XRF 120118A

T.Batsch,A.Majcher,A.Majczyna,K.Nawrocki,M.Sokolowski,G.Wrochna (NCBJ,
Swierk),
M.Cwiok,L.W.Piotrowski,A.F.Zarnecki (University of Warsaw),
K.Malek,L.Mankiewicz,R.Opiela,M.Siudek,V.Repei (CFT PAN),
G.Kasprowicz,M.Zaremba (Warsaw University of Technology),
from the "Pi of the Sky" collaboration ( http://grb.fuw.edu.pl ).

The wide field "Pi of the Sky South" telescope, installed in
the private observatory of Alain Maury in San Pedro de Atacama
(http://grb.fuw.edu.pl/pi/index.html#spda_site.htm) observed field of
XRF 120118A few minutes before and ~100s after the flash.
No new source brighter than about 11.3 mag has been identified on 10s
exposures and no source brighter than 11.7 mag on 20 coadded frames:

t_start - t0 [s]    t_exp     start (UT)  end (UT)     3-sigma limit

     -290             10s          06:00:14    06:00:24     11.2
      +99             10s          06:06:43    06:06:53     11.3
     +129           20x10s         06:07:13    06:12:12     11.7

where limit is based on the reference star magnitudo in V filter.

We acknowledge great support received from Alain Maury at SPdA Observatory.

J.C. Tello (IAA-CSIC), R. Sanchez-Ramirez (IAA-CSIC), J. Gorosabel
(IAA-CSIC), A.J. Castro-Tirado (IAA-CSIC), P. Kubanek (CTU Praha), W. Allen
(Vintage Lane Obs, New Zealand), Ph. Yock (Auckland Univ.), Kuan-Yu Lin
(Auckland Univ.),  report on behalf of a larger collaboration:

We observed the field of XRF 120118A (Gotz et al., GCNC 12849), detected by
INTEGRAL, with the 0.6m Yock-Allen telescope at the BOOTES-3 station in
Blenheim (New Zealand). Unfiltered images were obtained starting on
09:21:00 UT (03h16m after the burst, limited by setting of the Sun) and
were combined in two sets of 53x60s of exposure each.

We detect a fading source at

RA(J2000):    13:01:22.72 (195.344 [degrees])
DEC(J2000): -61:39:23.20 (-61.656 [degrees])

In the first set with a mean observation time of 09:31:06 UT we observe a
magnitude of 18.60 (calibrated against USNO-B1 R2 filter).
Roughly an hour later it's decayed more than 2 magnitudes.

This source is well within the INTEGRAL 2.7 arcmin 90% c.l. and is not
observed in catalog USNO-B1

Spectroscopic observations are encouraged. This message may be cited.

D. Gotz (CEA Saclay) and E. Bozzo (ISDC Versoix) on behalf of the IBAS Localisation Team report:

A deeper analysis of an extended IBIS/ISGRI dataset shows that the HMXB GX 304-1 is in an active state. Being this source just 3.4 arc min away from the position derived for XRF120118A (Gotz et al., GCN Circ. 1248
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 ), even if not formally compatible with the 90% c.l. error circle of the latter, we note that the chance of XRF120118A being produced by GX 304-1 can not be completely excluded at this stage.

D. Gotz (CEA Saclay), S.Mereghetti (IASF-Milano), J. Borkowski (CAMK, Torun), C.Ferrigno, E.Bozzo, 
C. Tchernin (ISDC, Versoix), on behalf of the IBAS 
Localization Team report:

a long gamma ray burst lasting about 60 s has been detected by IBAS in the IBIS/ISGRI data at 06:04:44 UT on January 18.

Its refined coordinates (J2000) are:

  RA: 195.403 [degrees]
  DEC: -61.644 [degrees]

with an uncertainty of 2.7 arcmin (90% c.l.).

The GRB is detected only in the 20-40 keV energy band. Due to its soft spectrum, we consider this event an XRF. The 20-200 keV fluence is about 2e-7 erg/cmsq, while its peak flux over 5 s in the same energy band is about 0.1 ph/cmsq/s.
A plot of the light curve will be posted at

http://ibas.iasf-milano.inaf.it/IBAS_Results.html