Outbursts of Four Transient Pulsar Systems in the SMC

Details Outbursts of Four Transient Pulsar Systems in the SMC Outbursts of Four Transient Pulsar Systems in the SMC

Apr 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999head....4.3901l&link_type=abstract

American Astronomical Society, HEAD meeting #4, #39.01; Bulletin of the American Astronomical Society, Vol. 31, p.742

Astronomy and Astrophysics

Astronomy

1

Scientific paper

We report on observations by RXTE of the outbursts of four x-ray transient pulsar systems in the Small Magellanic Cloud made from 1997 November to 1998 July. Each of these four systems, AX J0051-722 (pulsation period P=91.0s), XTE J0054-720 (P=168.9s), 1SAX J0054.9-7226 (P=58.9s), and 1WGA J0053.8-7226 (P=46.6s), had outbursts lasting approximately 30 days, but at times more than one source was active. All but XTE J0054-720 have confirmed optical counterparts indicating that they are Be-neutron star systems. After initial detection in 1997 November, two subsequent outbursts of AX J0051-722 in 1998 March and 1998 July point to a possible orbital period for this system of 116 days. Similarly, reappearances of 1SAX J0054.9-7226 imply an orbital period of 65 days. In addition, XTE J0054-720 and 1SAX J0054.9-7226 show a significant decrease in their pulsation periods, with the former large enough to suggest a spin-up of the neutron star due to accreting material. Spectra for these sources can be modeled as a power law with a high-energy cutoff. Because multiple sources were at times simultaneously active, discerning properties of individual sources is sometimes difficult. The observations show that the combined spectrum of 1WGA J0053.8-7226 and AX J0051-722 has a power law index of 0.8 and energy cutoffs between 10-16 keV. XTE J0054-720 has a power law index of 0.9, and a cutoff ranging between 10-15 keV. 1SAX J0054.9-7226 has power law index of 0.4 and cutoff of 7 keV. There is no significant evolution of these parameters through the course of the outbursts. Features in the folded light curves range from an eclipse-like dip in AX J0051-722 to sinusoidal-like variations in 1WGA J0053.8-7226. Further, in many of the observations of AX J0051-722 the hardness [(10-20 keV)/(6-10 kev)] shows an increase during the dip.

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