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ATEL # 1219; M.A.P. Torres (CfA), P. G. Jonker (SRON/UU/CfA), C. Bassa (McGill), G. Nelemans (Univ. of Nijmegen)
on 18 Sep 2007; 21:53 UT
Password Certification: Manuel Torres (firstname.lastname@example.org)
Subjects: Optical, Binaries, Neutron Stars, Transients
We observed the optical counterpart to the recurrent X-ray transient Aql X-1 on 2007 Sep 11 to Sep 14 UT using the IMACS camera mounted on the 6.5m Magellan Baade telescope at Las Campanas Observatory. Single 5-10s R-band images were acquired each night with a seeing of 0.8-1.4 arcsec.
Aperture photometry enclosing both Aql X-1 and the field star 0.46 arcsec away (Callanan, Filippenko & Garcia, 1999, IAUC 7086; Chevalier et al. 1999, A&A, 347, L51) yields the following magnitudes: R=17.22 (MJD 54354.00373), R= 17.05 (MJD 54355.00471), R = 16.96 (MJD 54356.00738) and R = 17.13 (MJD 54357.04706). The uncertainty in the absolute flux calibration is expected to be ~ 0.04 mag.
This indicates that the sum of flux from both stars has increased by more than 1.5 magnitudes compared to the optical brightness during quiescence (R=18.8; see e.g. Maitra & Bailyn 2007, ATel #1080) and confirms the RXTE detection of a second outburst of Aql X-1 during 2007 (Corbet et al. 2007, ATel #1216).