Download Progenitor stars of supernovae

Progenitor stars of supernovae
Poonam Chandra
Royal Military College of Canada
SUPERNOVAE
Energetic explosions in the universe
Energy emitted 1051 ergs (1029 times more than an
atmospheric nuclear explosion)
One SN explosion shines brighter than the host Galaxy
In universe few supernovae explosions every second
Two kinds of supernova explosions
Core collapse
Supernovae
Thermonuclear
Supernovae
•Type II, Ib, Ic
•Type Ia
•Neutron star or
Black hole remains
•No remnant
remaining
•Found only in Spiral
arms of the galaxy
(Young population of
stars)
•Found in elliptical
and Spiral galaxies
Supernovae
• Core collapse supernovae: explosion of a
massive star in a red supergiant phase.
– Progenitor star > 8 Msun.
• Thermonuclear supernovae: explosion of a
carbon-oxygen white dwarf in a binary system.
– Progenitor star 4-8 Msun in a binary.
Progenitors of supernovae
• Very few are known.
• Require pre-explosion images.
• The progenitor stars are much fainter than the
supernovae.
• Most supernovae at far away distances.
Circumstellar interaction
• The most reliable way to get indirect
information about the mass of the progenitor
star and the conditions of the surrounding
medium.
Circumstellar
matter
Density
Not to scale
Radius
SN explosion centre
Photosphere
Outgoing ejecta
Reverse shock shell
Contact discontinuity
Forward shock shell
Circumstellar Interaction
Shock velocity of typical SNe are ~1000 times the
velocity of the (red supergiant) wind. Hence, SNe
observed few years after explosion can probe the
history of the progenitor star thousands of years
back.
Interaction of SN ejecta with CSM gives
rise to radio and X-ray emission
• Radio emission from Supernovae:
Synchrotron non-thermal emission of relativistic
electrons in the presence of high magnetic field.
• X-ray emission from Supernovae: Both
thermal and non-thermal emission from the region
lying between optical and radio photospheres.
SN 1995N
A type IIn supernova
Discovered on 1995 May 5
Parent Galaxy MCG-02-38017 (Distance=24 Mpc)
Excellent Case: SN 1995N
Chandra et al. 2009, ApJ, Chandra et al. 2005, ApJ
Radio and X-ray observations:
Radio observations: for 11 years
-Very Large Array (VLA)
-Giant Meterwave radio telescope (GMRT)
X-ray observations:
-ROSAT HRI: Aug 1996, 1997
-ASCA: Jan 1998
-ChandraXO: March 2004
-XMM-Newton: 2005
Bremsstrahlung (kT=2.21 keV, NH=1.51 x 1021/cm2. )
Gaussians at 1.02 keV (N=0.34 +/- 0.19 x 10-5) and 0.87 keV
(N=0.36 +/- 0.41 x 10-5)
NeX
NeIX
Mass of the progenitor star
• If most of the Ne is in the Helium zone, close
to C+O boundary then
ne 
6.77 105
f
1
2
f is the fraction of NeIX to Ne
Mass of the progenitor
For f = 0.1, ne = 2 x 106 cm-3, nNe = 600 cm-3
Corresponding Neon mass ~ 0.016 Msun.
Compatible with 15-20 Msun progenitor star.
Radio light curves of SN 1995N
•How fast ejecta is decelerating?
R~t-0.8, this also implies n=8 (m=(n-3)/(n-2) in R~t-m)
•What is the mass loss rate of the progenitor star?
2
 .

    M uw T


2
ff
3
2
s
R 3
Mass loss rate = ~10-4 Msun yr-1
• Red supergiant star on 15 Msun in a superwind phase
•Density and temperature of the reverse shock
Forward shock: T=2.4 x 108 K, Density=3.3 x 105 cm-3
Reverse shock: T=0.9 x 107 K, Density= 2 x 106 cm-3
Presence of a cool shell
• Presence of a cool shell between the forward and
the reverse shock responsible for excessive
absorption of the X-rays.
• NHα Mass loss rate
NH~ 1.5 x 1021 cm-2
• If reverse shock is in He layers close to C-O
boundary (Fransson et al. 2002), then this
implies reverse shock mass of ~0.002M-0.8M.
SN 2006X, Patat, Chandra, P. et al. 2008 and 2007,
Science
•In Virgo cluster spiral Galaxy M100
•Feb 4, 2006, 70 million light years away
•Type Ia supernova
SN 2006X- Nature of progenitor?
•Type Ia supernova (Thermonuclear supernova)
•True nature of progenitor star system?
•What serves as a companion star?
•How to detect signatures of the binary system?
•Single degenerate or double degenerate
system?
How to investigate?
Search for signatures of the material tranferred to
the accreting white dwarf.
•Narrow emission lines
•Radio emission
•X-ray emission
Till date no detection.
ABSORPTION OF THE RADIATIONS COMING FROM
SUPERNOVA DUE TO THE CIRCUMSTELLAR MEDIUM
SURROUNDING SUPERNOVA.
Observations of SN 2006X:
•Observations with 8.2m VLT on day -2, +14, +61, +121
•Observations with Keck on day +105
•Observations with VLA on day ∼ 400 (Chandra et al.
ATel 2007).
•Observations with VLA on day ∼ 2 (Stockdale, ATel
729, 2006).
•Observations with ChandraXO on day ∼ 10 (Immler,
ATel 751, 2006).
Na I D2
line
Na vs Ca
RESULTS
•Variability not due to line-of-sight geometric
effects.
•Associated with the progenitor system.
•Ionization timescale τi < Recombination
timescale τr . Increase in ionization fraction till
maximum light. Recombination starts, ts.
Results
• Estimate of Na I ionizing UV flux:
SUV ∼ 5 × 10 50 photons s − 1
• This flux can ionize Na I up to ri ∼ 1018 cm.
• This and recombination time scale of ~10 days implies
ne ∼ 10 5 cm − 3 (ONLY PARTIALLY IONIZED HYDROGEN CAN
PRODUCE SUCH HIGH NUMBER DENSITY OF ELECTRONS )
• Confinement: rH ≈ 10 16 cm
• When all Na II recombined, no evolution. Agree with
results.
Mass estimation
From spectroscopic data:
Na I column density N (Na I) ≈ 1012 cm − 1
log(Na/H)= −6.3.
For complete recombination,
M (H) ≤ 3 × 10−4 M⊙ .
From radio:
3 − σ upper limit on flux density F (8.46GHz) <
70 µJy.
Mass loss rate ≤ 10 − 8M⊙ year − 1
CSM mass < 10 − 3 M⊙ Below detection limit.
Nature of the progenitor star
•CSM expansion velocity ∼ 50 − 100 km s − 1 .
•For R ∼ 1016 cm, material ejected ∼ 50 year
before!
•Double-degenerate system not possible. Not
enough mass.
•Single degenerate. Favorable.
•Not main sequence stars or compact Helium
stars.
•High velocity required.
•Compatible with Early red giant phase stars.