CaltechAUTHORS
Published May 1, 2014 | Version Published + Submitted
Journal Article Open

Simultaneous NuSTAR/Chandra Observations of the Bursting Pulsar GRO J1744-28 during Its Third Reactivation

Creators

  • 1. ROR icon Universities Space Research Association
  • 2. ROR icon National Space Science and Technology Center
  • 3. ROR icon Marshall Space Flight Center
  • 4. ROR icon California Institute of Technology
  • 5. ROR icon University of California, Berkeley
  • 6. ROR icon University of Maryland, Baltimore County
  • 7. ROR icon Inter-University Centre for Astronomy and Astrophysics
  • 8. ROR icon Observatory of Strasbourg
  • 9. ROR icon Massachusetts Institute of Technology
  • 10. ROR icon Technical University of Denmark
  • 11. ROR icon Lawrence Livermore National Laboratory
  • 12. ROR icon University of Michigan–Ann Arbor
  • 13. ROR icon University of Cambridge
  • 14. ROR icon Durham University
  • 15. ROR icon Sabancı University
  • 16. ROR icon Columbia University
  • 17. ROR icon Pennsylvania State University
  • 18. ROR icon Jet Propulsion Lab
  • 19. ROR icon Goddard Space Flight Center

Abstract

We report on a 10 ks simultaneous Chandra/High Energy Transmission Grating (HETG)–Nuclear Spectroscopic Telescope Array (NuSTAR) observation of the Bursting Pulsar, GRO J1744-28, during its third detected outburst since discovery and after nearly 18 yr of quiescence. The source is detected up to 60 keV with an Eddington persistent flux level. Seven bursts, followed by dips, are seen with Chandra, three of which are also detected with NuSTAR. Timing analysis reveals a slight increase in the persistent emission pulsed fraction with energy (from 10% to 15%) up to 10 keV, above which it remains constant. The 0.5–70 keV spectra of the persistent and dip emission are the same within errors and well described by a blackbody (BB), a power-law (PL) with an exponential rolloff, a 10 keV feature, and a 6.7 keV emission feature, all modified by neutral absorption. Assuming that the BB emission originates in an accretion disk, we estimate its inner (magnetospheric) radius to be about 4 × 10^7 cm, which translates to a surface dipole field B ≈ 9 × 10^(10) G. The Chandra/HETG spectrum resolves the 6.7 keV feature into (quasi-)neutral and highly ionized Fe xxv and Fe xxvi emission lines. XSTAR modeling shows these lines to also emanate from a truncated accretion disk. The burst spectra, with a peak flux more than an order of magnitude higher than Eddington, are well fit with a PL with an exponential rolloff and a 10 keV feature, with similar fit values compared to the persistent and dip spectra. The burst spectra lack a thermal component and any Fe features. Anisotropic (beamed) burst emission would explain both the lack of the BB and any Fe components.

Additional Information

© 2015 The American Astronomical Society. Received 2 December 2014; accepted for publication 18 February 2015; Published 29 April 2015. This work was supported under NASA Contract No. NNG08FD60C and made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software, and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA).

Attached Files

Published - 0004-637X_804_1_43.pdf

Submitted - 1502.05982v1.pdf

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0004-637X_804_1_43.pdf

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Additional details

Identifiers

Eprint ID
58059
Resolver ID
CaltechAUTHORS:20150605-135807207

Related works

Describes
http://arxiv.org/abs/1502.05982 (URL)

Funding

NASA
NNG08FD60C

Dates

Created
2015-06-05
Created from EPrint's datestamp field
Updated
2021-11-10
Created from EPrint's last_modified field

Caltech Custom Metadata

Caltech groups
NuSTAR , Space Radiation Laboratory
Other Numbering System Name
Space Radiation Laboratory
Other Numbering System Identifier
2015-64