Predicting the X-ray signatures of the imminent T Coronae Borealis outburst through 3D hydrodynamic modeling

Context . T Coronae Borealis (T CrB) is a symbiotic recurrent nova, with confirmed eruptions in 1866 and 1946. Mounting evidence suggests an imminent outburst, which would offer a rare opportunity to observe a nearby nova. Aims . We constrain the circumbinary medium (CBM) properties by modeling inter-eruption radio data, then simulate the hydrodynamic evolution of the upcoming T CrB outburst to predict its X-ray signatures, focusing on the impact of the red giant companion, accretion disk, and equatorial density enhancement (EDE) on the remnant and emission. Methods . We modeled the thermal radio signatures of a CBM that consisted of a spherical wind-like component and a torus-like EDE to quantify its density. We then ran three-dimensional hydrodynamic simulations of the nova outburst, varying the explosion energies, ejecta masses, and circumbinary configurations. From these, we synthesized X-ray light curves, spectra, and maps as observed by XMM-Newton and XRISM. Results . The CBM in T CrB is much less dense than in other symbiotic recurrent novae, with a mass-loss rate of Ṁ ≈ 4 × 10 −9 M ⊙ yr −1 for a 10 km s −1 wind. Despite the expected low-density CBM, the outburst’s blast will be strongly collimated along the poles by the combined influence of the accretion disk and EDE, producing a bipolar shock. The companion star partially shields the ejecta, thus forming a bow shock and a hot wake. The X-ray evolution proceeds through three phases: an early phase (the first few hours) dominated by shocked disk material; an intermediate phase (approximately one week to one month) driven by reverse-shocked ejecta; and a late phase dominated by shocked EDE. Soft X-rays trace shocked ejecta, while hard X-rays originate from shocked ambient gas. Synthetic spectra show asymmetric, blueshifted lines due to the absorption of redshifted emission by expanding ejecta. Conclusions . The predicted X-ray evolution of TCrB shows similarities to RS Oph and V745 Sco, as it reaches a comparable peak luminosity ( L X ≈ 10 36 erg s −1 ), but it has a more prolonged soft X-ray phase that reflects its less dense CBM and distinct ejecta-environment interaction.