Accreting millisecond pulsars, light houses with broken lamps to be or not to be

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Accreting millisecond pulsars, light houses with
broken lamps? (to be or not to be)

• P. Casella, A. Patruno,R. Wijnands, M. van der
  Klis and others

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• pulsations at ? 377.3 Hz
• Pulsations detected during only the first 2
  months
• Rms amplitude variations in timescales of days

HETE J1900.1-2455
Kaaret et al. 2006 Galloway et al. 2007
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Aql X-1
12 years
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Pulsations in Aql X-1 (Casella et al. 2008)
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So Aql X-1 is a normal LMXB that shows shows
burst oscillations
550.27 Hz
Same mechanism at work?
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HETE J1900.1-2455 and Aql X-1, are they unique?

• Can the rms amplitude variations in the
  pulsations of both sources be explained by a
  unique mechanism?

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So.. we searched more than 50 sources for
intermittent pulsations and. We got lucky!(no
time now to explain how we did the search, nor
tell about the caveats of our search ? but
please ask later!!!!!!!!)
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Complex relation with bursts
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SAX J1748-2021 (3 outbursts!)
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SAX J1748-2021
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Orbital parameters
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Current situation is

• 7 accreting millisecond pulsars with persistent
  pulsations
• HETE J1900.1-2455 only during the first 2
  months,pulsations related to bursts
• SAX J1748.8-2021 intermittent, hundreds of
  seconds, pulsations related to bursts?
• AQL X-1 only for 150 seconds,no relation with
  bursts
• Many many many non-pulsating sources ?

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Altamirano et al. 2008 (in prep)
Aql X-1
bright but not brightest
soft but not softest

• Pulsations at ? 550.27 Hz
• Detected in 0.01 of the exposure
• No special characteristic no burst, no extreme
  behavior, no energy spectral feature
• Only 150s of pulsations, not enough to better
  estimate the orbital parameters of the system
• (19hs period based on optical
  investigations)

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SAX J1748-2021
bright but not brightest
soft but not softest
Altamirano et al. 2008 (in prep)
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Energy dependence
SAX J1748.9-2021
Aql X-1
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SAX J1808
XTE J1814-338
XTE J1751 - 305
IGR J00291
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Question.

• Does this mechanism (or mechanisms) affect the
  disk? ? are there any signature on the power
  spectra that we can see?

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Aql X-1
Pulsations
Altamirano et al. 2008 (in prep)
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SAX J1748.9-2021
Power spectra of an observation with pulsations
(black) vs. one without pulsations (red)
Altamirano et al. 2008 (in prep)
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HETE J1900.1-2455
Power spectra for observations with pulsations
(black) vs. one without pulsations (red)
Altamirano et al. 2008 (in prep)
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What is going on?

• The pulsations are always there but usually
  smeared (e.g., talk by Lev Titarchuk)
• No smearing for AMXPs with persistent pulsations?
• windows for the intermittent AMXPs?
• Complete smearing for all other sources?
• The pulsations are ONLY some times there
• Alignment/disalignment of the poles (see
  Stratos talk)
• Occasional hot spot on the NS surface?
• change in the accretion flow? (Kuulkarnis talk?
  )
• Occasional quasi stable nuclear burning?... Is it
  possible?
• variable (multipolar) magnetic field
• competing magnetic field with...?

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Main Questions for all of you

• Are we dealing with a unique pulse mechanism? ?
  Valid for both persistent and intermittent AMXPs?
  
• And even among intermittent AMXPs?

Thanks!