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

Younes, G. and Kouveliotou, C. and Grefenstette, B. W. and Tomsick, J. A. and Tennant, A. and Finger, M. H. and Fürst, F. and Pottschmidt, K. and Bhalerao, V. and Boggs, S. E. and Boirin, L. and Chakrabarty, D. and Christensen, F. E. and Craig, W. W. and Degenaar, N. and Fabian, A. C. and Gandhi, P. and Göğüş, E. and Hailey, C. J. and Harrison, F. A. and Kennea, J. A. and Miller, J. M. and Stern, D. and Zhang, W. W. (2014) Simultaneous NuSTAR/Chandra Observations of the Bursting Pulsar GRO J1744-28 during Its Third Reactivation. Astrophysical Journal, 804 (1). Art. No. 43. ISSN 0004-637X. doi:10.1088/0004-637X/804/1/43.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Younes, G.0000-0002-7991-028X
Kouveliotou, C.0000-0003-1443-593X
Grefenstette, B. W.0000-0002-1984-2932
Tomsick, J. A.0000-0001-5506-9855
Fürst, F.0000-0003-0388-0560
Pottschmidt, K.0000-0002-4656-6881
Bhalerao, V.0000-0002-6112-7609
Boggs, S. E.0000-0001-9567-4224
Chakrabarty, D.0000-0001-8804-8946
Christensen, F. E.0000-0001-5679-1946
Fabian, A. C.0000-0002-9378-4072
Gandhi, P.0000-0003-3105-2615
Göğüş, E.0000-0002-5274-6790
Harrison, F. A.0000-0003-2992-8024
Kennea, J. A.0000-0002-6745-4790
Stern, D.0000-0003-2686-9241
Zhang, W. W.0000-0002-1426-9698
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).
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
Subject Keywords:pulsars: general; stars: individual (GRO J1744-28); X-rays: binaries; X-rays: bursts
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2015-64
Issue or Number:1
Record Number:CaltechAUTHORS:20150605-135807207
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Official Citation:Simultaneous NuSTAR/Chandra Observations of the Bursting Pulsar GRO J1744-28 during Its Third Reactivation G. Younes et al. 2015 ApJ 804 43
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:58059
Deposited On:05 Jun 2015 23:48
Last Modified:10 Nov 2021 21:58

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