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Title: HIGH-RESOLUTION X-RAY SPECTROSCOPY OF THE BURSTING PULSAR GRO J1744-28

The bursting pulsar GRO J1744-28 is a Galactic low-mass X-ray binary that distinguishes itself by displaying type-II X-ray bursts: brief, bright flashes of X-ray emission that likely arise from spasmodic accretion. Combined with its coherent 2.1 Hz X-ray pulsations and relatively high estimated magnetic field, it is a particularly interesting source to study the physics of accretion flows around neutron stars. Here we report on Chandra/High Energy Transmission Grating observations obtained near the peak of its bright 2014 accretion outburst. Spectral analysis suggests the presence of a broad iron emission line centered at E {sub l} ≅ 6.7 keV. Fits with a disk reflection model yield an inclination angle of i ≅ 52° and an inner disk radius of R {sub in} ≅ 85 GM/c {sup 2}, which is much further out than typically found for neutron star low-mass X-ray binaries. Assuming that the disk is truncated at the magnetospheric radius of the neutron star, we estimate a magnetic field strength of B ≅ (2-6) × 10{sup 10} G. Furthermore, we identify an absorption feature near ≅ 6.85 keV that could correspond to blue-shifted Fe XXV and point to a fast disk wind with an outflow velocity of v {sub out} ≅ (7.5-8.2)more » × 10{sup 3} km s{sup –1} (≅ 0.025c-0.027c). If the covering fraction and filling factor are large, this wind could be energetically important and perhaps account for the fact that the companion star lost significant mass while the magnetic field of the neutron star remained strong.« less
Authors:
;  [1] ;  [2] ;  [3] ;  [4] ;  [5]
  1. Department of Astronomy, University of Michigan, 1085 South University Avenue, Ann Arbor, MI 48109 (United States)
  2. Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)
  3. Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802 (United States)
  4. Space Science Office, ZP12, NASA Marshall Space Flight Center, Huntsville, AL 35812 (United States)
  5. Universities Space Research Association, 6767 Old Madison Pike, Suite 450, Huntsville, AL 35806 (United States)
Publication Date:
OSTI Identifier:
22364519
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 796; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; BINARY STARS; INCLINATION; IRON; KEV RANGE; MAGNETIC FIELDS; MASS; MILKY WAY; NEUTRON STARS; NEUTRONS; PULSARS; PULSATIONS; REFLECTION; RESOLUTION; STAR ACCRETION; X RADIATION; X-RAY SPECTROSCOPY