[vsnet-alert 15684] Unusual OT J231611.6+273450 (ASASSN-13aj)

[Denis Denisenko]

ASAS-SN team (Shappee et al.) has reported the discovery of 5 new
optical transients in ATel #5052,
<http://www.astronomerstelegram.org/?read=5052> with the brightest and
most recent one being ASASSN-13aj (23:16:11.6 +27:34:50) at 14.5m on
2013 May 3.59 UT.

The object at minimum is identical to the blue star SDSS
J231611.64+273449.7 with u=20.39 g=20.38 r=20.46 i=20.71 z=20.46, see
http://skyserver.sdss3.org/dr8/en/tools/explore/obj.asp?id=1237666185642836273

At the first glance it looks like a typical UGSU candidate with 6m
outburst amplitude. However, CRTS light curve of CSS J231611.6+273449
is extremely unusual. The object spends about half time at minimum
(20.0-20.5m), but undergoes several bright episodes (at least 4 in 8
years). Some of them are short-lived, as shown below, but none of them
were brighter than 16.76.

Date (MJD)    Mag
54391.29575  17.68
54391.30396  16.76
54391.32043  19.22

54421.18505  17.71
54421.19258  19.15
54421.20011  17.70
54421.20763  17.39

54801.15700  18.73
54801.16488  17.83
54801.17279  19.43

Either this is an eclipsing CV or there are some errors in CRTS
photometry. Hopefully Andrew Drake can check the Catalina Sky Survey
images and comment on the reality of this fast variaibility in the
past.

In any case, photometric time series are encouraged! The outburst is
still young, 4 days since the detection.

Denis Denisenko