Swift observations of the changes in the brightness of the recurrent nova T CrB

ATel #16114; N Paul Kuin (MSSL), Gerardo Juan Manuel Luna (CONICET/ U. of Hurlingham), Kim Page (Leicester U), Koji Mukai (NASA/GSFC & UMBC), Jennifer L Sokoloski (Columbia U), Julian P. Osborne (Leicester U), Bradley E. Schaefer (Louisiana U)
on 3 Jul 2023; 11:06 UT
Credential Certification: Paul Kuin (npkuin@gmail.com)

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Recent notices (Schaefer, ATEL #16107; Munari, RNAAS submitted; Teyssier et al, ATEL #16109) describe a dimming after having several years of brightening across the spectrum (Ilkiewicz et al., 2016; Munari et al., 2016, Luna et al, 2018). Based on the available data from the earlier outbursts of T CrB in 1866 and 1946, a precursor phase showing a dip in the photometric magnitudes B and V has begun around end of May 2023, with a duration of about a year whereafter the eruptive phase is expected to happen around April 2024.

Unlike previous eruptions, we have been able to monitor the gamma, X-ray, and ultraviolet-optical emissions with the Swift satellite since 2008.

We find that the X-ray flux and UV magnitude are now back to the level seen before the brightening. The X-Ray flux decreased in the 2015-2022 period from a count rate of 0.08 to 0.02 cps and recently in 2023 reached again a peak of 0.08 cps, though it shows excursions to levels the level seen before, see the figure: https://drive.google.com/file/d/1xs5ywUA2mpFjqSYMGbZQjOjOughcu2YK/view?usp=sharing . Prior to the active period of 2015-April 2023 the Swift uvm2 magnitudes (Vega system) averaged 14.5; during the active period uvm2 = 9.8 mag; currently uvm2 = 13.0 mag and still dropping, with orbital variations.

During the active period of the past years (2015-April 2023) the UV spectrum (in the range 1700-4000A) showed large changes in absorption depending on the orbital phase. The increased absorption variation is from the changing column density along the line-of-sight and in the UV is likely due to the forest of absorption lines (singly ionised uv lines crowd out the uv emission).

Swift will continue to observe T CrB, but the nova is expected to be too bright for useful observations near its peak.

swift light curves of T CrB