GRB 060904, GRB 060904A

H. Mito, T. Soyano, (Tokyo Univ.) and Y. Urata (Saitama Univ.)
on behalf of EAFON report:

"We have observed the position of X-ray afterglow using Kiso 1.05m
Schmited telescope.  The observation was started at 10:20 UT September
4, 2006. The combined image from 20 frames taken with 300 sec exposure
shows no optical afterglow associated with the X-ray afterglow
position brighter than 22.4 (R) mag.

  -------------------------------------------
  Start time  Exposure            Limit(SN=3)
  10:20       300 sec x 20 frame  > 22.4
  -------------------------------------------

This message may be cited."

M. Tashiro, K. Abe, K. Onda, Y. Sato, M. Suzuki, Y. Urata (Saitama U.),
  M. Ohno, T. Takahashi, T. Asano, T. Uehara, Y. Fukazawa (Hiroshima U.),
  K. Yamaoka, S. Sugita (Aoyama Gakuin U.), T. Enoto, R. Miyawaki,
  K. Kokubun, K. Makishima (Univ. of Tokyo), K. Nakazawa, T. Takahashi
  (ISAS/JAXA),   M. Suzuki, Y. Terada, T. Tamagawa (RIKEN),
  S. Hong (Nihon U.), on behalf of the Suzaku WAM team report:

  The bright, long burst, GRB 060904A (Swift-BAT trigger #227996;
  D. Grupe et al., GCN 5502
Loading...
 
 ; Krimm et al., GCN 5516
Loading...
 
 ), triggered
  the Suzaku Wideband All-sky Monitor (WAM) which covers an energy
  range of 50 keV - 5 MeV at 01:04:09.040 (UT).
  The three little peaks and following large peak (GCN 5502
Loading...
 
 ) are
  clearly seen in the light curve observed with the WAM.
  The T90 duration was ~79 seconds.
  The fluence in 100 - 1000 keV was 8.66(-4.19 +0.39)x10-6 erg/cm2,
  while the 1-s peak flux was 2.07(-1.12 +0.09) photons/cm2/s in the
   same energy range.

  Preliminary result shows that the time-averaged spectrum is
  well described with a single power-law model with the energy index
  of 1.16 (-0.18 0.20).

   All the quoted errors are at statistical 90% confidence level,
  in which systematic errors are not included.

Pablo Saz Parkinson (UC Santa Cruz) on behalf of the Milagro
collaboration reports:

We have searched Milagro data for emission at GeV/TeV energies from the
bright GRB 060904A detected by Swift (GCN Circ 5502
Loading...
 
 , D. Rupe et al.),
during the main period of emission lasting 80s (GCN Circ 5516
Loading...
 
 , H. Krimm et
al.). No evidence for prompt GeV/TeV emission was found. A preliminary
analysis, assuming a differential photon spectral index of -2.4, gives an
upper limit on E^2dN/dE at 99% confidence of:

E^2dN/dE at 2 TeV < 2.9 * 10^(-7) erg cm^(-2) (No EBL absorption)

TeV photons are attenuated by pair production with infrared photons in
intergalactic space. We calculate an upper limit assuming a
redshift of 0.5 using the extragalactic infrared background light (EBL)
absorption model of Primack et al. 2005 (AIP Conf. Proc. 745, p. 23).
We find 99% confidence level upper limits on E^2dN/dE of:

E^2dN/dE at 200 GeV < 5.5 * 10^(-5) erg cm^(-2) (Primack et al. EBL model)

The energies quoted represent the approximate median energy of the
events that would be detected assuming a power law spectrum with
differential index -2.4 convolved with the absorption model.
These upper limits are preliminary and will be refined with further
analysis.

S.R. Oates (UCL-MSSL), D. Grupe (PSU) report on behalf of the 
Swift/UVOT team:

The Swift/UVOT began observing the field of GRB 060904A at
01:04:36 on 2006-09-04, 75 s after the BAT trigger (Grupe
et al., GCN 5502
Loading...
 
 ). No new source was detected within the XRT error 
circle
in coadded images in any filter down to the following 3-sigma
magnitude upper limits:


Filter  Tstart   Tstop   Exposure  3-sigma UL
-------------------------------------------------
V        55       1888     1680    20.11

B        658      1984     97      19.85

U        634      1959     117     19.49

UVW1     610      1936     117     19.91

UVM2     586      1911     117     19.95

UVW2     687      2014     128     20.55

White    75       1997     352.2   21.69
------------------------------------------------

These upper limits are not corrected for Galactic extinction
E(B-V) = 0.018.

