Day 1148

Wednesday.  Thursday.

1609.01283
The search for failed supernovae with the large binocular telescope: confirmation of a disappearing star
Adams, Kochanik, Gerke, Stank, Dai

Present HST imaging confirming the optical disappearance of the failed SN candidate identified by Gerke+2015.  This ~25 Msun red supergiant experienced a weak ~1e6 Lsun optical outburst in 2009 and is now at least 5 magnitudes faster than the progenitor in the optical.  The mid-IR flux has slowly decreased to the lowest levels since the first measurements in 2004.  There is faint (2000-3000 Lsun) NIR emission likely associated with the source.  Find the late-time evolution of the source to be inconsistent with obscuration from an ejected, dusty shell. Models of the spectral energy distribution indicate that the remaining bolometric luminosity is >6 times fainter than that of the progenitor and is decreasing as ~t^-4/3.  Conclude that the transient is unlikely to be a SN imposter or stellar merger.  The event is consistent with the ejection of the envelope of a red supergiant in a failed SN and the late-time emission could be powered by fallback accretion onto a newly-formed black hole.  Future IR and X-ray observations are needed to confirm this interpretation of the fate for the star.


1609.01714
The effect of fiber collisions on the galaxy power spectrum multipole
Hahn, Scoccimarro, Blanton, Tinker ,Rodriguez-Torres

Fiber-Fed muti-object spectroscopic surveys, with their ability to collect an unprecedented number of redshifts, currently dominate LSS studies.  However, physical constraints limit these surveys from successfully collecting redshifts from galaxies too close to each other on the focal plane.  This ultimately leads to significant systematic effects on galaxy clustering measurements.  Using simulated mock catalogs, demonstrate that fiber collisions have a significant impact on the power spectrum, P(k), monopole and quadrupole that exceeds the sample variance at scales smaller than k~0.1 h/Mpc.  Present two methods to account for fiber collisions in the power spectrum.  The first statistically reconstruct the clustering of fiber collided galaxy pairs by modeling the distribution of the LoS displacements between them.  It also property accounts for fiber collisions i the shot-noise corruption term of the P(k) estimator.  Using this method, recover the true P(k) monopole of the mock catalogs with residuals of <0.5% at k=0.3 h/Mpc and <4% at k=0.83 h/Mpc -- a significant improvement over existing correction methods.  The quadrupole, however, does not improve significantly.  The second method models the effect of fiber collisions on the power spectrum as a convolution with a configuration space top-hat function that depends on the physical scale of fiber collisions.  It directly computes theoretical predictions of the fiber-collided P(k) multipoles and reduce the influence of smaller scales to a set of nuisance parameters.  Using this method, reliably model the effect of fiber collisions on the monopole and quadrupole down to the scale limits of theoretical predictions.  The methods presented in this paper will allow robust analysis of galaxy power spectrum multipole measurements to much smaller scales than previously possible.