Fermi Gamma Ray Burst Monitor detects bursts from Swift J181723.1-164300

ATel #10665; P. Jenke (UAH), V. Connaughton (USRA), M. Linares (UPC), C. Wilson-Hodge (NASA/MSFC)
on 23 Aug 2017; 18:44 UT
Credential Certification: Peter Jenke (peter.a.jenke@nasa.gov)

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A search in the archived GBM X-ray bursts for events consistent with Swift J181723.1-164300 was performed from a month prior to the July 28 Swift trigger (GCN #21369) to the present. The GBM X-ray burst monitor has detected 8 soft events that have a localization consistent with Swift J181723.1-164300 (ATel #10612) between July 20 and August 8, 2017 including the two events on which Swift triggered (GCN #21369, #21385, GCN #21400). Seven of the event localizations were within 2 sigma of the Swift source location while one was ~4 sigma from the source. GBM's localization error for these events was typically around 5-10 degrees statistical which precludes a firm association. We performed spectral analysis on all the events and found 6 of them to be consistent with the typical Type-1 blackbody spectrum with blackbody temperatures between 2.6 and 3.5 keV. The other two events had relatively hard spectra with blackbody temperatures ~4.2 keV. The blackbody temperature and flux were consistent with the Swift/BAT results for the July 28 and July 30 events that triggered Swift. The last two events occurred on August 06 and August 08 in which Swift/XRT detected no significant flux from the source (ATel #10624). The first may be excluded because of its hard spectrum while the last might be associated with a different Type-1 XRB source.

There are 15 sources within 10 degrees of Swift J181723.1-164300 that are known to produce Type-1 X-ray bursts. Three of them; GS 1826-238, GX 17+2 and GX 13+1 were showing considerable activity for July and August in MAXI (http://maxi.riken.jp/top/index.html). The GBM XRB monitor shows no significant increase in burst activity consistent with the location of Swift J181723.1-164300 ( = 0.3 events/day) over a typical month. We therefore can not attribute the 6 events not detected and localized by other instruments to the Swift source in preference to other sources consistent with the GBM localization.

The average energy flux for all the events was (2-5)e^8 erg/s-cm^2 from 10-100 keV. Details for the individual events are given in on our web site (see below) by clicking on the Swift J181723.1-164300 link. Methodology is given in P. A. Jenke, et al., "The Fermi-GBM 3-Year X-ray Burst Catalog." ApJ, 826:228 (2016).

GBM X-ray Burst Monitor