K. Aoki, I. Tanaka (Subaru Telescope, NAOJ) and N. Kawai (Tokyo Tech)
report on behalf of the Subaru GRB team:

"We began observing the field of GRB 060904A (Grupe et al., GCN 5502
Loading...
 
 )
with MOIRCS on the 8.2m Subaru Telescope at ~6 UT (5 hours after the
burst). 

In the stacked image of the 18 x 120 sec exposure (mid time UT 6:24)
in Ks band, we detected an object with 20.2 mag in the XRT error
circle, though the object may be extended.  In the the J band image
of 21 x 120 sec exposure (mid time UT 7:13), we did not detect an
object brighter than 21.0 mag in the XRT error circle.  The magnitudes
were estimated based on the 2 MASS objects in the field."

A. Pelangeon & J-L. Atteia (LATT-OMP) report:

We have used the spectral parameters of GRB 060904A
provided by Golenetskii et al. (GCNC 5518) to
compute the spectral pseudo-redshift** of this burst
detected by SWIFT-BAT (trigger #227996:
Grupe et al., GCNC 5502; Krimm et al., GCN 5516
Loading...
 
 ).

We find a pseudo-redshift pz= 1.84 � 0.85

We thank V. Pal'shin for providing the fluence of this GRB
during the main pulse (from T0 to T0+16.64 s, KONUS time).


** cf. http://www.ast.obs-mip.fr/grb/pz

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

The most intense part of the long GRB 060904A
(Swift-BAT trigger #227996;  Grupe et al., GCN 5502
Loading...
 
 ;
Krimm et al., GCN 5516
Loading...
 
 )
triggered Konus-Wind at T0=3853.821 s UT (01:04:13.821).

As observed by Konus-Wind the burst emission
started at T-T0 ~-56 s, peaked at T-T0 ~0 s,
and ended at T-T0 ~26 s, so the total burst duration
is ~80 s.
The burst fluence is 1.59(-0.21, +0.40)x10^-5 erg/cm2,
and the 256-ms peak flux measured from T0-0.128 s
1.38(-0.33, +0.46)x10^-6  erg/cm2/s
(both in the 20 keV - 2 MeV energy range).

The spectrum of the main pulse
(from T0 to T0+16.64 s)
is well fitted (in the 20 keV - 2 MeV range)
by GRBM (Band) model for which:
the low-energy photon index is alpha = -1.00(-0.17, +0.23),
the high energy photon index beta = -2.57(-1.00, 0.37),
the break energy E0 = 163 (-54, +65) keV (chi2 = 40/61 dof).
The peak energy Ep = 163 +/- 31 keV.

All the quoted errors are at the 90% confidence level.

H. Krimm (GSFC/USRA), L. Barbier (GSFC), S. D. Barthelmy (GSFC),
J. Cummings (GSFC/UMD), E. Fenimore (LANL), N. Gehrels (GSFC),
D. Grupe (PSU), D. Hullinger (BYU-Idaho), C. Markwardt (GSFC/UMD),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU),
G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC)
on behalf of the Swift-BAT team:
 
Using the data set from T-110 to T+843 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 060904 (trigger #227996)
(Grupe, et al., GCN Circ. 5502
Loading...
 
 ).  The BAT ground-calculated position
is (RA,Dec) = 237.730, 44.984 deg {15h 50m 55.3s, 44d 59' 3.7"} (J2000)
+- 1.5 arcmin, (radius, sys+stat, 90% containment).  The partial coding was 94%.
 
The mask-weighted lightcurve shows the emission starting at a very low level
at ~T-70 sec, then increasing slightly at ~T-7 sec for the trigger with several
small peaks until the main peak.  The main emission peak starts at T+45,
peaking at T+56, and ending at ~T+125 sec.  T90 (15-350 keV) is 80 +- 2 sec
(estimated error including systematics).  Note that the spacecraft slewed
to the field of view containing the burst approximately 110 seconds
before the trigger, so there is no BAT data before this time.
 
The time-averaged spectrum from T-23.9 to T+108.7 is best fit by 
a simple power-law model.  The power law index of the time-averaged spectrum
is 1.52 +- 0.04.  The fluence in the 15-150 keV band is 7.9 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+55.34 sec in the 15-150 keV
band is 4.9 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90%
confidence level.

