TITLE:   GCN CIRCULAR
NUMBER:  21733
SUBJECT: LIGO/Virgo G299232: Optical Transient Discovery by Swift/UVOT
DATE:    17/08/28 18:13:59 GMT
FROM:    Samuel Emery at UCL-MSSL/Swift  <samuel.emery.15@ucl.ac.uk>

S.W.K. Emery (UCL-MSSL), A.A. Breeveld (UCL-MSSL), F.E. Marshall (NASA/GSFC),
S.R. Oates (Uni. of Warwick), N.P.M. Kuin (UCL-MSSL), S.D. Barthelmy (NASA/GSFC),
A.P. Beardmore (U. Leicester), D.N. Burrows (PSU), S. Campana (INAF-OAB),
S.B. Cenko (NASA/GSFC), G. Cusumano(INAF-IASF PA), A. D'Ai (INAF-IASFPA),
P. D'Avanzo (INAF-OAB), V.D'Elia(ASDC), P.A. Evans (U. Leicester), 
P. Giommi (ASI), C. Gronwall (PSU), J.A. Kennea (PSU), H.A. Krimm (CRESST/GSFC/USRA),
A.Y. Lien (GSFC/UMBC), A. Melandri (INAF-OAB), J.A. Nousek (PSU), P.T. O'Brien (U. Leicester),
J.P. Osborne (U. Leicester), C. Pagani (U. Leicester), K.L. Page (U.Leicester),
D.M. Palmer (LANL), M. Perri (ASDC), J.L. Racusin (NASA/GSFC), T. Sakamoto (AGU),
B. Sbarufatti (INAF-OAB/PSU), M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB),
A. Tohuvavohu (PSU), E. Troja (NASA/GSFC/UMCP)
report on behalf of the Swift team:

Swift has performed a series of 525 observations, covering 497 separate
locations within the LVC error region for the GW trigger G299232
convolved with the 2MPZ catalogue (Bilicki et al. 2014, ApJS, 210, 9),
using the 'bayestar-HLV' GW localisation map. The observations currently
span from 11 ks to 256 ks after the LVC trigger.

We have detected an uncatalogued source with the Swift/UVOT, at the position:

RA(J2000) = 01h 40m 08.55s
Dec(J2000)= +34d 34' 03.6" 

We obtain the following magnitude using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373):

Filter          Exp(s)         Mag

u               57             18.00 +/- 0.16

The 57-s exposure started at 2017-08-27 T12:02:34
(about 1.95 days after the LVC trigger).

The magnitude is not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.04 in the direction of the source
(Schlegel et al. 1998).

No X-ray source was detected at this position, with a 0.3-10 keV upper limit
of 0.13 ct/sec, which corresponds to 5.2e-12 erg/cm^2/s (assuming a typical AGN spectrum).

There is no source in the DSS or SDSS at this position and there is no minor planet at this position.

Further Swift observations are planned.