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XMM-Newton X-ray pre-nova detection and current Swift non-detection of PNV J13544700-5909080 (= Nova Cen 2013)

ATel #5628; E. Kuulkers, J.-U. Ness, A. Ibarra, R. D. Saxton (ESA/ESAC), K. L. Page, J. P. Osborne (Univ. of Leicester), B. Skiff (Lowell Observatory), S. Starrfield (Arizona State Univ.), G. Schwarz (AAS)
on 4 Dec 2013; 16:59 UT
Credential Certification: Erik Kuulkers (Erik.Kuulkers@sciops.esa.int)

Subjects: X-ray, Nova, Transient, Variables

Referred to by ATel #: 5966

A bright new nova in Centaurus, PNV J13544700-5909080, was discovered on UT December 2.692 (mag 5.5; CBET #3732, see also ATel #5621). The nova, dubbed Nova Cen 2013 (CBET #3732), was observed by Swift (ObsID 00033048) on UT December 3, 20:37-20:56, for a total of 1 ks. No X-ray source at the position of the nova is seen with the XRT in WT mode, with a 3-sigma upper limit of 0.03 cts/s (0.3-10 keV). Because of the source brightness the UVOT was in Blocked mode.

As noted by Skiff (vsnet-alert 16675), there is an X-ray source in the XMM-Newton Serendipitous Source Catalogue at RA, Dec (J2000) = 13h 54m 45.5s,-59d 09' 04" (with an estimated positional error of 1.5"), only 2" away. This source, 3XMM J135445.1-590904, was detected during a Galactic Plane observation between UT 2002 February 20 16:57 and 21:08, for an exposure of 12 ks (ObsID 0007421501).

The X-ray light curve shows variability between 0.1 and 0.5 EPIC-pn cts/s. The average EPIC-pn X-ray spectrum is bright enough to test spectral models and we can exclude the shape of an absorbed black-body. A two-temperature absorbed APEC model is consistent with the X-ray spectrum yielding a reduced Chi^2 of about 1, with an absorbed flux of 0.3-10 keV flux of (1.0+/-0.1)x10^-12 erg/s/cm^2 and N_H of (2+/-1)x10^21 atoms cm^-2, and we conclude that we are dealing with a non-isothermal collisional plasma.

The Swift/XRT count-rate limit corresponds to an absorbed flux limit of about 1x10^-12 erg/s (0.3-10 keV) assuming a 3 keV optically thin X-ray spectrum, absorbed by 2e21 atoms cm^-2. This is consistent with the XMM-Newton detection.

We further note that the source was covered during an XMM-Newton slew on UT 2011 February 14 with an effective exposure time of 3.3 seconds. No source was seen with a 0.2-12 keV upper limit of 2.7x10^-12 erg/cm^2/s, consistent with the previous XMM-Newton detection.

We thank the Swift PI, Neil Gehrels, and the Swift mission operations team for the prompt Swift observations.