GRB 050824

J. Gorosabel, V. Casanova, R. Garrido, A.J. Castro-Tirado, 
M. Jelinek, de Ugarte Postigo, (IAA-CSIC), report:

  We have carried out R-band observations starting at 23:49 UT
  (~37 min after the GRB) with the 1.5m OSN telescope. A visual 
  comparison  reveals an object placed at:
   
   RA(J2000) = 00:48:56.1
   DEC(J2000)= 22:36:32
  
  not present on the DSS. A finding chart will be shortly available
  at http://www.dsri.dk/~jgu/grb050824/FCs/osn.R.gif

  The object has a magnitude of R~18. Further observations would
  be required to confirm whether the object is fading."

S. Campana (INAF-OAB), S. Barthelmy (GSFC), D. Burrows (PSU),
J. Cummings (GSFC/NRC), N. Gehrels (GSFC), S. Hunsberger (PSU),
M. Ivanushkina (PSU), F. Marshall (GSFC), D. Palmer (LANL),
G. Tagliaferri (INAF-OAB),
on behalf of the Swift team:

At 23:12:16 UT, Swift-BAT triggered and located GRB050824 (trigger=151905).
This was a 64-sec image trigger.  The spacecraft did not automatically slew
due to proximity to the moon (25 degrees).  Hence there will be no immediate
results from XRT or UVOT.  However, a TOO is being planned for this target.
The BAT on-board calculated location is RA,Dec 12.237d,+22.592d
{00h 48m 57s,+22d 35' 31"} (J2000), with an uncertainty of 3 arcmin
(radius, 90% containment, stat+sys).  The BAT light curve shows a broad peak
from T+30 to T+70 sec.  The emission is present only in the 15-50 keV band.
The peak count rate was ~500 counts/sec (15-50 keV) at ~40 seconds
after the trigger.  At this early stage of the analysis we think this is
likely a GRB, as there is no known gamma-ray source at this location
in the SIMBAD database and the galactic latitude is -40 degrees.

B. E. Schaefer (Louisiana State), Fang Yuan (U Mich), and K. Alatalo
(Berkeley)  report on behalf of the ROTSE collaboration:

ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia,
responded to GRB 050824 (Swift trigger 151905), producing images beginning
7.1 s after the GCN notice time. An automated response took the first
image at 23:22:02.1 UT, 585.8 s after the burst, under good conditions
although with the gibbous Moon only 25 degrees away. We took 10 5-sec, 10
20-sec and 130 60-sec eposures. These unfiltered images are calibrated
relative to USNO A2.0 (R).

ROTSE-IIId, located at the Turkish National Observatory at Bakirlitepe,
Turkey, also responded, producing images beginning 5.8 s after the GCN
notice time. An automated response took the first image at 23:22:00.8 UT,
584.5 s after the burst, under good conditions (but again, with the
gibbous Moon nearby). We took 10 5-sec, 10 20-sec and 80 60-sec eposures.
These unfiltered images are also calibrated relative to USNO A2.0 (R).

Comparison to the DSS (second epoch) reveals no new sources within the 
3-sigma error circle, for both single images and coadding into sets of 10. 
Individual images have limiting magnitudes ranging from 15.4-17.0; we set 
the following specific limits.

ROTSE  start UT       end UT     t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------------
III-c  23:22:02.1   23:23:27.1       85     17.3          585.8       Y
III-c  23:23:27.7   23:28:21.7      294     18.2          671.4       Y
III-d  23:22:00.8   23:24:20.8      140     17.4          584.5       Y
III-d  23:24:21.5   23:29:20.5      299     17.9          725.2       Y

In particular, we do not see the new source described by Gorosabel et al. 
(GCN 3865
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 ), with this source being near or below our detection threshold.

Corrected subject to GCN3868
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 .


V. Lipunov,  V.Kornilov,   N.Tyurina, A.Belinski,
E.Gorbovskoy, D.Kuvshinov,  A.Krylov, G.Borisov, V.Vladimirov, Krushinski V.

