Neutron Stars 2: Phenomenology Andreas Reisenegger Depto. de Astronomía y Astrofísica Pontificia...
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Transcript of Neutron Stars 2: Phenomenology Andreas Reisenegger Depto. de Astronomía y Astrofísica Pontificia...
Neutron Stars 2: Phenomenology
Andreas ReiseneggerDepto. de Astronomía y Astrofísica
Pontificia Universidad Católica de Chile
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]
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
BibliographyRadio 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 non-thermal
• Thermal X-ray bump cooling
• UV/soft X-ray “hole” from interstellar absorption
D. J. Thompson, astro-ph/0312272
Spin-down(magnetic dipole model)
Spin-down time (age?):
Lyne 2000, http://online.kitp.ucsb.edu/online/neustars_c00/lyne/oh/03.html
42
2
2
2
33
2 B
dt
d
cI
Magnetic field:
PPB
3
||
P
Pts 2||2
Spin-down time vs. age
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
0
2
020
2
3
andconstant if
12
11
2
1
constant,withIf
Ktt
Kt
KK
s
Problem: “Braking index”
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.
constantif3
3
2
23
Kn
KK
Kaspi et al. 1999
“Magnetars”
Classical pulsars
Millisecond pulsars
P
Pts 2
PPB
Magnetic field
strengths
From R. Duncan’s “magnetar” web page, http://solomon.as.utexas.edu/~duncan/magnetar.html
Manchester et al. 2002
“Magnetars”
Classical pulsars
Millisecond pulsars circled: binary systems
2 populations of radio pulsars“Classical”• P ~ 8 s – 16 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”
Millisecond• P ~ 20 ms – 1.4 ms
• 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
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
http://wwwastro.msfc.nasa.gov/xray/openhouse/ns/
Origin & evolution of pulsars: the standard paradigm
“Classical” radio pulsars
• born in core-collapse supernovae
• evolve to longer P, with B const.
• eventually turn off (“death line”)
Millisecond pulsars descend from low-mass X-ray binaries.
Mass transfer in LMXBs produces
• spin-up• magnetic field
decay?
Classical pulsars
Millisecond pulsars
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:
• 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 super-Eddington) 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.
G104~~~8
18max4
22max B
R
GMP
B
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 + high-energy 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
• No radio or gamma-ray emission
• No pulsar wind nebula
• Thermal X-ray spectrum: temperature & luminosity intermediate between magnetars and dim isolated neutron stars
Cas A - Hwang et al. 2004
• “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