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Swift follow-up observation of the optical transient PS16ccm

ATel #9247; A. K.H. Kong (National Tsing Hua University, Taiwan)
on 15 Jul 2016; 16:55 UT
Credential Certification: Albert Kong (akong@phys.nthu.edu.tw)

Subjects: Ultra-Violet, X-ray, Cataclysmic Variable, Transient

We report on a Swift follow-up observation of the optical transient PS16ccm (= Gaia16ara; ATel #9226). The field of this source was observed with Swift on 2016-07-13 04:36 UT for a total exposure of about 3 ks. No X-ray source was found at the optical position. Assuming an absorbed power-law model with N_H=2e20 cm^-2 and a photon index of 1.5, the 3-sigma unabsorbed 0.3-10 keV flux upper limit is 9.1e-14 erg/s/cm^2. Based on optical spectroscopy (ATel #9226), it was suggested that PS16ccm could be a black hole X-ray transient in the low/hard state. Even if the source is at 10 kpc, the corresponding X-ray luminosity limit would be 1.1e33 erg/s which is lower than a typical low/hard state black hole transient. The X-ray flux limit indicates that PS16ccm as a low/hard state black hole transient is unlikely. Alternatively, a WZ Sge-type dwarf nova in superoutburst is more possible.

We also examine the UVOT images taken with the uvm2 filter (central wavelength: 224.6 nm). PS16ccm is clearly detected in the UV band. The uvm2 magnitude of the source varies significantly between 17.2 mag and 17.4 mag on a timescale of ~5000s.

We wish to thank the Swift Team for approving this TOO observation.