SIMULTANEOUS NuSTAR/CHANDRA OBSERVATIONS OF THE BURSTING PULSAR GRO J1744-28 DURING ITS THIRD REACTIVATION
- Universities Space Research Association, 6767 Old Madison Pike, Suite 450, Huntsville, AL 35806 (United States)
- Astrophysics Office, ZP 12, NASA-Marshall Space Flight Center, Huntsville, AL 35812 (United States)
- Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, CA 91125 (United States)
- Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450 (United States)
- Center for Space Science and Technology, University of Maryland Baltimore County, Baltimore, MD 21250 (United States)
- Inter-University Center for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411007 (India)
- Observatoire Astronomique de Strasbourg, 11 Rue de l'Université, F-67000 Strasbourg (France)
- Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)
- DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby (Denmark)
- Department of Astronomy, University of Michigan, 1085 South University Avenue, Ann Arbor, MI 48109 (United States)
- Institute of Astronomy, Madingley Road, Cambridge CB3 0HA (United Kingdom)
- Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom)
- Sabancı University, Orhanlı-Tuzla, İstanbul 34956 (Turkey)
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{sup 7} cm, which translates to a surface dipole field B ≈ 9 × 10{sup 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.
- OSTI ID:
- 22522472
- Journal Information:
- Astrophysical Journal, Vol. 804, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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