GRB 050504

S. Mereghetti, D. Gotz (IASF, Milano), N. Mowlavi, S. Shaw, M. Beck, M. 
Turler (ISDC, Versoix) and J. Borkowski (CAMK, Torun) on behalf of the 
IBAS Localization Team report:

A long GRB has been detected by IBAS in IBIS/ISGRI data at 08:00:52.5 UT 
on May 4. Its coordinates (J2000) are:

RA:  200.9986 [degrees] 
DEC: +40.6959 [degrees]

with an uncertainty of 1.5 arcmin (90% c.l. radius).

Note that this burst is located at high galactic latitude (b=+75 deg) and 
not affected by Galactic absorption. It is therefore a good target for 
optical follow-up searches.

Analysis of the IBIS/ISGRI data yields a peak flux of 0.5 photons (6E-8
ergs)/cmsq/s (1 s integration time) and a fluence of 14.4 photons (1.5E-6 
ergs)/cmsq (80 s integration time). Both values refer to the 20-200 keV energy 
range.

The burst lasted about 80 s and had a FRED profile. A plot of the light curve 
can be found at:

http://ibas.mi.iasf.cnr.it/IBAS_Results.html

This message can be cited.

S. Bradley Cenko and Derek B. Fox report on behalf of the
Caltech-NRAO-Carnegie GRB Collaboration:

We have imaged the error circle of GRB050504 (GCN 3348
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 ) with the automated
Palomar 60-inch Telescope.  Observations began at ~ 8:04 UT, 3 minutes
after the burst.  A coaddition of our first five Kron R band images (3 x
60 s, 2 x 120 s, mean epoch 8:14 UT), yields no new sources in the error
circle compared with the Digital Sky Survey.  Our limiting magnitude,
calculated with respect to several Guide Star Catalog sources in the
field, is approximately R > 21.0.  We note, however, the bright source
mentioned by Bloom & Prochaska (GCN 3347
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 ) affects our sensitivity over a
significant fraction of the error circle.

Further observations are planned.

A. Monfardini, C. Guidorzi, I. Steele, C. Mottram, D. Carter,
A. Gomboc, C. Mundell and M. Bode (Liverpool) on behalf of the 
ROBONET collaboration report: 

"The 2m Faulkes Telescope North on Haleakala automatically reacted to the
INTEGRAL trigger for GRB050504 (GCN3348
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 ). The robotic pipeline, based on a
series of short exposures, didn't detect any new source up to R ~ 19 at
3.7 minutes after the burst. The bright source mentioned in GCN3347
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  and
GCN3349
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  by Cenko et al. affects our sensitivity over a significant
fraction of the error circle too.
Further observations are in progress."

Kuntal Misra, S. B. Pandey (ARIES Naini Tal), on behalf of larger Indian
GRB collaboration

We monitored the INTEGRAL error-box (GCN 3348
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 ) of GRB 050504 using 1-m
reflector at Naini Tal in R_c passband. In 300 sec exposure time, we
did not reveal any new source up to ~ 20 mag, in comparison to the
nearby USNO A2.0 star 1275-08249328.

This message can be cited.

M. De Pasquale (MSSL), A. Blustin (MSSL), A. Morgan (PSU),
T. Poole (MSSL), M. Still (GSFC), N. Gehrels (GSFC), K.
Mason (MSSL), J. Nousek (PSU), on behalf of the Swift UVOT
team

  The Swift UVOT began observing the field of GRB 050504
(Mereghetti et al, GCN 3348
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 ) 5.45 hours after the trigger.
We have co-added all UVOT V-band exposures of GRB 050504
taken between 13:27 UT and 13:45 UT, for a total exposure
time of 989 seconds.

  No new source is detected within a 2 arcmin radius error
circle around the position given by Mereghetti et al. We
obtain a three sigma upper limit from the summed image of
V=20.2.

  The magnitudes are based on preliminary zero-points, measured
in orbit, and will require refinement with further calibration.

GRB 050504 : R band observation at Lulin observatory

K. Sanchawala, Y.L. Wu, K.Y. Huang, W.H. Ip(NCU), Y. Urata, (RIKEN), 
Y. Qiu (BAO), Y.Q. Lou (THCA), on behalf of EAFON report:

" We have imaged the error region of GRB 050504(GCN 3348
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 ) using 1-m
telescope at Lulin Observatory, Taiwan. The R band observations ( 60s
x 15 frames) started from 13.27 UT to 13.55 UT (~ 5.26 hours to 5.54
hours after the burst). The limiting magnitude of R band co-added
image is R ~ 21 compared with USNOB1.0 stars. No new source was found
down to the limiting magnitude.  

