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.
We review an often-cited but seldom-accessed catalogue by Fourcade and Laborde (1966) of 785 variable stars near 47 southern Galactic globular clusters, and recover the locations of 85 stars that were not incorporated into subsequent variable star catalogues and hence have become “lost” to the literature. We match the positions of these stars with those of modern variable star databases (Gaia, ASAS-SN, and VSX) and find 96% appear in at least one of these catalogues. We used proper motions and radial velocities from the Gaia Third Data Release to assess cluster membership, finding that most are field stars, but up to five may be members of NGC 5927 and one of NGC 6624.
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.
In the year 1924, a paper by Carl Wirtz appeared in ‘Astronomische Nachrichten’, entitled ‘De Sitter's cosmology and the radial motion of spiral galaxies’. This paper and its author remained largely unnoticed by the community, but it seems to be the first cosmological interpretation of the redshift of galaxies as a time dilation effect and the expansion of the Universe. Edwin Hubble knew Wirtz' publications quite well. The modern reader would find Wirtz' own understanding diffuse and contradictory in some aspects, but that reflected the early literature on nebulae, to which he himself made important contributions. The 100th anniversary provides a good opportunity to present an English transcription to the community, which can be found in the appendix. This anniversary also provokes to ask for the present status of cosmology which many authors see in a crisis. From an observational viewpoint, it shall be illustrated that until today there is no consistent/convincing understanding of how the Universe evolved.
The ultra-luminous x-ray pulsar (ULXP) NGC 7793 P13 has been regularly monitored with XMM-Newton, NuSTAR, and Swift for the last 8 years. Here, we present the latest results of this monitoring campaign with respect to the pulse period evolution and spectral variability. We find that since the source recovered from an x-ray low state in 2020–2022 the spin-up rate has increased significantly compared with before the off-state, even though the x-ray luminosity has not shown an equivalent increase. We find that the x-ray and optical/UV flux are anti-correlated, and speculate that this variability might be driven by a large accretion disk, precessing at a super-orbital period of 7–8 years. We study the spectral behavior in the XMM-Newton and NuSTAR data, and find very little changes in the spectral shape, despite the large flux variability. This spectral consistency provides further indication that the observed flux variability is a geometric effect and not due to intrinsic changes of the accretion rate.
Observations show that the x-ray emission of the accreting weakly magnetized neutron stars (WMNSs) is polarized. In this article, we summarize the analytical models for the polarized emission of various components of the WMNSs. We introduce a missing theoretical model, where we assume the emission comes from the spreading layer, the extension of the boundary layer between the accretion disk and the neutron star. We show how these models and the results of the simulations provide new insights into the x-ray polarization from weakly magnetized neutron stars observed with the imaging x-ray polarimetry explorer (IXPE). We specifically focus on the most peculiar case of the X-ray burster GX 13+1.
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