TITLE:   GCN CIRCULAR
NUMBER:  25939
SUBJECT: LIGO/Virgo S190930t: Continued Swift/UVOT observations of Swift J221951-484240
DATE:    19/10/03 18:11:57 GMT
FROM:    Paul Kuin at MSSL  <npkuin@gmail.com>

S. R. Oates (Uni. of Warwick), N. P. M. Kuin (UCL-MSSL), A. A. Breeveld
(MSSL-UCL),
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:

Swift UVOT reobserved the field of Swift J221951-484240 (Oates et al., GCN
Circ.
25901), a candidate transient found in the UVOT search results of the LVC
event
S190930t (LIGO/VIRGO Collaboration GCN Circ. 25876).

A search of this source in various catalogs shows only a weak IR source,
however
Swift observed a blue source which maintained its brightness in the second
observation
suggesting that this is not a flaring M-dwarf.

The second tranche of observations began at 2019-10-02 16:14:34 UT 179ks
after
the LVC trigger.

Preliminary detections using the UVOT photometric system (Breeveld et
al. 2011, AIP Conf. Proc. 1358, 373) are:

Filter   Exp(s)        Mag
v         79        > 18.7
b         79        19.68+\-0.36
u         79        18.57+\-0.21
w1       157        17.95+\-0.16
m2       249        17.91+\-0.15
w2       315        18.11+\-0.13

In the combined 1.1 ks of data collected so far, no X-ray source is
detected to a 3-sigma upper limit of 9.9e-3 count s^-1 (equivalent to an
observed flux ~4e-13 erg cm^-2 s^-1, assuming a typical power-law
spectrum).

This new blue transient requires spectroscopy for further identification,
and we
 encourage spectroscopic followup of this transient.

This circular is an official product of the Swift team.