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Spitzer Observations of GX17+2: Confirmation of a Periodic Synchrotron Source

Harrison, Thomas E. and McNamara, Bernard J. and Bornak, Jillian and Gelino, Dawn M. and Wachter, Stefanie and Rupen, Michael P. and Gelino, Christopher R. (2011) Spitzer Observations of GX17+2: Confirmation of a Periodic Synchrotron Source. Astrophysical Journal, 736 (1). Art. No. 54. ISSN 0004-637X.

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GX17+2 is a low-mass X-ray binary (LMXB) that is also a member of a small family of LMXBs known as "Z-sources" that are believed to have persistent X-ray luminosities that are very close to the Eddington limit. GX17+2 is highly variable at both radio and X-ray frequencies, a feature common to Z-sources. What sets GX17+2 apart is its dramatic variability in the near-infrared, where it changes by ΔK ~ 3 mag. Previous investigations have shown that these brightenings are periodic, recurring every 3.01 days. Given its high extinction (A_V≥9 mag), it has not been possible to ascertain the nature of these events with ground-based observations. We report mid-infrared Spitzer observations of GX17+2 which indicate a synchrotron spectrum for the infrared brightenings. In addition, GX17+2 is highly variable in the mid-infrared during these events. The combination of the large-scale outbursts, the presence of a synchrotron spectrum, and the dramatic variability in the mid-infrared suggest that the infrared brightening events are due to the periodic transit of a synchrotron jet across our line of sight. An analysis of both new, and archival, infrared observations has led us to revise the period for these events to 3.0367 days. We also present new Rossi X-Ray Timing Explorer (RXTE) data for GX17+2 obtained during two predicted infrared brightening events. Analysis of these new data, and data from the RXTE archive, indicates that there is no correlation between the X-ray behavior of this source and the observed infrared brightenings. We examine various scenarios that might produce periodic jet emission.

Item Type:Article
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Gelino, Dawn M.0000-0003-1274-2784
Additional Information:© 2011 The American Astronomical Society. Received 2011 February 16; accepted 2011 May 4; published 2011 July 6.
Group:Infrared Processing and Analysis Center (IPAC)
Subject Keywords:infrared: stars; stars: individual (GX17+2); stars: neutron; X-rays: binaries
Issue or Number:1
Classification Code:PACS: 97.80.Jp; 97.10.Ri; 95.85.Hp
Record Number:CaltechAUTHORS:20110802-085610114
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Official Citation:Spitzer Observations of GX17+2: Confirmation of a Periodic Synchrotron Source Thomas E. Harrison et al. 2011 ApJ 736 54
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:24623
Deposited By: Ruth Sustaita
Deposited On:02 Aug 2011 16:19
Last Modified:03 Oct 2019 02:58

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