Discovery of the 18.7 Second Accreting X-Ray Pulsar GRO J1948+32

Details Discovery of the 18.7 Second Accreting X-Ray Pulsar GRO J1948+32 Discovery of the 18.7 Second Accreting X-Ray Pulsar GRO J1948+32

Jun 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...446..826c&link_type=abstract

Astrophysical Journal v.446, p.826

Astronomy and Astrophysics

Astronomy

25

X-Rays: Stars, Stars: Pulsars: Individual Alphanumeric: Gro J1948+32, Stars: Pulsars: Individual Alphanumeric: Gro J2014+34

Scientific paper

We have detected an 18.7 s accreting X-ray pulsar in the Cygnus region, using the BATSE large-area detectors on the Compton Gamma Ray Observatory. GRO J1948+32 has been localized to within 10 deg2 using a method we developed for positioning weak pulsed sources with BATSE. During the 33 day outburst, the phase-averaged 20-75 keV pulsed flux rose from 25 mCrab to 50 mCrab over 10 days and then decayed below our detection j-threshold over nearly 25 days. A photon spectral index of γ = 2.65±0.15 (assuming photon flux density dN/dE ∝ E-γ) was measured during a bright interval. The observed modulation of the neutron star's pulse frequency is suggestive of orbital variation over less than one orbit cycle. Assuming a constant spin frequency derivative over the outburst, we can place the following individual 95% confidence limits on each of the pulsar parameters: orbital period 35d < Porb < 70d; orbital radius 75 lt-sec < αx sin i < 300 lt-sec, eccentricity e < 0.25, spin frequency derivative 5 × 10-13 Hz s-1 < vdot < 2.5 × 10-11 Hz s-1, X-ray mass function 0.5 Msun < fx(M) < 5 Msun. As the stellar type of the mass-providing companion is still not known for this source, we briefly speculate on the nature of mass transfer in this system.

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