GRB 080520

D. Grupe (PSU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
A. P. Beardmore (U Leicester), J. R. Cummings (NASA/UMBC),
C. Gronwall (PSU), S. T. Holland (CRESST/USRA/GSFC),
J. A. Kennea (PSU), V. Mangano (INAF-IASFPA),
K. M. McLean (GSFC/UMD), J. P. Osborne (U Leicester),
D. M. Palmer (LANL), D. Perez (U Leicester), T. Sakamoto (NASA/UMBC),
M. Stamatikos (NASA/ORAU), M. C. Stroh (PSU) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:

At 22:20:24 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080520 (trigger=312047).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 280.192, -55.004 which is 
   RA(J2000)  =  18h 40m 46s
   Dec(J2000) = -55d 00' 13"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows two peaks
with a duration of about 15 sec.  The peak count rate
was ~700 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 22:22:04.3 UT, 99.5 seconds after
the BAT trigger.  Using promptly downlinked data we find a bright uncatalogued X-ray
source. The position, astrometrically enhanced by aligning promptly available
UVOT field source  positions to the USNO-B1 catalogue, is RA,Dec = 280.19337, -54.99181
(degrees) which is equivalent to:

RA  (J2000.0) = 18 40 46.41
DEC (J2000.0) = -54 59 30.5

with an uncertainty of 2.8 arcsec (radius, 90% containment). 
This position is 44.0 arcsec from the BAT position, inside the BAT
error circle. 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 106 seconds after the BAT trigger. There is a candidate
afterglow in the rapidly available 2.7'x2.7' sub-image at

RA  (J2000.0) =  18:40:46.41
Dec (J2000.0) = -54:59:31.1

with an estimated uncertainty of 0.6 arcsec (90%, radius). 
The estimated magnitude is white = 19.8 +/- 0.1 mag. No correction has been
made for Galactic extinction. 

Burst Advocate for this burst is D. Grupe (grupe AT astro.psu.edu). 
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.)

Dirk Grupe reports on behalf of the Swift-XRT team:


The XRT began observing the field of GRB 080520 (trigger=312047; Grupe 
et al.,
GCN Circ 7753
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 ) on 2008-May-20 at 22:22:04.3 UT, 99.5 seconds after
the BAT trigger.


The 0.3-10 keV X-ray light curve of the first two orbits
displays a single decay with a slope alpha=1.04+/-0.07.  

The spectrum of the Photon Counting data of the first two orbits
can be well fitted by an absorbed single powerlaw model with a photon
index Gamma = 2.12 +/- 0.20 and a column density consistent with the 
Galactic
value of 6.48e20 cm-2

If the underlying powerlaw decay continues as is, we predict an XRT 
count rate
of 1e-3 counts/s at T+24 hours or 5e-14 ergs/s/cm2 and at T+48 hours 4e-4
counts/s or 2e-14 ergs/s/cm2.

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

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

Using 497 s of overlapping XRT Photon Counting mode and UVOT
data for GRB 080520, 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 = 280.19385, -54.99160 which is equivalent
to:

RA (J2000): 18h 40m 46.52s
Dec (J2000): -54d 59' 29.8"

with an uncertainty of 1.9 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.

This is a multi-part message in MIME format.

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A.Rossi, R. Filgas (Tautenburg), T. Kruehler, J. Greiner (MPE Garching),
S. Klose (Tautenburg), A. Kupcu-Yoldas, A. Yoldas, and
G. Szokoly (Eoetvoes Univ. Budapest and MPE)
report on behalf of the GROND team:

We observed the field of GRB 080520 observed by SWIFT (D. Grupe et al. GCN 7753
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 )  simultaneously in grizJHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPI/ESO telescope at La Silla (Chile).
Observations started at 01:19 UT, about 2.9 hrs after the GRB.
At this time, the GRB location was becoming visible at 20 degrees
above horizon.
Observations were performed at relatively high airmass and under challenging sky conditions with cirrus and a bright moon.

The afterglow candidate detected by UVOT, reported by D.Grupe et al. 
(GCN 7753
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 ) is detected in g'r'i'z' J , implying a redshift smaller than 3.5.

We estimate a rough magnitude of i'=21.38 +/-0.4 at 3.25 hrs after the GRB, 
calibrated against USNO-B field stars. We stop observations due to bad sky
conditions.

--bound1211350827--

Pall Jakobsson (U. Hertfordshire), Johan P. U. Fynbo,
Daniele Malesani, Jens Hjorth and Bo Milvang-Jensen
(DARK, NBI) report on behalf of a larger collaboration:

Using FORS2 on the Very Large Telescope, we have obtained
3*30 min spectra (grism 300V) of the optical afterglow of
GRB 080520 (Grupe et al., GCN 7753
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 ). The acquisition image
shows it to have R = 23.0 +/- 0.5 on May 21.235 (7.3 hours
post burst).

A firm upper limit of z < 2.4 can be placed on the redshift
of GRB 080520 from the lack of Ly-alpha forest lines in the
spectrum of the afterglow. This is consistent with the GROND
observations (Rossi et al., GCN 7756
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 ).

