GRB 080604

V. La Parola (INAF-IASFPA), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), C. Guidorzi (INAF-OAB),
S. T. Holland (CRESST/USRA/GSFC), N. P. M. Kuin (MSSL),
J. Mao (INAF-OAB), P. T. O'Brien (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL),
D. Perez (U Leicester), B. Sbarufatti (INAF-IASFPA),
R. L. C. Starling (U Leicester), D. E. Vanden Berk (PSU) and
H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team:

At 07:27:01 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080604 (trigger=313116).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 236.970, +20.555 which is 
   RA(J2000) = 15h 47m 53s
   Dec(J2000) = +20d 33' 19"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a broad single peak
structure with a duration of about 70 sec.  The peak count rate
was ~300 counts/sec (15-350 keV), at ~10 sec after the trigger. 

The XRT began observing the field at 07:29:00.4 UT, 119.3 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 236.9648, +20.5572 which is equivalent to:
   RA(J2000)  = 15h 47m 51.5s
   Dec(J2000) = +20d 33' 25.9"
with an uncertainty of 5.4 arcseconds (radius, 90% containment). This
location is 19 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 


UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 128 seconds after the BAT trigger. There is a candidate
afterglow in the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	15:47:51.70 = 236.9654
  DEC(J2000) = +20:33:28.1  =  20.5578
with a 1-sigma error radius of about 0.5 arc sec. This position is 3.4 arc sec. 
from the center of the XRT error circle. The estimated magnitude is 20.1 with a
1-sigma error of about 0.5 mag. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.05. 




Burst Advocate for this burst is V. La Parola (laparola AT ifc.inaf.it). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)

E. Rol (U. Leicester), C. Guidorzi (INAF-OAB), A. Gomboc (U. Ljubljana), 
I.A. Steele (Liverpool JMU), P. O'Brien (U. Leicester), A, Melandri, D. 
Bersier, C.G. Mundell, R.J. Smith, D. Carter, S. Kobayashi, M. Burgdorf, 
M. Bode (Liverpool JMU), N. Bannister, N. Tanvir (U. Leicester) report:

The Faulkes Telescope North observed the position of GRB080604. We confirm 
the detection of an optical transient (La Parola, GCN 7800
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 ), with a 
position of (J2000):

RA =   15 47 51.65
Dec = +20 33 28.1

In the first 10 second exposure, starting 5:42 minutes after the BAT 
trigger, we estimate a magnitude of R = 20.12 +/- 0.15 with respect to the 
USNO-B1.0 star at 15:47:52.50, +20:34:24.4.

G. G. Williams (MMTO), P. A. Milne (Steward Observatory) and A. Updike
(Clemson) on behalf of the Super-LOTIS Collaboration, report:

The robotic 0.6-m Super-LOTIS telescope began observing the error box
of GRB 080604 (Swift Trigger 313116, La Parola et al. GCN 7800
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 ) at
07:28:59.0 UT, 118 seconds after the trigger.  Our initial
observations include 5 x 10s exposures, 5 x 20s exposures, and 30 x
60s exposures, all in the R-band.

We do not detect the afterglow reported by La Parola et al. (GCN 7800
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 )
and confirmed by Rol et al. (GCN 7801
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 ) in our earliest exposure to the
following 5-sigma limiting magnitude determined using the nearby
USNO-B1.0 star 1105-0256520 at RA=15:47:45.32, Dec=+20:33:38.4 with
R2mag=14.56:

t_start (UT)	exp t (s)	t_start-t_0 (s)	Limit
--------------------------------------------------------
07:28:59.0	10 		118.0 		R > 17.5

We also do not detect the afterglow in our later images or the sum of
our 20s images and 6x60s images.  Additional observations and analysis
are ongoing.

A. Cucchiara and D. B. Fox (Penn State) report:

"Starting on 2008 June 4.35 UT we used the Marcario LRS spectrograph
on the Hobby-Eberly Telescope (R ~ 230) to obtain a 1200s spectrum
of the optical afterglow of GRB 080604 (La Parola et al., GCN 7800
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 ).
The spectrum covers the wavelength range 4500 to 10,000 Angstrom.
Based on a preliminary calibration we detect absorption features
corresponding to the MgII doublet (2796, 2803 A) and MgI (2852 A)
as well as other metal absorption features at redshift z = 1.28.

The absence of Lyman break in our dataset suggests z < 2.7.

A refined analysis will be posted.

We thank the HET staff for performing this observation,
in particular Matthew Shetrone."

