Swift observations of Gaia17acy/2017it
ATel #10029; K. Sokolovsky (IAASARS NOA/ASC Lebedev/SAI MSU), L. Wyrzykowski, A. Hamanowicz, M. Gromadzki (Warsaw Observatory)
on 31 Jan 2017; 10:54 UT
Credential Certification: Kirill Sokolovsky (firstname.lastname@example.org)
Subjects: Optical, Ultra-Violet, X-ray, AGN, Supernovae, Tidal Disruption Event
The optical transient Gaia17acy was discovered on 2017-01-14
coinciding with an uncataloged galaxy. Follow-up spectroscopic
observations by NOT (ATel #9990) and PESSTO (ATel #10012) show blue
continuum and emission lines at z = 0.175. There is an indication
of a broad H-alpha emission component hinting this might be
a luminous Type IIn supernova (ATel #10012).
Swift observed Gaia17acy for 2.5ks spread across two visits between
2017-01-27 13:40 and 2017-01-28 09:12 UT. No X-ray source is
detected down to the upper limit of about
0.0004+/-0.0004 XRT counts/sec (a single photon counted within
the source region). Assuming power law emission with the photon
index of 2 and HI column density of 8.78x10^20 cm^-2 (Kalberla &
Haud 2015, A&A, 578, A78) this translates to the unabsorbed
0.3-10 keV flux limit of 1.5x10^-14 ergs/cm^2/s.
An optical-UV source is detected at the position of the transient
with the following UVOT magnitudes (Vega system):
Filter mag err
V 18.55 0.21
B 19.15 0.15
U 18.61 0.14
W1 18.75 0.17
M2 18.78 0.15
W2 19.32 0.16
Accounting for the Galactic reddening of E(B-V)=0.089 (Schlafly et
al. 2011, ApJ, 737, 103) and assuming no additional extinction from
the host galaxy, the measured magnitudes are consistent with
a T=11000K black-body radiation expected for a luminous supernova.
Further optical (photometry and spectroscopy) and UV observations
are necessary to observe the temperature evolution.
In the supernova scenario the temperature should eventually drop
below 10000K, while if this is a tidal disruption event or an AGN
flare, but diminished by internal extinction, the temperature would
remain high for weeks or months.
We thank the Swift team for rapid execution of this observation.
We acknowledge ESA Gaia,
DPAC and the Photometric Science Alerts Team (Rixon et al, 2014, ATel #6593).
Gaia Photometric Science Alerts