An Aqueye view of the Crab Pulsar L

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 LZ - Crab Pulsar - Bled, 27/03/2008

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 LZ - Crab Pulsar - Bled, 27/03/2008 2

Crab pulsar: Historical notes Hosted in the Crab nebula in Taurus (M 1), 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 * (d. E/dt)nebula = - (d. E/dt)pulsar 3

Basic physics Limiting period above which Fc>Fg (break-up period): shortest period observed P=1. 6074 ms (PSR B 1957+20) Rotation power and magnetic dipole radiation (Ghosh 2007): 4

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 The Crab pulsar is a fast rotating, young neutron star with (Ghosh 2007): Erot=2. 0 x 1049 erg d. Erot/dt=-5. 0 x 1038 erg/s B 12=7 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 d. P/dt=36 ns/day d. P/dt=4. 2 x 10 -13 Ptoday=33. 61 ms 6

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 7 FRAME

Xronos timing software: programs 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 LZ - Crab pulsar - Bled, 27/3/2008 8

Tests Simulated periodic (P=30 ms) signal with a superimposed Poissonian noise (S/N~5) 9

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 PROSAT=PEin+(d. P/dt)*Dt=33. 386 ms

Aqueye observations of the Crab Aqueye observation started at 23: 51 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 < 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’ LZ - Crab Pulsar - Bled, 27/3/2008 11

Aqueye: Crab period f=32. 5 Hz P=30. 77 ms Ptoday=33. 61 ms LZ - Crab pulsar - Bled, 27/3/2008 12

Aqueye: Crab folded light curve 3 s 300 s LZ - Crab pulsar - Bled, 27/3/2008 13

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 < 1 microsec Choice of data format for distribution: binned vs. unbinned data LZ - Crab pulsar - Bled, 27/3/2008 14