Sternberg Astronomical Institute, Moscow Union "Optic"

       MASTER (http://observ.pereplet.ru) responded to GRB 050824 (Swift trigger 
151905). The first image  was 764 sec after
SWIFT  GRB050824 detection    under the
     not very good weather condition (Moon light).
  We see OT J. Gorosabel (GCN 3865
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 ) with m =  17.5 (unfiltered close to R, 
exp.  45 sec) on 2-3 sigma level. On summ of 9 
images from 19.5 up to 28.5 minut after GRB Time (23 12 16.00 UT) m= 18.0 on 5 
sigma.

      UT                 After GRB time          m
     23 25 00               764s               17.9
     23 31 44        19.5min - 28.5 min        18.3
     23 31 44        19.5min - 37.75 min       18.8

The JPG-image of the summ   will be  available at
http://observ.pereplet.ru/images/GRB050824/1.jpg  .

The reduction is continuing.
This work is supported by RFFI  04-02-16411 grant.
This message can be cited.
Mailto: lipunov@sai.msu.ru

V. Lipunov,  V.Kornilov, A.Krylov,  N.Tyurina, A.Belinski,
E.Gorbovskoy, D.Kuvshinov,  G.Borisov, V.Vladimirov, G.Antipov, Krushinski V.

Sternberg Astronomical Institute, Moscow Union "Optic"

       MASTER (http://observ.pereplet.ru) responded to GRB 050824 (Swift trigger 
151905) (see GCN3869
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 ). The first image  was 764 sec after
SWIFT  GRB050824 detection    under the    not very good weather
condition (Moon light).
  We see OT-candidate  proposed by J. Gorosabel (GCN 3865
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 ) with m =  17.9 
(unfiltered, close to R, exp.  45 sec) on 2-3 sigma level.
Our m = 0.89R + 0.11B (R & B from USNO A).

    UT (start)           After GRB time          m

      23 25 00               764s              17.9      45 sec
     23 31 44        19.5min - 28.5 min        18.3      summ of 9 images
     23 42 07        29.8min - 36.7  min       19.4      summ of 7 images

The calibration will be continued.
The JPG-image of the summ   will be  available at
http://observ.pereplet.ru/images/GRB050824/1.jpg  .

This work is supported by RFFI  04-02-16411 grant.
This message can be cited.
Mailto: lipunov@sai.msu.ru

H. Krimm (GSFC/USRA), L. Barbier (GSFC), S. Barthelmy (GSFC),
J. Cummings (GSFC/NRC), K. Gendreau (GSFC), D. Hullinger (GSFC/UMD),
E. Fenimore (LANL), N. Gehrels (GSFC), C. Markwardt (GSFC/UMD),
P. Meszaros (PSU), D. Palmer (LANL), A. Parsons (GSFC),
T. Sakamoto (GSFC/NRC), G. Sato (ISAS), J. Tueller (GSFC)
on behalf of the Swift-BAT team:

Using the full data set from the recent telemetry downlink, we
report further analysis of Swift-BAT GRB 050824 (trigger #151905)
(Campana, et al., GCN 3866
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 ).  The ground-analysis position is
RA,Dec 12.256 +22.618 (J2000) with an uncertainty of 3 arcmin
(radius, 90%, stat+sys).  This is 1.9 arcmin from the onboard
position and 1.4 arcmin from the optical candidate reported by 
Gorosabel et al. in GCN Circ. 3865
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 .

The light curve shows a single peak with slow rise and slow decay.  
T90 is 25 +- 5 seconds.  Fitting a simple power law over the 
interval from T+38 to T+64 sec, the photon index is 2.7 +/- 0.4 
with a fluence of 2.3 +/- 0.5 x 10^-7 erg/cm^2 in the 15-150 keV 
band (90% c.l).  The peak flux in a 1-second wide window starting 
at T+53 sec is 0.5 +/- 0.2 ph/cm^2/sec (15-150 keV). 

The original GCN Notices were delayed in transmission to the ground 
by 500 sec due to the burst happening during a telemetry downlink 
session when the TDRSS real-time messages are held in a buffer until 
the end of the downlink.