D. Grupe (PSU) reports on behalf of the Swift/XRT team



We have analyzed the first  orbit with a total observing time
of 2.06 ks of Swift XRT data of GRB 060904A (Grupe et al., GCN 5502
Loading...
 
 ).

The X-ray light curve displays the end of a giant flare with a
flattening of the light curve at 200s after the burst. The initial
decay slope is 3.8+/-0.2 followed by 1.3+/-0.2.

Spectral fits to the Windowed Timing mode data during the flare phase
suggest a significant absorption column density in excess of the
Galactic value (1.41e20 cm**-2). The spectrum can be fitted by a
single power law with a photon index Gamma=1.93+/-0.04 and an
absorption column density NH=1.7+/-0.1e21.

Due to the detection of GRB 060904B (Grupe et al., GCN 5505
Loading...
 
 ) about
about 1.5 hours after the trigger of GRB 060904A, only one orbit has
been observed on GRB 060904A and the data were only taken in Windowed
Timing mode. Therefore no photon counting  mode data exist currently
and no improved position can be given yet.



This circular is an official product of the Swift XRT Team.

Kazuhisa Mitsuda on behalf of Suzaku team

  We have just started to observe GRB 060904A (GCN 5502
Loading...
 
 : D. Grupe et al.)
  at location (RA, Dec)={15h 50m 58s, +44d 57' 57"} (J2000)
  with the Suzaku narrow field instruments (the XIS and HXD).
  The observation has started at 10:30 UT, on 4 September (UT),
  and continue until 05:04 of 5 September, 2006 (UT).

  We encourage further follow-up observations with other wavelengths.

S. B. Cenko and A. Rau (Caltech) report on behalf of a larger
collaboration:

We have imaged the error circle of GRB 060904a (Grupe et al; GCN 5502
Loading...
 
 )
with the automated Palomar 60-inch telescope.  Observations began at
4:57 UT 4 September (3.9 hours after the burst) and consisted of 12 x 180
s images in the Kron R and Sloan i' and z' filters.  We find no sources
inside the XRT error circle, to a limiting magnitude of R > 22.0
(estimated by comparison with several USNO-B objects in the field).

Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report:

We imaged the field of GRB 060904 detected by SWIFT
(trigger 227996) with the TAROT robotic telescope (D=25cm)
located at the Calern observatory, France.

First image was acquired 26.8s after the GRB trigger
(9.4s after the notice). The field elevation decreased from
10 degrees above horizon and weather conditions
were excellents. First image was acquired during
the prompt phase.

Date of trigger : t0 = 2006-09-04T01:03:21.600

First image is 60.0 exposure trailed. No OT is visible
in the XRT error box (Grupe et al. GCNC 5502)
t0+26.8s to t0+86.8s : R > 16.0

Second image is 30.0 exposure. No OT is visible:
t0+93.7s to t0+123.7s : R > 17.3

We co-added a series of exposures. No OT is visible:
t0+93.7s to t0+376.2s : R > 19.5

Magnitudes were estimated with the nearby USNO-B1 stars
and are not corrected for galactic dust extinction.

N.B. Galactic coordinates are lon= 71.6566 lat=+50.2105
and the galactic extinction in R band is 0.0 magnitudes
estimated from D. Schlegel et al. 1998ApJ...500..525S.

This message may be cited.

Richard J. Cool (Arizona), Daniel J. Eisenstein (Arizona), David
W. Hogg (NYU), Michael R. Blanton (NYU), David J. Schlegel (LBNL),
J. Brinkmann (APO), Donald Q. Lamb (Chicago), Donald P. Schneider
(PSU), and Daniel E. Vanden Berk (PSU) report:

The Sloan Digital Sky Survey (SDSS) imaged the field of burst
GRB060904 prior to the burst.  As these data should be useful
as a pre-burst comparison and for calibrating photometry, we are
supplying the images and photometry measurements for this GRB field
to the community.

