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High-resolution X-Ray Spectroscopy of the Bursting Pulsar GRO J1744-28

Degenaar, N. and Miller, J. M. and Harrison, F. A. and Kennea, J. A. and Kouveliotou, C. and Younes, G. (2014) High-resolution X-Ray Spectroscopy of the Bursting Pulsar GRO J1744-28. Astrophysical Journal Letters, 796 (1). Art. No. L9. ISSN 2041-8205. doi:10.1088/2041-8205/796/1/L9.

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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 l ≃ 6.7 keV. Fits with a disk reflection model yield an inclination angle of i ≃ 52° and an inner disk radius of R_in ≃ 85 GM/c^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) × 10^10 G. Furthermore, we identify an absorption feature near sime 6.85 keV that could correspond to blue-shifted Fe XXV and point to a fast disk wind with an outflow velocity of v_out ≃ (7.5-8.2) × 10^3 km s^–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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Harrison, F. A.0000-0003-2992-8024
Kennea, J. A.0000-0002-6745-4790
Kouveliotou, C.0000-0003-1443-593X
Younes, G.0000-0002-7991-028X
Additional Information:© 2014 The American Astronomical Society. Received 2014 September 19; accepted 2014 October 17; published 2014 November 3. N.D. is supported by NASA through Hubble Postdoctoral Fellowship grant No. HST-HF-51287.01-A from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. J.M. gratefully acknowledges support from the Chandra guest observer program. N.D. thanks Ed Cackett, Felix Fürst and Rudy Wijnands for very helpful discussions. We extend our thanks to the anonymous referee. Facility: CXO (HETG)
Group:Space Radiation Laboratory
Funding AgencyGrant Number
NASA Hubble FellowshipHST-HF-51287.01-A
Subject Keywords:accretion, accretion disks; pulsars: individual (GRO J1744-28); stars: neutron; X-rays: binaries
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2014-23
Issue or Number:1
Record Number:CaltechAUTHORS:20141211-090443372
Persistent URL:
Official Citation:High-resolution X-Ray Spectroscopy of the Bursting Pulsar GRO J1744-28 N. Degenaar et al. 2014 ApJ 796 L9
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:52581
Deposited By: Jason Perez
Deposited On:11 Dec 2014 21:31
Last Modified:10 Nov 2021 19:42

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