3 research outputs found
UV to near-IR observations of the DART-Dimorphos collision
The impact of the Double Asteroid Redirection Test (DART) spacecraft with
Dimorphos allows us to study asteroid collision physics, including momentum
transfer, the ejecta properties, and the visibility of such events in the Solar
System. We report observations of the DART impact in the ultraviolet (UV),
visible light, and near-infrared (IR) wavelengths. The observations support the
existence of at least two separate components of the ejecta: a fast and a slow
component. The fast-ejecta component is composed of a gaseous phase, moving at
about 1.6 km/s with a mass of <10^4 kg. The fast ejecta is detected in the UV
and visible light, but not in the near-IR -band observations. Fitting a
simplified optical thickness model to these observations allows us to constrain
some of the properties of the fast ejecta, including its scattering efficiency
and the opacity of the gas. The slow ejecta component is moving at typical
velocities of up to about 10 m/s. It is composed of micrometer-size particles,
that have a scattering efficiency, at the direction of the observer, of the
order of 10^-3 and a total mass of about 10^6 kg. The larger particles in the
slow ejecta, whose size is bound to be in the range between ~1 mm to ~1 m,
likely have a scattering efficiency larger than that of the pre-impact Didymos
system.Comment: Submitted to MNRA
The Large Array Survey Telescope -- System Overview and Performances
The Large Array Survey Telescope (LAST) is a wide-field visible-light
telescope array designed to explore the variable and transient sky with a high
cadence. LAST will be composed of 48, 28-cm f/2.2 telescopes (32 already
installed) equipped with full-frame backside-illuminated cooled CMOS detectors.
Each telescope provides a field of view (FoV) of 7.4 deg^2 with 1.25
arcsec/pix, while the system FoV is 355 deg^2 in 2.9 Gpix. The total collecting
area of LAST, with 48 telescopes, is equivalent to a 1.9-m telescope. The
cost-effectiveness of the system (i.e., probed volume of space per unit time
per unit cost) is about an order of magnitude higher than most existing and
under-construction sky surveys. The telescopes are mounted on 12 separate
mounts, each carrying four telescopes. This provides significant flexibility in
operating the system. The first LAST system is under construction in the
Israeli Negev Desert, with 32 telescopes already deployed. We present the
system overview and performances based on the system commissioning data. The Bp
5-sigma limiting magnitude of a single 28-cm telescope is about 19.6 (21.0), in
20 s (20x20 s). Astrometric two-axes precision (rms) at the bright-end is about
60 (30)\,mas in 20\,s (20x20 s), while absolute photometric calibration,
relative to GAIA, provides ~10 millimag accuracy. Relative photometric
precision, in a single 20 s (320 s) image, at the bright-end measured over a
time scale of about 60 min is about 3 (1) millimag. We discuss the system
science goals, data pipelines, and the observatory control system in companion
publications.Comment: Submitted to PASP, 15p
Fermi LAT Gamma-ray Detection of the Recurrent Nova RS Ophiuchi during its 2021 Outburst
International audienceWe report the Fermi LAT Îł-ray detection of the 2021 outburst of the symbiotic recurrent nova RS Ophiuchi. In this system, unlike classical novae from cataclysmic binaries, the ejecta from the white dwarf form shocks when interacting with the dense circumstellar wind environment of the red giant companion. We find the LAT spectra from 50 MeV to ~20-23 GeV, the highest-energy photons detected in some subintervals, are consistent with Ï 0-decay emission from shocks in the ejecta as proposed by Tatischeff & Hernanz for its previous 2006 outburst. The LAT light curve displayed a fast rise to its peak >0.1 GeV flux of â6 Ă 10-6 ph cm-2 s-1 beginning on day 0.745 after its optically constrained eruption epoch of 2021 August 8.50. The peak lasted for ~1 day and exhibited a power-law decline up to the final LAT detection on day 45. We analyze the data on shorter timescales at early times and found evidence of an approximate doubling of emission over ~200 minutes at day 2.2, possibly indicating a localized shock-acceleration event. Comparing the data collected by the American Association of Variable Star Observers, we measured a constant ratio of ~ 2.8 Ă 10-3 between the Îł-ray and optical luminosities except for a ~5Ăsmaller ratio within the first day of the eruption likely indicating attenuation of Îł rays by ejecta material and lower high-energy proton fluxes at the earliest stages of the shock development. The hard X-ray emission due to bremsstrahlung from shock-heated gas traced by the Swift-XRT 2-10 keV light curve peaked at day ~6, later than at GeV and optical energies. Using X-ray derived temperatures to constrain the velocity profile, we find the hadronic model reproduces the observed >0.1 GeV light curve