////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3161
SUBJECT: GRB 050401: Prompt XRT position
DATE:    05/04/01 15:09:18 GMT
FROM:    David Burrows at PSU/Swift  <dxb15@psu.edu>

L. Angelini (GSFC), J. L. Racusin, S. Hunsberger, D. N. Burrows, J. E.
Hill, J. A. Kennea, D. C. Morris, D. Grupe, J. A. Nousek (PSU), J. P.
Osborne, K. L. Page, M. R. Goad, A. P. Beardmore, O. Godet, A. F. Abbey, A.
A. Wells (U. Leicester), S. Campana, A. Moretti, C. Pagani,  P. Romano, G.
Tagliaferri, G. Chincarini (INAF-OAB), G. Cusumano, V. La Parola, V.
Mangano, T. Mineo (INAF-IASF/Palermo), P. Giommi, M. Capalbi, M. Perri, F.
Tamburelli (ASDC), F. Marshall, N. White, N. Gehrels (GSFC), P. Roming, P.
Meszaros (PSU), P. Schady (MSSL), report on behalf of the Swift XRT team:

The Swift BAT instrument triggered on GRB050401 at 14:20:15 UT and Swift 
executed a prompt slew (delayed by 9 seconds due to an Earth constraint) 
.  The XRT found a bright source located at the following position (based 
on 38 counts in 2.5 seconds):

RA(J2000) = +16h 31m 29s,
Dec(J2000) = +02d 11' 14"

We estimate an uncertainty of about 6 arcseconds.   This source is located
42 arcseconds from the BAT position.

We note that Swift had a solid attitude solution during this observation.

The XRT reported a prompt raw spectrum that peaks at about 1 keV with a 
roughly power-law shape (based on 328 s of data in Windowed Timing mode).

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3162
SUBJECT: Swift-BAT detection of GRB 050401
DATE:    05/04/01 15:25:21 GMT
FROM:    Louis M Barbier at NASA/GSFC/Swift  <lmb@cosmicra.gsfc.nasa.gov>

 L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC),
 E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (UMD),
 H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), J. Norris (GSFC),
 J. Nousek (PSU), D. Palmer (LANL), A. Parsons (GSFC),
 T. Sakamoto (GSFC/NRC), G. Sato (ISAS), M. Suzuki (Saitama),
 J. Tueller (GSFC)
 on behalf of the Swift team:
 
 At 14:20:15 UT Swift-BAT triggered on burst GRB 050401 (trigger=113120).
 The BAT-derived position is RA,Dec=247.880,+2.184 (J2000).  We note this
 is 42 arcsec from the XRT Position GCN Notice.  The lightcurve
 shows 5 main peaks with a total burst duration of 38 sec.  The first peak
 started about 9 sec before the trigger, and the fifth peak started
 at T+23 sec.  The peak count rate was 5000 cnts/sec.  This burst
 was 56 deg of the BAT bore sight (<10% coding).  We note that
 the Swift Star Trackers were locked at the time of the trigger and
 all initial inspections indicate that the attitude solution for the s/c
 is normal (unlike yesterday's episode).

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3163
SUBJECT: GRB 050401: Optical afterglow candidate
DATE:    05/04/01 15:48:05 GMT
FROM:    Paul Price at IfA,UH  <price@ifa.hawaii.edu>

R. McNaught (RSAA, ANU) and P.A. Price (IfA, Hawaii) report on behalf of
a larger collaboration:

We have observed the XRT position of GRB 050401 (Swift trigger 113120)
with the 40-inch telescope at Siding Spring Observatory starting at
April 1.637 UTC.  In an unfiltered exposure of 120 sec, we identify a
source near the limiting magnitude of our observations, at approximate
coordinates:

	16:31:28.81 +02:11:14.2 J2000

This source is within the XRT error circle, and not present in the DSS. 
The source is about R ~ 20.3 mag.  A subsequent image reveals that the
source is stationary.

Further observations are planned.

