precsion pulsar timing and the interstellar mediumpulsar spectroscopy p. demorest nrao postdoc...
TRANSCRIPT
![Page 1: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/1.jpg)
Precsion Pulsar Timing and theInterstellar Medium
Paul Demorest, NRAO Charlottesville
April 30, 2009
![Page 2: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/2.jpg)
Outline
P. Demorest NRAO Postdoc Symposium 2009
Pulsar Timing and Gravitational Waves
Systematic Timing Effects / ISM
Advances in Pulsar Spectroscopy
Recent Observational Results
Collaborators:
• GW: NANOGrav collaboration (http://www.nanograv.org)
• ISM: Mark Walker, Willem van Straten
![Page 3: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/3.jpg)
Gravitational Waves
P. Demorest NRAO Postdoc Symposium 2009
![Page 4: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/4.jpg)
GW Detectors
P. Demorest NRAO Postdoc Symposium 2009
• LIGO = Laser Interferometer Gravitational Wave Observatory
• νGW ∼ kHz• Main targets are galactic sources (WD, NS, BH binaries)• Currently operating, major upgrade planned.
• LISA = Laser Interferometer Space Antenna
• νGW ∼ mHz• Both galactic and extragalactic (MBH) sources.• Still in planning stages.
• PTA = Pulsar Timing Array(s)
• νGW ∼ nHz• Extragalactic/cosmological sources (MBH, cosmic strings)• Several ongoing international efforts: NANOGrav (N.
America), PPTA (Parkes), EPTA (Europe).
![Page 5: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/5.jpg)
GW Spectrum
P. Demorest NRAO Postdoc Symposium 2009
Detector complementarity:
���
���
���
���
���
���
���
��� �� �� �� �� � � �
��� ���� ���� �������������
��������������������
� ���
��! �����
"#!$
"#%&
$'(���'�"#%&
)*$�
)!+� ��,,-�.��/�0�1"�22���
3$3&%�(������� 3$3&%�(����,)*$�����
![Page 6: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/6.jpg)
Pulsars as GW detectors
P. Demorest NRAO Postdoc Symposium 2009
![Page 7: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/7.jpg)
Pulsars as GW detectors
P. Demorest NRAO Postdoc Symposium 2009
Radio pulses travelling through GW to Earth acquire additionaldelays.
![Page 8: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/8.jpg)
Pulsar Timing Array
P. Demorest NRAO Postdoc Symposium 2009
![Page 9: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/9.jpg)
Pulsar Timing Array
P. Demorest NRAO Postdoc Symposium 2009
GW-induced timing fluctuations will be correlated between differentpulsars (Hellings & Downs, 1982):
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0 20 40 60 80 100 120 140 160 180
Cor
rela
tion
coef
ficie
nt
Angular separation
This method makes GW detection possible!
![Page 10: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/10.jpg)
Timing Results
P. Demorest NRAO Postdoc Symposium 2009
Best NANOGrav MSP timing results have RMS ∼ 100 ns:
-2.5-2
-1.5-1
-0.5 0
0.5 1
1.5
2004.5 2005 2005.5 2006 2006.5 2007 2007.5 2008 2008.5
Res
idua
l (us
)
Year
PSR J1713+0747
AreciboGBT
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2004.5 2005 2005.5 2006 2006.5 2007 2007.5 2008 2008.5
Res
idua
l (us
)
Year
PSR J1909-3744, GBT
8201400
Order-of-magnitude GW sensitivity is ∼ δt/T .
![Page 11: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/11.jpg)
Timing Array Limits
P. Demorest NRAO Postdoc Symposium 2009
Correlation analysis of first ∼4 years of NANOGrav data:hc(1 y−1) < 7 × 10−15
-100
-50
0
50
100
0 20 40 60 80 100 120 140 160 180
Cor
rela
ted
pow
er (
norm
aliz
ed)
Angular separation
![Page 12: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/12.jpg)
Improvement with time
P. Demorest NRAO Postdoc Symposium 2009
![Page 13: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/13.jpg)
GW Spectrum
P. Demorest NRAO Postdoc Symposium 2009
Improvement with time:
���
���
���
���
���
���
���
��� �� �� �� �� � � �
��� ���� ���� �������������
��������������������
� ���
��! �����
"#!$
"#%&
$'(���'�"#%&
)*$�
)!+� ��,,-�.��/�0�1"�22���
3$3&%�(������� 3$3&%�(����,)*$�����
![Page 14: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/14.jpg)
Timing Array Summary
P. Demorest NRAO Postdoc Symposium 2009
• Current NANOGrav PTA limits are comparable to the 20-yearsingle pulsar limit.
• Another ∼3–5 years reaches into plausible detection territory.
• Jenet et al. (2005) estimate that we need 20–40 pulsars at100 ns for 5 years for a “guaranteed” robust (> 4σ) detection.
• More good-timing pulsars are needed.
• Searching for new pulsars.• Increasing BW, G/T to improve currently known pulsars.• Reduce systematic effects, improve analysis algorithms.
(See also Demorest et al. (2009) Astro2010 WP)
![Page 15: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/15.jpg)
Systematic Timing Effects
P. Demorest NRAO Postdoc Symposium 2009
We compute arrival times (TOAs) by matching data:
-0.05
0
0.05
0.1
0.15
0.2
0.25
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
to a scaled, shifted “template”:
-5
0
5
10
15
20
25
30
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Any corruption in the measured profile shape can affect timing.100 ns ∼ 10−5 turns.
