[vsnet-alert 14935] 1RXS J210201.7+335932 outburst?

[Denis Denisenko]

Dear all,

I report on the first outburst detection of ROSAT X-ray source 1RXS
J210201.7+335932 (RX J2102.0+3359) with the Bradford Robotic Telescope
since I have found its variability on DSS plates in May 2008. The
object has attracted my special attention then because of quite a
large flux (>0.1 cnts/sec) with rather faint optical magnitudes. Note
also the negative hardness ratios in ROSAT catalogue which means a
very soft spectrum.

1RXS J210201.7+335932  0.133+/-0.024 cnts/s  HR1=-0.85+/-0.09 HR2=-0.33+/-0.58
USNO-B1.0 1239-0465359
21 02 01.41 +33 59 29.8 B1=19.92 R1=N/A B2=18.47 R2=17.47 I=18.01

Animation of two Blue POSS-II plates of 1989 and 1992 showing the
large variability:
http://master.sai.msu.ru/static/OT/J2102+3359-DSS-anim

10'x9' color-combined (BRIR) finder chart:
http://master.sai.msu.ru/static/OT/J2102+3359-comps

Comparison star used: R=13.3
Check star: R=15.3

  20100730.136 <190C  BRT
  20101025.955 <190C  BRT
  20101210.921 <190C  BRT
  20120904.046 <190C  BRT
  20120909.041 <195C  BRT
  20120913.057 <195C  BRT
  20120920.018  171CR BRT

Confirmation of outburst (or high state) and time-resolved photometry
with 40-cm and larger telescopes are needed! There is almost nothing
known about this variable. Motch et al. (1998) reported a "strong UV
excess" (U=20.5, B=21.6) and argued in favour of an AM Her system. I
note that the variable is identical to the ultraviolet source GALEX
J210201.5+335930 with the far and near UV magnitudes FUV=19.03+/-0.12,
NUV=18.62+/-0.07.

After my request back in 2009, the field of this variable in Cygnus
was observed with Astrotel-Caucasus telescope by Timur Kryachko et al.
from June 29 to Oct. 27. No outbursts of J2102.0+3359 were then found
on 790 five-minute exposures, but fifty five new variable stars down
to 18m were discovered which are published in PZP Vol. 10, No. 2
(2010), see <http://www.astronet.ru/db/varstars/msg/1237956>.
Amazingly, on just seven 60-sec BRT images I have found an additional
large-amplitude variable in the same field, likely an eclipsing
binary. The new variable is 2MASS 21022353+3401256 (J=13.26, H=12.82,
K=12.71) = USNO-A2.0 1200-16871559 (R=14.3, B=15.7). It is 4.4' from
the X-ray source. The periods of both variables are unknown.

Best regards,

Denis in Belgrade, Serbia (at the conference "Future Science with
Metre Class Telescopes")