An Aqueye view of the Crab Pulsar

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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/JPL-Caltech/Univ. Minn./R.Gehrz
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Outline

• Historical notes
• Basic physics
• Parameters of the Crab pulsar
• Xronos timing software
• Tests simulated signal
• and ROSAT data
• Aqueye observations
• Problems and future goals

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Crab pulsar Historical notes

• 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 (1108)
  and gradual slowing down of the period P
• (dE/dt)nebula - (dE/dt)pulsar

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Basic physics

• Limiting period above which FcgtFg (break-up
  period)
• shortest period observed P1.6074 ms (PSR
  B195720)
• 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 (10-5-10-7) 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
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Parameters of the Crab pulsar

• The Crab pulsar is a fast rotating, young neutron
  star with (Ghosh 2007)
• Erot2.0x1049 erg
• dErot/dt-5.0x1038 erg/s
• B127
• Period
• PEin33.235427(70) ms on Sep 14, 1979
  (Einstein Harnden Seward 1984)
• PXMM33.5341004590(5) ms on March 7, 2002
  (XMM Kirsh et al. 2006)
• PXMM - PEin0.298673 ms ?
  dP/dt36 ns/day ? dP/dt4.2x10-13
• Ptoday33.61 ms

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Xronos timing software

• 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
• Primary input/output format is FITS (Flexible
  Image Transport System). ASCII-to-FITS conversion
  routines available.

BIN
INTERVAL
FRAME
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Xronos timing software programs

• autocor/crosscor autocorrelation/crosscorrelation
  for one/two-simultaneous 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

• Simulated periodic (P30 ms) signal with a
  superimposed Poissonian noise (S/N5)

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Tests

• 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
PROSATPEin(dP/dt)Dt33.386 ms
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Aqueye observations of the Crab

• Aqueye observation started at 2351 on Dec 19,
  2007 and lasted 1 hour
• Binned ASCII data file (received from Tommaso)
• Processing chain
• ? data divided in 6 segments of 9 m (file
  size lt 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
f32.5 Hz P30.77 ms
Ptoday33.61 ms
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Aqueye Crab folded light curve
3 s
30 s
300 s
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Problems and future goals

• Crab crucial test for timing accuracy
• Xronos reliable package for the timing analysis
• 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 lt 1 microsec
• Choice of data format for distribution binned
  vs. unbinned data