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RX J0720.4 -31.25: a precessing X-ray pulsar?

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

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RX J0720.4 -31.25: a precessing X-ray pulsar?

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  1. 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

  2. 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 (B=24…27mag) 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)

  3. The M7

  4. RX J0720.4-3125: spectral variations

  5. 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)

  6. 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 @ MJD=53010days • 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

  7. φ RX J0720.4-3125: timing residuals  Phase coherent timing reference period P(Z12) or Cash-stat including new obs. closest in time φ+dφ obs. x+1 φ obs. x φ+dφ if:- 1/eP >> T(x)-T(x+1) - P does NOT change do not loose cycles! new P within eP, that dφ becomes close to zero new eP < old eP (minimising χ2 to zero solution)

  8. RX J0720.4-3125: coherent vs. non coherent

  9. 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/dt=6.989(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

  10. 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 >15Mjup (1Myr, 270pc) Mcomp=0.5-2.5Mjup -ongoing monitoring

  11. Thank you for your attention References de Vries, C. P., Vink, J., M\'endez, M., Verbunt, F., 2004, A&A, 415, 31 Haberl, F., 2007, Ap&SS, 308, 181 Haberl, F., Motch, C., Buckley, D. A. H., et al., 1997, A&A, 326, 662 Haberl, F., Turolla, R., de Vries, C. P., et al., 2006, A&A, 451, 17 Hohle, M. M., Haberl, F., Vink, J., et al., 2009, A&A, 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, ApJ, 628, 45 Kaplan, D.L., van Kerkwijk, M.H., Anderson, J., 2002, ApJ, 571, 447 Kaplan, D.L., van Kerkwijk, M.H., Anderson, J., 2007, ApJ, 660, 1428 Link, B., 2006, A&A, 458, 881 Liu, K., Yue, Y. L., Xu, R. X., 2007, MNRAS, 381, 1 Motch, C., Haberl, F., Zickgraf, F.-J., et al., 1999, A&A, 351, 177 Motch, C., Zavlin, V. E., Haberl, F., 2003, A&A, 408, 323 Posselt, B., Neuhäuser, R., Haberl, F., 2009, A&A, 496, 533 Schwope, A., Hambaryan, V., Haberl, F., Motch, C., 2005, A&A, 441, 597 Schwope, A., Hambaryan, V., Haberl, F., Motch, C., 2007, Ap&SS, 308, 619 van Kerkwijk, M.H., Kaplan, D.L., Pavlov, G. G., Mori, K., 2007, ApJ, 659, 149 Zane, S., Haberl, F., Cropper, M., et al., 2002, MNRAS, 334, 345 Zane, S., de Luca, A., Mignani, R.P., Turolla, R., 2006, A&A, 457, 619

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