R. Michelsen

The afterglow and the host galaxy of GRB 011211

We present optical, near-infrared, and X-ray observations of the optical afterglow (OA) of the X-ray rich, long- duration gamma-ray burst GRB 011211. Hubble Space Telescope (HST) data obtained 14, 26, 32, and 59 days after the burst, show the host galaxy to have a morphology that is fairly typical of blue galaxies at high redshift. We measure its magnitude to be R= 24:95 0:11. We detect a break in the OA R-band light curve which is naturally accounted for by a collimated outflow geometry. By fitting a broken power-law to the data we find a best fit with a break 1 :56 0:02 days after the burst, a pre-break slope of1 = 0:95 0:02, and a post-break slope of2 = 2:11 0:07. The UV-optical spectral energy distribution (SED) around 14 hours after the burst is best fit with a power-law with index = 0:56 0:19 reddened by an SMC-like extinction law with a modest AV= 0:08 0:08 mag. By comparison, from the XMM-Newton X-ray data at around the same time, we find a decay index ofX= 1:62 0:36 and a spectral index ofX= 1:21 +0:10 0:15 . Interpolating between the UV-optical and X-ray implies that the cooling frequency is located close to10 16 Hz in the observer frame at the time of the observations. We argue, using the various temporal and spectral indices above, that the most likely afterglow model is that of a jet expanding into an external environment that has a constant mean density rather than a wind-fed density structure. We estimate the electron energy index for this burst to be p 2:3.

Four new binary minor planets: (854) Frostia, (1089) Tama, (1313) Berna, (4492) Debussy

Aims. We present evidence that four minor planets of the main belt are binary systems. Methods. These discoveries are based on CCD photometric measurements made by many observers coordinated in a network of observatories. Results. Orbital and physical properties are derived from a total of 134 partial light curves involving 26 stations. (854) Frostia, (1089) Tama, (1313) Berna, and (4492) Debussy show mutual eclipses features on their light curves. In all cases, rotation and revolution are synchronous. Synodic periods are 37.728, 16.444, 25.464 and 26.606 h respectively. From a simple model, we have derived their bulk densities as follows: 0.89 ± 0.14, 2.52 ± 0.30, 1.22 ± 0.15 and 0.91 ± 0.10 g cm −3 respectively. Uncertainties in the bulk densities, arising from scattering and shadow effects are not taken into account. These could increase the density estimates by a factor up to 1.6. Our method of determining bulk density is completely independent of their mass and their diameter estimates. The low rotational periods and the low bulk densities clearly imply a collisional process to explain this kind of binary asteroid. Based on our database of a few thousand light curves of minor planets, the population of similar-sized objects in the main belt is estimated to 6 ± 3 percent in the 10–50 km diameter class.

Small-scale variations in the radiating surface of the GRB 011211 jet

We report the discovery of the afterglow of the X-ray rich, long-duration gamma-ray burst GRB 011211 and present evidence for oscillatory behaviour in its early optical light curve. The time-scale of the fluctuations, ∼1 hour, is much smaller than the time of the observations, ∼12 hours from the onset of the gamma-ray burst. The character and strength of the fluctuations are unprecedented and are inconsistent with causally connected variations in the emission of a symmetric, relativistic blast wave, i.e. flux variations which are produced uniformly throughout the shell surface are ruled out. Therefore, the wiggles are the result of spherically asymmetric density or energy variations. Additionally, there is evidence for fluctuations in the X-ray afterglow light curve. If real, the resulting difference in the observed time of the peaks of the short-term variations at X-ray and optical frequencies, would demonstrate that the energy content across the jet-emitting surface is not uniform.

The Bering Small Vehicle Asteroid Mission Concept

Abstract: The study of asteroids is traditionally performed by means of large Earth based telescopes, by means of which orbital elements and spectral properties are acquired. Space borne research, has so far been limited to a few occasional flybys and a couple of dedicated flights to a single selected target. Although the telescope based research offers precise orbital information, it is limited to the brighter, larger objects, and taxonomy as well as morphology resolution is limited. Conversely, dedicated missions offer detailed surface mapping in radar, visual, and prompt gamma, but only for a few selected targets. The dilemma obviously being the resolution versus distance and the statistics versus ΔV requirements. Using advanced instrumentation and onboard autonomy, we have developed a space mission concept whose goal is to map the flux, size, and taxonomy distributions of asteroids. The main focus is on main belt objects, but the mission profile will enable mapping of objects inside the Earth orbit as well.

Asteroid and NEA detection models

We determine the possible detection rate of asteroids with the Bering mission. In particular we examine the outcome of the Bering mission in relation to the populations of Near-Earth Asteroids and main belt asteroids. This is done by constructing synthetic populations of asteroids, based on the current best estimates of the asteroid size-distributions. From the detailed information obtained from the simulations, the scientific feasibility of Bering is demonstrated and the key technical requirement for the scientific instruments on Bering is determined.

Spins, shapes, and orbits for near-Earth objects by Nordic NEON

The Nordic Near-Earth-Object Network (NEON) observing program accrues knowledge about the physical and dynamical properties of near-Earth objects (NEOs) using state-ofthe-art inverse methods. Photometric and astrometric observations are being carried out at the Nordic Optical Telescope. Here, the NEON observations from June 2004 - September 2006 are reviewed. Statistical orbital inversion is illustrated by the application of the so-called Volume-of-Variation method to NEON observations. Spins and shapes are characterized using shape models that allow analytical computation of disk-integrated brightnesses in arbitrary illumination and observation geometries for Lommel-Seeliger and Lambert scattering laws. The analytical treatment allows error analyses for the spins and shapes using large numbers of discrete sample solutions to the statistical inverse problem. Currently, statistical spin and shape solutions have been derived for 2002 FF12, 2003 MS2, 2003 RX7, 2004 HW as well as for (1685) Toro and (1981) Midas. For (1862) Apollo, an unambiguous spin and shape solution has been obtained using the convex inversion method.