TITLE:   GCN CIRCULAR
NUMBER:  18231
SUBJECT: ANTARES neutrino detection and possible Swift X-ray counterpart
DATE:    15/09/03 11:43:31 GMT
FROM:    Phil Evans at U of Leicester  <pae9@leicester.ac.uk>

D. Dornic (CPPM), S. Basa (LAM), P.A. Evans (U. Leicester), J.A. Kennea 
(PSU), J.P. Osborne (U. Leicester) and V. Lipunov (MSU) report on behalf 
of the ANTARES Collaboration, the Swift-XRT team and MASTER team:

September 1st, 2015, at 07:38:25 UT, ANTARES has detected a bright 
neutrino at a location of:
   RA(J2000) = 16h 25m 42s
   DEC (J2000) = -27d 23m 24s
with an uncertainty of 18 arcmin (radius, 50% containment)

A target of opportunity alert has been sent immediately to Swift. The 
XRT onboard Swift followed the ANTARES error box 10 hours after the 
neutrino detection. An uncatalogued X-ray source has been detected above 
the limit of RASS, with the flux varying between 5e-13 and 1.4e-12 erg 
cm^-2 s^-1 (0.3-10 keV), at location:
   RA(J2000) = 16h 26m 2.12s
   DEC (J2000) = -27d 18m 14.8s
with an uncertainty of 2.4 arcsec (radius, 90% containment).

The detected X-ray source seems to be variable. By contrast no 
transient source in the visible domain with MASTER SAAO has been 
observed so far until the magnitude 18.5 with a galactic extinction of 
2 (Schlegel et al). Further Swift observations have been planned.

We encourage strongly further multi-wavelength observations to identify 
this X-ray source.