X-ray Spectroscopy of the gamma-ray Brightest Nova V906 Car (ASASSN-18fv)

Understand

Shocks in gamma-ray emitting classical novae are expected to produce bright thermal and non-thermal X-rays.

• We test this prediction with simultaneous NuSTAR and Fermi/LAT observations of nova V906 Car, which exhibited the brightest GeV gamma-ray emission to date.
• The nova is detected in hard X-rays while it is still gamma-ray bright, but contrary to simple theoretical expectations, the detected 3.5-78 keV emission of V906 Car is much weaker than the simultaneously observed >100 MeV emission.
• No non-thermal X-ray emission is detected, and our deep limits imply that the gamma-rays are likely hadronic.