Optical variability of 1RXS J173006.4+033813
ATel #2014; D. V. Denisenko (IKI, Moscow), T. V. Kryachko, B. L. Satovskiy (Astrotel Observatory, KSU/AST)
on 16 Apr 2009; 14:20 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: S.A.Grebenev (sergei@hea.iki.rssi.ru)
Subjects: Optical, X-ray, Request for Observations, Variables
Referred to by ATel #: 2015
In course of the search for optical identifications of poorly studied ROSAT sources we have found an unusual variable object coincident with 1RXS J173006.4+033813. The star USNO-B1.0 0936-0303814 at RA=17h30m06.45s, Dec.=+03o38'20.0" (J2000.0) is showing high-amplitude variability on the time scales from years to minutes, but no indications of orbital period has been found so far. The variability has become obvious from Digitized Sky Survey plates with the object varying by 1.5-3m in IR, R and B between different epochs (two POSS-II plates are available for each band covering the period of 1988-1997). Catalogue magnitude values are B2=17.09, R2=17.22 and I=18.16. The star was below the detection limit on the 1st epoch Blue and Red Palomar plates taken in July 1950, but appeared in its highest state on June 1982 Quick-V plate reaching ~16.5 mag. It is not present on 2MASS images taken 2000 May 27.
The analysis of 42 NEAT images available from the SkyMorph site has shown the unusual variability on the scale of 15-30 minutes. The light curve of J1730.1+0338 based on 17 nights between 1997 Aug. 30 and 2003 Aug. 11 is presented at http://hea.iki.rssi.ru/~denis/J1730+0338_LC-NEAT.gif . The object's behavior is unusual for cataclysmic variables, and the X-ray-to-optical flux ratio is high for the binary systems with WD.
Following the discovery of variability on the archival images we have observed J1730.1+0338 remotely with the 0.30-m Astrotel-Caucasus robotic telescope located at the Kazan State University's Mountain Station in Karachay-Cherkessia, Russia. Several sets of 300-sec exposures were obtained in July-August 2008 and February-April 2009 with around 350 images in total. The object was fainter than 20m on most occasions, but during the April 13, 2009 session we have observed it going into an outburst by at least 1.5 mag (from 19.5 to 18.0) within 10 minutes between 2009-04-14 00:55 and 01:05 UT.
The color-combined (BRIR) 10'x9' DSS finder chart is available at http://hea.iki.rssi.ru/~denis/J1730+0338-comps.gif (position of the variable object is marked with dashes). Note that the real range of variability may be well above the indicated 16.8-20.0. The object appears to be in the high state now. Our observations were unfortunately interrupted by the weather conditions. Multi-wavelength follow-up, spectroscopy and long-term photometric monitoring are requested to uncover the nature of this mysterious object.
1RXS J173006.4+033813 page
