Hunting for the nature of the enigmatic narrow-line Seyfert 1 galaxy PKS 2004-447 (2021) Berton M, Peluso G, Marziani P, Komossa S, Foschini L, Ciroi S, Chen S, et al. Journal article Evidence of 100 TeV gamma-ray emission from HESS J1702-420: A new PeVatron candidate (2021) Abdalla H, Aharonian F, Benkhali FA, Anguner EO, Arcaro C, Armand C, Armstrong T, et al. Journal article, Original article EC 22536-5304: a lead-rich and metal-poor long-period binary (2021) Dorsch M, Jeffery CS, Irrgang A, Woolf V, Heber U Journal article Tracking down the origin of superbubbles and supergiant shells in the Magellanic Clouds with Minkowski tensor analysis (2021) Collischon C, Sasaki M, Mecke K, Points SD, Klatt MA Journal article Long-term pulse period evolution of the ultra-luminous X-ray pulsar NGC 7793 P13 (2021) Furst F, Walton DJ, Heida M, Bachetti M, Pinto C, Middleton MJ, Brightman M, et al. Journal article X-ray emission from magnetized neutron star atmospheres at low mass-accretion rates: I. Phase-averaged spectrum (2021) Sokolova-Lapa E, Gornostaev M, Wilms J, Ballhausen R, Falkner S, Postnov K, Thalhammer P, et al. Journal article The EXTraS project: Exploring the X-ray transient and variable sky (2021) De Luca A, Salvaterra R, Belfiore A, Carpano S, D'Agostino D, Haberl F, Israel GL, et al. Journal article A proto-helium white dwarf stripped by a substellar companion via common-envelope ejection: Uncovering the true nature of a candidate hypervelocity B-type star (2021) Irrgang A, Geier S, Heber U, Kupfer T, El-Badry K, Bloemen S Journal article Potential origin of the state-dependent high-energy tail in the black hole microquasar Cygnus X-1 as seen with INTEGRAL (2021) Cangemi F, Beuchert T, Siegert T, Rodriguez J, Grinberg V, Belmont R, Gouiffès C, et al. Journal article Hubble spectroscopy of LB-1: Comparison with B+black-hole and Be+stripped-star models (2021) Lennon DJ, Maíz Apellániz J, Irrgang A, Bohlin R, Deustua S, Dufton PL, Simón-DÍaz S, et al. Journal article