This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3164
SUBJECT: GRB 050401: Optical afterglow confirmed
DATE:    05/04/01 16:34:27 GMT
FROM:    Paul Price at IfA,UH  <price@ifa.hawaii.edu>

P.A. Price (IfA, Hawaii) and R. McNaught (RSAA, ANU) report on behalf of
a larger collaboration:

Continued observations of the field of GRB 050401 (GCN ##3161,3162) with
the 40-inch telescope at Siding Spring Observatory reveals that the
optical afterglow candidate (GCN #3163) is variable.  In particular, in
the course of two unfiltered and four R-band images, the source appears
to have brightened and then faded.  This source is therefore likely to
be the optical afterglow of GRB 050401.

Observations are ongoing at Siding Spring Observatory.

A rough finding chart showing the afterglow is available from:
	http://www.ifa.hawaii.edu/~price/grb050401finder.ps

This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3165
SUBJECT: GRB050401: ROTSE-III Detection of Prompt Optical Counterpart
DATE:    05/04/01 18:49:02 GMT
FROM:    Eli Rykoff at U of Michigan/ROTSE  <erykoff@umich.edu>

E. S. Rykoff, S. A. Yost, D. A. Smith (Umich) report on behalf of the 
ROTSE collaboration:

ROTSE-IIIa, located at Siding Spring Observatory, Australia responded to 
Swift GRB050401 (Trigger #113120).  An automated response produced 
images beginning 6.2 seconds after the GCN trigger under good 
conditions.  The first image was taken at 01 Apr 14:20:39.2 UT, 33 
seconds after the updated burst time as reported by Barbier et al (GCN 
3162).  We took ten 5 second, ten 20 second and sixty 60 s exposures, 
and imaging is ongoing.  The images are unfiltered and were calibrated 
relative to USNO A2.0.

Individual images have limiting magnitudes ranging from 16.0-17.3. We 
compared sets of 10 co-added frames to the DSS (second epoch).  In our 
first co-added set of images we have a marginal detection of a source 
consistent with the XRT position (GCN 3161) and the candidate reported 
by McNaught & Price (GCN 3163).  The source is at 17.0+/-0.2 for a 151 
second co-add starting at 14:20:39.2 UT, with a limiting magnitude of 
17.4.  We do not detect any significant flux in our following images, to 
a limiting magnitude of 17.9/18.4 for sets of images beginning at 
14:28:22.3 UT/14:39:57 UT.

We also note that our first 5-s image was taken coincidentally with the 
end of the gamma-ray emission detected by Swift (GCN 3162).  We do not 
detect significant flux to a limiting magnitude of 16.0.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3171
SUBJECT: GRB050401: TNG R-band observation
DATE:    05/04/02 11:36:52 GMT
FROM:    Nicola Masetti at IASF,CNR,Bologna  <masetti@bo.iasf.cnr.it>

P. D'Avanzo, D. Fugazza (INAF-OAB), N. Masetti (INAF-IASF, Bologna) and
M. Pedani (TNG), on behalf of a larger collaboration, report:


"We have obtained R-band photometry of the optical afterglow (McNaught &
Price, GCN #3163; Rykoff et al., GCN #3165) of GRB050401 (Angelini et al.,
GCN #3161; Barbier et al., GCN #3162) using DOLoRes at TNG.
The observations, for a total exposure time of 30 minutes, were performed
under moderate seeing conditions (around 1.2 arcsec).

A preliminary analysis of the images allowed us to derive the following
photometry for the OT, calibrated after observing the SA104 Landolt
standard field:

R = 23.18 +/- 0.10  on 2005 April 2.072 UT, 11.39 hours after the burst

Using this OT magnitude and those reported in GCNs #3163 and #3165, and 
assuming a canonical power-law decay, we obtain for the OT a decay index 
alpha ~ 1, quite typical of GRB optical afterglows.

We are particularly grateful to the TNG staff for their remarkable support 
to these observations."

