GCN Circular 5901
Subject
GRB 060926: MASTER: discovery of the optical flare
Event
Date
2006-12-07T17:36:35Z (19 years ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <gcncirc@observ.inetcomm.ru>
V. Lipunov, V.Kornilov, D.Kuvshinov, N.Tyurina, A.Belinski, E.Gorbovskoy,
A.Krylov, G.Borisov, A.Sankovich, V.Vladimirov, P.Gritsyk
Sternberg Astronomical Institute, Moscow Union 'Optic'
MASTER robotic system (http://observ.pereplet.ru)
responded to GRB060926 (Holland et al., GCN Circ 5612) under the good
conditions (V. Lipunov et al., GCN Circ 5632).
The first image was started at 2006-09-26 16:49:57 UT, 76 s after the GRB
time (355 mm telescope, 6 square degrees FOV, 2.1'' per pix, CCD Alta U16).
The unfiltered image is calibrated relative to USNO A2.0 (0.8 R + 0.2 B).
We find (Lipunov et al., GCN5632) faint OT on the first and on the
coadded images at position:
aplha = 17 35 43.66
dec = 13 02 18.3
err = +- 0.7''
wich coincided with the Holland et al.(GCN Circ 5612) OT position.
We have refind analysis of the images. We discovery optical
flare around 500-700 s after the GRB time (see picture):
Start Mean Exposure Magnitude Flux,
time time time erg/(sm2*sec*eV)
76 s 91 s 30 s 17.3+-0.3 (1,4+-0,3)E-13
150 s 165 s 30 s 18.5+-0.3 (4,6+-1,1)E-14
165 s 343 s 5x30 s 19.3+-0.3 (2,2+-0,5)E-14
255 s 432 s 5x30 s 18.9+-0.3 (3,2+-0,8)E-14
343 s 519 s 5x30 s 18.5+-0.3 (4,6+-1,1)E-14
432 s 608 s 5x30 s 18.3+-0.3 (5,8+-1,3)E-14
519 s 707 s 5x30 s 18.4+-0.3 (5,1+-1,2)E-14
608 s 804 s 5x30 s 18.7+-0.3 (3,9+-0,9)E-14
707 s 1001 s 5x30 s 20.0+-0.3 (1,2+-0,3)E-14
804 s 1200 s 5x30 s 20.1+-0.3 (1,1+-0,3)E-14
901 s 1298 s 5x30 s > 20.1+-0.3 <(1,1+-0,3)E-14
The light curve is available at
http://observ.pereplet.ru/images/GRB060926/light_curve_new.jpg .
Between 91s and 255s a power-law decline with a temporal index
of -1.40+/-0.24 is estimated. Between 707s and 1200s a power-law decline
with a temporal index of -3.30+/-0.70 is estimated. After 1000 s a
power-law decline with a temporal index 0.73 +-0.1 was observed
(A. Stefanescu et al., GCN 5623).
We remember that X-ray flare in GRB 060926 was descovered
by XRT team (M. Perri et al., GCN 5622).
The X-ray spectrum covering the time period from T+67s to T+878s is well
fit by an absorbed power-law with a photon index of 2.1(+/-0.3) and column
density of (2.2+/-0.9)e21 cm**-2 (M. Perri et al., GCN 5622). They note
the Galactic column density in the direction of the source is 7.3e20
cm**-2 .
This means that absorbtion is about 1 magnitude in our band.
The optical-xray data is well fit by power-low with a photon index of
1.7+-0.2 during all our time observation.
We thanks to Dr.K.A.Postnov for usefull discussion and comments.
This work is supported by RFFI 04-02-16411 grant.
This message can be cited.
Mailto: lipunov@sai.msu.ru