Supernovae Supernova Remnants Gamma-Ray Bursts

1. 0 Supernovae Supernova Remnants Gamma-Ray Bursts

2. 0 Summary of Post-Main-Sequence Evolution of Stars Supernova Fusion proceeds; formation of Fe core. Subsequent ignition of nuclear reactions involving heavier elements M > 8 Msun Fusion stops at formation of C,O core. M < 4 Msun

3. 0 Fusion of Heavier Elements 126C + 42He → 168O + g 168O + 42He → 2010Ne + g 168O + 168O → 2814Si + 42He Onset of Si burning at T ~ 3x109 K → formation of S, Ar, …; → formation of 5426Fe and 5626Fe → iron core Final stages of fusion happen extremely rapidly: Si burning lasts only for ~ 2 days.

4. 0 Observations of Supernovae Total energy output: DEne ~ 3x1053 erg (~ 100 L0 tlife,0) DEkin ~ 1051 erg DEph ~ 1049 erg Lpk ~ 1043 erg/s ~ 109 L0 ~ Lgalaxy! Supernovae can easily be seen in distant galaxies.

5. 0 Type I and II Supernovae Core collapse of a massive star: Type II Supernova Light curve shapes dominated by delayed energy input due to radioactive decay of 5628Ni Type II P Collapse of an accreting White Dwarf exceeding the Chandrasekhar mass limit → Type Ia Supernova. Type II L Type I: No hydrogen lines in the spectrum Type II: Hydrogen lines in the spectrum Type Ib: He-rich Type Ic: He-poor

6. 0 The Famous Supernova of 1987:SN 1987A Unusual type II Supernova in the Large Magellanic Cloud in Feb. 1987 Before At maximum Progenitor: Blue supergiant (denser than normal SN II progenitor) 20 M0 lost ~ 1.4 – 1.6 M0 prior to SN Evolved from red to blue ~ 40,000 yr prior to SN

7. 0 The Remnant of SN 1987A Ring due to SN ejecta catching up with pre-SN stellar wind; also observable in X-rays. vej ~ 0.1 c Neutrinos from SN1987 have been observed by Kamiokande (Japan) Escape before shock becomes opaque to neutrinos → before peak of light curve provided firm upper limit on ne mass: mne < 16 eV

8. 0 Remnant of SN1978A in X-rays Color contours: Chandra X-ray image White contours: HST optical image

9. 0 Supernova Remnants X-rays The Crab Nebula: Remnant of a supernova observed in a.d. 1054 The Veil Nebula Optical Cassiopeia A The Cygnus Loop

10. 0 Synchrotron Spectra of SNR shocks (I) Electrons are accelerated at the shock front of the supernova remnant: Q(g,t) = Q0g-q . ∂Ne/∂t = -(∂/∂g)(gNe) + Q(g,t) g-q Ne (g,t) Uncooled Cooled g-(q+1) g gc

11. Synchrotron Spectra of SNR shocks (II) 0 Resulting synchrotron spectrum: Opt. thin, uncooled Opt. thick n-(q-1)/2 In n5/2 Opt. thin, cooled n-q/2 nsy,c = nsy (gc) n Find the age of the remnant from t = (gc/g[gc]) .

12. Gamma-Rays from SNRs HESS J1640-465

13. Gamma-Ray Spectra of SNRs SNR shocks may accelerate protons and electrons to ultrarelativistic energies → Two possible models for g-ray emission: HESS J1640-465 • Leptonic Model: Compton scattering of CMB photons by ultrarelativistic electrons • Hadronic model: p0 decay following p-p collisions of ultrarelativistic protons.

14. Multiwavelength Spectra of SNRs p0 decay bremsstrahlung e- synchrotron Compton HESS J1640-465

15. 0 Short (sub-second to minutes) flashes of gamma-rays Gamma-Ray Bursts (GRBs)

16. 0 The Burst and Transient Source Experiment (BATSE) on board the Compton Gamma-Ray Observatory (1991 – 2000) Source Localization through orientation effects: Aeff is proportional to cosQ 20 keV - 1 MeV Q Detector Shield

17. 0 GRB Light Curves Long GRBs (duration > 2 s) Short GRBs (duration < 1 s) Possibly two different types of GRBs: Long and short bursts

18. 0 General Properties • Random distribution in the sky • Approx. 1 GRB per day observed • No repeating GRB sources

19. GRB Spectra in the BATSE Era • Spectra often well described by "Band Spectrum" (Band et al. 1993): Smoothly broken power-law. • Routinely explained as synchrotron emission from shock-accelerated, ultrarelativistic electrons nFn N(E) ~ Eae-E/E0 N(E) ~ Eb 0.1 1 10 E [MeV] • Some GRB spectra with a > -2/3 pose problem to synchrotron interpretation!

