GRO J1744-28

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Other names : 2EG J1746-2852 ([1])

Available data: NuSTAR ObsID 80202027002

Monitoring data: Swift/BAT

Type

  • Transient Low-mass X-ray Binary (Neutron Star)
  • Type I and II X-ray bursts and pulsations (next to Rapid Burster one of a few sources where Type II bursts are observed)
  • Discovered on 1995 December 2 with the Burst And Transient Source Experiment (BATSE) on-board the Compton Gamma Ray Observatory ([1])

Coordinates

RA 17h 44‘ 33.09“ DEC -28° 44‘ 27.0“

Binary system

  • Distance: 7.5-8.5 kpc ([2], [3])
  • Optical companion: G4 III star ([4], [5]) with M<0.3Msun and inclination i>15° ([4])

Orbit

Parameters inferred from 2014 outburst (see [6], NSSTC Gamma Ray Astrophysics: GRO J1744)

  • Porb = 11.836 days
  • Tπ/2 = 2456696.19880 (JED)
  • ax sin(i) = 2.637 light-sec
  • no constrains on the longitude of periastron or eccentricity


Pulsations & Magnetic field

GRO J1744-28 is special because it exhibits X-ray bursts and pulsations at the same time. Sources which show X-ray bursts are generally believed to have surface conditions (low B-fields) which do not allow pulsations.

  • Pulse period: 2.14Hz [7]
  • B = 2–6 x 1010 G from disk reflection models ([8])
  • B = 5.27±0.06 x 1011 G from CRSF measurements ([9])


Outbursts

  • 1995 December: Discovery and first report of Type II X-ray bursts ([7])
  • 1996 December: Similar burst characteristics ([10]), CRSF report at 5keV in BeppoSAX data (not yet proven) ([11])
  • 2014 February: Outburst after 18 years of quiescence ([12], no CRSF), CRSF report at 5keV, 10keV and 15keV in XMM-Newton/INTEGRAL data, still under debate ([9])
  • 2017 February: Fourth outburst with ~two orders of magnitude lower luminosity (Koenig et al. in prep.)

X-ray Spectrum

  • Spectrum shows typical cut-off powerlaw, like expected from accreting X-ray binary
  • Broad iron line at 6-7 keV (disk reflection or fast disk wind [8])

Cyclotron Features

Cyclotron line in this source is under debate. GRO J1744−28 is one of the few LMXBs where a CRSF has been reported below 10 keV (other candidates are X1822−371, ECRSF=0.7keV [13], SWIFT J0051.8−7320, ECRSF=5keV [14])

  • Fundamental CRSF at 4.68±0.05 keV (gabs, XMM-Newton/INTEGRAL, 2014 outburst [9]) / ∼4.5 keV (gabs, BeppoSAX, 1997 outburst [11])
  • Indication of second and third harmonic at 10.4±0.1 keV and 15.8+1.3-0.7 keV in XMM-Newton/INTEGRAL data (using gabs) ([9])
  • No cyclotron line in low-flux 2017 February outburst (gabs strength upper limit at 0.07keV, 90% CL) (König et al. in prep.)


References

  1. ↑ Kouveliotou et al., 1996, Nature, Volume 379, Issue 6568, pp. 799-801 (1996) (NASA ADS)
  2. ↑ Augusteijn, T. & Greiner, J., et al., 1997, ApJ 486, 1013 (NASA ADS)
  3. ↑ Nishiuchi, M. et al., 2018, ApJ, Vol. 517, Issue 1, pp. 436-448. (NASA ADS)
  4. ↑ 4.0 4.1 MNRAS, Vol. 380, Issue 4, pp. 1511-1520. (NASA ADS)
  5. ↑ Masetti et al., ATel, No.5999, March 2014 (NASA ADS)
  6. ↑ Pintore, F. et al., ATEL, No.5901, Feb 2014 (ATEL)
  7. ↑ 7.0 7.1 Finger, M. H. et al., Nature, Volume 381, Issue 6580, pp. 291-293 (1996) (NASA ADS)
  8. ↑ 8.0 8.1 Degenaar et al., 2014, ApJL, Vol. 796, Issue 1, article id. L9, 6 pp. (2014) (NASA ADS)
  9. ↑ 9.0 9.1 9.2 9.3 D'Ai, A. et al., MNRAS, Volume 449, Issue 4, p.4288-4303 (NASA ADS)
  10. ↑ Woods, P. M. et al., ApJ, Vol. 517, Issue 1, pp. 431-435 (NASA ADS)
  11. ↑ 11.0 11.1 Doroshenko et al., 2015, Monthly Notices of the Royal Astronomical Society, Volume 452, Issue 3, p.2490-2499 (NASA ADS)
  12. ↑ Younes, G. et al, ApJ, Vol. 804, Issue 1, article id. 43, 16 pp. (2015) (NASA ADS)
  13. ↑ Iaria et al., 2015, A&A, Volume 577, id.A63, 14 pp. (NASA ADS)
  14. ↑ Maitra et al., 2018, Monthly Notices of the Royal Astronomical Society: Letters, Volume 480, Issue 1, p.L136-L140 (NASA ADS)
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