X-ray observations of the nova shell IPHASX J210204.7+471015

Abstract: We present the analysis of XMM-Newton European Photon Imaging Camera (EPIC) observations of the nova shell IPHASX J210204.7$+$471015. We detect X-ray emission from the progenitor binary star with properties that resemble those of underluminous intermediate polars such as DQ Her: an X-ray-emitting plasma with temperature of $T_\mathrm{X}=(6.4\pm3.1)\times10^{6}$ K, a non-thermal X-ray component, and an estimated X-ray luminosity of $L_\mathrm{X}=10^{30}$ erg s$^{-1}$. Time series analyses unveil the presence of two periods, the dominant with a period of $2.9\pm0.2$ hr, which might be attributed to the spin of the white dwarf, and a secondary of $4.5\pm0.6$ hr that is in line with the orbital period of the binary system derived from optical observations. We do not detect extended X-ray emission as in other nova shells probably due to its relatively old age (130-170 yr) or to its asymmetric disrupted morphology which is suggestive of explosion scenarios different to the symmetric ones assumed in available numerical simulations of nova explosions.

• The paper identifies X-ray spectral properties that suggest an underluminous intermediate polar with a plasma temperature near 6.4×10^6 K.
• It reveals distinct periodicities of approximately 2.9 and 4.5 hours, linking them to the white dwarf's spin and the binary orbit.
• The absence of extended X-ray emission challenges symmetric explosion models and supports the need for asymmetric nova scenarios.

Analysis of X-ray Observations of the Nova Shell IPHASX J210204.7$+$471015

The paper presents a detailed examination of X-ray emissions from the nova shell identified as IPHASX J210204.7$+$471015 using data from the {\it XMM-Newton} telescope. This research adds significant insights into the characterization of nova shells, particularly in systems suspected to harbor intermediate polars (IPs).

Overview of Findings

The study primarily focuses on the progenitor binary system's X-ray properties, which indicate features consistent with underluminous IPs. The X-ray spectrum reveals a plasma temperature of $T_\mathrm{X} = (6.4 \pm 3.1) \times 10^6$ K and a non-thermal component suggestive of an IP origin for the system. The estimated X-ray luminosity of $$L_\mathrm{X} = 10^{30} \, \text{erg} \, \text{s}^{-1}$$ aligns with the luminosity observed in known underluminous IPs such as DQ Her.

Time Series and Periodicity Analysis

Time series analysis conducted on the progenitor system's X-ray light curve uncovered distinct periodicities. A primary period of approximately 2.9 hours is observed, likely associated with the white dwarf's spin. An additional period of 4.5 hours correlates with the binary system's orbital period as determined through optical studies. The identification of these periods strongly suggests the presence of a magnetic white dwarf similar to those found in IP systems.

Absence of Extended X-ray Emission

Interestingly, the study did not detect the anticipated extended X-ray emission typically associated with the adiabatic shocks formed by nova explosions. This absence might relate to the shell's age, approximately 130-170 years, or possibly due to its complex, asymmetric morphology. The authors suggest that the observed asymmetry could result from anisotropic ejection scenarios, unlike the symmetric explosions often modeled in simulations.

Theoretical and Practical Implications

The findings emphasize the diversity observed in nova shell morphologies and question conventional assumptions of symmetric nova ejections. From a theoretical viewpoint, this suggests the necessity for nova explosion models to incorporate asymmetric scenarios to reflect realistic astrophysical environments.

From a practical standpoint, the lack of extended X-ray emission in this nova shell raises questions about the conditions under which X-rays could be used as diagnostics for shell characteristics. Future work could leverage high-resolution, deeper X-ray observations to ascertain more granular details of the physical processes at play in such systems.

Conclusion and Future Directions

This research contributes valuable observations to the study of nova shells, particularly in systems where the nature of the white dwarf is under investigation. The findings encourage future studies to consider asymmetries in modeling nova events and their aftermath. Extending these observational studies to a broader array of nova shells will be crucial in refining our understanding of the dynamics and evolution of binary systems undergoing nova eruptions.