[vsnet-grb-info 5543] X-ray transient in NGC 2770: RTT150 optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7206
SUBJECT: X-ray transient in NGC 2770: RTT150 optical observations
DATE:    08/01/23 14:55:26 GMT
FROM:    Rodion Burenin at IKI, Moscow  <rodion at hea.iki.rssi.ru>

I. Bikmaev, A. Galeev, N. Sakhibullin (KSU/AST)
R. Burenin, M. Pavlinsky, R. Sunyaev (IKI),
I. Khamitov, Z. Eker (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.)

report:

The optical counterpart to X-ray transient in NGC 2770, SN2008D (GCN
Rep. 110.1, GCN Circ. 7160, 7161) was observed also with Russian-Turkish
1.5-m telescope (RTT150, Bakirlitepe, TUBITAK National Observatory, Turkey)
during the first two nights after the XRF.

Series of BVRI direct images and low resolution spectra (during the second
night) were taken.

The object shows no variability during the few hours of observations in
every nignt at the level >~ 0.05m, but we detect the decline of the OT in
all filters betwen two nights. Assuming R=17.3 and B=17.7 magnitudes for
USNO-A2.0 1200-06240802 star (as it was done in GCN's 7162 and 7187), we
estimate the following magnitudes for the transient:

Time, UT    t-t0,days   mag

Jan 11.03   0.46        R = 18.06
Jan 11.14   0.57        B = 18.72     
Jan 12.11   1.55        R = 18.15   
Jan 12.12   1.55        B = 18.98

However, these measurements are preliminary, more accurate subtraction of
the galaxy is to be done.

A low resolution spectrum was obtained, using TFOSC spectrometer. We take
3x1200s exposures, centered at Jan 12.00 UT. The spectrum has resolution
about 15~A, covering 3900 to 9000~A. Strong H_alpha and other narrow
emission lines are detected in the galaxy near the object, so that it was
difficult to correctly subtract background near these lines. Hovewer, we
believe, that the overall shape of our spectrum is correct. We definitely
see much less amount of supernova signatures as compared to Blondin et
al. (GCN 7173), in agreement with Soderberg et al. (GCN 7165) and
Thorstensen (ATEL #1358).

The finding chart and the plot of our spectrum can be found at:

http://hea.iki.rssi.ru/grb/080110-SN2008D/indexeng.html