Various lines of evidence suggest that very massive stars experience extreme mass-loss episodes shortly before they explode as a supernova.[1−4] Interestingly, several models predict such pre-explosion outbursts. [5−7] Establishing a causal connection between these mass-loss episodes and the final supernova explosion will provide a novel way to study pre-supernova massive-star evolution. Here we report on observations of a remarkable mass-loss event detected 40 days prior to the explosion of the Type IIn supernova SN 2010mc (PTF 10tel). Our photometric and spectroscopic data suggest that this event is a result of an energetic outburst, radiating at least 6 × 10 47 erg of energy, and releasing about 2 Ofek et al. 10−2 M ⊙ at typical velocities of 2000 km s −1 . We show that the temporal proximity of the mass-loss outburst and the supernova explosion implies a causal connection between them. Moreover, we find that the outburst luminosity and velocity are consistent with the predictions of the wave-driven pulsation model [6] , and disfavour alternative suggestions [7] . An outburst from a SN progenitor 3 Spectra of the supernova, showing a blue continuum with Balmer emission lines, are presented in Figure 2. The continuum becomes redder with time, and its slope corresponds to an effective temperature of over 16,000 K at day five and drops to about 8,000 K at day 27. The Hα line has an initial width of ∼ 3×10 3 km s −1 at day 6, decreasing to ∼ 10 3 km s −1 at day 14. A broad (10 4 km s −1 ) P-Cygni profile emerges by day 27. The spectra also show He I lines with decreasing strength, presumably due to the drop in temperature.The nature of the precursor bump is very intriguing and can potentially tell us a great deal about the SN explosion and the progenitor. The only interpretation that is fully consistent with the photometric and spectroscopic evidence is that the first bump represents an outburst from the SN progenitor about one month prior to explosion, while the brighter bump is initiated by a full explosion of the star a few weeks later. Below we analyse this model in the context of the photometric and spectroscopic data. In SI §6 we discuss some alternative models and conclude that they are unlikely.The mass ejected by the precursor burst can be estimated in various independent ways.By requiring that the precursor integrated bolometric luminosity, E bol,prec , is lower than the kinetic energy of the precursor outburst (moving at velocity v prec ) which powers it, we can set a lower limit on the mass ejected in the precursor outburstThe outburst velocity is estimated from the line widths of 1000-3000 km s −1 , seen in the early-time spectra of the SN. As this mass was presumably ejected over a period of about one month (i.e., the outburst duration), the annual mass-loss rate is about 10 times higher. A similar order of magnitude argument can be used to put an upper limit on the mass in the precursor outburst. If some of the SN bolometric energy, E bol,SN , is due to interaction between the SN ejecta, moving a...

Motivated by the nonlinear star formation efficiency found in recent numerical simulations by a number of workers, we perform high-resolution adaptive mesh refinement simulations of star formation in self-gravitating turbulently driven gas. As we follow the collapse of this gas, we find that the character of the flow changes at two radii, the disk radius r d , and the radius r * where the enclosed gas mass exceeds the stellar mass. Accretion starts at large scales and works inwards. In line with recent analytical work, we find that the density evolves to a fixed attractor, ρ(r, t) → ρ(r), for r d < r < r * ; mass flows through this structure onto a sporadically gravitationally unstable disk, and from thence onto the star. In the bulk of the simulation box we find that the random motions v T ∼ r p with p ∼ 0.5, in agreement with Larson's sizelinewidth relation. In the vicinity of massive star forming regions we find p ∼ 0.2 − 0.3, as seen in observations. For r < r * , v T increases inward, with p = −1/2. Finally, we find that the total stellar mass M * (t) ∼ t 2 in line with previous numerical and analytic work that suggests a nonlinear rate of star formation.

We present the discovery and follow-up observations of a broad-line type-Ic supernova (SN), PTF 10bzf (SN 2010ah), detected by the Palomar Transient Factory (PTF) on 2010 February 23. The SN distance is 218 Mpc, greater than GRB 980425 / SN 1998bw and GRB 060218 / SN 2006aj, but smaller than the other SNe firmly associated with gamma-ray bursts (GRBs). We conducted a multi-wavelength follow-up campaign with Palomar-48 inch, Palomar 60-inch, Gemini-N, Keck, Wise, Swift, the Allen Telescope Array, CARMA, WSRT, and EVLA. Here we compare the properties of PTF 10bzf with those of SN 1998bw and other broad-line SNe. The optical luminosity and spectral properties of PTF 10bzf suggest that this SN is intermediate, in kinetic energy and amount of 56 Ni, between non GRB-associated SNe like 2002ap or 1997ef, and GRB-associated SNe like 1998bw. No X-ray or radio counterpart to PTF 10bzf was detected. X-ray upper-limits allow us to exclude the presence of an underlying X-ray afterglow as luminous as that of other SN-associated GRBs like GRB 030329 or GRB 031203. Early-time radio upper-limits do not show evidence for mildly-relativistic ejecta. Late-time radio upper-limits rule out the presence of an underlying off-axis GRB, with energy and wind density similar to the SN-associated GRB 030329 and GRB 031203. Finally, by performing a search for a GRB in the time window and at the position of PTF 10bzf, we find that no GRB in the IPN catalog could be associated with this SN.

We present results of hydrodynamic simulations of massive star forming regions with and without protostellar jets. We show that jets change the normalization of the stellar mass accretion rate, but do not strongly affect the dynamics of star formation. In particular, M * (t) ∝ f 2 (t − t * ) 2 where f = 1 − f jet is the fraction of mass accreted onto the protostar, f jet is the fraction ejected by the jet, and (t − t * ) 2 is the time elapsed since the formation of the first star. The star formation efficiency is nonlinear in time. We find that jets have only a small effect (of order 25%) on the accretion rate onto the protostellar disk (the "raw" accretion rate). We show that the small scale structurethe radial density, velocity, and mass accretion profiles are very similar in the jet and no-jet cases. Finally, we show that the inclusion of jets does drive turbulence but only on small (parsec) scales.