This message is citeable.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3173
SUBJECT: GRB 050401 BAT refined analysis
DATE:    05/04/02 20:14:18 GMT
FROM:    Takanori Sakamoto at NASA/GSFC  <takanori@milkyway.gsfc.nasa.gov>

T. Sakamoto (GSFC/NRC), S. Barthelmy, L. Barbier (GSFC), 
J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), 
D. Hullinger (UMD), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), 
D. Palmer (LANL), A. Parsons (GSFC), G. Sato (ISAS), 
M. Suzuki (Saitama), M. Tashiro (Saitama U.), J. Tueller (GSFC), 
on behalf of the Swift/BAT team: 
 
At 14:20:15 UT Swift-BAT detected GRB 050401 (trigger=113120) 
(GCN Circ 3162,  Barbier et al.). The refined BAT ground position is 
(RA,Dec) = 247.880, +2.191, [deg; J2000] +- 3 arcmin, (95% containment).  
This is 38 arcseconds from the XRT (GCN Circ 3161, Angelini et al.) and 
confirmed optical afterglow (GCN Circ 3163, McNaught et al.) positions. 
 
The burst had 4 distinct peaks. There were three initial peaks of roughly 
comparable intensity, at times T-6, T-1 and T+3.  These peaks all had 
durations of between 1 and 2 seconds.  These peaks were followed by 
a stronger peak beginning at T+23 and lasting ~6 seconds.  The total 
burst duration T90 is estimated at 33 seconds +/- 2 s 
(including systematics) 
 
The fluence derived from the event data is 1.4 X 10^-5 erg/cm^2 
in the 15-350 keV band.  The 1-s peak flux (T+24.6 s) is 14 ph/cm^2/s 
(also 15-350 keV).  The photon index of the 1-s peak spectrum 
(T+0 s) is 1.17 +/- 0.12 (90% confidence).  The time-averaged 
spectrum yields a photon index of 1.50 +/- 0.06 (90% confidence). 
Both the 1-s and time-averaged spectra are well fit by a simple power-law. 

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3174
SUBJECT: GRB050401: Maidanak optical observation
DATE:    05/04/02 22:10:22 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

B. Kahharov, M. Ibrahimov,  D. Sharapov (MAO), A.Pozanenko (IKI),
V.Rumyantsev (CrAO),  G.Beskin (SAO) report:



We observed the afterglow   (McNaught and Price, GCN 3163; Rykoff et al.,
GCN 3165) of the Swift  GRB050401 (Angelini et al., GCN 3161; Barbier et
al., GCN 3162) with 1.5m telescope of  Maidanak Astronomical Observatory
(MAO), Uzbekistan under good weather conditions (seeing is 1.0 arcsec).
Preliminary R-photometry against of USNO-B1.0 Catalog is following:



Mean time    Exposure    Mag.

(UT)          (s)



Apr. 1.988   8x300       22.2 +/- 0.2





This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3175
SUBJECT: GRB 050401 Optical Observations 
DATE:    05/04/03 08:33:13 GMT
FROM:    Kuntal Mishra at ARIES,Nainital,India  <kuntal@upso.ernet.in>

Kuntal Misra ((ARIES Naini Tal), Atish P. Kamble (Raman Reserach 
Institute, Bangalore) and S. B. Pandey (ARIES Naini Tal), on behalf of 
larger Indian GRB collaboration

The Swift GRB 050401 (trigger = 113120) was monitored from 1.04-m
reflector at ARIES, Naini Tal in V, R and I bands. The OT candidate
reported by McNaught and Price (GCN 3163), seen in our R band
(900 sec exp) frame taken on April 01.8359 UT was at 21.5 +/- 0.2 mag.

Using this magnitude of the optical afterglow and those reported in
GCN 3163 and GCN 3171, we derive a flux temporal decay index of ~ 1.0,
consistent to D'Avanzo et al. 2005 (GCN 3171).

This message can be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3176
SUBJECT: GRB 050401: VLT spectroscopic redshift
DATE:    05/04/03 19:59:02 GMT
FROM:    Jens Hjorth at U.Copenhagen  <jens@astro.ku.dk>

Johan P. U. Fynbo, Brian L. Jensen, Jens Hjorth (Niels Bohr Institute),
Klaas Wiersema, Rhaana Starling (U. Amsterdam), Paul Vreeswijk (ESO),
Evert Rol, Andrew Levan (U. Leicester), Sara Ellison (U. Victoria), 
Nicola Masetti (IASF-Bologna) report on behalf of a larger collaboration:

"Using FORS2 on the Very Large Telescope we have obtained spectra of the 
afterglow of GRB 050401 (GCN 3161, 3162, 3163) on 2005, April 2. We detect 
several absorption lines consistent with two absorption systems at redshifts 
z = 2.50 and z = 2.90. The likely redshift of GRB 050401 is hence z = 2.90.
For a standard cosmology (H_0 = 70 km/s/Mpc, Omega_m = 0.3, Omega_w = 0.7, 
w = -1) the Swift fluence (GCN 3173) corresponds to an isotropic energy 
release of 2.6 x 10^53 erg.

