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Detection of absorbed X-ray emission from TCP J17154683-3128303 by Swift

ATel #6015; E. Kuulkers (ESA/ESAC), K. L. Page (U. Leicester), R. D. Saxton, J.-U. Ness (ESA/ESAC), N. P. Kuin (UCL-MSSL) & J. P. Osborne (U. Leicester)
on 27 Mar 2014; 14:48 UT
Credential Certification: Erik Kuulkers (Erik.Kuulkers@sciops.esa.int)

Subjects: X-ray, Nova, Transient, Variables

Referred to by ATel #: 6025, 6032, 6034, 6035

Swift observed a new source in Scorpius, TCP J17154683-3128303, discovered in the optical at unfiltered CCD magnitude 10.1 on UT 2014 March 26 20:22 by Nishiyama & Kabashima (no source was seen in prior optical exposures of the field on UT March 22 19:39 and March 23 20:04, with limiting unfiltered CCD magnitudes of 12.5 and 12.9, respectively; http://www.cbat.eps.harvard.edu/unconf/followups/J17154683-3128303.html ).

Two Swift snapshots, taken 7.3 and 8.4 hours after the discovery (i.e., on UT March 27 03:39-03:51 and 04:42-04:51), reveal a new, bright, X-ray source with XRT-PC (0.3-10 keV) count rates of 0.35 +/- 0.02 c/s and 0.43 +/- 0.03 c/s, respectively. The source is also seen in UVOT, with uvw1 magnitudes of 12.58 +/- 0.02 and 12.61 +/- 0.02, for the 2 snapshots, respectively.

The enhanced XRT position (Goad et al., 2007, A&A, 476, 1401; Evans et al., 2009, MNRAS, 2009, 397, 1177) is at RA, Dec (J2000.0) = 17h 15m 47s, -31d 28' 29" (90% confidence error radius of 2.1'). From the summed UVOT/uvw1 data we derive RA, Dec (J2000.0) = 17h 15m 46.8s, -31d 28' 30.2" (90% confidence error radius of 0.3"). Both are consistent with the optically reported position.

The mean X-ray spectrum can be best fit with an absorbed optically thin emission model. Using an APEC model, we derive kT = 6.4 +3.8/-2.1 keV and N_H = (5.8 +1.2/-1.0)e22 cm^-2 (C-stat: 164/216 dof; equivalent to chi^2 of 249/219 dof). A black-body or cut-off power law fit give somewhat worse fits. The Galactic N_H is about 4e21 cm^-2; this indicates most of the absorption is intrinsic to the source, and would be consistent with an (expanding) shell in a nova.

The source was covered during an XMM-Newton slew on UT 2011 March 4. No source was seen with a 0.2-12 keV 2-sigma upper limit of 0.54 c/s. This upper limit corresponds to about 0.05 c/s for the Swift XRT-PC (0.3-10 keV) assuming our best fit spectral model.

Follow-up Swift ToO observations for the next days have been approved. We thank the Swift PI, Neil Gehrels, and the Swift mission operations team for the prompt Swift observations.