The supersoft X-ray phase of RS Oph
Abstract
RS Oph is being monitored with NICER almost daily. In the most recent observations, we detected a luminous supersoft X-ray source, in agreement with recent measurements (ATel #14894, ATel #14901) with very few counts above 1.5 keV. The count rates were 942.0 & plusmn; 0.5 cts/s on 2021 September 19 (averaged over a net exposure time of 6580 s, in different snapshots lasting up to about 1000 s each), 898.5 & plusmn; 0.6 cts/s on 2021 September 19 (with a total net exposure of 5950 s), and 2072.0 & plusmn; 0.9 cts/s on 2021 September 20 (with a total net exposure of 2460 s). We estimate an average absorbed flux 7.7 x 10-10 erg/cm2/s on September 19, 7.3 x 10-10 erg/cm2/s on September 20, and a large increase to approximately 1.6 x 10-9 erg/cm2/s on September 21. On all these dates, the spectrum can be approximately fitted with a blackbody at a temperature around 40 eV, absorbed with a column density of in the range 5-6 x 10 22 cm-2 and a component of thermal plasma at 1.1 keV. Pulsations with a period of 35.10 & plusmn; 0.01 s and amplitude of up to 20% were measured on September 18, and with a period 34.95 & plusmn; 0.01 s and smaller amplitude on September 19. The amplitude of the pulsations varied, and an irregular drift of the period around the mean value of about 35 s was also apparent.
- Publication:
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The Astronomer's Telegram
- Pub Date:
- September 2021
- Bibcode:
- 2021ATel14926....1O
- Keywords:
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- Nova