Transcript An Aqueye view of the Crab Pulsar

An Aqueye view of the Crab Pulsar
L. Zampieri & C. Germana'
X-ray: NASA/CXC/ASU/J.Hester
et al.; Optical:
NASA/ESA/ASU/J.Hester &
A.Loll; Infrared: NASA/JPLCaltech/Univ. Minn./R.Gehrz
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Outline
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Historical notes
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Basic physics
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Parameters of the Crab pulsar
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Xronos timing software
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Tests: simulated signal
and ROSAT data
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Aqueye observations
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Problems and future goals
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Crab pulsar: Historical notes
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Hosted in the Crab nebula in Taurus (M1), remnant of a bright supernova
recorded by Chinese and Arab astronomers in 1054
Central star identified by Minkowski (1942); radio emission discovered in
1949 (Bolton et al. 1949)
Pulsating radio emission discovered in 1968 (Staelin & Reifenstein 1968,
Comella et al. 1969; one year after the detection of the first pulsar by Bell &
Hewish in Cambridge), providing strong evidence for the connection with
supernova explosions
X-ray and gamma-ray emission discovered in 1963 (Bowyer et al. 1964) and
1967 (Haymes et al. 1968)
Optical and X-ray pulsations discovered in 1969 (Cocke et al.; Fitz et al.)
Overwhelming evidence that pulsars are rotating neutron stars (Pacini 1967;
Gold 1968, 1969):
* shortness (~ms-s), stability (1:108) and gradual slowing down of the period P
* (dE/dt)nebula = - (dE/dt)pulsar
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Basic physics
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Limiting period above which Fc>Fg (break-up period):
shortest period observed P=1.6074 ms (PSR B1957+20)
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Rotation power and magnetic dipole radiation (Ghosh 2007):
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Basic physics
• Rotational energy goes into
intense low-frequency
radiation and into
accelerating charged
particles (relativistic wind),
that power the nebula
• Crossing magnetic field
lines, they emit synchrotron
radiation
• Only a small fraction (10-510-7) of Erot goes into
beamed, narrow radio
pulses
Pulses usually have single components and small duty cycles (100). But the
pulse shape of the Crab has two sharp peaks separated by 1400 in phase,
similar at all wavelengths  emission of the two polar beams from an almost
orthogonal rotator
Parameters of the Crab pulsar
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The Crab pulsar is a fast rotating, young neutron star with
(Ghosh 2007):
Erot=2.0x1049 erg
dErot/dt=-5.0x1038 erg/s
B12=7
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Period
PEin=33.235427(70) ms on Sep 14, 1979 (Einstein; Harnden & Seward 1984)
PXMM=33.5341004590(5) ms on March 7, 2002 (XMM; Kirsh et al. 2006)
PXMM - PEin=0.298673 ms
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dP/dt=36 ns/day
 dP/dt=4.2x10-13
Ptoday=33.61 ms
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Xronos timing software
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General purpose timing analysis software, developed since
1987 to analyse EXOSAT data but designed to be detector and
wavelength-independent
Developed on Unix/Linux platforms; present release (v. 5.18)
fully integrated within the HEAsoft distribution (HEASARC)
Consists of a number of independent programs:
autocor, crosscor, efold, efsearch, lcurve, powspec
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Primary input/output format is FITS (Flexible Image Transport
System). ASCII-to-FITS conversion routines available.
BIN
INTERVAL
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FRAME
Xronos timing software: programs
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autocor/crosscor: autocorrelation/crosscorrelation for one/twosimultaneous time series, computed by a FFT algorithm (or a
direct Fourier algorithm)
lcurve/efold: lightcurve vs. time/folded lightcurve vs. phase
efsearch: after folding data over a range of periods, determines
chi-square of the folded light curve wrt a constant
powspec: power spectral density for one time series, computed
by a FFT algorithm (or a direct Fourier algorithm)
 We are developing our own software to automatically search
for powers exceeding a certain detection level and quantify the
signal power in terms of a relative rms variation
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Tests
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Simulated periodic (P=30 ms) signal with a superimposed
Poissonian noise (S/N~5)
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Tests
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PSPC/ROSAT
observation of the
Crab pulsar
performed on
March 1, 1991 (667
counts/s, including
part of the nebula)
Standard reduction
applied and photon
extracted from a 2’
circular region
centered on the
source position
660 s
PROSAT=PEin+(dP/dt)*Dt=33.386 ms
Aqueye observations of the Crab
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Aqueye observation started at 23:51 on Dec 19, 2007 and
lasted ~1 hour
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Binned ASCII data file (received from Tommaso)
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Processing chain:
 data divided in 6 segments of ~9 m (file size < 50 MBytes)
 converted in FITS format
 corrected for arrival time at the solar system barycenter
(~0.1 s difference in photon arrival time in a 1 hour observation
due to the Earth motion)
 sequence of Xronos programs launched using a python
‘interface’
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Aqueye: Crab period
f=32.5 Hz
P=30.77 ms
Ptoday=33.61 ms
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Aqueye: Crab folded light curve
3s
30 s
300 s
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Problems and future goals
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Crab crucial test for timing accuracy
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Xronos reliable package for the timing analysis
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Development of other timing software to perform additional
analyses
Main problem: stability of the internal Aqueye ATFU  error in
determining P and lack of coherence in the folded lighcurve
Timing accuracy needed for calculating stable Crab pulse
profiles up to 10 m < 1 microsec
Choice of data format for distribution: binned vs. unbinned data
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