Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aas...19915903g&link_type=abstract
American Astronomical Society, 199th AAS Meeting, #159.03; Bulletin of the American Astronomical Society, Vol. 34, p.568
Astronomy and Astrophysics
Astrophysics
Scientific paper
The X-ray source 4U 1700+24 may be only the second neutron star known in a symbiotic binary. The companion in this case is the M3 II star HD 154791. We present Rossi X-ray Timing Explorer (RXTE) data from observations in 1997 February and November. The first observation found the source in quiescence at a mean flux of 7.4*E-11\ erg cm-2 s{-1} (2--10 keV, equivalent to ≈3 mCrab). The second observation was allocated from director's discretionary time, in response to an outburst (the only one seen to date by RXTE) lasting ~ 100 d. At the peak of the outburst the 1-day averaged ASM count rate reached around 3 count s-1 (2--10 keV; around 40 mCrab). Given the known source distance of 730 kpc, the 2--10 keV X-ray luminosity range is 5--70*E33\ erg s-1. The PCA/HEXTE spectra could be reasonably well fit by a combination blackbody and powerlaw, with blackbody kT=1.3 keV and spectral index α =2.4 in quiescence compared with kT=2.0 keV and α =2.0 during the outburst. In addition to the spectral variation observed with the transition to the outburst state was a significant increase in variability. In both observations we detected multiple flares on timescales of <1 s. While the hard X-ray spectrum appears to confirm that the compact object is a neutron star, no evidence for pulsations or quasi-periodic oscillations in the range 0.01-1000 Hz was found. We discuss the characteristics of this source and compare it to the only other symbiotic neutron-star binary system, GX 1+4. This work was funded in part by NSF grant INT-9902665 to J.L.S., and also the NASA Long Term Space Astrophysics program under grant NAG 5-9184.
Galloway Duncan K.
Sokoloski Jennifer L.
Uttley Phil
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