[vsnet-grb-info 24709] LIGO/Virgo S200115j: Swift/UVOT observations of Swift/XRT S200115j_X136

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26808
SUBJECT: LIGO/Virgo S200115j: Swift/UVOT observations of Swift/XRT S200115j_X136
DATE:    20/01/17 22:24:22 GMT
FROM:    Samantha Oates at MSSL  <sro at mssl.ucl.ac.uk>

S. R. Oates (U. of Birmingham), A. A. Breeveld (MSSL-UCL), N. P. M. Kuin (UCL-MSSL),
F. E. Marshall (NASA/GSFC), P. Brown (TAMU), M. De Pasquale (Istanbul U.), C. Gronwall (PSU),
M. J. Page (UCL-MSSL),  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.), K. L. Page (U.Leicester),
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), 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 Swift/UVOT observations of S200115j_X136 (Evans et al., GCN Circ. 26798), a rank 2 XRT source
found during the search for the EM counterpart of the LVC event S200115j (LIGO/VIRGO 
Collaboration GCN Circ. 26759).

Swift/UVOT took a 75s u-band exposure 17.7 hours after the LIGO/VIRGO trigger (LIGO/VIRGO 
Collaboration GCN Circ. 26759) we obtain a u-band magnitude of 16.54 +/- 0.07. Comparing this
to archival UVOT measurements (u = 17.04 +/- 0.07 mag; July 2012), we find S200115j_X136 has
brightened by 0.5 magnitudes. As noted by Evans et al., (GCN Circ. 26798), S200115j_X136 is
consistent with a 2MASS galaxy. Therefore the flux increase compared to previous Swift
observations may reflect AGN activity, or may indicate a transient within that galaxy.

Preliminary magnitudes were determined using the UVOT photometric system (Breeveld et al. 
2011, AIP Conf. Proc. 1358, 373) and have not corrected for the Galactic extinction due to
the reddening of E(B-V) = 0.03 along the line of sight (Schlegel et al. 1998).

This circular is an official product of the Swift team.