RX J0720.4 -31.25: a precessing X-ray pulsar?Spectral and temporal variations/ phase coherent timing

Markus HohleAstrophysikalisches 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

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)

“Magnificent Seven”(M7)

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

The M7

RX J0720.4-3125:spectral variations

RX J0720.4-3125:spectral variations

XMM-Newton/EPIC-pn full frame (Hohle et al. 2009)

-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

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 Zn

2 (in Kaplan & van Kerkwijk 2005)

Zn2

XMM/EPIC-pn ReNo 1454 400-1000eV

-inclusion of ROSAT, BeppoSAX, Chandra

-XMM/EPIC-pn: phase shift between soft (120-400eV) and hard (400-1000eV)band

φ

φ +dφ

RX J0720.4-3125:timing residuals Phase coherent timing

φobs. x

reference period P(Z12)

or Cash-stat

φ+dφobs. x+1

if:- 1/eP >> T(x)-T(x+1)- P does NOT changedo not loose cycles!

new P within eP, that dφ becomes close to zeronew eP < old eP (minimising χ2 to zero solution)

including new obs. closest in time

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

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/HRCobservations

P(t0)=8.39111532159(81)sdP/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

RX J0720.4-3125:timing residuals – free precession, glitch, orbital motion?

-free precession over some hundred cyclesmay 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 companionis impossible

-glitch: still not excluded, but unlikely

-companion causes motion around the barycenter time delay(may mimic a glitch if orbit is eccentric), but does not explain the spectra

Mcomp=0.5-2.5Mjup

-Posselt et al. (2009): no companion with >15Mjup (1Myr, 270pc)-ongoing monitoring

-Tkatchenkov waves in comb. with glitch

References

de Vries, C. P., Vink, J., M\'endez, M., Verbunt, F., 2004, A&A, 415, 31Haberl, F., 2007, Ap&SS, 308, 181Haberl, 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, 811Hohle, M. M., Haberl, F., Vink, J., et al., 2009, timing, to be submittedKaplan, D.L., 2005, in Physics and Astrophysics of Neutron Stars, July 28 - August 1, 2003, Santa Fe, New Mexico, Optical Observations of Isolated Neutron StarsKaplan, 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, 1428Link, B., 2006, A&A, 458, 881Liu, K., Yue, Y. L., Xu, R. X., 2007, MNRAS, 381, 1Motch, C., Haberl, F., Zickgraf, F.-J., et al., 1999, A&A, 351, 177 Motch, C., Zavlin, V. E., Haberl, F., 2003, A&A, 408, 323Posselt, 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, 149Zane, 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

Thank you for your attention