GRO J1744-28

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Other names : 2EG J1746-2852 ([1])

Monitoring data: Swift/BAT

Type

Transient Low-mass X-ray Binary exhibiting Type I and II X-ray bursts and pulsations. Next to the Rapid Burster this is 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<0.4M_sun and inclination i>15° ([4])

Orbit

The orbital parameters were approximated to Porb = 11.836 days, T π/2 = 2456696.19880 (JED), ax sin(i) = 2.637 light-sec on the basis of the 2014 outburst with no constrains on the longitude of periastron or eccentricity ([6]). See NSSTC Gamma Ray Astrophysics.


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]

The magnetic field strength deduced from disk reflection models lies in the 2–6×10^10 G range (Degenaar et al. 2014), mismatching the values deduced from the CRSF measurements (5.27±0.06 × 10^11 G [8]) by one order of magnitude.


Outbursts

  • 1995 December: Discovery and first report of Type II X-ray bursts ([7])
  • 1996 December: Similar burst characteristics ([9]), CRSF report at 5keV in BeppoSAX data (not yet proven) ([10])
  • 2014 February: Outburst after 18 years of quiescence ([11], no CRSF), CRSF report at 5keV, 10keV and 15keV in XMM-Newton/INTEGRAL data, still under debate ([8])
  • 2017 February: Fourth outburst with ~two orders of magnitude lower luminosity (Koenig et al. in prep.)

X-ray Spectrum

Cyclotron Features

  • Fundamental CRSF at 4.68±0.05 keV (gabs, XMM-Newton/INTEGRAL, 2014 outburst [8]) / ∼4.5 keV (gabs, BeppoSAX, 1997 outburst [10])
  • 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) ([8])
  • GRO J1744−28 one of the few LMXBs where a CRSF has been reported below 10 keV (Other candidates are X1822−371 with a claimed cyclotron line energy of 0.7 keV ([12]) and SWIFT J0051.8−7320 at 5 keV ([13])
  • Cyclotron line in this source is under debate


References

  1. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Kouveliotou96A
  2. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Augusteijn97
  3. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Nishiuchi99
  4. ↑ 4.0 4.1 Cite error: Invalid <ref> tag; no text was provided for refs named Gosling07A
  5. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Masetti14Atel
  6. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Pintore14Atel
  7. ↑ 7.0 7.1 Cite error: Invalid <ref> tag; no text was provided for refs named Finger96A
  8. ↑ 8.0 8.1 8.2 8.3 Cite error: Invalid <ref> tag; no text was provided for refs named DAi15A
  9. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Woods99
  10. ↑ 10.0 10.1 Cite error: Invalid <ref> tag; no text was provided for refs named Doroshenko15A
  11. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Younes15
  12. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Iaria15A
  13. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Maitra18A
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