S. Campana (INAF-OAB), V. Mangano (INAF-IASF Palermo), G. Chincarini 
(INAF-OAB &
Uni. Bicocca), G. Tagliaferri (INAF-OAB), D.N. Burrows (PSU), L. 
Cominsky (Sonoma
State U.) and J. Norris (GSFC) report on behalf of the Swift XRT team:

We have analyzed the Swift XRT data from the first orbit observation of 
GRB 050824
(Campana et al., GCN3866
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 ). The new refined coordinates are:

RA(J2000)  = 0h48m56.05s
Dec(J2000) = +22:36:28.5

This position is 59 arcseconds from the BAT position given in GCN3866
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(and 83
arcsec from the refined BAT position, Krimm et al. GCN3871
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 ) and 3.4 
arcsec from
the suggested optical counterpart (Gorosabel et al., GCN3865
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 ).
We estimated an uncertainty of 6.8 arcseconds radius (90% confidence 
level, throughout
the circular). A second fainter X-ray source is located 2.5 arcmin from 
the suggested
afterglow position (and further away from the BAT refined position).

The 0.5-10 keV light curve XRT started 2005-08-25 UT00:53:45, 6089 
seconds after
the BAT trigger, following an uploaded TOO since Swift did not 
automatically
slewed on source (due to the Moon constraint). At the moment we have 
data from
one Swift orbit. During the first orbit we accumulated 1346 seconds of 
good data.
The afterglow candidate is detected with a count rate of (4.1+/-1.1)x10^-2
counts/second (55 total counts). We found no indication of count rate decay.

The number of counts is too low to perform a full spectral analysis.
Fixing the column density to the Galactic value (3.6x10^20 cm-2) a 
preliminary
spectral fit to the PC data gives a spectral power law photon index of 
2.6+/-0.6
in the 0.5-10 keV band. The average unabsorbed 0.5-10 keV flux is about
(1.2+/-0.7)E-12 erg cm-2 s-1.

GRB 050824: Spectroscopic redshift from the VLT

J. P. U. Fynbo, B. L. Jensen, J. Sollerman, J. Hjorth,
D. Watson, K. Pedersen, P. Jakobsson, J. M. Castro Cerón
(DARK Cosmology Centre/Niels Bohr Institute), Javier Gorosabel
(IAA-CSIC) report:

"Using FORS2 on the ESO Very Large Telescope (VLT) we have obtained 
spectra of the afterglow of GRB 050824 (GCN 3865
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 , 3866
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 ) on 2005, 
Aug 25.4 UT. We detect [OII], [OIII], H-beta, and [NeIII] in emission 
and MgII in absorption, corresponding to a redshift of z=0.83.

We acknowledge excellent support from the Paranal staff, especially 
Emmanuel Jehin."

P. B. Cameron (Caltech) and D. A. Frail (NRAO) report on behalf of a
larger collaboration:

"We have undertaken VLA observations at a frequency of 8.46 GHz toward
GRB 050824 (GCN 3866
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 ) on August 25.32 UT. No radio afterglow is
detected. At the position of the optical afterglow (GCN 3865
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 ) the
point-source limit is 44 +/- 50 microJy.  No further observations are
planned.

The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."

D. Hohman (Stone Edge Observatory, NY) reports on behalf of
the AAVSO International High Energy Network on optical observations
of the Swift burst GRB050824 (Campana et al., GCN3866
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 ).
Images taken with a 20cm SCT and Ic filter with midpoint time
of 050825 0530UT (6.3hrs after the burst) do not show
any object at the candidate afterglow location by Gorosabel
et al. (GCN3865
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 ) down to the DSS-2 N-plate limit (about I=18).
The full report is given below.

