Optical observations of MAXI J1957+032

ATel #8149; Tolga Guver, Tansel Ak, Hakan Urgup, Selcuk Bilir (Istanbul University), Murat Kocak (TUG), Emrah Kalemci, Ersin Gogus (Sabanci University), Tolga Dincer (Yale University), Halil Kirbiyik (TUG)
on 11 Oct 2015; 11:23 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Tolga Guver (tolgaguver@sabanciuniv.edu)

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Following the recent reports of an outburst (ATel #8143 and #8146), we observed the field of MAXI J1957+032 (=IGR J19566+0326) with the TUBITAK National Observatory (TUG) T100 telescope. We obtained four R band images of the field with an exposure time of 60s each, starting at 2015-10-10 16:24:55.73 UT.

In the combined image (240 s exposure time), we detect a source at the location reported by Rau et al. (ATel #7524). Using an USNO B1.0 star as a reference (USNO B1.0 0934-0560330, R1 = 16.64, R2 = 16.65) we measure the R band magnitude of the object as 18.27 +/- 0.06 mag, where the error only shows the 1 sigma formal uncertainty and this measurement is not corrected for the Galactic extinction.

Using the conversions given by Smith et al. (2002, AJ, 123, 2121) and the magnitudes reported by Rau et al. (ATel #7524, r' = 20.03, g'=20.28) the brightness of the source in the R band can be estimated as 19.86 in May 15th 2015. Therefore, our measurements show that the source brightness increased by approximately a magnitude compared to the earlier state.

An image of the field showing both the object and our reference USNO star can be found from the following address in png or ps formats : http://194.27.131.4/~tolga/atels/MAXI_J1957+032/

Further observations will be performed using both the T100 and robotic T60 telescopes.

We are grateful to TUBITAK National Observatory for their support in using T100 telescope with project numbers 432 and 612 and technical support.