We thank Paul Price for providing a finding chart for the optical afterglow 
and the ESO staff for excellent support."

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3177
SUBJECT: GRB050401, radio observation at 4.8 GHz and 8.64 GHz
DATE:    05/04/04 12:21:42 GMT
FROM:    Kinwah Wu at MSSL-UCL  <kw@mssl.ucl.ac.uk>

L. Saripalli (ATNF, CSIRO), K. Wu (MSSL, UCL), K. K. Ghosh (NASA-NSSTC),
D. A. Swartz (NASA-NSSTC) and A. F. Tennant (NASA-MSFC) report of radio
observations of GRB050401.

We observed the field of the GRB050401 using ATCA (6 km configuration)
at Narrarbri, Australia on 2005 April 02 15.02 UT and April 03 14.22 UT.
The duration of each observation was 1 hour.

We do not detect signals above rms of 0.5 (4.8 GHz) and 0.6 mJy (8.64 GHz)
in the field in each individual data set for the two observations. We also
do not find significant signal above an rms of 0.4 mJy for the combined
data set at 8.64 GHz. There appears to be a 2.5-sigma feature (rms of
0.3 mJy) at the position of the source (ref GCN 3163) in the combined 
data set at 4.8 GHz. The feature could be spurious given that the uv
coverage was poor and the observation duration was short.

The observations were granted as ToO (April 02) and discretion observation
(April 03) by the ATNF director.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3178
SUBJECT: GRB050401: Radio observation at 610 MHz with GMRT
DATE:    05/04/05 06:45:08 GMT
FROM:    Poonam Chandra at Tata Inst. Fund.Res.  <poonam@tifr.res.in>

GRB050401: Radio observation at 610 MHz with GMRT

Poonam Chandra and Alak Ray (Tata Institute of Fundamental Research
(TIFR), Mumbai) report the observation of GRB 050401 with the Giant
Metrewave Radio Telescope (GMRT) on 2005 April 2.77 (UT) at 617 MHz
frequency with a bandwidth of 32 MHz. No radio emission is seen either at
the Optical Transient afterglow position (GCN 3163) or the revised Swift
BAT position (GCN 3173).  The map rms is 0.23 mJy and 2-Sigma upper limit
to the GRB flux density is 0.46 mJy.

We thank the GMRT staff, in particular the National Centre for Radio
Astrophysics (NCRA) Director Dr. Rajaram Nityananda for making the
observations possible, and Dr. Paolo Freire, Yashwant Gupta and
collaborators for allowing a part of their time to be used for this
observation. GMRT is run by NCRA-TIFR.  This observation was Target of
Opportunity observation and the observing time was granted as
discretionary time at the GMRT.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3179
SUBJECT: Konus-Wind observation of GRB 050401
DATE:    05/04/05 14:16:26 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred@mail.ioffe.ru>

S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, and
T. Cline on behalf of the Konus-Wind team report:

A long multipeak GRB 050401 (Swift-BAT trigger 113120, GCN 3162,3173)
triggered Konus-Wind at 51611.344 s UT (14:20:11.344).
As observed by Konus-Wind, it had a duration of ~36 s,
fluence (1.93 +/- 0.04)10-5 erg/cm2, peak flux (2.45 +/- 0.12)10-6 
erg/cm2 s (both in the 20 keV - 2 MeV energy range).
We derived two spectra: the first one integrated over three initial
peaks (0 - 16.6 s) and the second integrated over the last, strongest
peak (24.8 - 32 s). Both spectra are well fitted by a GRB (Band) model.

