Daily Image
15-01-2024
Lunar occultation of Sagittarius A
| Submitter: | Tammo Jan Dijkema, Thomas Telkamp, Ard Hartsuijker |
| Description: | On 13 December, the Moon occulted the bright radio source Sagittarius A located at the galactic center. We observed this occultation with the Dwingeloo telescope, sharing the results in a livestream. The observation was challenging, since the elevation of Sagittarius A was only 4 to 8 degrees above the horizon during the occultation. The observation was hindered by RFI from LTE towers in the South transmitting in band 32 (1456 MHz), against which the current observing system of the telescope is insufficiently shielded. Moreover, the Sun was only 7 degrees from the pointing. We observed at three frequencies: 1330 MHz, 1420 MHz (around the hydrogen line) and 415 MHz. The data at 415MHz was almost totally swamped by RFI, although the egress is visible. At 1330 MHz at 1420 MHz, the continuum signal show a dip at the time the Moon went in front of the Moon. The image shows the spectral line observations around 1420 MHz. The top-right panel shows all data, where a linear decrease in continuum over the observation (presumably due to disappearing ground noise) was removed. The bottom-left panel shows the spectrum during and after the observation. The absorption feature at 50km/s disappears almost completely during the occultation. We used the MeerKAT observation of Heywood et al. 2022 to simulate the effects of the occultation on the total power received by the Dwingeloo telescope during the occultation. This simulation, though intended for continuum, matches the depth of the two absorption features quite well, which is shown in the bottom-right plot (we allowed a vertical shift and scale of the simulation here). The recorded spectra are available as open data on Zenodo as DOI 10.5281/zenodo.10395914. |
| Copyright: | CC-BY 4.0 Tammo Jan Dijkema |
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