4U 1626-67

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Other names : 3U 1626-67 (Simbad)

Monitoring data: CGRO/BATSE, RXTE/ASM, Swift/BAT, MAXI, Fermi/GBM pulsed flux,Fermi/GMB Occultation Project

Coordinates

Simbad

RA 16h 32' 16.8" Dec -67° 27' 43"
RA 248.0699 Dec -67.4617

Binary system

Distance

The distance is estimated to be between 5 and 13 kpc ([1]).

Orbit

Parameter Value Unit Reference
Porb 42 min [1]
i 18 deg [2]

Note : Porb was obtained from the optical lightcurve, due to reprocessed emission, it has not yet been detected from the neutron star pulsed X-ray emission ([3] and therein).


Optical Companion

Names :' V* KZ TrA ([4])

Parameter Value Unit Reference
Mass 0.04 M⊙ [2]
V ~ 17.5 [4]

Available data

  • ASCA: one observation in 1993 of ~75 ksec
  • RXTE: many monitorings between 1996 and 2010, ranging from 1.2-73.6 ksec in exposure time
  • Chandra: three observations (2000, 2003, 2010) > 30 ksec
  • XMM Newton: four observations
  • BeppoSAX: one observation in 1996
  • INTEGRAL: many observations since 2003
  • Swift: twelve observations in 2005 and one in 2008
  • Suzaku: two observations in 2007 of 100 ksec and in 2011 of 20 ksec, respectively

Description

Discovered in 1972 by Uhuru ([5]). 4U 1626-67 is a LMXB, with a very compact system composed of a faint blue star and an accreting X-ray pulsar with an almost completely face-on orbit ([4], [2]). The accretion occurs through Roche-lobe overflow ([6]). The neutron star has a magnetic field in the range 2.4-6.3 x 1012 G ([7]). The source has shown stable spin-up or spin-down with two torque reversals in 1991 ([8]) and 2008 ([9]).

Flux

4u1626-67 flux camero12.png Figure above obtained from [10].

The source has shown gradually decreasing flux and luminosity (~2.5 x 1034 d2kpc - 10 x 1034 d2kpc ([10]) until the torque reversal in 2008, when the intensity started increasing.
A QPO frequency of 40 mHz, was found from Ginga observations ([11]). Later with BeppoSAX ([12]), ASCA ([13]), RXTE ([14]), and XMM-Newton ([15]) a QPO frequancy of 48 mHz was determined. [16] found that the QPO frequency trend in 4U 1626-67 went from positive to a negative. During the spin-up period, the QPO central frequency increased from ~36 mHz in 1983 to ~49 mHz in 1993. In the spin-down period, it gradually decreased at a rate ~(0.2 ± 0.05) mHz yr-1. After the last torque reversal, no QPO was observed ([3]).

Spectrum

4u1626 suzspec camero12.png Figure above obtained from [10].

The spectrum consists of a low-energy absorption, a blackbody and a high-energy cutoff power law.
The spectrum also shows a cyclotron line feature at ~37 keV an iron K fluorescence line at ~6.4 keV and additional emission lines between 0.5 and 1.5 keV ([10]).


Pulse Profile

A 7.7s X-ray pulsar, 4U 1626-67 has a complex, energy- and time-dependent pulse profile ([17]).

Figure below obtained from [17].
4u162667 pulse period rappaport77 new.png

Figure below obtained from [3].
4u1626 pulse profile jain10.png

Pulse Period Evolution

The source showed an abrupt torque reversal in mid-1990 ([8]).
Observed with Swift/BAT, a second large torque reversal occurred on Feb 2008, with a transition lasting ~150 days ([9]).


Figure below obtained from [9].

4u1626 pulse per evol camero10.png


References

  1. ↑ 1.0 1.1 Chakrabarty, D., 1998, ApJ, 492, 342 (NASA ADS)
  2. ↑ 2.0 2.1 2.2 Levine, A., Ma, C. P., McClintock, J., et al., 1988, ApJ, 327, 732 (NASA ADS)
  3. ↑ 3.0 3.1 3.2 Jain, C., Paul, B., Dutta, A., 2010, MNRAS, 403, 920 (NASA ADS)
  4. ↑ 4.0 4.1 4.2 McClintock, J. E., Bradt, H. V., Doxsey, R. E., 1977, Nature, 270, 320 (NASA ADS)
  5. ↑ Giacconi, R., Murray, S., Gursky, H., et al., 1972, ApJ, 178, 281 (NASA ADS)
  6. ↑ Reynolds, A.P., Quaintrell, H., Still, M.D., et al., 1997, MNRAS, 288, 43 (NASA ADS)
  7. ↑ Orlandini M., dal Fiume, D., Frontera, F., et al., 1998, ApJ, 500, L163 (NASA ADS)
  8. ↑ 8.0 8.1 Bildsten, L., 1993, ApJ, 418, L21 (NASA ADS)
  9. ↑ 9.0 9.1 9.2 Camero-Arranz, A., Finger, M. H., Ikhsanov, N. R., et al. 2010, ApJ, 708 (NASA ADS)
  10. ↑ 10.0 10.1 10.2 10.3 Camero-Arranz, A., Pottschmidt K., Finger, M. H., et al. 2012 (in progress)
  11. ↑ Shinoda, K., Kii, T., Mitsuda, K., et al., 1990, PASJ, 42, 27 (NASA ADS)
  12. ↑ Owens, A., Oosterbroek, T., Parmar, A. N., A&A, 324, L9 (NASA ADS)
  13. ↑ Angelini, L., White, N. E., Nagase, F., et al., 1995, ApJ, 449, 41 (NASA ADS)
  14. ↑ Kommers, J., Chakrabarty, D., Lewin, W. H. G., 1998, ApJ, 497, L33 (NASA ADS)
  15. ↑ Krauss, M. I., Schulz, N. S., Chakrabarty, D., et al., 2007, ApJ, 660, 605 (NASA ADS)
  16. ↑ Kaur, R., Paul, B., Kumar, B., et al., 2008, ApJ, 676, 1184 (NASA ADS)
  17. ↑ 17.0 17.1 Rappaport, S., Markert, T., Li, F. K., et al., 1977, ApJ 217L, 29 (NASA ADS)
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