P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 749 s of overlapping XRT Photon Counting mode and UVOT
data for GRB 080604, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 236.96516, +20.55777 which is equivalent
to:

RA (J2000): 15h 47m 51.64s
Dec (J2000): +20d 33' 28.0"

with an uncertainty of 1.7 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest position
can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is
described by Goad et al. (2007, A&A, 476, 1401
http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an
extension of this method.

This circular was automatically generated, and is an official product of the
Swift-XRT team.

V. La Parola, B. Sbarufatti, V. Mangano (INAF-IASF Pa) report on behalf
of the Swift-XRT team

The Swift-XRT observed GRB 080604 (trigger 313116, La Parola et
al. GCN Circ 7800
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 ) for 6.3 ksec, starting 119.3 seconds after
the BAT trigger.

We detect an X-ray counterpart at the position
(astrometrically corrected using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 236.96516, +20.55777 which is equivalent to:

RA (J2000): 15h 47m 51.64s
Dec (J2000): +20d 33' 28.0"

with an uncertainty of 1.7 arcsec (radius, 90% confidence).

The X-ray light curve shows a power law decay with slope -2.18 +/-0.06, with a hint of a flare at ~T+1000 s.

The spectrum accumulated over the whole observation can be modelled with an absorbed powerlaw with the following parameters (Galactic nH is
4.0e20cm**-2):

nH = (8 +/- 4)e20 cm**-2
Gamma= 1.8 +/- 0.2
Flux (0.3-10 keV) 4.18E-12 ergs cm**-2 s**-1
Unabsorbed Flux (0.3-10 keV) = 4.9E-12 ergs cm**-2 s**-1

The predicted XRT count rate after 24 hours from the burst is 1.5e-5
counts/s

This circular is an official product of the Swift-XRT team.

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S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC), J. Cummings (GSFC/UMBC),
E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA),
V. La Parola (INAF-IASFPA), C. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD),
D. Palmer (LANL), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+963 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 080604 (trigger #313116)
(La Parola, et al., GCN Circ. 7800
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 ).  The BAT ground-calculated position is
RA, Dec = 236.960, 20.557 deg, which is 
   RA(J2000)  =  15h 47m 50.3s 
   Dec(J2000) = +20d 33' 25.4" 
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
 
The mask-weighted light curve shows a single peak starting at ~T-25 sec
and ending at ~T+100 sec.  T90 (15-350 keV) is 82 +- 13 sec (estimated error
including systematics).
 
The time-averaged spectrum from T-27.3 to T+67.2 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.78 +- 0.18.  The fluence in the 15-150 keV band is 8.0 +- 0.9 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-3.02 sec in the 15-150 keV band
is 0.4 +- 0.1 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/313116/BA/
 
This burst satisfies Sakamoto/Ukwatta Swift-BAT possible high-z criteria
(Ukwatta et al. arXiv:0802.3815):
1) Pawer Law photon index = 1.78 (PL photon index < 2)
2) 1-s peak photon flux   = 0.4 (1-s peak photon flux < 1.0 ph/cm2/s)
3) Light curve variance   = 1.1e-05 (Variance < 0.0001)
4) T90/(Peak photon flux) = 218 (T90/(Peak photon flux) > 100)
Based on a limited sample of bursts, these criteria yield an 85% chance
it has a redshift greater than 3.5.  We note that the Cucchiara (GCN Circ 7805
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 )
HET spectrum yields a z = 1.28.

K. Wiersema (U. of Leicester), J. Graham (STScI), N. Tanvir, E. Rol (U. of 
Leicester), A. Levan (U. of Warwick) and A. Fruchter (STScI) report on 
behalf of a larger collaboration:

We observed the optical afterglow of GRB 080604 (GCNC 7800, 7801) with 
Gemini-North, using the GMOS-N instrument. Spectroscopy was performed with 
the R400 grism, using 4 x 450 seconds integration time, starting at
2008 June 04, 08:58 UT.

Several absorption lines of, among others, Fe II (2382,2586,2600), Mg II 
(2796,2803) and Mg I (2026,2852) are found at a redshift of 1.416. The 
discrepancy with respect to the redshift reported in GCN 7805
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  may be due 
to provisional calibration files used for the HET reduction (Cucchiara 
priv. comm.).

We thank the Gemini staff astronomers for their support in obtaining these 
observations.

A. Cucchiara and D. B. Fox  (Penn State) report:

Based on updated calibration files we re-analyzed the GRB080604 spectrum
taken at HET (GCN 7805
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 ). The features reported in the previous GCN are no
longer significant at a 3-sigma confidence level.
Furthermore, only an upper limit of z < 2.8 can be derived from our dataset.

