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					Searching for a Pulsar in SN 1987A
             R. N. Manchester
   Australia Telescope National Facility, CSIRO Sydney
                        Australia


                   Summary
        • Short introduction
        • Optical searches - a short history
        • A new radio search - a new limit
        • Implications of limits
          Spin-Powered Pulsars: A Census
• Number of known
pulsars: 1772
• Number of millisecond
pulsars: 171
• Number of binary
pulsars: 131
• Number of AXPs: 12
• Number of pulsars in
globular clusters: 99*
• Number of
extragalactic pulsars: 20


* Total known: 129 in 24 clusters
                                               Data from ATNF Pulsar Catalogue, V1.29
    (Paulo Freire’s web page)
                                    (www.atnf.csiro.au/research/pulsar/psrcat; Manchester et al. 2005)
  Period - Period
    Derivative
     Diagram
• SNR-associated pulsars have
large magnetic fields and low
characteristic ages
• Pulsars probably evolve
roughly parallel to constant-Bs
lines
• Significant population of
pulsars with Bs ~ 1011 G and P ~
200 ms which were probably
born near there
                   .
• Pulsars with low E have no
detectable PWN - of 25 PWN
associated with known pulsars,
only 2 have P > 200 ms
The Search for a Pulsar in SN 1987A
• Initial searches at optical wavelengths since radio likely to be (more)
absorbed/scattered by ejecta and circumstellar material
• First AAT (4m) observations with Bruce Peterson on 26 February 1987 (dust
cover nearly closed!)
• Starting 10 March 1987 used 8-inch Celestron on ground beside the AAT
• AAT observations continued at ~monthly intervals through 1987 and 1988
• Limit on pulsed fraction ~10-5, corrsponding to >20 mag for pulsed emission
(Manchester 1988)
• Similar limit from Las Campanas, Cerro Tolo, observations commencing
March 1987 (Pennypacker et al. 1989)
        Detection!!
• Cerro Tolo 4-m telescope, 7-hr
observation, January 1989
• 0.508 ms period!!
• Sinusoidal period variation ~8 hr period -
Jupiter-sized planet at 106 km?
  (Kristian et al., Nature, 338, 234, March 1989)

• About 50 theoretical papers published
in next year or so on interpretation
Whoops!

In 1990, revealed that
the signal was
spurious.




   (Nature, 349, 747,
   February 1991)
                 (Paul Murdin, Nature, 347, 511, October 1990)
Not confirmed!
(Nature N&V, 360, 628, December, 1992)
          A New Detection?
Preprints circulated by John Middleditch in 1992, 1993.
            Submitted 1996, published 2000.
   A 2.14-ms pulsar?
• Significance low
• Period variable
• Pulsations intermittent
• Not confirmed by other observers




                   (Middleditch et al. 2000)
          More Recent Searches




HST: V mag > 24 for P in range 0.2 ms - 10 s   (Percival et al. 1995)
AAT: V mag > 24.6, same period range   (Manchester & Peterson, 1996)
                      Radio Searches
• Radio searches made at intervals of 1-2 years since 1988 using the Parkes 64-m
radio telescope. No detection. (Reported in Gaensler et al. 1997)
• Most recent search in December 2006
• Three frequencies, sampling interval 250 s
• Observation time: one or two x 2.3 hours at each frequency/bandwidth
• Dedispersion, FFT search using SigProc package
• No significant detection
          Frequency          Bandwidth      DM Range        Flux Density
            (MHz)             (MHz)          (cm-3 pc)       Limit (Jy)

             1400             256/0.5       10 - 2420            29

             1400             576/3         10 - 2170            13

             3100             874/3         10 - 2100            13

             8400             874/3         20 - 6200             8
                                                   (Manchester & Lustri, 2007)
              Birth Properties of Pulsars
• ~12 PSR - SNR associations with reasonably good estimate of SNR age
                                      .
• Pulsar characteristic age, c = P/(2P), assumes braking index of 3, zero initial
period and is effectively an upper limit on true age
• For SNR age << c, Pinit is                                  Pulsar    SNR       Initial
close to present period              PSR       SNR          Period Age Age        Period
                                                                (ms)    (kyr)    (kyr)    (ms)
• Derived Pinit in range 10 -
425 ms                            J0205+6449   3C58 (SN1181) 65.7         5.4     0.82     60
                                  B0531+21     Crab             33.1     1.2      0.95     19
• Monte-Carlo simulations of J0537-6910        N157B            16.1      4.9       >3    <11
birth population suggest 40% J0538+2817        S147            143.2    618.0      20-60 136-140
born with periods in range 100 B0540-69        0540-693         50.4       1.7    0.8-1.5 28-38
                                  B0833-45     Vela             89.3     11.3     10-30 10-50
- 500 ms (Vranesevic et al. 2004) J1124-5916   G292.0+1.8      135.3      2.9    2.0-2.6 45-90
or a normal distribution          J1210-5226   G296.5+10.0     424.1    336.0      3-20 413-423
centred at 300 ms with std dev B1706-44        G343.1-2.3(?)   102.5      17.5     ~10    60-80
150 ms (Faucher-Giguere &         J1811-1925   G11.2-0.3(SN386) 64.7      23.3     1.62     62
                                  J1833-1034   G21.5-0.9(SN-48) 61.9       4.9      2.05    47
Kaspi 2006)                       B1951+32     CTB80             39.5    107.0     46-88 21-33
• Magnetic fields at birth very J1957+2831     G65.1+0.6        307.6    1570      40-140 293-303
uncertain - probably in range          (Ng & Romani 2007, Gaensler & Psaltis 2007, Wang et
1011 - 1013 G                          al. 2006, Tian & Leahy 2006)
 Limits on Properties of a Central Pulsar
• No evidence for central source (PWN or pulsar) at any wavelength: optical
luminosity limit ~8 x 1033 erg s-1 (Graves et al. 2005), X-ray limit (2-10 keV)   ~5
x 1034 erg s-1 (Shtykovskiy et al. 2005)
• Radio limit of central source from 8 GHz image ~ 1 mJy
• Assume flat spectrum, effective bandwidth 20 GHz, LPWN ~ 3 x1031 erg s-1
                                      .
• For the most conservative limit . E of central pulsar, assume PWN only emits
                                  on
at radio frequencies and LPWN = EPSR
                    .
• For Po = 200 ms, EPSR = 3 x1031 erg s-1,
then Bo ~ 6 x 1010 G                                   ATCA 3cm (8 GHz) May 04
• Well within the range of possible pulsar
birth parameters

  PWN limits do not rule
 out a perfectly plausible
 20-year old pulsar at the
   centre of SN 1987A
               Why No Detection?
 • Possible that neutron star has accreted matter and turned into a
 black hole
 • Possible that the pulsar is not beamed toward us - if slowish
 pulsar, expected beaming fraction ~ 0.2
 • Pulsar magnetic field may take time to develop
                .
 • A slow, low E pulsar would not pulse at optical or X-ray
 wavelengths (except maybe thermal emission from NS surface)
 • Although outer parts of nebula probably have low optical
 depth, we really know very little about conditions right in centre
 - could be absorption/scattering of radio pulses
Bottom Line:
Keep searching for a radio pulsar and point X-ray source!
HST Near IR Images of SN 1987A




                (Bouchet et al., 2006, ApJ, 650, 212)
ATCA 3cm Super-resolved Images of SN 1987A




                               (Gaensler et al., soon)
V mag > 24.6
               (Manchester & Peterson, 1996)

				
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