V1935 Cen becomes the second brightest super-soft source yet detected by Swift

ATel #17459; K. L. Page (U. Leicester), A. P. Beardmore (U. Leicester), N. P.M. Kuin (UCL/MSSL), G. J. M. Luna (UNAHUR/CONICET/Argentina), K. Sokolovsky (TTU)
on 28 Oct 2025; 16:30 UT
Credential Certification: Kim Page (kpa@star.le.ac.uk)

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V1935 Cen (Nova Cen 2025, PNV J14372177-5847400) was discovered in outburst on 2025 September 22.396 UT (CBAT). Observations by the Neil Gehrels Swift Observatory began the following day, revealing a detection of early X-ray shock emission (Sokolovsky et al., ATel #17418). Regular monitoring by Swift continued, with the discovery of a new soft component on October 9, reported by Luna et al. in ATel #17444, #17446). At this time, the X-ray count rate was 0.55 +/- 0.01 count s^-1 over 0.3-10 keV. Continuing observations showed a similar count rate until October 13, while the next observation on October 15 showed brighter X-ray emission, around 2.91 +/- 0.02 count s^-1, with the increase in flux occurring below 1 keV. Three days later, on October 18, the X-ray count rate was found to be dramatically brighter, reaching a count rate of 327.5 +/- 0.6 count s^-1 (snapshot mean). This peak count rate makes V1935 Cen the second brightest super-soft source component Swift-XRT has ever detected, after RS Oph (e.g., Osborne et al., 2011, ApJ, 727, 124), and ahead of KT Eri (e.g., Beardmore et al., ATel #2423).

A search was made for a quasi-periodic oscilations (QPOa) during the bright super-soft interval. During observations on October 18, 20 and 24, there is intermittent evidence for a QPO of around 40 s. When visible, the amplitude of the QPO is around 10 per cent. These results are reminiscent of RS Oph, which also showed a somewhat "erratic" frequency at earlier times (e.g., Osborne et al., 2011, ApJ, 727, 124)

The UV grism observation obtained on October 18 shows double-peaked lines corresponding to NIII] 1750, CIII] 1909, Mg II 2800 and OIII 3133, indicating V1935 Cen is a CO nova.

V1935 Cen has now entered the solar observing constraint for Swift, and cannot be observed again until December 19.