[vsnet-alert 15587] IGR J18245-2452 in M28, possible bright optical counterpart

[Berto Monard]

RE: IGR J18245-2452 (ATel 4925/E Bozzo and later Atels)

Images of M28 were taken at the Kleinkaroo Observatory before and after the alert by INTEGRAL. They  show a brightened star at 
position (2000)
18 24 32.93 -24 51 59.6 (astrometric uncertainty of less than 0.5 arcsec (<0.03 in RA and <0.5 in Decl)) as measured against UCAC2. 
This
star is located about 10 arcsec North of the clusters 'apparent' centre.
Photometry of the unfiltered CCD images gives magnitudes of 12.70 and 11.76 CR on dates UT 2013 Mar 22.140 and April 5.138 
respectively.

It's not impossible that it concerns a new object coinciding with a previously existing star but it's very likely that this is the 
optical counterpart of the reported transient.

Further observations will be carried out, including timeseries photometry to probe for any optical variability.

Note: the fact that an image was taken just one week before the activities is coincidental  ;-) .


Berto Monard / Kleinkaroo Observatory