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Optical and Near-IR Observations of the Current Outburst of Aql X-1

ATel #1218; D. Maitra (Univ. of Amsterdam), D. M. Russell (Univ. of Southampton), F. Lewis (Las Cumbres Observatory Global Telescope Network (LCOGTN)/Open Univ.), C. Bailyn (Yale Univ.), R. P. Fender (Univ. of Southampton), P. Roche (LCOGTN)
on 18 Sep 2007; 21:52 UT
Credential Certification: Dipankar Maitra (maitra@astro.yale.edu)

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

Referred to by ATel #: 1229, 1557, 1970, 2871

As part of a monitoring campaign of quiescent and outbursting low-mass X-ray binaries with the CTIO/SMARTS telescopes and the Faulkes telescopes , we report observations of Aql X-1 and confirm the optical counterpart of the new X-ray outburst (ATel #1216).

On 2007 Aug 30 (MJD 54342.26) we performed optical observations of Aql X-1 for 100 sec each in V and i' filters using the Faulkes Telescope North in V and i'-bands and detected the source with a confidence of 20 and 63 sigma in V and i', respectively. The apparent magnitudes (flux calibrated using stars C1 and C2 in the field of view; Chevalier et al. 1999, A&A, 347, L51) are V=18.71 +- 0.08; i'=17.28 +- 0.05. During a quiescent period (8 observations between MJD 53833.6 and 54215.6) before the May 2007 outburst (ATel #1079, #1080) we measure V=19.21 +- 0.10; i'=17.74 +- 0.07 for Aql X-1 (all are > 5 sigma detections) which agree with the values measured in April 1999 by Chevalier et al. (1999).

As of the latest observations using the CTIO/SMARTS 1.3m telescope on September 18, 3.2h UTC (mid-exposure), the source was at R=17.10 +- 0.05 mag and J=15.5 +- 0.1 mag, compared to mean quiescent values of R=18.8 +- 0.09 mag and J=16.7 +- 0.10 mag. All magnitudes quoted above include the unrelated star 0.5" away (Chevalier et al. 1999) of magnitude V=19.42 +- 0.06; i'=18.02 +- 0.06 mag.

The OIR data from both telescopes show an increasing trend in the V, R, i' and J band fluxes from the source from 2007 Aug 29th (MJD 54341). Latest OIR and ASM data however suggest that the increasing trend may have arrested and the source might have reached peak or near-peak luminosity. The latest fluxes are still lower than the maximum observed peak fluxes from this source during the FRED outburst of 2003 and 2000 by factors of ~3-5 at all wavelengths. Multiwavelength observations are encouraged.

FL acknowledges support from the Dill Faulkes Educational Trust.

The Faulkes light curves can be found at:
and the SMARTS light curves at: