GRB 050128

L. A. Antonelli (INAF-OAR), S. Campana, G. Tagliaferri, C. Pagani, A. 
Moretti, P. Romano, G. Chincarini (OAB), G. Cusumano, V. Mangano (ISAF/Palermo),
P. Giommi (ASI), D. N. Burrows, J. E. Hill, J. A. Kennea, J. Racusin,
J. A. Nousek (PSU), J. Osborne, K. Page, M. Goad, A. Beardmore,
A. Wells (U. Leicester), K. Mason (MSSL), N. White, N. Gehrels (NASA/GSFC),
report on behalf of the Swift XRT team:

The Swift BAT instrument detected an apparent burst at 04:20:04 UT on 2005 
January 28.  The spacecraft initiated a prompt automated slew and 
observation sequence.  The XRT began taking data on the burst at 2005-01-28 
04:23:51 and continued until 2005-01-28 05:55:27.  The XRT was in Photon 
Counting mode performing calibration observations of PG1311+129 when the 
burst occurred, and continued to collect data in Photon Counting mode 
during the slew and after settling onto the BAT field.  As a result, no 
prompt XRT position was reported to the ground.  However, analysis of the 
XRT data shows a bright, rapidly fading point source at:

RA(J2000): 14 38 17.87
DEC(J2000): -34 45 56.6

These positions were processed through the ground pipeline and have an 
estimated uncertainty of 8 arcseconds, dominated by systematic 
uncertainties in the XRT boresight, which is not yet fully calibrated.  We 
note, however, that our final position for GRB050126 was 30 arcseconds from 
the optical candidate (GCN 2985
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 ) in spite of our estimated uncertainty of 8 
arcseconds.

The XRT count rate is 1.29+/-0.28 c/s (0.5-10 keV) in a 1745 s exposure, 
which corresponds roughly to a 1 mCrab source.

The XRT is continuing to observe this burst when it is visible to the Swift 
observatory.

[GCN OPS NOTE (28jan05):  Per D.Burrows request, the authors G. Cusumano, V. Mangano
were added to the list.]

J. Cummings (GSFC), G. Sato (ISAS), L. Antonelli (INAF-OAR), S. Barthelmy, 
L. Barbier (GSFC), P. Boyd (GSFC-UMBC), E. Fenimore (LANL), N. Gehrels 
(GSFC), D. Hullinger (GSFC/UMD), H. Krimm (GSFC/USRA), F. Marshall (GSFC), 
C. Markwardt (GSFC/UMD), K. McLean (LANL), M. Capalbi (ASDC), D. Palmer 
(LANL), A. Parsons (GSFC), T. Sakamoto (GSFC), M. Suzuki (Saitama), J. 
Tueller (GSFC), S. Zane (MSSL) on behalf of the Swift-BAT team:

At 04:19:54 UT, the Swift Burst Alert Telescope (BAT) triggered and 
located on-board GRB050128.  The spacecraft autonomously slewed to the 
burst and an x-ray afterglow source was detected by XRT (GCN 2991
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 , 
Antonelli et al.).

The BAT on-board calculated location is RA,Dec 219.587, -34.762 (J2000) 
with an uncertainty of 3 arcmin (radius, 3-sigma, including a systematic 
uncertainty dominated by the GRB being 51 deg off axis).  This is 39 
arcsec from the XRT position.  The lightcurve is multi-peaked with a T90 
duration of 13.8 sec.  The fluence is 4.5e-6 erg/cm^2 and the peak flux (1 
sec interval) is 4.6 ph/cm^2/s in the 15-350 keV band.  The spectrum is 
consistent with a power-law of photon index 1.5 +- 0.05.

[GCN OPS NOTE (28jan05):  As per D.Burrows request, the "C.Milvia" 
was changed to "M. Capalbi".]

S.Maeno,E.Sonoda,Y.Matsuo,M.Yamauchi
(University of Miyazaki)


"We have observed the field covering the error box of
GRB 050128 (GCN 2992
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 ;Swift-BAT Trigger time is 04:19:54 UT) 
with the unfiltered CCD camera on the 30-cm telescope
at University of Miyazaki.
The observation was started 19:23:52 UT on Jan.28.
Observed field of view is 43 arcmin centerd on 
R.A.=14h 38m 11s
Dec= -34d 42' 34"
After co-adding a set of 3 images of 30 sec exposures,
we have compared with the USNO A2.0 catalog. Preliminary analysis
shows there is no new source brighter than 17.5 mag.

S. Covino, P. Filliatre, P. D'Avanzo, L.A. Antonelli,  A. Melandri, V.
Testa, G. Chincarini, G.  Tagliaferri, F.M. Zerbi, G. Tosti, A.
Monfardini, M. Rodono', E. Molinari, F. Vitali, G. Cutispoto, L.
Nicastro, E. Palazzi, on behalf of the REM/ROSS team, report:

We imaged the field of GRB050128 (Antonelli, et al., GCN 2991
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 ) with the
60cm REM robotic telescope located in La Silla (Chile). Observations
were carried out in the V, R, I, z', J, H and K filters, starting on
2005 Jan 28, at 7:10 UT, and ending at 9:45 UT (approximately 3 hours
after the burst). Observations were carried out under good seeing
conditions (1"). Due to a technical problem only IR images have been
analysed.

No new sources have been detected within the XRT error circle (GCN 2991
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 )
down to a limiting magnitude of H>17 mag.

We note a source (H = 16.8+/-0.3 mag) at RA= 14:38:18.16,
DEC=-34:45:44.7 (J2000) at about 13 arcsec far from the XRT position. At
this position a very faint source, close to the detection limit, is
present in the optical DSS frame but it is not present in the Infrared
DSS frame which is deeper than our image.

Further observations are planned to look for any variability.

This message can be cited.

[GCN OPS NOTE(28jan05): Per author's request, the SUBJECT line has been
corrected to contain the proper GRB identification.]

A. Monfardini (Liverpool), N. Tanvir (Hertfordshire), R. Smith
(Liverpool), C. Mottram (Liverpool), D. Carter (Liverpool), C. Mundell
(Liverpool), C. Guidorzi (Liverpool), B. Chapman (Hertfordshire),
P. O'Brien (Leicester) on behalf of the larger Robonet consortium, report:

"We obtained BVRI images centered on the SWIFT-XRT detection of GRB050128
(GCN 2991
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 ; BAT detection: GCN 2992
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 ) with the 2-m Faulkes Telescope South
on Siding Spring, Australia.
Observations started on January 28.658 UT, i.e. 11.455 hours after the GRB.
The robotic GRB pipeline did not find any new objects with reference to
USNOB, GSC2.3 and 2MASS catalogues.

We report the preliminary R-band limit:

Time from GRB   ExpTime    Filter    Limit Mag.
(days)          (s)
-----------------------------------------------
0.477           240         R        ~20.5
-----------------------------------------------

The above limit magnitude has been derived by comparison with USNOB
catalog and refers to a single out of five 240s exposures.
Analysis is in progress on I images (5x300s). Further observations are
planned for variability check that requires a comparison image deeper than
the DSS-2.

This message can be cited."

A. Melandri, E. Palazzi, L. A. Antonelli, S. Covino, P. D'Avanzo,
G. Tagliaferri, G. Chincarini, F. M. Zerbi, G. Tosti, A. Monfardini,
N. Masetti, L. Nicastro, G. Cutispoto, E. Molinari, M. Rodono'  and
F. Vitali on behalf of the REM/ROSS team, report:

"We imaged the field of GRB050128 (Antonelli, et al., GCN 2991
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 ) with
the 60cm REM robotic telescope located in La Silla (Chile).
Optical observations were carried out in V, R, I filters starting on 
2005
Jan 28, at 7:10 UT, and ending at 9:45 UT (approximately 3 hours after
the burst) . Observations have been partly affected by the presence
of the bright Moon close to the field, so only frames with short 
exposure
time can be used. The field was imaged in each filter for a total 
exposure
time of 50s.

No new sources are detected within the XRT error circle (Antonelli et
al.  GCN 2991
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 ) down to a limiting magnitude of V >18.2, R >18.2 and
I >17.9.

The source noted in the H band (Covino, et al., GCN 2999
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 ) at RA=
14:38:18.16, DEC=-34:45:44.7 (J2000) at about 13 arcsec far from the
XRT position is not visible in the optical bands. We derive a 3-sigma
upper limit of R > 18.2 at the position of this source.

Further optical-infrared observations with REM are planned to look for
any variability.

This message can be cited."

D. A. Frail (NRAO) and A. M. Soderberg (Caltech) report on behalf of
the Caltech-NRAO-Carnegie GRB Collaboration:

"We observed the field centered on the XRT position of the Swift burst
GRB 050128 (GCN#2991
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 ) with the VLA on February 8.53 UT at a frequency
of 8.46 GHz. There are no bright radio sources (>150 microJy) within
1 arcminute of the XRT position, and no peak emission above 100
microJy (rms=31 uJy) within the 8-arcsec XRT error circle.

No further observations are planned."