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Optical Observations of the February 2015 Outburst of Aql X-1: the Only Fading Stage

ATel #7134; V. V. Vlasyuk, O. I. Spiridonova (Special Astrophysical Observatory ot the Rus. Ac. Sci.)
on 24 Feb 2015; 11:15 UT
Credential Certification: Alexander Moskvitin (mosk@sao.ru)

Subjects: Optical, Neutron Star, Transient

After the reported X-ray outburst of Aql X-1 (ATel #7088, ATel #7095) we begun photometrical observations in BVR passbands with 1-meter Zeiss-1000 telescope of Special Astrophysical Observatory of Rus.Ac.Sci. Despite on inconvenient observations conditions (object airmass was above 2.0) we have measured Aql X-1 within three last nights on the twilight sky. Due to excellent atmospheric state we found this transient object at fading stage: it's brightness decreased systematically in all filters from February, 22 to February, 24. Results of preliminary data reduction are presented in the table. Relatively large errors (mainly in B) are explaining both by high background level and by some inaccurate standard calibration. More precise data are in preparation. Further observations at all wavelengths are encouraged.

Date JD B_mag +/- B_err V_mag +/- V_err R_mag +/- R_err
20150222 2457075.61 18.40 +/- 0.07 17.05 +/- 0.05 16.80 +/- 0.05
20150223 2457076.61 18.90 +/- 0.08 17.50 +/- 0.06 17.00 +/- 0.04
20150224 2457077.61 19.20 +/- 0.10 17.73 +/- 0.04 17.14 +/- 0.03