For the 1st spectrum:
the low-energy photon index is alpha = -1.15 +/- 0.16,
the high energy photon index beta = -2.65 +/- 0.31,
the break energy E0 = 156 +/- 45 keV,
and the peak energy Ep = 132 +/- 16 keV.

For the 2nd spectrum:
the low-energy photon index is alpha = -0.83 +/- 0.21,
the high energy photon index beta = -2.37 +/- 0.14,
the break energy E0 = 102 +/- 30 keV,
and the peak energy Ep = 119 +/- 26 keV.

Assuming z = 2.90 (GCN 3176) and a standard cosmology model
with H_0 = 70 km/s/Mpc, Omega_M = 0.3, Omega_\Lambda = 0.7,
the isotropic energy release is E_iso = (3.53 +/- 0.07)1053 erg,
the maximum luminosity is (L_iso)_max = (1.75 +/- 0.09)1053 ers/s,
and the rest-frame peak energies are Ep_rest = (515 +/- 62) keV and
Ep_rest = (464 +/- 101) keV correspondingly for the first and second
spectrum.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3187
SUBJECT: GRB050401: Radio Detection
DATE:    05/04/07 16:37:38 GMT
FROM:    Alicia Soderberg at Caltech  <ams@astro.caltech.edu>

A. M. Soderberg (Caltech) reports on behalf of the
Caltech-NRAO-Carnegie GRB collaboration:

"Using the Very Large Array at 8.5 GHz, we observed the
field of GRB050401 (GCN 3162) on 2005 Apr 7.29 UT.
We detect a radio source at our detection threshold at
the following position:

RA(J2000) = +16h 31m 28.82s,  Dec(J2000) = +02d 11' 14.83"

with an estimated uncertainty of 0.5 arcsec in each coordinate.

This source is within the XRT error circle (GCN 3161) and
consistent with the optical afterglow position (GCN 3163).
The flux density of the source is 122 +- 33 uJy.

Further observations are planned."

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3233
SUBJECT: GRB 050401: Optical limit
DATE:    05/04/11 11:57:48 GMT
FROM:    Ken ichi Torii at RIKEN  <torii@crab.riken.go.jp>

K. Torii (Osaka U.) reports

 "The error region of GRB 050401 (Angelini, et al. GCN 3161; Barbier,
et al. GCN 3162) was observed with the ART 14-inch telescope. BVRcIc
imaging started at 2005 April 1, 14:22:23 UT (128-s after trigger) and
60-s exposure in each filter was repeated.

 The optical afterglow (McNaught & Price GCN 3163) is not detected in
our frames and the following 3-sigma upper limits are derived relative
to USNO-B1.0 magnitudes.

MeanEpoch(UT) Magnitude Exposure
14:22:53 >12.8Rc 60s
14:24:02 >13.2Ic 60s
14:27:27 >13.4Rc 60s
14:28:34 >13.4Ic 60s
14:32:00 >13.7Rc 60s
14:33:07 >14.0Ic 60s
"

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3319
SUBJECT: GRB 050401: Rc observation
DATE:    05/04/27 15:23:16 GMT
FROM:    Corrado Bartolini at Universita di Bologna  <corrado.bartolini@unibo.it>

G. Greco, C. Bartolini, A. Guarnieri, A. Piccioni (Bologna University),
G. Pizzichini (IASF-CNR, Sezione di Bologna), S. Bernabei and S. Marinoni
(Osservatorio di Bologna) report:

"We observed the optical afterglow (Mc Naught and Price, GCN 3163) of the Swift
GRB050401 (Angelini et al. GCN 3161) with the 152-cm G. D. Cassini telescope
of Bologna University equipped with the BFOSC CCD imager.

We obtained 2x1800s Rc images on 2005 April 2.056 and April 2.092 UT.
From the first image, in good sky conditions (seeing about 2"), we find
Rc =3D 22.7 +- 0.4, using the calibration kindly provided to us by P. D'Avanzo
and N. Masetti, performed at TNG telescope.
In the second image, less deep, the object is hardly visible.

The first image of the OT is posted into a public directory from where
it can be retrieved by sftp using
hostname: ermione.bo.astro.it
username: publicGRB
password: GRB_bo
directory: GRB050401".