The AAVSO thanks the Curry Foundation for support of the
AAVSO International High Energy Network.
---------------------------

Report filed on Thu Aug 25 08:37:34 2005:

 Name: Dennis Hohman
 email: dhohman@txrx.com
 Observer: HDF
 Site: Stone Edge Observatory
 Location: Orchard Park, NY
 LatitudeLongitude: 
 Elevation: 275 meters
 Scope: SCT 20 cm
 ScopeFocalRatio: F5.9
 CCDVendor: ST7XME
 CCDDetector: KAF402E
 CCDSize: 752x512
 CCDPixelScale: 1.5
 CCDFOV: 13x19 arc min
 Object: 050824
 ObsDate: 08/25/05
 ObsMidPointTime: 05:30
 TimePerFrame: 240 sec
 NumberOfFrames: 13
 Filters: I
 Processing: Flats/Darks/coadd
 Seeing: 4 - 4.5
 LimitingMag: 
 Sky: Clear
 afterglowmag: 
 afterglowerr: 
 compstars: 
 Report: Full error circle covered. No new object to the limit of the POSS2/UKSTU IR plate.
 comments: 

A FITS image has been uploaded to ftp://ftp.aavso.org/grb/DennisHohman_050824_2453608.02609_.fits

S. Campana (INAF-OAB), A. Moretti (INAF-OAB), V. Mangano (INAF-IASF
Palermo), D.N. Burrows (PSU), report:

We have analyzed 13 ks of Swift XRT data of GRB 050824
(Campana et al., GCN3866
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 ).

The 0.2-10 keV light curve XRT (started 6089 seconds after the BAT
trigger) now shows an indication of a temporal decay with a power
law index of -0.4+/-0.2 (90% confidence level).
The power law fit is better than a constant fit at a 3.3 sigma
level (F-test). This indicates that the source suggested in the
previous XRT circular (Campana et al., GCN3872
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 ) is the X-ray
afterglow of GRB050824.

The 307 photons in the 0.3-10 keV evergy band were also used for
spectral analysis. We fixed the column density to the Galactic value
(3.6x10^20 cm-2) and added a free local absorption at z=0.83 (Fynbo
et al., GCN3874
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 ) plus a power law. We found an accepetable model
(chi2_red=1.01) with a NH_loc=(1.7+/-1.3)x10^21 cm-2 and a power
law photon index of 2.0+/-0.2 (90% confidence level).

[GCN OPS NOTE(25aug05): Per author's request, "...afterglow of GRB050724"
was changed to "...afterglow of GRB050824".]

The Swift Ultra-Violet/Optical Telescope (UVOT) observations began at
00:53:49 UT, 1.8 hrs after the BAT trigger. UVOT detects a fading source at a 
position consistent with that reported by Gorosabel et al. (GCN 3865
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 ) in 5 
of its 6 filters. The magnitudes or 3-sigma upper limit in the first 
exposure taken in each filter are as follows:

Filter  Mid Time (hrs)  Exp (s)  Mag/3-sig UL
V	1.8		109	20.02+/-0.39
B	5.1		305	20.88+/-0.36
U	3.6		217	19.55+/-0.32
W1	9.5		205	19.85+/-0.33
M2	11.7		121	19.34+/-0.36
W2	12.3		1457	> 20.79	

The afterglow has faded below 2-sigma above background 11hrs after the 
burst trigger in all filters apart from the V and U, where it is still 
detected at the 2.3-sigma and >3-sigma level, respectively.

The magnitudes have not been corrected for extinction. These magnitudes 
are based on preliminary zero-points, measured in orbit, and will require 
refinement with further calibration.

P. Schady (MSSL/PSU), R. Fink (GSFC), M. Ivanushkina (PSU), S. Holland 
(GSFC/USRA), K. McGowen (MSSL), N. Gehrels (GSFC) on behalf of the Swift 
UVOT team

CORRECTION: The mid time and exposure durations previously reported for 
observations made by Swift/UVOT of GRB050824 are incorrect (Schady et al. 
GCN 3878
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 ). The correct times are given below.

