THE EXTRAORDINARY X-RAY LIGHT CURVE OF THE CLASSICAL NOVA V1494 AQUILAE (1999 NO. 2) IN OUTBURST: THE DISCOVERY OF PULSATIONS AND A 'BURST'

摘要

V1494 Aql (Nova Aql 1999 No. 2) was discovered on 1999 December 2. We obtained Chandra ACIS-I spectra on 2000 April 15 and June 7 which appear to show only emission lines. Our third observation, on August 6, showed that its spectrum had evolved to that characteristic of a Super Soft X-ray Source. We then obtained Chandra LETG+HRC-S spectra on September 28 (8 ks) and October 1 (17 ks). We analyzed the X-ray light curve of our grating observations and found both a short timescale "burst" and oscillations. Neither of these phenomena has previously been seen in the light curve of a nova in outburst. The "burst" was a factor of ～10 rise in X-ray counts near the middle of the second observation, and which lasted about 1000 s; it exhibited at least two peaks, in addition to other structure. Our time series analysis of the combined 25 ks observation shows a peak at ～2500 s which is present in independent analyses of both the zeroth-order image and the dispersed spectrum and is not present in similar analyses of grating data for HZ 43 and Sirius B. Further analyses of the V1494 Aql data find other periods present which implies that we are observing nonradial g~+ modes from the pulsating, rekindled white dwarf.