RX J0720'4 31'25: a precessing Xray pulsar

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RX J0720.4 -31.25 a precessing X-ray
pulsar? Spectral and temporal variations/ phase
coherent timing
Markus Hohle Astrophysikalisches Institut und
Universitäts - Sternwarte Jena Max Planck
Institut für extraterrestrische Physik,
Garching in coop. with Frank Haberl, Max Planck
Institut für extraterrestrische Physik, Garching
Prerow, Oct. 12 2009
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• among 2000 neutron stars most of them are radio
  pulsars
• -radio quiet
• -thermal emission (young hot ? X-ray)
• black-body an absorption feature in some cases
• -faint (B2427mag) blue optical counterparts
• -large B-field 1013 Gauss
• -long periods 3-12s

Magnificent Seven (M7)?
Haberl et al. (2006), Hohle et al. (2009), Kaplan
et al. (2002), Kaplan (2005), Kaplan et al.
(2007), Motch et al. (1999), Motch et al. (2003),
Schwope et al. (2005), Schwope et al. (2007),
Zane et al. (2006)
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The M7
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RX J0720.4-3125 spectral variations
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RX J0720.4-3125 spectral variations
-RX J0720 discovered by Haberl et al.
(1997) -variations in kT, EW and radius
sinusoidal/precession (Haberl et al. 2006) with
(7.1 /- 0.5) yrs period versus single
event/glitch (Kaplan van Kerkwijk 2005) -since
that six new XMM observations
XMM-Newton/EPIC-pn full frame (Hohle et al. 2009)
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XMM/EPIC-pn ReNo 1454 400-1000eV
RX J0720.4-3125 timing residuals

• -P(t)P(t0) dP/dt (t-t0)
• P(t0) 8.3911153s _at_ MJD53010days
• using C-statistic (in Zane et al. 2002)
• or Zn2 (in Kaplan van Kerkwijk 2005)

Zn2
-inclusion of ROSAT, BeppoSAX, Chandra
-XMM/EPIC-pn phase shift between soft
(120-400eV) and hard (400-1000eV) band
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f
RX J0720.4-3125 timing residuals ? Phase
coherent timing
reference period P(Z12) or Cash-stat
including new obs. closest in time
fdf obs. x1
f obs. x
f df
if- 1/eP gtgt T(x)-T(x1) - P does NOT change ?do
not loose cycles!
new P within eP, that df becomes close to
zero new eP lt old eP (minimising ?2 to zero
solution)
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RX J0720.4-3125 coherent vs. non coherent
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RX J0720.4-3125 timing residuals
-for P(t0) and dP/dt phase coherent timing -in
Kaplan van Kerkwijk (2005) and van Kerkwijk
2007, without energy restriction
-now restricting to the hard band (except for
ROSAT and Chandra/HRC ) six new XMM-Newton two
new Chandra/HRC observations P(t0)8.39111532159(
81)s dP/dt6.989(57) 10-14 s/s
-long term period (7.20 /- 0.17) yrs Haberl
(2007) (7.70 /- 0.60) yrs for two hot
spots abs(sine) with 13-15.5yrs period
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RX J0720.4-3125 timing residuals free
precession, glitch, orbital motion?
-free precession over some hundred cycles may be
unlikely (Link, 2006)

• -given long term and pulse period,
• neutron star mass, oblatness
• using Eq. 2 in Liu, Yue Xu (2007)
• precession powered by a companion
• is impossible

-glitch still not excluded, but unlikely
-Tkatchenkov waves in comb. with glitch
-companion causes motion around the barycenter
?time delay (may mimic a glitch if orbit is
eccentric), but does not explain the spectra
-Posselt et al. (2009) no companion with gt15Mjup
(1Myr, 270pc)
Mcomp0.5-2.5Mjup
-ongoing monitoring
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Thank you for your attention
References de Vries, C. P., Vink, J., M\'endez,
M., Verbunt, F., 2004, AA, 415, 31 Haberl, F.,
2007, ApSS, 308, 181 Haberl, F., Motch, C.,
Buckley, D. A. H., et al., 1997, AA, 326, 662
Haberl, F., Turolla, R., de Vries, C. P., et
al., 2006, AA, 451, 17 Hohle, M. M., Haberl,
F., Vink, J., et al., 2009, AA, 498, 811 Hohle,
M. M., Haberl, F., Vink, J., et al., 2009,
timing, to be submitted Kaplan, D.L., 2005, in
Physics and Astrophysics of Neutron Stars, July
28 - August 1, 2003, Santa Fe, New Mexico,
Optical Observations of Isolated Neutron
Stars Kaplan, D.L., van Kerkwijk, M.H., 2005,
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