measuring magnetar velocitiesusers.monash.edu/~dgallow/heat/20-11-2008/shami-heat.pdf ·...
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Measuring Magnetar Velocities
Shami Chatterjee
The University of Sydney
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Neutron Stars are a high velocity population
Mean 3D birth velocity of young pulsars ∼ 400 km s−1.
Distribution has a high velocity tail >∼1000 km s−1.
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Neutron Stars are a high velocity population
Mean 3D birth velocity of young pulsars ∼ 400 km s−1.
Distribution has a high velocity tail >∼1000 km s−1.
Origin of these high velocities?
• Binary disruption → Insufficient.
• Electromagnetic rocket effect → May play a role?
• Natal kicks from supernovae → Very plausible.
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Core Collapse and Kicks
SN core collapse → ? → Birth kicks.
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Core Collapse and Kicks
SN core collapse → ? → Birth kicks.
• Convective or hydrodynamic instabilities?
(e.g., SASI, acoustic modes, etc.)
• Driven by ultra-strong magnetic fields?
(e.g., Parity violation and asymmetric ν−
e emission?)(or, e.g., Magnetorotational instabilities?)
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Core Collapse and Kicks
Hydrodynamic core collapse simulations → large kicks:
2D simulations find cases with V > 1000 km/s.(e.g., Burrows & Hayes 1996; Muller & Janka 1997; Scheck et al. 2004)
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Core Collapse and Kicks
But the first 3-dimensional simulations (Fryer 2004) have
trouble producing kicks > 200 km s−1 due to fallback.
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An Observational Test
• Hydrodynamic simulations show promise — e.g., recentsimulations by Burrows et al., Janka et al., Fryer et al.
• Magnetic field-driven mechanisms, either with asymmetricneutrino emission, or with magnetorotational instabilities, mayalso work...
How do we discriminate between models?
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An Observational Test
• Hydrodynamic simulations show promise — e.g., recentsimulations by Burrows et al., Janka et al., Fryer et al.
• Magnetic field-driven mechanisms, either with asymmetricneutrino emission, or with magnetorotational instabilities, mayalso work...
⇒ Nature provides a way to twiddle the settings on the dial:Compare velocities of magnetars and ordinary radio pulsars.
[e.g., Magnetar V ≫ 1000 km/s? (Duncan & Thompson 1992)]
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VLBA: Parallaxes and Proper Motions
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Astrometric Results for PSR B1508+55
µa = −73.61 ± 0.04 mas yr−1
µd = −62.62 ± 0.09 mas yr−1
π = 0.42 ± 0.04 mas
(with Vlemmings, Brisken, Lazio, Cordes,
Goss, Thorsett, Fomalont, Lyne, Kramer)
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Astrometric Results for PSR B1508+55
µa = −73.61 ± 0.04 mas yr−1
µd = −62.62 ± 0.09 mas yr−1
π = 0.42 ± 0.04 mas
Distance = 2.37+0.23−0.20 kpc
V⊥ = 1083+103−90 km s−1
The highest measured model-independent velocity yet!
(Chatterjee et al. 2005)
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The Birth Site of B1508+55
Orbit of B1508+55 overlaid on Axel Mellinger’s image of the Galaxy.
• Current Galactic latitude = 52.3◦.
• Trace back orbit in Galaxy: born in Galactic plane.
• Birth in or near Cygnus OB associations.
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B1508+55: Getting its Kicks
• B1508+55: implied birth velocity ≈ 1100 km s−1.
• Binary disruption is unlikely to impart such a high velocity;a kick is required. (Chatterjee et al. 2005)
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B1508+55: Getting its Kicks
• B1508+55: implied birth velocity ≈ 1100 km s−1.
• Binary disruption is unlikely to impart such a high velocity;a kick is required. (Chatterjee et al. 2005)
• Core collapse: first 3D simulations (Fryer 2004) do notproduce such large kicks.
• Work ongoing: better simulations, SASI, acoustic modes.
(e.g., recent work by Janka et al., Fryer et al., Blondin et al.,Burrows et al.)
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B1508+55: Getting its Kicks
• B1508+55: implied birth velocity ≈ 1100 km s−1.
• Binary disruption is unlikely to impart such a high velocity;a kick is required. (Chatterjee et al. 2005)
• Core collapse: first 3D simulations (Fryer 2004) do notproduce such large kicks.
• Work ongoing: better simulations, SASI, acoustic modes.
