Neutron Stars 2: Phenomenology
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Transcript Neutron Stars 2: Phenomenology
Chandra x-ray images of the PWNs surrounding the (A) Crab and (B) Vela
pulsars. [Credit: NASA/CXC/Smithsonian Astrophysical Observatory,
NASA/Pennsylvania State University, and G. Pavlov]
Neutron Stars 2:
Phenomenology
Andreas Reisenegger
Depto. de Astronomía y Astrofísica
Pontificia Universidad Católica de Chile
Outline
• “Radio” pulsars:
– Classical pulsars
– Millisecond pulsars
– Binary radio pulsars & General Relativity
•
•
•
•
•
X-ray binaries: high & low mass
Evolution, connections of pulsars & XRBs
Magnetars
Thermal emitters: isolated & in SNRs
RRATs
Bibliography
Radio pulsars:
• Lyne & Graham-Smith, Pulsar Astronomy, 2nd ed.,
Cambridge Univ. Press (1998)
• Lorimer & Kramer, Handbook of Pulsar Astronomy,
Cambridge Univ. Press (2005)
• Manchester, Observational Properties of Pulsars, Science,
304, 542 (2004)
Binary systems:
• Stairs, Pulsars in Binary Systems: Probing Binary Stellar
Evolution & General Relativity, Science, 304, 547 (2004)
• Lorimer, Binary & Millisecond Pulsars, Living Reviews in
Relativity, 8, 7 (2005)
Others: See below.
NS Phenomenology
• The structure of a NS is almost entirely
determined by its mass.
• The observable phenomenology, however,
depends much more on several kinds of “hair”:
– Rotation ()
– Magnetic field (B)
– Accretion ( M )
“Radio”
pulsars
• Very wide range
of photon
energies
• Mostly nonthermal
• Thermal X-ray
bump cooling
• UV/soft X-ray
“hole” from
interstellar
absorption
D. J. Thompson, astro-ph/0312272
Spin-down
(magnetic dipole model)
2
2 d
2 4
I 3
B
2
3c dt
2
Magnetic field:
|
|
B
P
P
3
Lyne 2000,
http://online.kitp.ucsb.edu/online/neustars_c00/lyne/oh/03.html
Spin-down time
(age?):
P
ts
| 2 P
2|
Spin-down time vs. age
K 3 with K constant,
If
2
1 1
1
2 2
1
t
2K 0
2 0
t t s if K constantand 0
The spin-down time generally agrees (roughly) with
independent ages from:
• historic SNe (Crab)
• expansion of SNRs
• travel time from Galactic disk
• cooling of white-dwarf companions
Problem:
“Braking index”
K3
3K 2
n 2 3 if K constant
K involves the dipole moment (strength & orientation)
& the moment of inertia of the star.
can only be measured in cases when
is large &
rapidly changing: young pulsars
When measured, n 2.0 - 2.8 (< 3):
– The dipole spin-down model is wrong,
or
– the dipole moment is increasing with time.
“Magnetars”
P
ts
2 P
B PP
Classical pulsars
Millisecond pulsars
Kaspi et al. 1999
Magnetic
field
strengths
From R. Duncan’s “magnetar” web page, http://solomon.as.utexas.edu/~duncan/magnetar.html
“Magnetars”
Classical pulsars
Millisecond pulsars
circled: binary systems
Manchester et al. 2002
2 populations of radio pulsars
“Classical”
• P ~ 8 s – 16 ms
Millisecond
• P ~ 20 ms – 1.4 ms
ts P/(2P’) ~ 103-8 yr
B (PP’)1/2 ~ 1011-13 G
Very few binaries.
Many of the youngest are
associated with supernova
remnants (SNRs).
• Galactic disk.
“Population I”
• ts P/(2P’) ~ 108-10 yr
• B (PP’)1/2 ~ 108-9 G
• Most in binaries, esp.
with cool white dwarfs.
• No associations with
SNRs.
• Many in globular clusters.
