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Optical Monitoring Observations of AQL X-1

ATEL # 2891; Tolga Guver (Univ. of Arizona), Andrea Kunder (CTIO), and Feryal Ozel (Univ. of Arizona)
on 30 Sep 2010; 18:03 UT
Password Certification: Tolga Guver (

Subjects: Optical, Binaries, Neutron Stars, Transients
Referred to by ATEL #: 2911

AQL X-1 has been in a bright outburst in the X-rays and optical since September 1st and 7th (Atel #2850, #2871). We report on our observations of the source on September 26th UTC with the 4m CTIO BLANCO Telescope.

Using MOSAIC II detector we obtained 3 R band images with exposure times of 200 seconds. We converted instrumental magnitudes to the standard system using several nearby stars and the USNO B1.0 catalog (Monet et al. 2003). Our results are given below. Atmospheric seeing during our observations was ~ 1.5 arcseconds, hence our magnitudes include the unrelated interloper 0.5" away (Chevalier et al. 1999; Maitra & Bailyn 2008).

Based on MAXI (Matsuoka, M. et al., 2009) observations, the source X-ray count rate in 2-20 keV range during our observations was ~0.59 counts /s/cm^2 . During the peak, 2-20 keV MAXI count rate was ~ 1.0 counts /s/cm^2. This shows that the source flux continues to slowly decrease in the X-rays, although it is still much higher than typical quiescent flux levels, which is < 0.1 counts/s/cm^2.

Our R band magnitudes are at the same level as the SMARTS measurements obtained a week before our observation and thus show no decline (see,

MJD R Mag Err*
55465.0894 16.690 +/- 0.002
55465.1100 16.695 +/- 0.002
55465.1315 16.723 +/- 0.005
*Errors represent only the formal uncertainties of the measurements and not the systematic uncertainties from the conversion.

The Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, is operated by the Association of Universities for Research in Astronomy, by cooperative agreement with the National Science Foundation. This research has made use of the MAXI data provided by RIKEN, JAXA and the MAXI team.


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