(e.g., recent work by Janka et al., Fryer et al., Blondin et al.,Burrows et al.)
⇒ High velocities impose severe constraints on core collapseand kick velocity scenarios.
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Astrometry with Chandra
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Astrometry with Chandra
• Chandra has the best resolution of any X-ray telescope,past, present, or on the drawing board.
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Astrometry with Chandra
• Chandra has the best resolution of any X-ray telescope,past, present, or on the drawing board.
• Even so, precision astrometry is hard!
ChandraVLBA
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Astrometry with Chandra
• Chandra has the best resolution of any X-ray telescope,past, present, or on the drawing board.
• Even so, precision astrometry is hard!
⇒ Need observations separated by many years.
(With Kaplan, Gaensler, Slane; student Chris Hales)
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AXP 1E 2259+586 with Chandra in 2000
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AXP 1E 2259+586 with Chandra in 2006
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Astrometry with Chandra
• Construct reference frame with background sources.
• Extract magnetar position by cross-correlation with piledup PSF model.
• Verify astrometry against standard source extraction:lower precision, especially due to pile up.
• Verify astrometry using read-out streak.
(Kaplan, Chatterjee, Hales, Gaensler, Slane, 2008, AJ, in press)
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Reference Frame
-4 -3 -2 -1 0 1 2-5
-4
-3
-2
-1
0
1
2
3
X offset (pixels)
Y o
ffset
(pi
xels
)
1E 2259+586
12
3
4
5
6
-6 -4 -2 0 2
-6
-4
-2
0
2
4
6
X offset (pixels)
Y o
ffset
(pi
xels
)
SGR 1900+14
1
2
3
4 5
6
7
8
9
10
11
1213
1415
16
17
18
192021
2223
2425 2627
Reference frames matched to:• ≈ 0.2 pixels for SGR 1900+14,• ≈ 0.25 pixels for AXP 1E2259+586.
We have 2-epoch results:will need at least 3 to get firm answers.
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Astrometry Results: AXP 1E2259+586
6 arcmin
10 kyr from now
10 kyr ago
99.7%
95%
68%
1E 2259+586
• 〈µ〉 = 42 mas/yr; 90% upper limit is 65 mas/yr.⇒ V⊥,90 < 930 d3 km/s.
• Asymmetric expansion of the remnant CTB 109?
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Astrometry Results: SGR 1900+14
6 arcmin
10 kyr from now
10 kyr ago
99.7%
95%
68%
SGR 1900+14
20 arcsec
1 kyr from now
1 kyr ago
99.7%
95%
68%
SGR 1900+14
• 〈µ〉 = 33 mas/yr; 90% upper limit is 54 mas/yr.⇒ V⊥,90 < 1300 d5 km/s.
• An association with the SNR G42.8+0.6 may be viable?But birth in a nearby massive cluster is not ruled out.
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Magnetar proper motion with the VLBA?
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Magnetar XTE J1810–197
• Camilo et al. (2006): Transient pulsed radio emission!
• Rapidly fading...
(from Camilo et al. 2006)
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Magnetar XTE J1810–197
• Camilo et al. (2006): Transient pulsed radio emission!
• Rapidly fading...
• But bright enough for the VLBA at 5 GHz, 8.4 GHz.
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A Magnetar Proper Motion
µa = −6.60 ± 0.06 mas yr−1
µd = −11.7 ± 1.0 mas yr−1
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A Magnetar Proper Motion
µa = −6.60 ± 0.06 mas yr−1
µd = −11.7 ± 1.0 mas yr−1
⇒
For D = 3.5 ± 0.5 kpc,
V⊥ ∼ 220 km s−1
[180 − 270 km s−1]
For this one object, no exotic kick mechanism is required.
(Helfand, Chatterjee, Brisken et al. 2007)
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Concluding Thoughts
The energy dissipation, initial spins, surface magnetic fields,birth kick velocities and progenitor masses of NS are allinterwoven with the physics of supernova core collapse.
With precise astrometry:
→ Determine distances, velocities, associations, ages.
→ PSR B1508+55 sets a high bar for natal kick models.
→ SGR 1900+14 may, in fact, be associated with a distantSNR? If so, high velocity. Or birth in nearby massive cluster.
→ Upper limits on velocity of magnetars.
→ Magnetar XTE J1810−197 does not require exotic kicks.
⇒ We can tease apart the various threads of theinterdependence.