Fireworks and surprises from two recent luminous novae

In the Summer of 2021 two interesting nova outbursts were observed:

   the eruption of V1674 Her, a nova with a highly magnetized white dwarf,

   and the seventh observed explosion of RS Oph, a sort of Rosetta stone 

   of symbiotic recurrent  novae. RS Oph appears to host a massive

   carbon-oxygen white dwarf and is a candidate progenitor of a thermonuclear

   supernova. Both novae were observed at all wavelengths, from gamma rays

   (even with Cherenkov telescopes for RS Oph) to radio. This talk will focus

   especially on the X-ray range. Both novae became extremely luminous,

   allowing high resolution spectra to be taken with X-ray gratings,

   and both showed intriguing modulations of the supersoft X-ray flux.

   V1674 Her displayed a periodic pulsation every 501 seconds, and RS Oph,

   exactly like in its 2006 outburst, a quasi-periodic pulsations 

   about every 35 seconds. These periodicities are difficult to model

   and understand, but they reveal some fundamental physics of the

   underlying white dwarf undergoing shell nuclear burning.