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Outburst behavior in Aql X-1

ATel #10450; Tolga Dincer, Charles D. Bailyn, Bryndis Cruz (Yale)
on 31 May 2017; 20:48 UT
Credential Certification: Tolga Dincer (tolga.dincer@yale.edu)

Subjects: Infra-Red, Optical, Neutron Star, Transient

Referred to by ATel #: 10452, 10541

ATEL#10441 has reported on the possible start of a new outburst in Aql X-1. As part of our X-ray binary monitoring program, we perform optical and near-infrared photometric observations of Aql X-1 with the SMARTS 1.3m telescope, located at CTIO. From our last four observations the optical magnitudes are:

MJD (UTC)	           V-mag     R-mag     I-mag
57888.3 (May 15) 19.46 18.54 17.83
57893.3 (May 20) 19.26 18.48 17.64
57901.3 (May 28) 18.58 17.86 16.95
57904.2 (May 31) 18.15 17.49 -
The combined errors due to photometry and calibration are typically ~0.05 mag. The flux from the first two observation sets is dominated by the unresolved nearby star (Dipankar & Bailyn 2008, ApJ, 688, 549), but the last two observations clearly show a significant brightening in all bands. Furthermore, the Swift BAT light curve (https://swift.gsfc.nasa.gov/results/transients/AqlX-1/) of the source within the last several days (MJD 57899-57904) show hard X-ray activity significantly above the detection limit. Both results confirm the start of a new outburst in Aql X-1. Our regular monitoring observations of Aql X-1 will continue. We encourage further multiwavelength observations of Aql X-1.