.

PROMPT (Panchromatic Robotic Optical Monitoring and PolarimetryTelescopes) observed the early-time optical afterglow of GRB 060607A and obtained a densely sampled multiwavelength light curve that begins only tens of seconds after the GRB. Located at Cerro Tololo Inter-American Observatory in Chile, PROMPT is designed to observe the afterglows of γ-ray bursts using multiple automated 0.4-m telescopes that image simultaneously in many filters when the afterglow is bright and may be highly variable. The data span the interval from 44 seconds after the GRB trigger to 3.3 hours in the Bgri filters. We observe an initial peak in the light curve at approximately three minutes, followed by rebrightenings peaking around 40 minutes and again at 66 minutes. Although our data overlap with the early Swift γ-ray and x-ray light curves, we do not see a correlation between the optical and high-energy flares. We do not find evidence for spectral evolution throughout the observations. We model the variations in the light curves and find that the most likely cause of the rebrightening episodes is a refreshment of the forward shock preceded by a rapidly fading reverse shock component, although other explanations are plausible.