Aql X-1: still at maximal levels

ATel #16840; V. V. Vlasyuk, O. I. Spiridonova (Special Astrophysical Observatory of the Rus. Ac. Sci.)
on 3 Oct 2024; 21:14 UT
Credential Certification: Alexander Moskvitin (mosk@sao.ru)

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Within a course of optical monitoring campaign of Soft X-ray Transient (SXT) Aql X-1 performed with the 1-m and 0.5-m SAO RAS optical telescopes we have detected the growing part of it's new outburst. According to our preliminary results in R-band, it's brightness increased between September 13th and 14th, as it was noted also in ATel #16822. Our preliminary estimates of brightness of Aql X-1 optical counterpart in R-band in first decade of September were between 18.0 and 18.2 mag. Meanwhile, R-magnitude for epochs after September 13th demonstrated smooth trend for increasing, as seen in Table.

Date	MJD	R_mag	Err_R
20240913	60566.74	18.02	0.07
20240914	60567.81	17.65	0.06
20240917	60570.76	17.40	0.05
20240925	60578.77	16.61	0.03
20240926	60579.75	16.40	0.02

The first 3 epochs were estimates using by 0.5-m telescope, the others after one week delay --- with 1-m reflector. The last data demonstrate flux increasing up to R = 16.0 +/- 0.02 (MJD=60583.7 and 60586.7) with some stable phase between September 26th and 28th.

Typical errors of brightness estimates are about 0.03--0.05 mag and should be decreased after more accurate data reduction. Some overestimating of data from 0.5-m telescope may exist due to rough image scale for photometry in dense star field. Further observations of Aql X-1 in X-ray, UV, Optical, IR and Radio ranges are highly encouraged.