Astronomische Nachrichten最新文献

Hunting for white dwarfs in eROSITA surveys 1-4 with special processing. The Gaia color-magnitude diagram shows all white dwarf candidates from the Gaia white dwarf catalogue (Gentile Fusillo et al. 2021), colour-coded with the probability of being a white dwarf. Black circles mark sources in the ROSAT white dwarf catalogue (Fleming et al. 1996) that match entries in the Gaia white dwarf catalogue (light blue crosses indicate those in the German half of the eROSITA sky). Orange crosses mark eROSITA sources with a hardness ratio of ≤ −0.94 and with counterparts in the Gaia white dwarf catalogue. Those highlighted with a dark green circle have a probability larger than 90 % of being a white dwarf in that catalogue. The cooling tracks of white dwarfs with masses between 0.4 and 1.2 solar masses are shown as gray lines in steps of 0.1 solar masses (top to bottom). For more details see the related paper by S. Friedrich et al. published in this issue e240139.

Pulsating Ultraluminous X-ray Sources (PULXs) are a class of extragalactic sources with high X-ray luminosity, in excess of $��{10}^{39}�$ erg $��s^{�-�1�}�$, and showing pulsations that associate them with neutron stars accreting at a super-Eddington rate. A simplified model is presented, which describes the thermal emission from an accreting, highly magnetized neutron star and includes the contributions from an accretion disk and an accretion envelope surrounding the star magnetosphere. Through numerical calculations, we determine the flux, pulsed fractions, polarization degree, and polarization angle considering various viewing geometries. The model is confronted with the XMM-Newton spectra of M51 ULX-7, and the best fitting viewing geometries are estimated. A measurement of the polarization observables, which will be available with future facilities, along with spectroscopic data obtained with XMM-Newton, will provide considerable additional information on these sources.

Shocks in novae outbursts are ubiquitous, but in symbiotic novae, they are particularly powerful, probably because of the surrounding red giant wind. The recurrent nova RS Oph is the best example of this phenomenon. The presence of shocked plasma in outburst was inferred from optical spectra, and it was confirmed by X-ray observations since 1985. Since 2010, the gamma-ray observatory Fermi has proven that novae in general are the site of particle acceleration, producing copious gamma-ray flux in the few-GeV range. In the last outburst of the symbiotic RS Oph in 2021, gamma-rays were not only detected with Fermi in the GeV range but also detected in the TeV range of the Cherenkov telescopes, for about 3 weeks. Diesing et al. in 2023 showed that there must have been at least two distinct episodes of shocks, likely of hadronic nature, both generating particle acceleration. We present new NuSTAR data and re-discuss XMM-Newton high-resolution grating spectra and NICER data that we recently published. We concluded that the primary shock causing the particle acceleration observed in the range of TeV gamma-rays with the Cherenkov telescopes was the same phenomenon observed and studied with the x-ray observatories. However, the shocked plasma from which the particles were accelerated causing the gamma-ray flux observed after 1 day with Fermi was—at least initially—unobservable. We suggest that this first episode of shock occurred when the nova ejecta collided with a dense outflow close to the atmosphere of the red giant, with such a high absorbing column that x-rays were absorbed.

Denoising a medium resolution stellar spectrum with neural networks. Top: Example of a noiseless simulated stellar spectrum (blue) transformed to an “observation” by adding a realistic noise component (gray) such that the effective S/N≈19. Middle: Comparison of the original noiseless simulated spectrum (blue) and the reconstructed spectrum (dashed orange) using a trained denoising autoencoder. The two lines overlap almost entirely, indicating the high accuracy of the machine learning method. Bottom: Relative error calculated as the fraction of pixel-wise residual noise and the original noiseless flux. The mean and maximum of the relative error are 0.175% and 1.806%, respectively. Formore details see the related paper by Pál and Dobos, published in this issue e240049.

eROSITA is the soft X-ray instrument aboard the Spectrum Roentgen Gamma (SRG) satellite that is most sensitive in the energy range between 0.2 and 2.3 keV. Between December 2019 and December 2021, eROSITA completed four all-sky surveys, producing all-sky X-ray source lists and sky maps of unprecedented depth. In the energy range between 0.2 keV and 1 keV, we detected about 38,000 sources with a hardness ratio below −0.94, covering a small sample of known white dwarfs found with eROSITA in the dataset to which the German eROSITA consortium has rights (half sky). Two hundred and sixty four of these soft sources have a probability of more than 90% to be a white dwarf. This is more than the 175 white dwarfs ROSAT found in the whole sky. Here we present the results of a pilot study to increase the sensitivity of eROSITA for soft sources by extending the detection threshold down to 0.1 keV. First tests with dedicated sky regions are promising.

With the present first issue of volume 346 in 2025, we enter the 204th year of continuous appearance of Astronomische Nachrichten/Astronomical Notes (AN). The continuing complexity of worldwide scientific publishing had kept us busy over the years; it also impacts AN. The tricky part for our comparably small journal is maintaining a high standard, but also being openly accessible at the same time, preferably without costs. The end product shall be a peer-reviewed, content-oriented, and thus user-oriented, widely distributed and easily accessible journal with original research papers that one is happy to cite.

This is achieved with accompanying editorial changes. While we currently still rely on the ScholarOne submission platform for user interaction, it will be replaced with the new editorial system Research Exchange (ReX) that is being rolled out as a peer-review tool to all Wiley journals during the course of this year. eLocators instead of the sequential page numbers for easy identification, a modern web appearance where you can find the latest but also all historical volumes of AN, and open access as part of the European DEAL treaty remain cornerstones. AN's most recent Journal Impact Factor (Clarivate) is 1.1.

As before, the Leibniz-Institute for Astrophysics Potsdam (AIP) continues hosting the editorial office in close collaboration with Wiley. The editorial team can be contacted through [email protected]. Papers are welcomed in all fields of astronomy, astrophysics, and solar-system research, as well as related aspects in instrumentation, astrobiologic, and historic studies. Many thanks in advance. We are looking forward to another year of submissions.

The author declares no conflicts of interest.