Outburst of a possible new cataclysmic variable 1RXS J063214.8+253620

S. A. Korotkiy (Ka-Dar Obs.) and K. V. Sokolovsky (ASC Lebedev/SAI MSU)

A bright (unfiltered magnitude 12.65) optical transient source was detected on 2012 January 27 at position 06:32:13.06 +25:36:22.5 (+/-0.3", J2000). Inspection of previous images of this field revealed that the object is also present on images from January 24, 25, and 26 but is below the detection limit (typically around 13.5m) on January 20 and 21.

   Date           JD         mag.
2012-01-20.740  2455947.240 >13.5
2012-01-21.701  2455948.207 >13.5
2012-01-24.759  2455951.259  13.10 +/-0.05
2012-01-25.845  2455952.346  12.81 +/-0.03
2012-01-26.833  2455953.333  12.66 +/-0.03
2012-01-27.897  2455954.397  12.61 +/-0.03
The observations were obtained with a survey camera (F=135mm f/2.0 telephoto lens equipped with ST8300M CCD) operated by Ka-Dar Observatory at the Mountain station of Kazan State University (Karachay-Cherkessia, Russia). The instrumental magnitude scale is calibrated using V magnitudes of Tycho-2 (Hog et al., 2000, A&A, 355L, 27) stars in the field of view.

The optical transient is associated with an ultraviolet object GALEX J063213.0+253623 (FUV=18.42 +/-0.05, NUV=17.90 +/-0.03) located 0.7" away from the measured optical position (see http://galex.stsci.edu/GR6/ ). The transient is 24" away from an unidentified X-ray source 1RXS J063214.8+253620 listed in the ROSAT All Sky Survey Faint Source Catalog (Voges et al., 2000, IAUC, 7432) and is likely associated with it.

The All Sky Automated Survey (ASAS-3, Pojmanski 2001, ASPC, 246, 53; http://www.astrouw.edu.pl/asas/ ) database lists two detections of a source at the above position:

  Date          JD          V
2009-03-17  2454907.54944 12.82 +/-0.06
2009-03-21  2454911.53385 12.95 +/-0.06
which may be the previous outburst of this object. We conclude that the observed optical transient source is likely a previously unknown cataclysmic variable in outburst.

Follow-up photometric and astrometric observations are requested.

Discovery images of 1RXS J063214.8+253620

On the discovery images East is up, North is to the right. The reference image is rotated by 180 degrees with respect to the discovery images. Each image is 2.8'x2.8'.

Date (UTC) JD(UTC) mag. R.A. & Dec.(J2000) Image
Discovery image 1 2012 01 27.8969 2455954.3969 12.68 06:32:12.82 +25:36:17.2 /mnt/usb/Gem1_2012-1-27_21-32-20_001.fts
Discovery image 2 2012 01 27.8976 2455954.3977 12.63 06:32:13.01 +25:36:14.8 /mnt/usb/Gem1_2012-1-27_21-33-12_002.fts
Mean magnitude and position on the discovery images: 2012 01 27.8973 2455954.3973 12.65 06:32:12.92 +25:36:16.0 Position difference between discovery images is 0.000977 degrees (3.517200 arcsec). The object was not found in GCVS. The object was found in SIMBAD: 1RXS J063214.8+253620 -- X-ray source The object was not found in VSX. The object was not found in astcheck.

Preview of the reference and discovery images:

Original FITS images are available here.