20. 0 BeppoSAX (1996 – 2003) Wide-field Camera and Narrow-Field Instrument (NFI; X-ray telescope) allowed localization of GRBs to arc-minute accuracy First identification of X-ray and optical afterglows of g-ray bursts in 1997

21. 0 Afterglows of GRBs On the day of the GRB 3 days after the GRB X-ray afterglow of GRB 970228 (GRBs are named by their date: Feb. 28, 1997) Most GRBs have gradually decaying afterglows in X-rays, some also in optical and radio.

22. 1 day after GRB 2 days after GRB 0 Optical afterglow of GRB 990510 (May 10, 1999) Optical afterglows of GRBs are extremely difficult to localize: Very faint (~ 18 – 20 mag.); decaying within a few days.

23. 0 Optical Afterglows of GRBs Host Galaxy Long GRBs are often found in the spiral arms (star forming regions!) of very faint host galaxies Optical Afterglow Optical afterglow of GRB 990123, observed with Hubble Space Telescope (HST/STIS)

24. Connection of GRBs with Star Forming Regions and Supernovae • Spatial and temporal coincidence of GRB 980425 with SN 1998bw (Type Ic) • Reddened supernova emissions in late-time optical afterglow spectra • GRBs in low-metallicityhosts Host galaxy of SN 1998bw Galama et al. (1998)

25. Redshifts of Gamma-Ray Bursts

26. 0 Energy Output of GRBs Observed brightness combined with large distance implies huge energy output of GRBs, if they are emitting isotropically: E ~ 1054 erg L ~ 1051 erg/s Compactness argument (Assignment set 1, problem 2) implies that the gamma-rays must be relativistically boosted with G > 100

27. Blast-Wave Model of GRBs Coasting phase – internal shocks (prompt GRB) Deceleration phase – external shock (afterglow) Entrainment of ions – conversion of EM to kinetic energy Impulsive electromagnetic energy release rext G0 Msw = M0 G0 Relativistic Mass swept-up from the external medium (in co-moving frame) Lorentz factor G G0 M0 c2 = EBW time

28. 0 Beaming Evidence that GRBs are not emitting isotropically (i.e. with the same intensity in all directions), but they are beamed: E.g., achromatic breaks in afterglow light curves. GRB 990510

29. 0 Swift (launched 2004) Dedicated GRB misssion with on-board soft g-ray, X-ray, and optical telescopes; Rapid automated localization and electronic distribution of GRBs with arc-second precision Localization of the first short GRBs; Some with significant offsets from host galaxies, favoring binary-compact-object merger models:

30. 0 (Launched June 11, 2008) Two main science instruments: Fermi Gamma-Ray Space Telescope • LAT (Large Area Telescope) • GBM (GLAST Burst Monitor)

31. The GLAST Burst Monitor (GBM) 0 All-sky Monitor optimized to detect X-ray / soft g-ray flashes (~ 8 keV – 30 MeV) Source localization to < 15o

32. Fermi Autonomous Response to GRB 090902B • Blue line = LAT FoV (±66°)‏ • White points = LAT events • Yellow dot: Sun Fermi-LAT skymap from -120 s to 2000 s • Red cross = GRB 090902B • Dark region = occulted by Earth

33. Spectral Complexity in GRBs: The Case of GRB 090926A • High-Energy (GeV: Fermi-LAT) gamma-rays often delayed with respect to prompt MeV emission • Many bursts show hard power-law component in addition to thermal (photosphere) MeV emission. GBM: 8 – 14.3 keV GBM: 14.3 – 260 keV GBM: 260 keV – 5 MeV LAT: All events LAT: E > 100 MeV E > GeV photons Ackermann et al. 2011

34. 0 Models of GRBs (I) Leading model for long GRBs: Hypernova: Supernova explosion of a very massive (> 25 Msun) star Iron core collapse forming a black hole; Material from the outer shells accreting onto the black hole Accretion disk => Jets =>GRB!

35. 0 Models of GRBs (II) Black-hole – neutron-star merger: Black hole and neutron star (or 2 neutron stars) orbiting each other in a binary system Neutron star will be destroyed by tidal disruption; neutron star matter accretes onto black hole => Accretion disk => Jets => GRB! Model works probably only for short GRBs.