This message may be cited."

J. A. Kennea, D. N. Burrows (PSU), K. Page, C. P. Hurkett (U. 
Leicester), B. Zhang (UNLV) and N. Gehrels (NASA/GSFC) report on behalf of 
the Swift XRT team:

INTEGRAL detected GRB050504 at 08:00:52 UT on 4th May 2005 (GCN Circ 
3348
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 ). The Swift observatory executed an Target of Opportunity observation 
of the INTEGRAL position and the XRT began taking data at 13:27:40 UT. 
In ground processing of 9218s of Photon Counting mode data we detect a 
faint uncataloged X-ray source located at:

RA(J2000) = 13:24:01.3,
Dec(J2000) = +40:42:12

We estimate an uncertainty of 6.9 arcseconds radius (90% containment). 
This position is 35 arcseconds from the INTEGRAL position reported in GCN 
3348
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 .

J. A. Kennea, D. N. Burrows (PSU), B. Zhang (UNLV) and N. Gehrels
(NASA/GSFC) report on behalf of the Swift XRT team:

Swift perfomed a follow up observation of the X-ray afterglow candidate of 
GRB050504 repored in GCN 3359
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 . The new observation began on 01:38:23UT on 
14th May 2005, and Swift-XRT collected 7 ks of photon counting mode data. 
Analysis of the ground processed data on GRB050504 from the second epoch 
observations reveal no detection of the source found in the first epoch. 
The 90% confidence level upper limit is 7.9 x 10^-4 cts/s compared to a 
source brightness in the first epoch of 3.5+/-0.7 x 10^-3 cts/s.

We therefore conclude that the X-ray source reported in GCN 3359
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  has 
faded, and is most likely the X-ray afterglow of GRB050504.

M.Sasaki, N.Manago, Y.Aita, T.Aoki, Y.Asaoka, M.Jobashi, K.Noda,
A.Okumura (ICRR, Univ.Tokyo), S.Ogawa (Toho Univ.), T.Chonan, Y.Watanabe
(Titech) report on behalf of the Ashra collaboration:

We have observed the field of GRB050504 (08:00:59 UT) covering the
Integral error circle (Mereghetti et al, GCN 3348
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 ) by Ashra-P2/3
(Prototype of 2/3 scale) and Ashra-AFT at the Haleakala observatory in
Hawaii (latitude = 20d 42' 37" N, longitude = 156d 15' 31" W, altitude =
3020m) in conditions of variable clouds across the field. 

The Ashra-P2/3 continuously monitored the Integral field with 5sec-repeat
of unfiltered 4sec exposures from 1 second before the burst. The
Ashra-AFT automatically responded to the Integral trigger and took the
first image of 4sec-exposure at 08:01:57 UT (58 seconds after the burst
and 37 seconds after the alert socket). We also took following 10
unfiltered images of 4sec-exposure every 9 to 10 seconds (08:01:57 UT -
08:03:29 UT). 

No new source was found within the Integral position by the two telescopes.
We compared the co-added 10 images (10 x 4sec) from Ashra-P2/3 with BT
in the Tycho catalog and the earliest 3 images and the co-added images
(10 x 4sec) from Ashra-AFT with the USNO-B1.0 respectively. We preliminarily
obtained 4-sigma limiting magnitudes as follows:

Ashra-P2/3 limiting magnitude
 -----------------------------------------------------
   start    end      exposure     limit mag.
   after GRB (s)          (s)     BT
 -----------------------------------------------------
      -1      49    40.0           8.0
 -----------------------------------------------------

Ashra-AFT limiting magnitude
 -----------------------------------------------------
   start    end      exposure     limit mag.
   after GRB (s)          (s)     B1          R1
 -----------------------------------------------------
      58      62     4.0          16.7        15.0
      68      72     4.0          16.9        15.1
      77      81     4.0          16.8        15.1
 -----------------------------------------------------
      58     150    40.0          17.7        16.0
 ----------------------------------------------------- 

URL: http://www.icrr.u-tokyo.ac.jp/~ashra/

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