Transcript Chandra Observation of Pulsar Wind Nebula

Supernova remnants and pulsars
Fangjun Lu
卢方军
Institute of High Energy Physics
Chinese Academy of Sciences
（中国科学院高能物理研究所）
Classification of SNe
SNe are divided into two catergies from their optical spectra. Physically, they are
either due to thermonulcear explosion or due to the core collapse of a massive
star.
Structure of a supernova remnant
Type II
Type Ia
Outline
• Properties of the progenitor star of a type Ia
SN
• Dynamic evolution of the reverse shock
• Interaction of the pulsar with its enviroments.
Two scenarios of Type Ia SNe
degenerate star
The whitedwarf
accretes mass from the
companion star to
reach the upper mass
limit (1.4 solar mass)
and then explode.
Collision and merge
of two white dwarfs
The single degenerate scenario is widely favored today because it
can naturally explain the uniform peak luminosity of type Ia SNe. But,
little observational evidence has been detected to distinguish the
two scenarios.
The explosion process and the expected
consequence of a single degeneration SN
In the single degeneration scenario, the binary system contains a normal star,
and so signature of such an event should come from the interaction of the
explosion and the companion star:
 Fast moving companion star
 Mass stripped from the companion star during the explosion.
In his publication Astronomiae
instauratae progymnasmata, Tycho
Brahe writes that during an afterdinner stroll on November 11th, 1572,
“I suddenly and unexpectedly beheld
near the zenith an unaccustomed star
with a bright radiant light.” He goes
on to describe how it rivaled Venus
(magnitude -4.6 at the time) and how
sharp-eyed “country folk” could spot
it in the daytime sky.
Tycho Brahe recorded an SN in 1572
X-ray
Radio
Nearby (3 kpc)
Bright
Young (1572-2009)
Small absorption (6×1021 cm-2)
A well proved Ia SNR
The Tycho SNR is one of the best places to find
such information.
Nature 2004, 431 1069
Tycho G
Tycho G, a star similar to the Sun and with a distance to the Tycho SNR,
is found to have proper motion and radial velocity significantly higher
than the other stars in the field. It is suggested to be the companion star
in the progenitor binary system.
0.2-10 keV X-ray image and spectrum of the Tycho SNR
Dominated by the
thermal emission from
SN ejecta
Intriguing properties of the Xray arc:
(1) Half way from the
remnant center;
(2) Bright, narrow and sharp
as these at the outer rim;
(3) Convex to the remnant
center (SN site);
(4) Nonthermal spectrum.
4-6 keV
X-ray arc
Result of the interaction of blast wave with a cloud.
4-6keV
Sulfur
Silicon
Iron
Comparison between the remnant in different energy bands. A
shadow is cast beyond the X-ray arc.
Azimuth mean brightness profiles of the Tycho SNR beyond the
radius of the X-ray arc in different energy bands. A shadow is obvious
in all energy bands.
Azimuth mean brightness profiles of the Tycho SNR within the
radius of the X-ray arc in different energy bands. Local
enhancements immediately within the arc are evident.
Is the arc a feature in the outer layer or in the
interior of the remnant?
If it represents the blast wave in the
outer layer:
(1) The arc could be quite diffused;
(2) It should be convexed outward, like
the filaments in the outer boundary.
Line of
sight
If it represents the interactions of the
shock with a cloud inside the remnant:
(1) The arc could be as sharp as those in
the outer boundary;
(2) The cloud will block the SN ejecta in
this direction.
Possible origins of the cloud
• A cloud unrelated to the progenitor system
of the SN.
• Materials ejected by the binary system
during its evolution.
Matter stripped from the companion star
during the SN explosion.
A cloud unrelated to the progenitor system?
Arc Position
12CO
observations of Tycho region
(Lee et al. 2004, ApJ 605, L113)
In this case it should be a
cold molecular cloud to be
consistent with the long
lifetime. However, no
molecular cloud or optical
emission filament has been
detected spatially coincide
with the X-ray arc. This
origin is unlikely.
Materials ejected by the binary system
during its evolution?
 The mass donor is suggested to be very
similar to the Sun but a slightly evolved,
it can not contribute to the cloud during
its lifetime.
 The planetary nebula surrounding the
exploded white dwarf could be a source
of the cloud material. However, the
planetary nebulae observed always have
a spherically or axially symmetric
morphology.
Images of planetary nebulae
 The singleness of the X-ray arc makes
the possibility of the planetary nebula
origin of the cloud very low.
Matter stripped from the companion star during the
SN explosion?
