Significant Optical Rebrightening of SN 2010da in NGC 300
ATel #3726; R. Chornock, I. Czekala, & E. Berger (Harvard)
on 31 Oct 2011; 01:20 UT
Credential Certification: Ryan Chornock (rchornock@cfa.harvard.edu)
Subjects: Optical, Supernovae, Transient, Variables
We report continuing observations of the dust-enshrouded supernova impostor
SN 2010da in NGC 300 (CBET #2289, ATEL #2632, #2633, #2636, #2637, #2638, #2639, #2640,
#2642, #2648, #2658, #2660). After the initial optical outburst to an
unfiltered magnitude of 16.0 on 2010 May 23 (CBET #2289), this object faded
rapidly (ATEL #2640, #2660). We measured i~20.7 mag (AB) on 2011 January
13.10 UT using LDSS on the Magellan/Clay 6.5-m telescope. Further LDSS
observations obtained on 2011 October 21.16 UT reveal that the object has
now rebrightened by about 2 magnitudes in the optical to i~18.7 mag. This
second outburst from the source provides further evidence that the initial
event was not a true supernova.
Followup spectroscopy was obtained on 2011 October 22.11 UT with the
Magellan Echellette spectrograph (MagE), also mounted on the Magellan/Clay
telescope. The moderate-resolution (FWHM~60 km/s) spectrum broadly
resembles spectra during the initial outburst (ATEL #2636, #2637), with
lines of H I, He I, He II, O I, Fe II, and Ca II displaying complex profiles
with multiple velocity components. In addition, weak unresolved emission
from the [Ca II] 7291, 7324 doublet is present.
The initial outburst from this source was accompanied by strong X-ray
emission (ATEL #2639), so we obtained 10 ks of exposure with the Swift X-ray
Telescope (XRT), centered on 2011 October 27.05 UT. No source is detected
at the position of SN 2010da, to a limit of < 4e-14 erg/s/cm^2. This
upper limit is a factor of ~35 below the earlier detection (ATEL #2639), but
is close to the flux level recorded with Chandra on 2010 September 24 UT by
Binder et al. (2011, ApJL, 739, L51).
We thank the Swift team for approving our Target of Opportunity request.