Constraining the white-dwarf mass in the intermediate polar IGR J17014-4306 using X-ray and optical spectroscopy

Abstract

Intermediate polars (IPs), a subclass of magnetic cataclysmic variables, often show discrepancies between white-dwarf (WD) mass measurements from X-ray spectral modeling and optical dynamical studies. We investigate the IP IGR J17014-4306. We performed a joint spectral analysis of NuSTAR observations combined with archival XMM-Newton and Swift data, modeling the broad-band X-ray spectrum with a multi-temperature cooling-flow model. Additionally, we obtained time-resolved optical spectroscopy with the SOAR telescope to measure the radial velocity of the donor star and constrain the system's orbital parameters. The X-ray spectral analysis reveals a very high post-shock plasma temperature of $k{T}_{\max }=50_{-8}^{+11}\mathrm{keV}$, corresponding to a WD mass of $M_{\mathrm{WD}}=0.94_{-0.07}^{+0.09}{M}_{\odot }$. We also fitted the NuSTAR spectrum above 10 keV with the ipolar30KK model, obtaining $M_{\mathrm{WD}}=0.88_{-0.12}^{+0.14}{M}_{\odot }$. Our optical spectroscopy yields a radial-velocity semi-amplitude for the companion star of $K_2=165\pm 4\mathrm{km}{\mathrm{s}}^{-1}$ and an optical mass function of $f(M)=0.249\pm 0.018M_{\odot }$. Combined with the eclipse geometry and the WD mass estimate from the X-ray models, these results favor a high mass ratio, $0.76\lesssim q\lesssim 0.95$, and a donor-star mass of approximately $0.67\lesssim M_2/M_{\odot }\lesssim 0.89$. In the limiting case of $q=1$, the WD mass has an upper limit of $1.14M_{\odot }$. Together with the X-ray measurements, this indicates a relatively massive WD. The lack of an independent measurement of the WD dynamical mass leaves it unclear whether the dynamical mass is consistent with the X-ray measurements or whether the X-ray mass is underestimated, as has been found for other IPs. Thus, our constraints make IGR J17014-4306 an important system for improving our understanding of IPs.

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