The combined spectrum shows an emission line, presumably
corresponding to [O II] 3727 at z = 1.545. At this redshift
we also find the Mg II doublet (2796,2803) and Mg I (2852).

We thank the Paranal staff for excellent support, especially
Yuri Beletsky and Patricia Guajardo.

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

The Swift/UVOT began settled observations of the field of GRB 080520, 105s 
after the BAT trigger (Grupe et al., GCN 7753
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 ). We detect the afterglow in 
the white, v filters at the position:

RA(J2000.0)  =  18:40:46.30
DEC(J2000.0) = -54:59:31.0

with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence).
This position is consistent with the UVOT enhanced XRT position (Goad et 
al., GCN 7755
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 ).

UVOT magnitudes and 3 sigma upper limits are reported below for the single
and coadded images:

Filter    Tstart(s)  Tstop   Expo(s)   Magnitude/3sigUL
-----------------------------------------------------
white       105      204    98       19.59 +/- 0.12
white       858      958    98       20.58 +/- 0.28
v           211      610    400      20.26 +/- 0.38
v           964      1299   330      19.96 +/- 0.45
b           691      6273   216      > 20.92
u           666      6068   197	     > 20.60
w1          641      5862   236      > 20.33
m2          617      7079   418      > 20.38
w2          720      6684   216      > 20.25
-----------------------------------------------------

These magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E{B-V} = 0.08 mag (Schlegel et al.
1998). The photometry is on the UVOT flight system described in Poole
et al. (2008, MNRAS, 383, 627).

T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
D. Grupe (PSU), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD),
K. McLean (GSFC/UMD), D. Palmer (LANL), G. Sato (GSFC/ISAS),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 080520 (trigger #312047)
(Grupe, et al., GCN Circ. 7753
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 ).  The BAT ground-calculated position is
RA, Dec = 280.179, -54.964 deg which is 
   RA(J2000)  =  18h 40m 42.9s 
   Dec(J2000) = -54d 57' 51.2" 
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
 
The mask-weighted light curve shows a single peak starting at T_zero and
ending at ~T+3 sec.  T90 (15-350 keV) is 2.8 +- 0.7 sec (estimated error
including systematics).
 
The time-averaged spectrum from T-0.3 to T+2.8 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.90 +- 0.51.  The fluence in the 15-150 keV band is 5.5 +- 1.4 x 10^-8 erg/cm2.
The 1-sec peak photon flux measured from T-0.31 sec in the 15-150 keV band
is 0.5 +- 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/312047/BA/
 
We note that the fluence ratio in a simple power-law fit between the
25-50 keV band and the 50-100 keV band is 1.88.  This fluence ratio is larger
than 1.32 which can be achieved in the Band function of alpha=-1.0, beta=-2.5,
and Epeak=30 keV.  Thus, preliminary analysis shows that Epeak of the burst
is very likely around or below 30 keV.  Therefore the burst can be classified
as an X-ray flash (e.g. Sakamoto et al. ApJ, 679, 570).

D. Malesani (DARK), P. Jakobsson (Univ. Hertfordshire), J. P. U. Fynbo, 
J. Hjorth, B. Milvang-Jensen (DARK), report on behalf of a larger 
collaboration:

We further inspected our images and spectra (Jakobsson et al., GCN 7757
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 ) 
of the afterglow of GRB 080520 (Grupe et al., GCN 7753
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 ). A faint 
extension is visible in our images (seeing 0.7") underlying the 
afterglow emission, which may be due to a relatively bright host galaxy. 
This is consistent with the 2D trace of the spectrum, which reveals the 
proposed [O II] line to be also spatially extended.

Using the relations by Kennicutt (1998, ARA&A, 36, 189), the flux of the 
[O II] line (not corrected for extinction) corresponds to a star 
formation rate (SFR) of approximately 15 M_Sun/yr.

Aquib Moin (Curtin Institute of Radio Astronomy / Australia Telescope
National Facility), Steven Tingay (Curtin Institute of Radio Astronomy),
Chris Phillips (Australia Telescope National Facility), Gregory Taylor
(University of New Mexico), Mark Wieringa (Australia Telescope National
Facility) and Ralph Martin (Perth Observatory) report:

We observed the BAT refined position of the GRB 080520 (GCN 7761
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 ) at 4.8
GHz with the Australia Telescope Compact Array (ATCA) on June 01, 2008
between 08:41:15 UT and 09:45:25 UT.

We did not detect a radio source at the BAT position of the GRB 080520
(GCN 7761
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 ). The radio flux density at the GRB position is 0.297 +/-
0.217 mJy at 4.8 GHz (1-sigma).

The Australia Telescope Compact Array (/ Parkes telescope / Mopra
telescope / Long Baseline Array) is part of the Australia Telescope
which is funded by the Commonwealth of Australia for operation as a
National Facility managed by CSIRO.

See field image at:

http://cira.ivec.org/dokuwiki/doku.php/grb/grb_080520_field_image