The Swift Ultra-Violet/Optical Telescope (UVOT) observations began at
00:53:49 UT, 1.8 hrs after the BAT trigger. UVOT detects a fading source 
at a
position consistent with that reported by Gorosabel et al. (GCN 3865
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 ) in 5
of its 6 filters. The magnitudes or 3-sigma upper limit in the first
exposure taken in each filter are as follows:

Filter  Mid Time (hrs)  Exp (s)  Mag/3-sig UL
V       1.8             900     20.02+/-0.39
B       5.1             900     20.88+/-0.36
U       3.6             545     19.55+/-0.32
W1      3.4             900     19.85+/-0.33
M2      2.1             532     19.34+/-0.36
W2      7.8             1457    > 20.79

The afterglow has faded below 2-sigma above background 11hrs after the
burst trigger in all filters apart from the V and U, where it is still
detected at the 2.3-sigma and >3-sigma level, respectively.

The magnitudes have not been corrected for extinction. The reddening in
this direction is E_{B-V} = 0.04mag. These magnitudes are based on
preliminary zero-points, measured in orbit, and will require refinement
with further calibration.

V. Lipunov,  V.Kornilov, A.Krylov,  N.Tyurina, A.Belinski,
E.Gorbovskoy, D.Kuvshinov,  G.Borisov, V.Vladimirov, G.Antipov, Krushinski V.

Sternberg Astronomical Institute, Moscow Union "Optic"

       MASTER (http://observ.pereplet.ru) responded to GRB 050824 (Swift trigger 
151905) (see GCN3869
Loading...
 
 ). The first image  was 764 sec after
SWIFT  GRB050824 detection    under the   Moon light.
  We see OT-candidate  proposed by J. Gorosabel (GCN 3865
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 ).
Our m = 0.89R + 0.11B (R & B from USNO A2).
We made new reduction and confirm previous our OT-decay result (GCN3870
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 ):
New reduction give next results about OT:

        UT               After GRB      m        error     expotime
                         mean time

     23 25 00               788s      >17.8                   45  s
23 25 00 - 23 47 55       24.0 min    18.6       +-0.3      15x30 s 
23 49 00 - 00 09 35       47.0 min    19.4       +-0.3      15x30 s


The JPG-images    available at
http://observ.pereplet.ru/images/GRB050824/1.jpg  .

This work is supported by RFFI  04-02-16411 grant.
This message can be cited.
Mailto: lipunov@sai.msu.ru

V. Lipunov,  V.Kornilov,  N.Tyurina, A.Belinski,
E.Gorbovskoy, D.Kuvshinov

Sternberg Astronomical Institute, Moscow Union "Optic"

We have analysed all photometric points obtained during first 2 hours (see 
picture http://observ.pereplet.ru/images/GRB050824/2.jpg ) from ROTSE
(GCN Circ 3867
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 ), MASTER (GCN Circ 3883
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 ), J. Gorosabel et al. (GCN Circ 
3865
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 ) and Swift UVOT(GCN Circ 3880
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 ) in similar colors .

The upper limits of ROTSE and MASTER for 500-750 sec (GRB time) are in 
agreement. Both instrumental systems are more or less similar.
There is some contradiction with J. Gorosabel  et al. (GCN 3865
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 ) and 
MASTER data (GCN Circ 3880
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 )  for 24 - 47 minutes.
But there is no error bar in  J. Gorosabel et al.(GCN 3865
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 ).
The SWIFT UVOT V-band  is  most closed to MASTER in color sense.
If we include only 2 MASTER points and Swift UVOT V-point we can obtain 
next  power low:


m = 2.1(+-0.2) log (t) + 19.5  ,

t in hours. This corresponds to usual flux  power law

  F ~ t^-0.9

However there is strong contradiction with  ROTSE (11 min) uper limit and
J. Gorosabel et al. (GCN 3865
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 ) point.




JPG-images are available at 
http://observ.pereplet.ru/images/GRB050824/2.jpg  .