Our revised results are consistent with the results from Gemini-North 
spectroscopy
(Wiersama et al., GCN 7818
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 ).  The low signal to noise of our spectrum 
does not
permit detection of the absorption features associated with the z=1.416 
system
seen in those data.

M. De Pasquale (MSSL/UCL), V. La Parola (INAF-IASFPA),
F. E. Marshall (GSFC) report:
The Swift UltraViolet/Optical Telescope (UVOT) began its
first finding chart exposure of GRB080604 (La Parola
et al., GCN circ. 7800
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 ) 129 seconds after the trigger
in white filter and detected the optical afterglow (GCN
circ. 7800
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 ). The coordinates of this transient are:

  Dec:  15:47:51.68
  RA:  +20:33:28.0

  The afterglow is detected only in the white filter.
Magnitudes and 3 sigma upper limits are listed in the
table below.


  Filter  T_start(s)  T_stop(s)  Exp(s)     Magnitude

  white     129         228       99     20.1 +/- 0.2

  white     730         739       10        > 19.7

  white     869         968       99     21.0 +0.3 -0.2

  white    1479        1651       39        > 20.7

  white    5369        7031      393     21.8 +0.5 -0.4


   v        235         635      393        > 20.1

   v        769        1373      412        > 20.0

   v       1519        1701       39        > 18.8

   v       5807        7441      393        > 19.9

   v      17489       18395      885        > 20.3


   b       716          725       10        > 19.0

   b      1454         1637       39        > 19.8

   b      5191         6826      393        > 21.0


   u      691           862       39        > 19.4

   u      1430         1612       39        > 19.4

   u      4896         6621      393        > 20.7

   u     12600        13306      689        > 21.0


  uw1     667          1738       46        > 19.6

  uw1    6217         12591     1082        > 21.2


  um2     641        19090      1931        > 21.6


  uw2     745        17482      1395        > 21.4



  The values quoted above are on the UVOT Photometric System
(Poole et al, 2008, MNRAS 383,627). They are not corrected
for the expected Galactic reddening of E(B-V) = 0.049 in the
direction of the burst (Schlegel et al. 1998).

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M. Yoshida, K. Yanagisawa, D. Kuroda, Y. Shimizu, S. Nagayama,
H. Toda (OAO, NAOJ) and N. Kawai (Tokyo Tech) report on behalf of
the MITSuME collaboration:

We observed the field of GRB 080604 (La Parola et al., GCN7800
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 ) with
the 50cm MITSuME Telescope at Okayama Astrophysical Observatory on
June 4 UT. We detected a faint point source at the UVOT position
(La Parola et al., GCN7800
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 ; Rol et al., GCN7801
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 ; De Pasquale et al.,
GCN7820
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 ) in our Ic band image. Photometric calibration was done using
USNO-B1.0 catalog.

      mid-UT        exp-T      g'      Rc           Ic
------------------------------------------------------------
2008-6-4 12:41:48   49min    >20.0    >19.2    18.6 +/- 0.4
------------------------------------------------------------

X.M. Meng, Y.N. Zhu, L.P. Xin, Q.C. Feng, M. Zhai,
Y.L. Qiu, J.Y. Wei, J.Y. Hu, J.S. Deng, J. Wang,
Y. Urata and W.K. Zheng on behalf of EAFON report:

We observed GRB080604 (La Parola et al., GCN 7800
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 ) with
Xinglong 2.16m telescope + BFOSC on Jun 4, 8.024 hours
after the burst. We marginally detected the OT (La Parola et al.,
GCN 7800
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 ; Rol et al., GCN 7801
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 ; De Pasquale et al., GCN 7820
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 )
at 3 sigma level. The estimated brightness was R ~ 21.6
+/- 0.3 calibrated to USNO-A2.0 stars.
This message may be cited.

For more information about Xinglong GRBs Follow-up 
observations, please visit the website:
http://www.xinglong-naoc.org/grb/

Poonam Chandra (NRAO/UVA) and Dale A. Frail (NRAO) report on
behalf of the Caltech-NRAO-Carnegie GRB Collaboration:

"We used the Very Large Array to observe the field of view toward GRB
080604 (GCN 7800
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 ) at a frequency of 8.46 GHz on 2008 June 05.22 UT.
The GRB radio afterglow is undetected and the peak radio flux at the
SWIFT-UVOT position (GCN 7800
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 ) is -8 � 39 uJy.

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