GCN Circular 18569

Phil A. Evans (U. Leicester), Jamie A. Kennea (PSU), Scott Barthelmy
(NASA/GSFC), Dave Burrows (PSU), Sergio Campana (INAF-OAB), Brad Cenko
(NASA/GSFC), Neil Gehrels (NASA/GSFC), Paolo Giommi (ASI), Frank
Marshall (NASA/GSFC), John Nousek (PSU), Paul O'Brien (U. Leicester),
Julian Osborne (U. Leicester), David Palmer (LANL), Matteo Perri
(ASDC), Judy Racusin (NASA/GSFC), Mike Siegel (PSU), Gianpiero
Tagliaferri (INAF-OAB) on behalf of the Swift team:

P. D'Avanzo (INAF-OAB), S. Piranomonte (INAF-OAR), E. Cappellaro 
(INAF-OAPd), M. Branchesi (Urbino University/INFN Pisa), E. Brocato 
(INAF-OAR) on behalf of the INAF-GW collaboration:

Alessandra Corsi (Texas Tech), Shri Kulkarni (Caltech), Mansi Kasliwal 
(Caltech), Dale Frail (NRAO) Avishay Gal-Yam (Weizmann Institute) on 
behalf of the iPTF team:

Swift has observed the location of iPTF15dld (Singer at al., LVC Circ. 
18497), which may be a type Ic supernova (Benetti et al., LVC Circ. 
18563). The observations were gathered from 15.4 d to 15.9 d after the 
aLIGO trigger, for a total of 10 ks observing time.

No X-ray emission is detected from iPTF15dld, with a 3-sigma upper limit 
of 9.8e-4 ct/sec; this corresponds to an approximate 0.3-10 keV flux 
limit of 4.9e-14 erg cm^-2 s^-1.

Swift-UVOT detected a bright source with a magnitude of 17.51 +/- 0.10 
in the uvw1 filter, however this lies within the host galaxy, whose uvw1 
magnitude is not known, thus the above magnitude is a combination of 
host+source. Once the transient has faded, we will perform repeat 
observations to measure the host flux and determine the correct 
transient magnitude.

These Swift observations were performed in part through the Swift-GI 
program 1114155 (PI: Corsi).

This circular is an official product of the Swift GW follow-up team.