Johannes Kepler’s original drawing from “de stella nova” (1606)

¡  Rise time < 10 days ¡  Luminous & Blue

(M<-16.5) ¡  Rare!

!  SN 2002bj (Poznanski+10, SN Ia like spec, but Helium line)

!  SN 2010X (Kasliwal+10, faint, thermonuclear?)

!  SN 2015U (Shivvers+16, narrow Helium lines, CSM interactions?)

SN 2002bj (Poznanski+10)

¡  First samples with new surveys !  PS1 (6-16 events, Drout+14) !  SNLS/PTF (4 events, Arcavi+16) !  Subaru (5 events, Tanka+16)

PS1 gold sample, Drout+14

¡  Blue colors ¡  Blue feature-less

continuum

peak

-21 days -2 month

+14 days

DECam images

¡  K2 Campaign 6 ¡  KSN 2015K Lightcurve:

!  Rises to peak in 2.2 days !  Time above half-

maximum: 6.8 days ¡  Host:

!  star-forming spiral !  z=0.09

¡  KSN 2015K is blue, ground-based colors: !  R-I = -0.15 +- 0.05 at

peak !  g-r = -0.17 +- 0.20 at +8

days

¡  Green: SDSS SN Ia ¡  Purple: .Ia models

(Shen+10) ¡  Dotted lines: Arnett's

rule for a range of synthesized 56Ni masses.

¡  Dashed line: Pure 56Ni envelope is ejected at 10000 km s-1.

Rest+18

¡  Possible explosion mechanisms !  Radioactive decay !  .Ia model !  Kilonova !  Central engine (magnetar

or accreting black hole) ▪  B∼5×1015 Gauss ▪  Unusually small ejecta mass

!  GRB orphan afterglow !  Shock-breakout into CSM

shell Armin Rest, STScI

Rest+18

¡  Possible explosion mechanisms !  Radioactive decay !  .Ia model !  Kilonova !  Central engine (magnetar

or accreting black hole) ▪  B∼5×1015 Gauss ▪  Unusually small ejecta mass

!  GRB orphan afterglow !  Shock-breakout into

CSM shell Armin Rest, STScI

Rest+18

¡  Shock-breakout into CSM shell !  Simple model: mass loss

episode 2×10-1 Msun occuring 20 days before explosion

!  Numerical simulations:

Armin Rest, STScI

¡  Fast-evolving, luminous transients !  Blue colors, blue, feature-less spectrum !  Difficult to discover in time !  Diverse

¡  Recent surveys: first real samples! (PS1, SNLS/PTF, Subaru)

¡  KSN 2015K: !  Excellent light curve !  2.2 days rise, t1/2=6.8 days !  Host: star-forming spiral at z-0.09 !  Possible mechanism: ▪  Central engine (magnetar) ▪  Orphan afterglow ▪  Shock-breakout into CSM shell

!  Shock-breakout into CSM shell favored.