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
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