Circumstellar interaction in the extreme white dwarf merger remnant ZTF\,J1901+1458: A new class of white dwarf merger remnants with X-ray emission

Aayush Desai; Ilaria Caiazzo; Stephane Vennes; Adela Kawka; Tim Cunningham; Gauri Kotiwale; Andrei A. Cristea; John C. Raymond; Maria Camisassa; Leandro G. Althaus; J. J. Hermes; Iris Traulsen; James Fuller; Jeremy Heyl; Jan van Roestel; Kevin B. Burdge; Antonio C. Rodriguez; Ingrid Pelisoli; Boris T. Gänsicke; Paula Szkody; Sumit K. Maheshwari; Zachary P. Vanderbosch; Andrew Drake; Lilia Ferrario; Dayal Wickramasinghe; Stephen Justham; Ruediger Pakmor; Kareem El-Badry; Thomas Prince; S. R. Kulkarni; Matthew J. Graham; Ben Rusholme; Russ R. Laher; Josiah Purdum

arXiv · 2509.03216

Circumstellar interaction in the extreme white dwarf merger remnant ZTF\,J1901+1458: A new class of white dwarf merger remnants with X-ray emission

View original source ↗Read source document ↗Export metadata ↓

Abstract

Double degenerate white dwarf (WD) mergers can exhibit extreme magnetic fields exceeding $10^{8}$ G and rapid rotation, but their spectral-energy distributions and high-energy emission mechanisms remain poorly characterised. ZTF J1901+1458 stands out as the most compact and strongly magnetised object discovered in this class to date. Recent Chandra observations have revealed that the white dwarf is also a source of soft X-ray emission, inconsistent with a photospheric origin. We analyse new phase resolved UV spectroscopy from the HST combined with optical and near-infrared photometry and spectroscopy, with newly developed magnetic atmosphere models to determine its effective temperature, radius, mass, average surface magnetic field strength, and cooling age. Our results demonstrate that the spectral break at $\approx$3000 Å, observed in several highly magnetised WDs, is well-reproduced by our new models, which take into account the effect of magnetic opacities on the structure of the atmosphere. Our best-fit parameters for the WD yield an effective temperature ($T_{\rm{eff}}=28,015\pm 20$ K) and larger radius ($2630\pm10$ km) than previously reported. Furthermore, the near-infrared data exclude the presence of a stellar or brown dwarf companion hotter than $\approx$700 K. We also jointly analyse the previously published Chandra data and new XMM-Newton X-ray spectra. The faint X-ray emission, $L_X =(1.3\pm0.2)\times10^{27}$ erg/s is very soft and highly pulsed on the rotation period of the WD. We suggest that the X-rays are powered by accretion or via the interaction of the WD magnetosphere with CSM. If the rapidly rotating magnetic field could power a weak wind along open field lines, material could be extracted directly from the surface of the WD. Alternatively, accretion of fallback material from the merger or the tidal disruption of a planetary body are possible sources of CSM.

Explore related subjects

astro-ph.SR astro-ph.HE

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Aayush Desai, Ilaria Caiazzo, Stephane Vennes, Adela Kawka, Tim Cunningham, Gauri Kotiwale, Andrei A. Cristea, John C. Raymond, Maria Camisassa, Leandro G. Althaus, J. J. Hermes, Iris Traulsen, James Fuller, Jeremy Heyl, Jan van Roestel, Kevin B. Burdge, Antonio C. Rodriguez, Ingrid Pelisoli, Boris T. Gänsicke, Paula Szkody, Sumit K. Maheshwari, Zachary P. Vanderbosch, Andrew Drake, Lilia Ferrario, Dayal Wickramasinghe, Stephen Justham, Ruediger Pakmor, Kareem El-Badry, Thomas Prince, S. R. Kulkarni, Matthew J. Graham, Ben Rusholme, Russ R. Laher, Josiah Purdum. 2026-07-27. Circumstellar interaction in the extreme white dwarf merger remnant ZTF\,J1901+1458: A new class of white dwarf merger remnants with X-ray emission. https://arxiv.org/abs/2509.03216

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Host-star metallicities and kinematics of directly imaged brown-dwarf companions