Data from the SDSS, including 5 FITS images, 3 JPGS, and
3 files of photometry and astrometry, are being placed at
http://mizar.as.arizona.edu/~grb/public/GRB060904

We supply FITS images in each of the 5 SDSS bands of a 8'x8'
region centered on the GRB position (ra=237.743 (15:50:58.3),
dec=44.9660 (44:57:57.6); Swift-BAT TRIGGER 227996), as well as 3
gri color-composite JPGs (with different stretches). The units in
the FITS images are nanomaggies per pixel.  A pixel is 0.396 arcsec
on a side. A nanomaggie is a flux-density unit equal to 10^-9 of
a magnitude 0 source or, to the extent that SDSS is an AB system,
3.631e-6 Jy.  The FITS images have WCS astrometric information.

In the file GRB060904_sdss.calstar.dat, we report photometry
and astrometry of 309 bright stars (r<20.5) within 15' of the
burst location.  The magnitudes presented in this file are asinh
magnitudes as are standard in the SDSS (Lupton 1999, AJ, 118,
1406). Beware that some of these stars are not well-detected in
the u-band; use the errors and object flags to monitor data quality.

In the files GRB060904_sdss.objects_flux.dat and
GRB060904_sdss.objects_magnitudes.dat, we report photometry of
451 objects detected within 6' of the GRB position.  We have
removed saturated objects and objects with model magnitudes
fainter than 23.0 in the r-band.  The fluxes listed in
GRB060904_sdss.objects_flux.dat are in nanomaggies while the
magnitudes listed in GRB060904_sdss.objects_magnitudes.dat are
asinh magnitudes.

All quantities reported are standard SDSS photometry, meaning that
they are very close to AB zeropoints and magnitudes are quoted
in asinh magnitudes.  Photometric zeropoints are known to about
2% rms.  None of the photometry is corrected for dust extinction.
The Schlegel, Finkbeiner, and Davis (1998) predictions for this
region are A_U=0.089 mag, A_g=0.065 mag, A_r = 0.047 mag, A_i=0.036
mag, and A_z=0.025 mag.

The file GRB060904_sdss.spectro.dat contains a list of the 3 objects
with SDSS spectroscopy within 6 arcminutes of the GRB position.
In addition to the redshift and 1-sigma error for each object,
this file also lists the object spectroscopic classification.

SDSS astrometry is generally better than 0.1 arcsecond per
coordinate.  Users requiring high precision astrometry should take
note that the SDSS astrometric system can differ from other systems
such as those used in other notices; we have not checked the offsets
in this region.

More detailed information pertaining to our SDSS GRB releases
can be found in our initial data release paper (Cool et al. 2006,
astro-ph/0601218).  See the SDSS DR4 documentation for more details:
http://www.sdss.org/dr5.

These data have been reduced using a slightly different pipeline
than that used for SDSS public data releases.  We cannot guarantee
that the values here will exactly match those in the data release
in which these data are included.  In particular, we expect the
photometric calibrations to differ by of order 0.01 mag.

This note may be cited, but please also cite the SDSS data release
paper, Adelman-McCarthy et al. (2006, ApJS, 162, 38), when using
the data or referring to the technical documentation.

D. Grupe (PSU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
M. M. Chester (PSU), N. Gehrels (NASA/GSFC),
S. T. Holland (GSFC/USRA), S. D. Hunsberger (PSU),
J. A. Kennea (PSU), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC/UMD), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL), M. Stamatikos (NASA/ORAU) and M. C. Stroh (PSU)
report on behalf of the Swift Team:

At 01:03:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060904 (trigger=227996).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA,Dec 237.743, +44.966 {15h 50m 58s, +44d 57' 57"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows 3 little peaks
starting out and then a large peak at T+55 sec and a total burst duration
of about 85 sec.  The peak count rate was ~9000 counts/sec (15-350 keV),
at ~55 sec after the trigger. 

The XRT began observing the field at 01:04:27 UT, 66 seconds after the
BAT trigger. XRT found a bright, fading, uncatalogued X-ray source
located at RA(J2000) = 15h 50m 54.9s, Dec(J2000) = +44d 59' 07.8", with an
estimated uncertainty of 5.4 arcseconds (90% confidence radius). 
This location is 79 arcseconds from the BAT on-board position, within
the BAT error circle. The initial flux in the 0.1s image was
2.7e-08 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 75 seconds after the BAT trigger. No
afterglow candidate has been found in the initial data products. The
2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical
3-sigma upper limit has been about 18.5 mag. The 8'x8' region for the
list of sources generated on-board covers 100% of the XRT error
circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to
E(B-V) of 0.02.