Central Bureau for Astronomical Telegrams
IAUC 6291: GRO J1744-28
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Circular No. 6291
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
Phone 617-495-7244/7440/7444 (for emergency use only)
GRO J1744-28
S. Sazonov and R. Sunyaev, Space Research Institute, Moscow, on
behalf of the Granat/WATCH Team, report: "On Jan. 14-15 the Galactic
Center region was observed by the Granat/WATCH instrument. At the edge
of the field of view, a strong flux, 4.4 +/- 0.3 Crab (8-20 keV), was
detected from the direction of the new transient x-ray burster and
pulsar GRO J1744-28, discovered by BATSE. The WATCH data show that the
source's spectrum is much flatter in the standard x-ray band than in the
BATSE sensitivity range. It is similar to typical spectra of accreting
x-ray pulsars. At the distance of the Galactic Center, the luminosity
of GRO J1744-28 in the 8-20 keV band is approximately 4 x 10**38 erg/s,
a value that exceeds the Eddington luminosity for a neutron star.
However, super-Eddington luminosity was observed earlier in SMC X-1
and several other x-ray pulsars. GRANAT/WATCH will continue to observe
GRO J1744-28 in scanning mode, while observational conditions are
improving daily."
J. Swank, NASA Goddard Space Flight Center, reports, for the
X-Ray Timing Explorer instrument and operations team: "XTE observed
the new galactic transient GRO J1744-28 (IAUC 6272, 6275, 6276, 6284,
6285, 6286, 6290) for 11 hours on Jan. 18-19. A source pulsing at
2.1 Hz, as well as nine bursts 2-8 times brighter than the persistent
emission, was observed from a position within the error box reported
by Hurley et al. (IAUC 6286). The XTE best-fit position, from
scans across the source, is R.A. = 17h44m.5 +- 0m.2, Decl. = -28d45' +/- 2'
(equinox 2000.0), where the errors are systematic. A sinusoidal pulse
shape was observed, and the burst flux was sometimes strongly modulated.
Following each burst, the flux is depressed and takes a few minutes to
recover. The spectra of both the pulsed and the burst flux are
characteristic of bright accreting pulsars; they are consistent with a
power law with number index about 1.2 and a rollover above 13 keV with an
e-folding energy of 14 keV. The absorbing column density is less than
10**22 cm**-2. The low column density implies that the source is
probably closer than the galactic center and that at least the
non-burst luminosity probably does not exceed the Eddington limit.
The non-burst flux was about 2 times 10**-7 erg cm**-2 s**-1 (2-100 keV).
These observations were taken during the period of initial instrument
verification, so the calibrations are preliminary. See
http://heasarc.gsfc.nasa.gov/docs/xte/SOF/TOONews.html for further
information about results, data and future observations."
(C) Copyright 1996 CBAT
1996 January 21 (6291) Brian G. Marsden
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