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Outburst Ephemeris for the Supergiant Fast X-ray Transient IGR J17544-2619

ATel #6227; David M. Smith (UC Santa Cruz)
on 11 Jun 2014; 23:37 UT
Credential Certification: David M. Smith (dsmith@ssl.berkeley.edu)

Subjects: X-ray, Binary, Transient

I present an ephemeris for the supergiant fast x-ray transient IGR J17544-2619 using 69 bright outbursts from INTEGRAL, RXTE, Swift, and Suzaku (see Table). The ephemeris was calculated by finding the orbital period that minimized the standard deviation of the outburst phases about their mean, then defining the mean outburst phase as periastron (phase=0). The derived period is 4.92693 +/- 0.00036 dy with periastron at MJD = 53732.65 +/- 0.23. The errors were calculated by creating 10,000 artificial sets of 69 outburst times, each with a Gaussian distribution around zero phase sampled using the same standard deviation (0.148 periods) and period as the data, then re-fitting according to the same procedure. The artificial data sets were constructed with the same approximate rate of detections versus time as the data over the total range of 15.15 years.

Other ephemerides have been based on folded lightcurves from INTEGRAL/IBIS alone (Clark et al. 2009 MNRAS 399, L113; Drave et al. 2012 A&A 539, A21; Drave et al. 2014 MNRAS 439, 2175), but Drave et al. 2014 demonstrate that bright outbursts seen by IBIS peak near the same phase as the overall emission. Our period is consistent with that of Drave et al. 2014, 4.9272 +/- 0.0004 dy, but not independent. Excluding the events in Drave et al. 2014 to get an independent sample of 41 events, we find a period of 4.92646 +/- 0.00040 and periastron MJD = 53733.11 +/- 0.27. This period differs by 1.3 sigma from Drave et al. 2014.

An earlier version of this ephemeris, produced in 2012, was used to schedule the NuSTAR observations of the source on 2013 June 18-19, using period 4.9264 dy and periastron at MJD = 53733.10.

Table: MJD, Observatory, Reference

54546.048 Suzaku (1)
54412.255 Swift (2)
54556.869 Swift (3)
54713.013 Swift (4)
54945.472 Swift (5)
54988.326 "
55002.115 "
55024.458 "
55063.137 "
55074.524 "
55132.808 "
55259.968 Swift (6)
55644.081 Swift (7)
56029.026 Swift (8)
56132.203 Swift (9)
56471.310 Swift (10)
56546.667 Swift (11)
56802.935 Swift (12)
51269.822 RXTE (13)
52062.543 "
52195.428 "
52393.843 "
52411.864 "
52535.900 "
52556.532 "
52945.108 "
53063.276 "
53137.709 "
53270.735 "
53613.391 "
53787.885 "
53980.518 "
54620.234 "
54708.367 "
54747.306 "
54870.814 "
54911.703 "
55124.164 "
55668.582 "
55767.444 "
52732.370 INTEGRAL (14)
52899.315 "
52904.295 "
53062.775 "
53067.385 "
53072.430 "
53072.620 "
53269.985 "
53422.350 "
53441.240 "
53451.455 "
53481.295 "
53628.800 "
53658.380 "
53806.955 "
53850.990 "
53987.555 "
53998.510 "
54343.595 "
54364.263 "
54367.240 "
54378.457 INTEGRAL (15)
54560.435 INTEGRAL (14)
54570.445 "
54886.385 "
54938.385 "
55067.800 "
55437.990 "
56708.581 INTEGRAL (15)

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(15) from Kuulkers et al. 2007 using the OSA9 software, distributed by the ISDC (Courvoisier et al. 2003), at http://integral.esac.esa.int/BULGE/SOURCES/IGR_J17544-2619/IGR_J17544-2619_isgri_lc_18-40.all, accessed 9 June 2014