bogdanov - msps at x-ray energies
TRANSCRIPT
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Millisecond Pulsars at
X-ray Energies
Slavko Bogdanov
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In collaboration with:
Scott Ransom (NRAO)
Ingrid Stairs (UBC)
Paulo Freire (MPIfR)
Fernando Camilo (Columbia)
Maura McLaughlin(WVU)
Duncan Lorimer(WVU)
Jason Hessels(ASTRON)
Werner Becker (MPE)
Josh Grindlay (Harvard/CfA)
George Rybicki (Harvard/CfA)
Maureen van den Berg (UvA)
Craig Heinke (U of Alberta)
Vicky Kaspi (McGill)
Anne Archibald (McGill)
Haldan Cohn (Indiana U)
Phyllis Lugger (Indiana U)
Mathieu Servillat (Harvard/CfA)
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� First detected in ROSAT All-Sky Survey- PSR J0437−4715(Becker & Trümper 1993)
� ~10 MSPs detected by ROSAT
� ~50 detected to date with Chandra and XMM-Newton
� Most (~30) detected in deep Chandra
observations of globular clusters
� Very faint X-ray sources (L
X ≤1033 erg s–1,
typical: LX
≈1030–31 erg s–1)
MSPs in X-rays (~0.1−−−−10 keV)
Becker & Trümper (1993)
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47 TucChandra ACIS-S
0.3−6 keV281 ks
Heinke et al. ApJ, 625, 796 (2005)
Bogdanov et al. ApJ, 646, 1104 (2006)
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M28 (NGC 6626)
ACIS–S
0.3–6 keV
237 ks
Bogdanov et al. ApJ, 730, 81 (2011)
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NGC 6397
Chandra ACIS-S
0.3−2 keV
290 ks
D ≈≈≈≈ 2.5 kpcNH ≈≈≈≈ 1 ×××× 1021 cm-2
PSR J1740–5340
U18
Bogdanov et al. ApJ, 709, 241 (2010)
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I - Energetic MSPs
� Ė ≥≥≥≥ 1036 erg s−−−−1 LX ≈≈≈≈ 1033 erg s−−−−1
� Hard, non-thermal radiation
� Narrow pulses
⇒ particle acceleration in magnetosphere
Zavlin AP&SS, 308, 297 (2007)Bogdanov et al. ApJ, 730, 81 (2011)
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PSR J0024–7204W (47 Tuc)
PSR J1740–5340 (NGC 6397)
II - Eclipsing Binary MSPs
� LX ≈≈≈≈ 1031−−−−32 erg s−−−−1
� Hard, non-thermal emission
� Orbital variability
⇒ intra-binary shock due to interaction of pulsar wind with companion
Bogdanov et al. ApJ, 730, 81 (2011)
PSR J1824-2452H
(M28)
Bogdanov et al. ApJ, 709, 241 (2010)
Bogdanov et al. ApJ, 630, 88 (2005)
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Eclipsing Binary MSPs: PSR J1023+0038 – “the missing link”
Bogdanov et al. ApJ, 762, 96 (2011)
Chandra ACIS-S
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Eclipsing Binary MSPs: PSR J1723−−−−2837
Bogdanov et al. in prep.
Chandra ACIS-S
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Eclipsing Binary MSPs
� Pronounced X-ray eclipses due to geometric occultation of intra-binary shock by secondary star
Arons & Tavani, ApJ, 403, 249 (1993)
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Bogdanov et al. ApJ, 762, 96 (2011)
� Depth and duration of X-ray eclipses imply a shock localized at face of companion and/or L1.
� Shock luminosity & location constrain pulsar geometry & physics:
• Pulsar wind has to be anisotropic & concentrated in orbital plane
⇒ pulsar spin axis aligned with orbital angular momentum axis
• At shock, wind is magnetically dominated
PSR J1023+0038
Eclipsing Binary MSPs
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III Typical MSPs
� Ė ≈≈≈≈ 1033−−−−34 erg s−−−−1 LX ≈≈≈≈ 1030−−−−31 erg s−−−−1
� Soft, thermal X-rays from Reff ≤≤≤≤ 2 km
� Broad pulses ⇒ surface PC emission
Bogdanov ApJ, 762, 96 (2013)
PSR J0437−4715
Bogdanov & Grindlay ApJ, 703, 1557 (2009)
PSR J0030+0451
XMM–Newton
130 ks
130 ks
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e±
e±
X-rays
� Thermal X-ray emission due to polar cap heating by a return current of
relativistic particles from pulsar magnetosphere
X-rays
� Surface radiation can serve as a valuable probe of neutron star properties
(compactness, B-field geometry, surface composition,…)
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Modeling thermal X-ray emission from MSPs
� Ingredients:
- rotating neutron star
- two X-ray emitting hot spots
- general & special relativity * Schwarzschild metric
(or approximation)
* Doppler boosting/aberration
* propagation time delays
- optically thick hydrogen atmosphere
Viironen & Poutanen (2004)
αααα = pulsar obliquity
ζζζζ = ∠∠∠∠ b/w line of sight & pulsar spin axis
φφφφ(t) = rotational phase
θθθθ = photon ∠∠∠∠ w.r.t surface normal
ψψψψ = photon ∠∠∠∠ at infinity
b = photon impact parameter at infinity
ζζζζαααα
θθθθ
ζζζζ
Viironen & Poutanen (2004)
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Nollert et al. (1989)
Flat
Schwarzschild
Bending of photon trajectories
For M = 1.4 M�, R = 10 km~80% of the neutron
star surface is visible at a given instant.
