Calvera: A low-mass strangeon star torqued by debris disk?

• Published in: arXiv.org 2017-09
• Main Authors: Li, Yunyang, Wang, Weiyang, Ge, Mingyu, Liu, Xiongwei, Tong, Hao, Xu, Renxin
• Format: Article
• Language: English
• Subjects: Accretion disks; High temperature; Neutron stars; Neutrons; Observatories; Pulsar magnetospheres; Pulsars; Soft x rays; Stellar magnetic fields; Thermal emission; X-rays; XMM (spacecraft)
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1709.07679

Calvera is a \(59\,\mathrm{ms}\) isolated pulsar, being unique due to its non-detection in radio, optical and gamma-rays but the purely thermal emission in soft X-rays. It is suggested that Calvera could be an ordinary middle-aged pulsar with significant magnetospheric activity at a large distance. Alternatively, it is proposed in this paper that Calvera is a low-mass strangeon star with inactive magnetosphere (dead). In this scenario, we jointly fit the spectra obtained by the {\it XMM-Newton} Observatory and the {\it Chandra} X-ray Observatory with the strangeon star atmosphere model. The spectral model is successful in explaining the radiation properties of Calvera and X-ray Dim Isolated Neutron Stars, both showing similar observation features. Within the dead pulsar picture, Calvera might be of high temperature at \(0.67\,\mathrm{keV}\), possessing a small stellar radius \(R\la4\,\mathrm{km}\) and a presumably small magnetic field \(B\la10^{11}\,\mathrm{G}\) and is probably braked by the fall-back disk accretion. Future advanced facilities may provide unique opportunities to know the real nature of Calvera.