![Page 16: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/16.jpg)
Systematic timing effects
P. Demorest NRAO Postdoc Symposium 2009
• Local:
• Polarimetry / calibration procedures• Radio-frequency interference• Instrumental effects
• ISM:
• DM variation with time (and maybe frequency)• Scattering/scintillation• Refraction
• Intrinsic:
• Pulse-to-pulse “jitter”• “Timing noise”
![Page 17: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/17.jpg)
ISM
P. Demorest NRAO Postdoc Symposium 2009
![Page 18: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/18.jpg)
ISM effects
P. Demorest NRAO Postdoc Symposium 2009
• Come from radio wave propagation through interstellar e−
plasma; strongly λ-dependent, based on plasma dispersionrelation.
• Effects include DM(t), scattering/scintillation.• One solution: Observe at higher RF, but psrs get weaker.
-0.005 0
0.005 0.01
0.015 0.02
0.025 0.03
0.035 0.04
0.045
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
-0.005 0
0.005 0.01
0.015 0.02
0.025 0.03
0.035 0.04
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
![Page 19: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/19.jpg)
DM Variation
P. Demorest NRAO Postdoc Symposium 2009
Total electron column density varies due to motions of Earth, PSR,and ISM:
(PSR B1937+21; Ramachandran et al. 2006)Can be measured/removed with multi-frequency timingmeasurements.
![Page 20: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/20.jpg)
Scattering/Scintillation
P. Demorest NRAO Postdoc Symposium 2009
Electron density variation transverse to the line-of-sight causesconstructive/destructive interference:
(Walker et al. 2008)
Typical scales ν ∼ kHz–MHz,T ∼ sec–hours. Determinedby LOS/ISM velocity and ISMlength scales.
Can be thought of as a (time-varying) “filter” with transfer functionH(ν) or impulse response h(t). This affects profile shapes!
![Page 21: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/21.jpg)
Pulsar Spectroscopy
P. Demorest NRAO Postdoc Symposium 2009
How to compute spectra from measured pulsar voltage signal x(t):
Standard pulsar spectroscopy:
• Signal is divided into many radio frequency channels.• In each channel, on-pulse and off-pulse flux are detected,
integrated for some time and subtracted (“gating”).• Results in dynamic spectrum S(t, ν).
Limitations of this approach:
• Gate width and frequency resolution are coupled (via usualuncertainty principle).
• Discards all pulse shape information.• Can only directly determine |H(ν)|2.
![Page 22: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/22.jpg)
Pulsar Spectroscopy
P. Demorest NRAO Postdoc Symposium 2009
In cyclic spectroscopy, we compute correlations as a function ofpulse phase:
• Signal is delayed by many different lags τ .• Each is cross-multiplied with original signal and averaged
modulo the pulse period for some integration time (“folding”).• Results in periodic correlation C(t, τ, φ) → S(t, ν, φ).
Advantages of this approach:
• Number of lags (hence freq resolution) not constrained by pulsewidth or period.
• Makes full use of pulse shape information.• Directly recovers H(ν) with phase!• see reviews by Gardner (1991, 1992), Antoni (2007)
![Page 23: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/23.jpg)
Cyclic Spectra
P. Demorest NRAO Postdoc Symposium 2009
PSR B1937+21 at 430 MHz, Arecibo/ASP:
![Page 24: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/24.jpg)
Cyclic Spectra
P. Demorest NRAO Postdoc Symposium 2009
Same thing, zoomed in:
428.75
428.8
428.85
428.9
428.95
429
0.5 0.55 0.6 0.65 0.7 0.75 0.8
0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2
Fre
quen
cy (
MH
z)
Pulse Phase (turns)
Time (ms)
![Page 25: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/25.jpg)
ISM De-scattering
P. Demorest NRAO Postdoc Symposium 2009
“Snapshot” ISM impulse response h(t) determined from data:
![Page 26: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/26.jpg)
ISM De-scattering
P. Demorest NRAO Postdoc Symposium 2009
Comparison of uncorrected and intrinsic pulse profiles:
![Page 27: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/27.jpg)
Dynamic Spectra
P. Demorest NRAO Postdoc Symposium 2009
B1937+21, ν=430MHz, BW=4 MHz, ∆ν=0.64 kHz, T∼1 hour
![Page 28: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/28.jpg)
Secondary Spectra
P. Demorest NRAO Postdoc Symposium 2009
2-D FT of dynamic spectrum, shows clear “arc” structure.
![Page 29: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/29.jpg)
Secondary Spectra
P. Demorest NRAO Postdoc Symposium 2009
Contrast with methods based on traditional dynamic spectra:
![Page 30: Precsion Pulsar Timing and the Interstellar MediumPulsar Spectroscopy P. Demorest NRAO Postdoc Symposium 2009 How to compute spectra from measured pulsar voltage signal x(t): Standard](https://reader030.vdocuments.net/reader030/viewer/2022041009/5eb4677ae323b004c24abe5a/html5/thumbnails/30.jpg)
Future Directions
P. Demorest NRAO Postdoc Symposium 2009
• Get scattering-corrected TOAs, improve timing
• Investigate polarimetry aspects
• Explore more strongly scattered sources
• Work towards physical ISM images
• . . .