Article

A Possible Period for the K-Band Brightening Episodes of GX 17+2

The Astrophysical Journal (Impact Factor: 6.73). 08/2009; 701(2):L110. DOI: 10.1088/0004-637X/701/2/L110
Source: arXiv

ABSTRACT The low-mass X-ray binary and Z source GX 17+2 undergoes infrared K-band brightening episodes of at least 3.5 mag. The source of these episodes is not known. Prior published K-band magnitudes and new K-band measurements acquired between 2006 and 2008 suggest that the episodes last at least 4 hr and have a period of 3.01254 ± 0.00002 days. Future bright episodes can be predicted using the ephemeris JDmax(n) = 2454550.79829 + (3.01254 ± 0.00002)(n) days. A growing body of evidence suggests that the GX 17+2 could have a synchrotron jet, which could cause this activity.

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    ABSTRACT: 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.
    The Astrophysical Journal 07/2011; 736(1):54. · 6.73 Impact Factor

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