X-ray detection of the old nova T Aurigae
ATel #7024; K. Bancroft (Commonwealth School and CfA), D. Takei (RIKEN), J. J. Drake (CfA), T. Sakamoto (AGU), A. Fruscione (CfA)
on 3 Feb 2015; 23:36 UT
Credential Certification: Jeremy J. Drake (jdrake@cfa.harvard.edu)
We report the detection of the progenitor of the old nova T Aurigae using the Chandra X-Ray Observatory's ACIS-S CCD imaging spectrometer. T Aur exploded in 1891 and reached a brightness of 4.1mag (Duerbeck, H.W.,1981,PASP,93,165), which has since decreased to 15th mag. Chandra observed it on 2015 January 16 with an exposure of 5ks. The source comprised 81 counts centered on coordinates (J2000) 05:31:59.1 +30:26:45. The distribution of X-ray photon events on the sky is consistent with a point source, with no obvious emission from the nova remnant. No significant variations in the source count rate of 0.016 count/s were found.
The source X-ray spectrum was quite hard for a cataclysmic variable and reasonably well-matched by a variety of emission models, including a power-law, optically-thin plasma, and a cooling flow. Best-fit model parameters were kT >55 keV (optically-thin plasma), Tmax>65 keV and Mdot=(6+/-2)e-13 Msun/yr (cooling flow model), and gamma=0.6+/-0.2 (power law). The best-fit absorbing column was in the range NH=1-4e21 atoms/cm^3. The flux in the 0.5-10keV bandpass was 2.5+/-0.5e-13 erg/cm^2/s. For a distance of 600pc (Duerbeck, 1981), this corresponds to an X-ray luminosity of 1.1e31 erg. Assuming the X-rays are a result of mass transfer onto the white dwarf, the relatively hard spectrum suggests a magnetic cataclysmic variable star origin rather than a non-magnetic CV, and that at least some of the emission is likely non-thermal in nature.