Suggested by many theoretic works (Wheeler et al. 1975; Fryxell & Arnett 1981;
Taam & Fryxell 1984; Chugai 1986; Marietta et al. 2000; Meng et al. 2007, etc.)
but no direct observational evidence has been detected (Leonard 2004).
Reason to attribute the cloud as the stripped mass
20°
The opening angle of the arc to the explosive centre and the lack of Xray line emission in the volume shadowed by the arc is well consistent
with the simulations of type Ia SN explosion (Marietta et al. 2000).
Binary parameters of the progenitor sysem
Summary (1)
 The nonthermal X-ray most probably represents the interaction
between the ejecta and a bulk of materials in the interior of the remnant,
which is most likely between SN ejecta and the stripped envelop of the
companion star.
 We obtained a stripped mass of ≤0.0083Mʘ,which is consistent with
that observed for two extragalactic Ia SNe (Leonard 2007) and close to
the simulations by Pakmor et al. (2008).
 The orbital period of the progenitor binary system is about a few days,
and the separation of the two component stars is about 1/10 of the
distance from the Earth to the Sun.
Most of the spin-down power of a
pulsar is not released through
direct radiation
(Li, Lu, & Li 2008, ApJ 682, 1166)
http://chandra.harvard.edu/
Most (90%) of the spin-down power of a
pulsar is released via a relativistic wind.
The basic configuration of a PWN
Pulsar
•
Pulsar wind
Therefore, the properties of
a pulsar
Terminal shock
wind nebula are highly determined
Pulsar wind nebula
by the composition and geometry
of
Interface with the
the pulsar wind as well Interstellar
as the
Medium
interaction
thetheenvironments.
The
magnetized pulsarwith
wind leaves
pulsar with almost the
speed of c (γ~103-106).
• A termination shock forms at the radius where the wind rampressure balances the pressure of the environments, and over there
the particles are randomized ( and probably accelerated) and begin
to emit synchrotron photons.
• The PWN is a magnetized particle bubble surrounded by the ISM.
( Rees & Gunn 1974)
• I will show pulsar wind nebula properties in
various conditions:
–
–
–
–
“Freely” expands;
Within a supernova remnant;
Moves supersonically in space;
In high velocity interstellar wind.
PWNe in various environment conditions
Interfaces
The morphology of a PWN is
determined by the geometry of the
pulsar wind and the distribution of
the ISM surrounding the PWN.
8.7 10
tsy  3/2
( s)
3/2
1/2
B  sin   m
11
or t x ~ 40 yr B41.5 keV 0.5
The X-ray image represents
the distribution of fresh wind
particles, and the X-ray spectral
evolution traces the particle flow.
The radio images could be
affected by the distribution of the
aged particles.
SNR G54.1+0.3: A PWN without significant confinement
Pulsar
G54.1+0.3 is powered by
the 136 ms pulsar in the
center. The Chandra X-ray
image shows bright ring
surrounding the pulsar, and
two elongations roughly
perpendicular to the ring.
The wind of the central
pulsar can be divided into
two components: equatorial
flow and polar flow.
(Lu et al. 2002)
The downstream velocity could be derived as 0.4 c by fitting the
brightness variations, which means that the wind is particle dominated.
(Lu et al. 2002)
(Lang, Wang, Lu, & Clubb 2010)
The X-ray and radio images look very much similar to each other, and
the magnetic field is well organized.
The radio and X-ray
extents are almost the
same for G54.1+0.3.
(Lang, Clubb, Lu, & Wang 2010)
• Similarity of the radio and X-ray morphology: there
is no significant accumulation of old particles.
• Similar radio and X-ray sizes: the size of the nebula
is determined mainly by the diffusing of the
particles rather than by their lifetime. The quick
diffusion lowers both the particle number density
and the magnetic field (if we assume equipartition)
and so the radio synchrotron brightness decreases
very rapidly.
G54.1+0.3 is very weakly
confined by the environment
The pulsar wind usually has a torus+jets geometry
PSR B1951+32
The PWN of PSR B1951+32 is in the center of SNR CTB 80.
S II
O III
(Hester & Kulkarni 1989)
Hα
Log (OIII/H α) & H α
In the center of CTB 80 (surrounding the pulsar), small nebulae
have been detected in optical emission lines.
Radio image of core of CTB 80
Chandra X-ray image
Migliazzo et al. (2002)
Li, Lu & Li (2005)
The PWN of PSR B1951+32 shows a shell-like structure in both radio and Xrays, suggesting strong confinement by the SNR ejecta. The high brightness
region is well within the OIII and S II line filaments, while the Hα filaments
define the edge of the low brightness region.
