TITLE:   GCN CIRCULAR
NUMBER:  25901
SUBJECT: LIGO/Virgo S190930t: Transient found in Swift/UVOT counterpart search
DATE:    19/10/01 17:25:07 GMT
FROM:    Samantha Oates at MSSL  <sro@mssl.ucl.ac.uk>

S. R. Oates (Uni. of Warwick), A. A. Breeveld (MSSL-UCL), N. P. M. Kuin (UCL-MSSL),
F. E. Marshall (NASA/GSFC), P. Brown (TAMU), C. Gronwall (PSU),
M. J. Page (UCL-MSSL), M. De Pasquale (Istanbul U.), M. H. Siegel (PSU),
A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), 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), V. D'Elia(ASDC),
P. A. Evans (U. Leicester), P. Giommi (ASI), D. Hartmann (Clemson U.),
J. A. Kennea (PSU),  N. J. Klingler (PSU), H. A. Krimm (NSF), A. Y. Lien (GSFC/UMBC),
D. B. Malesani (DTU Space), 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),
G. Tagliaferri (INAF-OAB), A. Tohuvavohu (U Toronto), and
E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift team:

We report a candidate transient found in the UVOT search results of the
LVC event S190930t (LIGO/VIRGO Collaboration GCN Circ. 25876).

On 2019-09-30 at 18:33:40 UT Swift UVOT took a 74 s exposure in the
u band with exposure ID uu591561225I (target ID 07021582001). The new source is
not listed in the USNO-B1, Gaia DR1, GSC2.3 or 2MASS and is not listed as a minor planet.

The UVOT position is

    RA (J2000)  22:19:51.82 = 334.96592
   Dec (J2000) -48:42:40.1  = -48.71114

with an estimated uncertainty of 0.7 arcsec (radius, 90% confidence).

The magnitude using the UVOT photometric system  (Breeveld et al. 2011, AIP
Conf. Proc. 1358, 373) is u = 18.47 +/- 0.20 mag (Vega).

A faint unresolved counterpart consistent with this position is identified in
the DSS archival image and in the Dark Energy Camera Legacy Survey (DECaLS; http://legacysurvey.org/decamls/),
with reported magnitudes g = 22.76, r = 21.18, and z = 20.29. A source is also
observed at this position in VISTA archival images with magnitudes of J = 18.82,
H = 18.35, Ks = 17.88. The infra-red archival detection may indicate
that this source is a flare of a red dwarf star.

In 72 s of XRT data, there is no X-ray source detected, with a 3-sigma
upper limit of 0.12 count s^-1 (corresponding to an observed flux of
~5e-12 erg cm^-2 s^-1, assuming a typical power-law spectrum).

This circular is an official product of the Swift team.

[GCN OPS NOTE(01oct19): Per author's request, the extra copy of the Notice
in development was removed from the end of this Circular as submitted.
And  N. J. Klingler was added to the author list.]