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Modeling thermal emission from MSPs
Courtesy of G.B. Rybicki
BB
H atm.
• Non-magnetic (B < 1010 G ~ 0 G) Hydrogen Atmosphere:
- harder than blackbody for same effective temperature
- anisotropic emission pattern ⇒ limb-darkening- 100% pure H due to gravitational sedimentation
McClintock, Narayan, & Rybicki (2004)
} Zavlin et al. (1996)
Romani (1987)
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Bogdanov, Grindlay, & Rybicki, ApJ, 689, 407 (2008)
Synthetic MSP X-ray pulse profiles- R = 10 km, M = 1.4 M�- Teff = 2 × 106 K (H atmosphere)
- 2 antipodal, point-like polar caps
Thermal X-ray emission is observable for all (α, ζ)
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- P = 4 ms, R = 10 km, M = 1.4 M�
- Teff = 2 × 106 K (H atmosphere)
- 2 antipodal, point-like polar caps
Blackbody
Blackbody + Doppler
H atmosphere
H atmospere + Doppler
- Can determine emission properties of NS surface
(H atm. vs blackbody)
- Can constrain magnetic field and viewing geometries ⇒ input for γ-ray modeling
α=10°, ζ=30°
α=30°, ζ=60°
α=60°, ζ=80°
α=20°, ζ=80°
Model MSP X-ray pulse profiles
Bogdanov, Rybicki, & Grindlay, ApJ, 670, 668 (2007)
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9 km12 km16 km
for M = 1.4 M
�
* Fits to X-ray pulse profiles of MSPs can be used to infer NS compactness
1 + zg = (1 – 2GM/c2R)–1/2
⇒ constrain NS EOS(Pavlov & Zavlin 1997; Zavlin
& Pavlov 1998)
}
α=10°, ζ=30°
α=30°, ζ=60°
α=60°, ζ=80°
α=20°, ζ=80°
Model MSP X-ray pulse profiles
Bogdanov, Rybicki, & Grindlay, ApJ, 670, 668 (2007)
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Lattimer & Prakash (2004)
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Probing the EoS of Cold Ultra-dense Matter
Lattimer & Prakash (2004)
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� NH ≈≈≈≈ 2 ×××× 1019 cm–2
� LX = 3 ×××× 1030 ergs s–1
� MPSR = 1.76 ± 0.20 M�
(radio timing; Verbiest et al. 2008)
� D = 156.3 ± 1.3 pc (VLBI; Deller et al. 2008)
PSR J0437−−−−4715
Bogdanov ApJ, 762, 96 (2013)
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PSR J0437−−−−4715
R > 11.1 km (3σσσσ conf.) for M = 1.76 M�
130 ks
- Pulsations inconsistent with blackbody
- Anisotropic emission pattern required ⇒ atmosphere on surface
Bogdanov ApJ, 762, 96 (2013)
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PSR J0437−−−−4715
- Magnetic dipole not centered on star!Bogdanov ApJ, 762, 96 (2013)
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� Solitary MSP
� νννν = 205 Hz � D ≈≈≈≈ 300 pc� NH ≈≈≈≈ 1 ×××× 1020 cm–2
� LX = 4 ×××× 1030 ergs s–1
PSR J0030+0451
Bogdanov & Grindlay, ApJ, 703, 1557 (2009)
R > 10.7 km (95% conf.)
R > 10.4 km (99.9% conf.)
for M = 1.4 M�
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X-ray Emission from MSPs
• Majority of radio MSPs have soft, thermal X-ray spectradue to heated magnetic polar caps (Teff ~ 106 K)
• Eclipsing binary MSPs can constrain pulsar wind physics
• Modeling thermal X-ray Emission: promising method for constraints on elusive NS EOS:
� Non-transient (always “on”) and non-variable
� “Weak” magnetic fields (Bsurf~108–9 G)⇒ B-field does not affect radiativeproperties of atmosphere
� Dominant thermal emission(≥95% of total counts @ 0.1–2 keV)
� Radiation from small fraction of NS surface(Reff ≤ 2 km) ⇒ emission region size and shape important at ≤1% level
� High precision distances (±0.8% for PSR J0437−4715; Deller et al. 2008)⇒ uncertainty in (Reff/D)2 greatly reduced
� Independent, accurate mass measurements possible from radio timing ⇒ unique constraint on RNS
MSPs: important targets for future X-ray missions
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Section Title - 28GSFC and partner competition sensitive and proprietary – do not share or copy .
Explorer AO Site Visit
50 phase-resolved spectra
� Dramatic increase in photon statistics (>10-fold for PSR J0437−4715 compared to best available XMM-Newton data) enables use of novel 2-D modeling approach in the E − φ plane.
� ≤5% RNS
measurement in ~1 Ms with NICER
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Section Title - 29GSFC and partner competition sensitive and proprietary – do not share or copy .
Explorer AO Site Visit
50 phase-resolved spectra
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Pulsed thermal X-ray emission is observable for all
combinations of viewing angle (ζ) and pulsar magnetic inclination (α) due to light bending
Blind X-ray timing searches could discover all nearby MSPs in field and in GCs (with Gen-X?)
Bogdanov, Grindlay, & Rybicki, ApJ, 689, 407 (2008)
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Proof of concept:
Blind discovery of PSR J0437-4715 in acceleration search
in 20 ks Chandra HRC-S observation