X-ray tail
Termination
shock
Shell
Pulsar
Contours: X-ray Greyscale: Radio
The PWN is produced by the supersonically moving pulsar in SNR ejecta.
(Li, Lu, & Li 2005)
We find intriguing spectral hardening in regions of the radio and X-ray shell,
which can only be explained by the new particle acceleration. This shows
that the pulsar wind bubble can expand supersonically and generate
shocks, even in such an old (5×105 yr) system. The optical filaments are
also produced by the shock wave propagating into the ejecta.
(Li, Lu, & Li 2005)
G359.94-0.04: A cometary PWN near the
Galactic Center
Sgr A*
Chandra X-ray image of the Galactic
center.
X-ray contours overlaid on the IR
image
(Wang, Lu, & Gotthelf 2006)
(van der Swaluw et al. 2003)
(Gaensler et al. 2004)
When a pulsar moves supersonically in the ISM, a bow shock will be
running into the ISM, a termination shock will be ahead of the pulsar, and
most of the the pulsar wind will be confined to the direction opposite to the
pulsar proper motion. The radius of the termination shock is determined
by the spin-down power and proper motion velocity of the pulsar as well
as the ISM density.
Linear brightness profile
Photon index evolution
The cometary morphology is a sign of the ram-pressure confined
PWN. The spectral steepening with increasing distance from the
point source further confirms such an identification.
HESS J1745-290
G359.95-0.04
TeV gamma-ray astronomy Wei Cui 2009 RAA, 9 841
Evidence for G359.95-0.04 (rather than Sgr A*) as
the counterpart of HESS J1745-290
• Many PWNe are observed as TeV sources.
• G359.95-0.04 is consistent with HESS J1745-290
positionally .
• G359.95-0.04 can contribute comparable TeV flux
through inverse compton scattering to the ambient seed
photons (Wang et al. 2006, Hinton & Aharonian 2007, ApJ 657, 302).
• HESS J1845-290 does not show any variation, especially
when Sgr A* (the other candidate) experiences flares
(Hinton et al. 2007, @ICRC 30).
A deep Chandra image of the GC region.
Main morphological and spectral properties of
the filaments
• Most of the filaments contain point-like sources at
their heads.
• All
the filaments
cometaryare
morphology.
The
X-ray show
filaments
most
• The
spectra
are
non-thermal,
with
photon
indices
probably
close
to
Sgr
A*
and
32
34
1.0-2.5, Lx 10 to 10 erg/s, and absorption
powered
by23 pulsars
younger
column
density 10
cm-2.
5 yrs.counts, a spectral
• When
there
are enough
than
3*10
softening with distance from the point-like source
can be detected.
Galactic Plane
Sgr A*
Most of the X-ray filament tails point away from Sgr A*
• The fact that most of the X-ray filament tails point away from
Sgr A* suggests that there exists a radial flow from GC.
This flow (Galactic wind) blows the pulsar wind particles to
the anti-GC direction and shapes the cometary morphology.
These filaments thus represent PWNe in strong windy
environment.
• Since the pulsars are expected to move in random
directions with peculiar velocities of ~400 km/s, the speed of
the Galactic wind should be comparable to or greater than
~400 km/s.
Summary (3)
• The morphology of a PWN is determined by the interaction with
the environment. If the pulsar
– is in a low density cavity, then the structure of the PWN reflects
mainly the pulsar wind geometry.
– is surrounded by the SNR ejecta, the wind materials will be well
confined, and the expansion of the PWN can generate a strong
shock into the ejecta.
– moves supersonically in the ISM, the PWN will be like a comet with
the tail points to the opposite direction of the pulsar proper motion.
• The filamentary PWNe in the Galactic center shows that there is a
high velocity radial Galactic wind.
• The PWNe can be thus used as tools to explore the physics
conditions of the environments.
Thanks!
Star formation rate
15 pulsars younger than 3*105 yrs within 7 pc
from Sgr A*
=>
Star formation rate of 6*10-4 solar mass yr-1,
~100 times higher than the mean star formation
rate of the Galaxy.
ThereArches
are many cluster
massive stars in Quintuplet
the GC region. The
mass
cluster
function of stars in this region suggests a star formation rate
of 10-7 solar mass yr-1 pc-3, about 250 times higher than the
mean of the Galaxy, consistent with our estimate basing on
the number of X-ray PWNe in this region.