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Swift-XRT detection of V1369 Cen

ATel #5966; K. L. Page, A. P. Beardmore, J. P. Osborne (U. Leicester) and G. J. Schwarz (AAS)
on 10 Mar 2014; 12:49 UT
Credential Certification: Kim Page (kpa@star.le.ac.uk)

Subjects: X-ray, Nova

Referred to by ATel #: 15310

V1369 Cen (Nova Cen 2013) was discovered on 2013 December 2.692 (CBET 3732; IAUC 9265) and is the fifth LAT-detected nova (ATel #5649), detected in gamma-rays between 2013 December 7 and 10. Swift monitoring of V1369 Cen began on 2013 December 03, collecting XRT data in Windowed Timing (WT) mode, in order to mitigate the optical loading caused by the optical brightness of the nova. [WT mode provides only 1-dimensional imaging, but has a much short frame time than Photon Counting mode (PC), which would usually be the mode of choice when looking for faint sources.] No X-ray source was detected throughout December and January (see also ATEL #5628).

An observation on 2014 February 18 suggested a possible detection of an X-ray source at a count rate of 0.059 +/- 0.009 count s-1. After this date, the optical magnitude had decreased sufficiently such that PC mode could be used. In the next observation, on February 25, a hard X-ray source was clearly detected, with a count rate of 0.057 +/- 0.005 count s-1. The spectrum was well-fitted as strongly absorbed optically-thin emission (the APEC component in XSPEC was used), with kT = 2.3 +3.9/-0.9 keV and NH = (4.1 +2.0/-1.6) x 1022 cm-2.

A further observation on March 8 revealed that the X-ray source had brightened to 0.217 +/- 0.008 count s-1. The majority of the spectrum is consistent with that of the previous observation [kT = 2.2 +1.3/-0.7 keV; NH = (2.8 +1.0/-0.8) x 1022 cm-2], though there is a significant excess of counts below 0.7 keV, suggesting the onset of softer emission. Further observations are planned and will confirm or deny this as the start of the super-soft source phase.

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