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V339 Del (Nova Del 2013) is a weak non-super-soft X-ray source

ATel #5429; K. L. Page and A. P. Beardmore (U. Leicester)
on 27 Sep 2013; 16:03 UT
Credential Certification: Kim Page (kpa@star.le.ac.uk)

Subjects: X-ray, Nova

Referred to by ATel #: 5470

V339 Del (Nova Del 2013) is currently being monitored approximately daily by Swift-XRT. X-ray analysis has been complicated due to optical loading caused by photons from the very bright optical source. (For a discussion of optical loading in the XRT, see our help page.) At early times, the data were collected mainly in Windowed Timing mode to mitigate this issue, and no X-ray source was detected (ATel #5283, #5305, #5318). From 2013 September 6 onwards, observations have been made using Photon Counting mode instead, since the level of optical loading is diminishing. However, optical loading is still an issue, albeit at a lower level, so care must still be taken in the interpretation of the X-ray observations.

Donato (ATel #5408) reported X-ray detections on 2013 September 12 and 19, claiming that the source was relatively soft, with more photons below 2 keV than above. While the detection on September 19 (together with a further detection from data collected on September 26) does appear to be real, the apparent softness is most likely caused by the optical loading. (The September 12 data are almost completely optical contamination.) If grade 0 (single pixel event) photons only are considered (these are unlikely to be strongly affected by optical loading), the spectrum appears to be heavily absorbed optically-thin emission. Combining the data from September 19 to 26, the grade 0 spectrum can be fitted with an APEC kT > 0.8 keV and NH = (4.9 +7.5/-3.2) x 1022 cm-2. The mean grade 0 count rate over this time is (1.8 +/- 0.4) x 10-3 count s-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.3 x 10-13 (7.8 x 10-13) erg cm-2 s-1. The detected X-ray emission is consistent with shocked gas in an expanding nova shell, with no evidence for super-soft emission at this time.

We thank the Swift PI and mission operations team for their ongoing support.