The newly discovered X-ray pulsar 4U 1822-37

Details The newly discovered X-ray pulsar 4U 1822-37 The newly discovered X-ray pulsar 4U 1822-37

Sep 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001tysc.confe..41j&link_type=abstract

Two Years of Science with Chandra, Abstracts from the Symposium held in Washington, DC, 5-7 September, 2001, meeting abstract.

Computer Science

Black Hole And Neutron Star Binaries

Scientific paper

We report the discovery of 0.59 s X-ray pulsations from the low-mass X-ray binary, 5.57 hr dipping and eclipsing ADC source 2A 1822-371. Pulse arrival time analysis indicates a circular orbit with e <0.03 (95% confidence) and an asini for the neutron star of 1.006(5) lightseconds, implying a mass function of (2.03±0.03)×10-2 Msolar. The barycentric pulse period was 0.59325(2) s in 1996.270 and 0.59308615(5) s in 1998.205, indicating an average spin up with dot P/P = (-1.52±0.02)×10-4 Yr-1. For a magnetic field strength of ~1-5×1012 G as derived from the X-ray spectrum the implied intrinsic X-ray luminosity is ~2-4×1037erg s-1. The pulse amplitude is low, but increases steeply as a function of energy from a sinusoidal amplitude of 0.25% in 2-5.4 keV to ~3% above 20 keV. 4U 1822-37 is optically bright and has a well-constrained inclination (because it is eclipsing), measuring the radial velocity of the companion star would therefore allow for a full binary solution, providing the first accurate mass of a neutron star in an LMXB. Harlaftis, Charles, & Horne (1997, MNRAS, 285, 673) tried measuring the radial velocity of the companion in 4U 1822-37 using spectra obtained with the 3.9 m AAT using He Iλ5876. The presence of an extra absorption component in the same part of the spectrum and the relatively low resolution (~75 km/s for Hα) which kept them from resolving the two components, yielded a lower limit on the radial velocity of the companion star of 225 km/s. This constrains the mass of the neutron star to be >0.6+1.0-0.3Msolar. Here, we report on the discovery of the pulsar and of our recent attempts using the VLT and the 6.5 m Magellan to measure the radial velocity curve.

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