This work is supported by RFFI  04-02-16411 grant.
This message can be cited.
Mailto: lipunov@sai.msu.ru

G. Crew, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley, on
behalf of the HETE Science Team;

M. Arimoto, T. Donaghy, E. Fenimore, M. Galassi, C. Graziani,
J. Kotoku, M. Maetou, M. Matsuoka, Y. Nakagawa, T. Sakamoto, R. Sato,
Y. Shirasaki, M. Suzuki, T. Tamagawa, K. Tanaka, Y. Yamamoto,
and A. Yoshida, on behalf of the HETE WXM Team;

N. Butler, J. Doty, G. Prigozhin, R. Vanderspek, J. Villasenor,
J. G. Jernigan, A. Levine, G. Azzibrouck, J. Braga, R. Manchanda,
and G. Pizzichini, on behalf of the HETE Operations and HETE
Optical-SXC Teams;

M. Boer, J-F Olive, J-P Dezalay, and K. Hurley, on behalf of the HETE
FREGATE Team;

report:

The FREGATE instrument onboard HETE also detected the Swift burst GRB
050824 (Campana, et al., GCN 3866
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 ) as an untriggered event (U11648)
with a significance of 6 sigma.  The direction to the burst source was
about 50 degrees from the instrument boresight, placing it outside the
WXM and SXC fields-of-view.

We have analyzed the spectrum of the event.  A power-law (PL) fit to
the full FREGATE energy range (6-400 keV) yields a best-fit power-law
index of 2.35 +0.88/-0.48 (90% CL), consistent with the PL index
reported by the Swift BAT team (Krimm et al., GCN 3871
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 ).  Assuming the
best-fit PL index, the value of the fluence ratio S(2-30)/S(30-400) is
2.7.  GRB 050824 is thus an X-Ray Flash.

A PL fit restricted to photons with energy above 20 keV yields a
best-fit PL index of 3.29 +2.50/-1.36 (90% CL).  This steepening of 
the PL index suggests that the spectrum is representable by a Band
model with a value of E_peak near or below the low end of the FREGATE
energy range, so that the PL fit to the full energy range represents 
an average of the contributions from the high- and low-energy parts of 
the Band model.

Because of the low S/N of the event, a PL times exponential fit and a
Band-function fit are not statistically preferred over the simple PL
model.  Nonetheless, in order to constrain E_peak, we have performed a
"constrained-Band model" analysis of the spectrum (see Sakamoto et al.,
ApJ 602, 875), and find E_peak < 12.7 keV (90% CL).

FREGATE light curve data and plots will be available soon at the
following URL: http://space.mit.edu/HETE/Bursts/U11648.

D. Sharapov,  G. Abdullaeva, M. Ibrahimov (MAO), A.Pozanenko (IKI),
V.Rumyantsev (CrAO) on  behalf of larger GRB follow up collaboration report:

We observed the field of OT (GCNs  3865
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 , 3868
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 , 3880
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 ) of GRB050824 (GCN
3866
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 )  with 1.5m telescope of Maidanak Astronomical Observatory. A set of  R
images were taken between (UT) 21:27 - 22:01, on August 25.

We do not detect the OT  in a stacked image.  Based on USNO A2.0 nearby
stars  we estimate limiting magnitude (3 sigma) of the stacked image (6x300
s) as R ~ 22.0.  Detailed calibration of the stacked image is underway.

This message may be cited.

J. P. Halpern (Columbia U.) and N. Mirabal (U. Michigan) report on behalf of
the MDM Observatory GRB follow-up team:

"We observed the Swift GRB 050824 afterglow (Gorosabel et al., GCN #3865
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 )
in the R band on five consecutive nights using the MDM 1.3m telescope.
Photometry was established using two Landolt standard-star fields on one
photometric night.  From 5.6 to 12.6 hours, the decay is consistent with
a power law of index -0.55+/-0.05, which extrapolates well to the MASTER 
photometry at 24 and 47 minutes (Lipunov et al., GCN #3883
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 ).  This decay 
index is similar to that seen in the Swift XRT light curve, -0.4+/-0.2
(Campana et al., CGN #3877), immediately preceding the MDM observations.
An unobserved inflection in the optical light curve then occurs, and from
1.3 to 4.4 days the decay index is -0.43+/-0.04.  Our final measured point 
is R=22.18+/-0.06 on Aug. 29.32.

Images and light curves are posted at 
http://www.astro.columbia.edu/~jules/grb/050824/

This message may be cited."