No abstract

Abstract. 232 hours of data were accumulated from 1997 to 1999, using the HEGRA Stereoscopic Cherenkov Telescope System to observe the supernova remnant Cassiopeia A. TeV γ-ray emission was detected at the 5 σ level, and a flux of (5.8 ± 1.2stat ± 1.2syst) 10 −9 ph m −2 s −1 above 1 TeV was derived. The spectral distribution is consistent with a power law with a differential spectral index of −2.5 ± 0.4stat ± 0.1syst between 1 and 10 TeV. As this is the first report of the detection of a TeV γ-ray source on the "centi-Crab" scale, we present the analysis in some detail. Implications for the acceleration of cosmic rays depend on the details of the source modeling. We discuss some important aspects in this paper.

We present 0. ′′ 1 resolution near-infrared integral field spectroscopy of Hα in a z=1.4781 star forming galaxy, Q2343-BM133. These observations were obtained with OSIRIS (OH Suppressing Infra-Red Imaging Spectrograph) using the W.M. Keck Observatory Laser Guide Star Adaptive Optics system. Hα emission is resolved over a 0. ′′ 8 (6.8 kpc) x 0. ′′ 5 (4.3 kpc) region with a 0. ′′ 1 spatial resolution. We find a global flux of 4.2±0.6×10 −16 ergs s −1 cm −2 , and detect a spatially resolved velocity gradient of ∼134 km s −1 across the galaxy and a global velocity dispersion of 73±9 km s −1 . An upper limit of [Nii]/Hα 0.12 is inferred, which implies that this galaxy is not dominated by an active galactic nucleus and has a metallicity at or below 1/2 solar metallicity. We derive a star formation rate (SFR) of 47±6 M ⊙ yr −1 , and a dereddened SFR of 66±9 M ⊙ yr −1 . Two-dimensional kinematics for Q2343-BM133 fit well with an inclined-disk model, with which we estimate an enclosed mass of 4.3×10 9 M ⊙ within 5.5 kpc. A possible merger scenario is also presented, and can not be fully ruled out. We derive a virial mass of 1.1×10 10 M ⊙ for a disk geometry, using the observed velocity dispersion. We propose that Q2343-BM133 is currently at an early stage of disk formation at a look-back time of 9.3 Gyr.

No abstract

The IRS 13E complex is an unusual concentration of massive, early-type stars at a projected distance of ~0.13 pc from the Milky Way's central supermassive black hole Sagittarius A* (Sgr A*). Because of their similar proper motion and their common nature as massive, young stars it has recently been suggested that IRS 13E may be the remnant of a massive stellar cluster containing an intermediate-mass black hole (IMBH) that binds its members gravitationally in the tidal field of Sgr A*. Here, we present an analysis of the proper motions in the IRS~13E environment that combines the currently best available data with a time line of 10 years. We find that an IMBH in IRS 13E must have a minimum mass of ~10^4 solar masses in order to bind the source complex gravitationally. This high mass limit in combination with the absence so far of compelling evidence for a non-thermal radio and X-ray source in IRS 13E make it appear unlikely that an IMBH exists in IRS 13E that is sufficiently massive to bind the system gravitationally.Comment: accepted by AP