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GCN Circular 27400

LIGO/Virgo S200213t: Continued Swift UVOT and XRT observations of ZTF20aamvmzj (AT2020cja)
2020-03-17T13:54:01Z (4 years ago)
Samantha Oates at MSSL <>
S. R. Oates (U. of Birmingham),  N. J. Klingler (PSU), K. L. Page (U.Leicester), A. A. Breeveld (MSSL-UCL),
P. Brown (TAMU), M. De Pasquale (Istanbul U.), C. Gronwall (PSU), N. P. M. Kuin (UCL-MSSL),
F. E. Marshall (NASA/GSFC), 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.),
J. A. Kennea (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 continued Swift/UVOT and XRT observations of ZTF20aamvmzj (AT2020cja; Kasliwal et al.,
GCN Circ. 27051) found by Zwicky Transient Facility during the search for the EM counterpart
of the LVC event S200213t (LIGO/VIRGO Collaboration GCN Circ. 27042). This object was also
observed by Lulin (Li et al., GCN Circ. 27082) and spectroscopically by DBSP (Ho et al., GCN Circ. 27074). 
The Swift/UVOT detection was reported in Oates et al., (GCN Circ. 27153).

Swift/UVOT and XRT has monitored this source from 6.7 days until 29 days after the LIGO/VIRGO trigger
(LIGO/VIRGO Collaboration GCN Circ. 27042). During this time the source was observed to decay and we
no longer detect the source in any filter. In the following we give preliminary 3 sigma upper limits,
combining images from the last two observations, using the UVOT photometric system (Breeveld et al. 
2011, AIP Conf. Proc. 1358, 373):

Filter   T_start(s)   T_stop(s) Exp(s)     3sigUL

v        1714547      2505112    428        > 19.8
b     	 1713986      2504817	 428        > 20.7
u     	 1713871      2504756	 428        > 20.2
w1     1713647      2504694	 857        > 20.2
m2     1714661      2505297	 1238       > 20.5
w2     1714102      2505050    1717       > 20.8

The magnitudes in the table are not corrected for the Galactic extinction due to the
significant reddening of E(B-V) = 0.23 in the direction of the burst (Schlegel et al. 1998).

Combining all 14.4 ks of XRT data collected to date, no source is detected down to a count rate
of 6.7x10^-4 count s^-1. This corresponds to a 3-sigma upper limit of 2.9x10^-14 erg cm^-2 s^-1,
assuming a standard power-law spectrum with NH=3x10^20 cm^-2, and photon index (Gamma)=1.7.

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