“Population II”
•
•
•
•
“The Sounds of Pulsars”: Jodrell Bank obs. Web page:
http://www.jb.man.ac.uk/~pulsar/Education/Sounds/sounds.html
X-ray binaries
http://wwwastro.msfc.nasa.gov/xray/openhouse/ns/
High-mass companion (HMXB):
• Young
• X-ray pulsars: magnetic
chanelling of accretion flow
• Cyclotron resonance features
B=(1-4)1012G
Low-mass companion (LMXB):
• Likely old (low-mass
companions, globular cluster
environment)
• Mostly non-pulsating (but
QPOs, ms pulsations): weak
magnetic field
Origin & evolution of pulsars:
the standard paradigm
“Classical” radio
pulsars
Classical pulsars
• born in corecollapse
supernovae
• evolve to
longer P, with
B const.
• eventually
turn off
(“death line”)
Millisecond pulsars
Millisecond pulsars
descend from
low-mass X-ray
binaries.
Mass transfer in
LMXBs
produces
• spin-up
• magnetic field
decay?
The
binary
pulsar &
GR
Kramer et al. 2006, Science, 314, 97
Magnetars: Brief history- 1
• Strongest magnetic field that could possibly be contained in a NS:
2
Bmax
GM 2
18
~P~
B
~
4
10
G
max
8
R4
• Woltjer (1964): Flux conservation from progenitor star could lead to
NSs with B~1014-15G.
• Mazets & Golenetskii (1981): Multiple soft gamma-ray bursts from a
single source (SGR 1806-20) detected by Venera spacecraft since Jan
1979.
• Mazets et al. (1979): “March 5 event”: Giant flare (highly superEddington) from SGR 0526-66 in LMC (possibly associated w. SNR
N49).
• Fahlman & Gregory (1981): First “Anomalous X-ray Pulsar” (AXP):
soft spectrum, at center of SNR, no optical counterpart.
• Koyama et al. (1987): AXP is spinning down, but X-ray luminosity
much too high to attribute to rotational energy loss of a NS.
Bursting
magnetar in
supernova
remnant N49
From R. Duncan’s
“Magnetar” web site,
http://solomon.as.utexas.edu/~
duncan/magnetar.html
Magnetars: Brief history- 2
• Thompson & Duncan (TD 1993): Dynamo action just after formation of
a rapidly spinning NS can lead to B~1016G.
• DT (1992), Paczynski (1992), TD (1995, 1996): Strong, decaying field
could explain super-Eddington bursts and persistent emission of SGRs
& AXPs. TD 1996 predict slow pulsations and fast spin-down.
• Kouveliotou et al. (1998) measure P=7.5 s & B~1015G in SGR 1806-20.
• Gavriil et al. (2002); Kaspi et al. (2003): Several bursts detected from 2
different AXPs.
• SGRs & AXPs share
– fairly long periods ~5-12 s,
– persistent X-ray luminosities ~1035-36 erg/s (BB T ~ 0.4-0.7 keV + highenergy tail), too high to be explained from rotation,
– strong spin-down (inferred B~ 1014-15 G).
Woods & Thompson,
astro-ph/0406133
Woods & Thompson,
astro-ph/0406133
Woods & Thompson,
astro-ph/0406133
Isolated, dim, thermal X-ray emitters
Burwitz et al. 2003, A&A, 399, 1109
Nebula around isolated NS
van Kerkwijk & Kulkarni 2001, A&A, 380, 221
Compact
Central
Objects
(CCOs)
•
•
•
•
Near center of SNRs
Cas A - Hwang et al. 2004
No radio or gamma-ray emission
No pulsar wind nebula
Thermal X-ray spectrum: temperature & luminosity intermediate
between magnetars and dim isolated neutron stars
• “Rotating RAdio Transients” (RRATs; McLaughlin et al. 2006, Nature, 439,
817) emit occasional, bright radio bursts of 2-30 ms duration
• Intervals 4 min – 3 hr are multiples of a period P ~ 0.4 - 7 s, like slow radio
pulsars or magnetars
• Hard to detect (visible ~ 1 s/day): True number should be much larger than
for radio pulsars.
McLaughlin et al. 2006; Nature, 439, 817
RRATs vs.
pulsars &
magnetars
• pulsars (dots)
• magnetars (squares)
• the 1 radio-quiet isolated
neutron star with a
measured period and period
derivative (diamond)
• the 3 RRATs having
measured periods and
period derivatives (stars)
• vertical lines at the top of the
plot mark the periods of the
other 7 RRATs
McLaughlin et al. 2006; Nature, 439, 817