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Optical and hard X-ray detections of an outburst from Aquila X-1

ATel #1970; D. M. Russell (Univ. of Amsterdam), F. Lewis (Las Cumbres Observatory Global Telescope Network (LCOGTN)/Open Univ.)
on 14 Mar 2009; 20:02 UT
Credential Certification: David M. Russell (D.M.Russell@uva.nl)

Subjects: Optical, X-ray, Binary, Neutron Star, Transient

Referred to by ATel #: 1977, 2000, 2288, 2296, 2871, 9306

We report a new outburst from the neutron star X-ray transient Aquila X-1. Optical monitoring with the Faulkes Telescopes North and South show a rise above quiescence by 0.4 mag in V and i' on 2009-03-07. The magnitudes on that date (MJD 54897.76) were V=18.82 +- 0.09; i'=17.32 +- 0.12. Three days before, on 2009-03-04 (MJD 54894.65) we had V=19.31 +- 0.15; i'=17.73 +- 0.18, which are consistent with the quiescent magnitudes of V=19.21 +- 0.10; i'=17.74 +- 0.07 (ATel #1218). Below is a link to the light curves.

By 2009-03-10 the source had risen above the detection limit of BAT on Swift and was detected at the 3 sigma level. The Swift/BAT light curve shows it is clearly brightening, reaching 0.014 +- 0.002 ct/s/cm2 (15-50 keV) ~ 60 mCrab on 2009-03-14. The source is not yet detected by the RXTE/ASM and is still in the rising phase; we encourage multiwavelength observations. Aquila X-1 performs quasi-regular outbursts every ~ 9 months (Maitra & Bailyn 2008, ApJ, 688, 537); the last outbursts were reported in June 2008 (ATel #1553, #1557), September 2007 (ATel #1216, #1218, #1219, #1229, #1232) and May 2007 (ATel #1079, #1080, #1087).

The Swift/BAT transient monitor results are provided by the Swift/BAT team. The Faulkes Telescope observations are part of an ongoing monitoring campaign of ~ 30 low-mass X-ray binaries (Lewis et al. 2008, arXiv:0712.2751). The Faulkes Telescope Project is an educational and research arm of the Las Cumbres Observatory Global Telescope Network (LCOGTN). FL acknowledges support from the Dill Faulkes Educational Trust.

Aql X-1 optical light curves