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Optical observations of Aql X-1

ATel #5129; Tolga Guver (Sabanci Univ.), Tansel Ak (Istanbul Univ.), Can Gungor (ITU), Yavuz Eksi (ITU)
on 13 Jun 2013; 11:57 UT
Credential Certification: Tolga Guver (tguver@email.arizona.edu)

Subjects: Optical, Neutron Star, Transient

Referred to by ATel #: 5136, 5148, 5158

Following the recent reports by Meshcheryakov et al. (ATel #5114) and Degenaar & Wijnands (Atel #5117) showing that the X-ray binary Aql X-1 is entering a new outburst, we obtained R and I band images of the field with the 1.0 meter T100 telescope (TUBITAK National Observatory, Antalya - Turkey) on June 12 using an SI 1100 CCD.

We obtained 3 R and 3 I band images with 150 second exposure each. In each frame we clearly detect the source. We converted the instrumental magnitudes to the standard system using the R2 and I band photometry of 6 nearby stars as given in the USNO B1.0 catalog (Monet et al. 2003).

Our results are given below.
JD Filter Mag Err*
2456456.39464 R 16.35 +/-0.32
2456456.39701 R 16.34 +/-0.31
2456456.39938 I 16.16 +/-0.17
2456456.40651 R 16.31 +/-0.30
2456456.40889 I 16.05 +/-0.19
2456456.42789 I 16.07 +/-0.16
*The magnitude errors contain both the formal uncertainties of the measurements (typically ~0.028 and ~0.034 mag for R and I bands) and the uncertainties in the conversion to the standard system.

The last two detections of the source with MAXI performed on MJD 56456.0313 and 56456.0938 show that the 2-20 keV count rate is still increasing with values 0.314 and 0.353 counts s^-1 cm^-2, respectively.

Comparing these optical magnitudes with earlier outburst data from SMARTS (see, i.e., http://www.astro.lsa.umich.edu/~dmaitra/xrb/AqlX-1/AqlX-1.lc.jpg, Maitra et al. ATel #2744) and the fact that the source still increases its brightness in the X-rays suggests that this may be another bright outburst observed from the source, similar to 2003, 2004, and 2011 events.