Brown dwarfs are common as free-floating objects but rare as close companions to Sun-like stars, a disparity known as the "brown-dwarf desert". Host-star metallicity can constrain whether these companions form mainly through metal-sensitive core accretion or through less metal-dependent disc or cloud fragmentation. We extend our homogeneous spectroscopic analysis of directly imaged planet hosts into the brown-dwarf regime and compare their metallicities with those of planet hosts and close-in brown-dwarf hosts. We compiled 54 unique directly imaged brown-dwarf systems selected over an inclusive 13-80 M_Jup interval and projected separations from about 5 au to several thousand au. Objects near the model-dependent 70-75 M_Jup hydrogen-burning boundary may instead be very-low-mass stars. For 31 hosts with archival high-resolution spectra, we derived atmospheric parameters and metallicities using Bayesian spectral synthesis. Literature companion masses and projected separations are heterogeneous and are used only for demographic context. Galactic velocities were calculated for 46 hosts solely to characterise the youth-biased imaging sample. The host stars have a broadly solar metallicity distribution, with a median [Fe/H] of +0.06 dex and a median absolute deviation of 0.11 dex, and show no strong metal-rich bias. No statistically significant metallicity difference is detected between the lower- and higher-mass directly imaged subsamples. The hosts are kinematically cold, as expected from the youth-biased selection of direct-imaging surveys. The absence of a strong metal-rich bias suggests that classical core accretion does not dominate the wide-orbit brown-dwarf population. Disc instability and cloud fragmentation remain plausible, but the current sample and heterogeneous companion properties do not permit object-by-object discrimination between these channels.

astro-ph.SR↗

arXiv2026

Stability Analysis of the Proton Hammerhead Distribution Observed by Parker Solar Probe: Linear Theory and Fully Kinetic Simulations under Idealised Conditions

The non-adiabatic heating of the slow Solar Wind (SW) remains an open problem, with wave--particle interactions as a primary candidate mechanism. Novel in situ Parker Solar Probe (PSP) observations reveal strongly perpendicular anisotropic velocity distribution functions (VDFs), called "hammerhead", correlated with intense wave activity. These VDFs are systematically measured at the Heliospheric Current Sheet (HCS), making the hammerhead an important kinetic signature of the slow SW. In this work, we employ a fully kinetic particle-in-cell approach, complemented by a linear Vlasov solver to cross-validate the simulation results, to investigate the stability of these VDFs, the timescales over which they evolve, and their interaction with plasma waves. Our main findings indicate that the hammerhead distribution is primarily susceptible to drift-type instabilities, while energy is nonlinearly transferred back to the plasma through a combination of Landau and cyclotron resonances, resulting in net heating in the parallel direction, preferentially energizing the beam proton population. Crucially, these nonlinear interactions do not drastically alter the morphology of the distribution. This suggests the possibility that the hammerhead may be generated locally within the HCS in the inner heliosphere and subsequently advected outward, where it is eventually measured by PSP. This work lays the ground for future investigations into the kinetic physics of the HCS.

astro-ph.SR↗

arXiv2026

The independence of the mid-infrared RR Lyrae Period-Luminosity relation from metallicity from a study of three globular clusters in the Large Magellanic Cloud

RR Lyrae are pulsating variable stars tracing old ($>10$ Gyr) stellar populations, and exhibit a strong mid-infrared Period-Luminosity (PL) relation that can be calibrated with known parallaxes to infer distances. Here we present Period-Luminosity relations and distance moduli for three isolated globular clusters in the Large Magellanic Cloud: Reticulum, NGC 1841, and NGC 1466. Our analysis uses legacy \textit{Spitzer Space Telescope} images obtained by the Carnegie RR Lyrae Program, and an internally self-consistent sample restricted to RRab stars, with cluster membership confirmed using Gaia DR3 proper motions and photometry. In the Spitzer 3.6~$μ$m band, we simultaneously fit a PL for these clusters using a slope derived from Galactic Globular Clusters, yielding extinction-corrected distance moduli of $18.47\pm0.09$ mag for Reticulum, $18.29\pm0.09$ mag for NGC 1841, and $18.61\pm0.09$ mag for NGC 1466. The latter two are the first RR Lyrae PL-based distance moduli for these clusters, and all three are consistent with literature values from other techniques. Additionally we fit a PL with slope as a free parameter, and find that this LMC-derived PL is consistent with that derived from Galactic GCs. Simultaneously fitting a PLZ for the three clusters yields a metallicity coefficient $c= -0.03\pm0.05~\mathrm{mag}~\mathrm{dex}^{-1}$ which can be considered a negligible dependence of the PL on metallicity ($|c| <0.1$ mag dex$^{-1}$). Modelling an intrinsic width, $W$, to the PL/ PLZ yields a consistent value $W\approx0.1\pm0.02~\mathrm{mag}$, suggesting intrinsic width is not driven by metallicity.

astro-ph.SR↗