Gaia16aqg/AT2016ecm was a Supernova Type Ia near the nucleus of the galaxy
ATel #10293; K. Sokolovsky (IAASARS NOA/ASC Lebedev/SAI MSU), M. Gromadzki, L. Wyrzykowski, A. Hamanowicz (Warsaw Observatory)
on 20 Apr 2017; 16:06 UT
Credential Certification: Kirill Sokolovsky (firstname.lastname@example.org)
Subjects: Optical, Ultra-Violet, X-ray, Supernovae
The optical transient Gaia16aqg/AT2016ecm was discovered on
2016-05-23 coinciding with the center of the galaxy LEDA 581422.
SALT/RSS spectroscopy on 2016-07-08 revealed broad H_alpha and HeI
emission at z=0.060 superimposed on the continuum dominated by
the galaxy light (ATel #9497). The spectrum of host galaxy was
obtained with VLT/FORS2 on 2017-03-20. It shows similar emission
lines but the continuum is more smooth/flat compared to the SALT
spectrum obtained while the transient was bright. The difference
may be attributed to broad metal lines typical for SN Ia, which are
not as strong as usual due to a significant contribution of the
host galaxy light. The spectroscopic classification was done using
SNID code (Blondin & Tonry 2007, ApJ, 666, 1024) on residual
spectrum after host subtraction and is consistent with SN Type Ia
37 days after maximum.
Swift observed Gaia16aqg for 2.1ks on 2017-03-25. Swift/XRT
detected no X-ray source at the position of the transient with an
upper limit of 0.0014 +/-0.0008 cts/s. Assuming power law emission
with the photon index of 2 and HI column density of
1.43x10^20 cm^-2 this translates to the unabsorbed 0.3-10 keV flux
limit of 5.1x10^-14 ergs/cm^2/s.
An ultraviolet source is detected at the position of the transient
with the following Swift/UVOT magnitudes:
Band AB_mag. Err.
W2 19.30 0.06
M2 19.26 0.07
W1 19.15 0.06
Taking into account the Galactic reddening of E(B-V)=0.011
(Schlafly et al. 2011 ApJ, 737, 103) these magnitudes suggest
a black-body emission with the temperature ~18000 K.
An ultraviolet source associated with this galaxy was previously
observed by GALEX having AB magnitudes FUV=19.05 +/-0.14,
NUV=18.79 +/-0.08 (Bianchi et al. 2011 Ap&SS, 335, 161). GALEX NUV
band approximately corresponds to the wavelength range covered by
three UVOT filters (W2, M2, W1). The high color temperature
observed before and after the transient appearance is consistent
with the galaxy LEDA 581422 having an increased star formation.
Lack of clear ultraviolet excess is consistent with the spectral
classification as SN Type Ia occurring near the center of
We acknowledge ESA Gaia, DPAC and the Photometric Science Alerts
Team (ATel #6593). We thank Brad Cenko and the Swift team for
making this observation possible.
Gaia Photometric Science Alerts