GRB 080320

F. Yuan (U Mich), E.S. Rykoff (UCSB), W. Rujopakarn (Steward), report on 
behalf of the ROTSE collaboration:

ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB 
080320 (Swift trigger 306858), producing images beginning 6.5 s after 
the GCN notice time. An automated response took the first image at 
04:38:10.5 UT, 32.1 s after the burst, under fair conditions. We took 10 
5-sec, 10 20-sec and 20 60-sec exposures. These unfiltered images are 
calibrated relative to USNO A2.0 (R). Imaging is on going.

Comparison to the DSS (second epoch) reveals no new sources within the 
3-sigma Swift/BAT error circle or the XRT error circle, for both single 
images and coadding into sets of 10. Individual images have limiting 
magnitudes ranging from 16.4-17.5; we set the following specific limits.

start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
04:38:10.5   04:38:15.5         5     16.5           32.1       N
04:38:10.4   04:39:17.5        67     18.1           32.0       Y

D. Grupe (PSU), D. N. Burrows (PSU), M. M. Chester (PSU),
N. Gehrels (NASA/GSFC), S. Immler (CRESST/GSFC/UMD),
J. A. Kennea (PSU), C. B. Markwardt (CRESST/GSFC/UMD),
D. M. Palmer (LANL), A. M. Parsons (GSFC), J. L. Racusin (PSU),
M. Stamatikos (NASA/ORAU), T. N. Ukwatta (GSFC/GWU),
D. E. Vanden Berk (PSU) and L. Vetere (PSU) report on behalf of the
Swift Team:

At 04:37:38 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080320 (trigger=306858).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 177.780, +57.144 which is 
   RA(J2000) = 11h 51m 07s
   Dec(J2000) = +57d 08' 38"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a FRED
structure with a duration of about 25 sec.  The peak count rate
was ~1200 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 04:40:29.4 UT, 171.0 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 177.73502,
57.15776 which is equivalent to:
   RA(J2000)  = 11h 50m 56.41s
   Dec(J2000) = +57d 09' 27.9"
with an uncertainty of 2.5 arcseconds (radius, 90% containment). This
location is 100 arcseconds from the BAT onboard position, within the
BAT error circle. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
1.35e+20 cm^-2 (Kalberla et al. 2005), so we cannot constrain the
redshift at this time using the relation from Grupe et al. (2007). A
summary of the promptly downlinked data is given at
http://www.swift.ac.uk/sper/306858/. 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 177 seconds after the BAT trigger. No afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of
the BAT error circle but does not overlap 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
BAT 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
0.01. 

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.)

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
GRB080320 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/GRB080320

We supply FITS images in each of the 5 SDSS bands of a 8'x8'
region centered on the GRB position (ra=177.780 (11:51:07.2),
dec=57.1440 (57:08:38.4); Swift-BAT Trigger 306858), 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 GRB080320_sdss.calstar.dat, we report photometry
and astrometry of 178 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 GRB080320_sdss.objects_flux.dat and
GRB080320_sdss.objects_magnitudes.dat, we report photometry
of 349 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 GRB080320_sdss.objects_flux.dat are in nanomaggies while
the magnitudes listed in GRB080320_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=0.079 mag, A_g=0.058 mag,
A_r = 0.042 mag, A_i=0.032 mag, and A_z=0.023 mag.

The file GRB080320_sdss.spectro.dat contains a list of the
6 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, PASP 118, 733).  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. (2007, ApJS, 172, 634),
when using the data or referring to the technical documentation.

Martin Jelinek, Alberto J. Castro-Tirado (IAA-CSIC Granada),
and Jorge Pl� (IAC La Laguna), on behalf of a larger
collaboration,

report:

"We observed the XRT localization of the GRB080320 (Grupe et
al. GCN 7473
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 ) with the 0.8m IAC80 at Obs. del Teide in
Tenerife, with exposure mean time 5:33UT (i.e. 1hour after
the GRB). We do not detect any source within or near the XRT
error box down to the limiting magnitude of  R~20.0."

this message may be cited

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

Using 995 s of overlapping XRT Photon Counting mode and UVOT
data for GRB 080320, 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 = 177.73526, +57.15746 which is equivalent
to:

RA (J2000): 11h 50m 56.46s
Dec (J2000): +57d 09' 26.8"

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.

N. R. Tanvir, P. T. O'Brien, J. Osborne and P. Evans (U. Leicester) note:

We note here is an SDSS source in the centre of the UVOT enhanced
XRT error circle (GCN 7479
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 ).  The source is reported as having r=22.38
and a photometric redshift estimate of z=0.35+/-0.13 according to
the SDSS web site:

 http://cas.sdss.org/dr6/en/tools/explore/obj.asp?id=587731890577605599

A provisional analysis of Gemini-N/GMOS observations obtained about 90
mins post-burst also shows this source (at roughly the same magnitude),
but nothing else in the error circle.

If this is the host, then the photo-z is interestingly low, and the burst
interestingly faint in the optical.

Further analysis is ongoing.

N. R. Tanvir, E. Rol (U. Leicester), A. Stephens (Gemini), report
on behalf of a larger collaboration:

We obtained griz observations of the field of GRB 080320 starting
approximately 80 mins post-burst with Gemini-N/GMOS.  Conditions were
rather poor, with some cirrus, which reduced the depth of the images.
A 2nd epoch of i-band imaging was obtained 9 hours post-burst.

A fading point source is seen in both i-band images, somewhat outside
the enhanced XRT error circle (GCN 7479
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 ).  The position (J2000) of
this counterpart, with respect to nearby SDSS stars, is (to 0.25
arcsec in each coordinate):

 RA =  11 50 56.427
 dec= +57 09 23.90

The SDSS galaxy noted in GCN 7480
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  is about 3 arcsec away from the
counterpart, and therefore probably unrelated to it.

Preliminary photometry (again relative to SDSS field stars) gives
i'=22.9, and fading between the epochs of 0.37+/-0.03 mag. This
relatively slow rate of fading could indicate a contribution from a
host galaxy.  The counterpart is seen in the z-band, but is absent (or
very faint) in the r-band image with a limit of about r~24.  This red
r-i colour could be explained by a Lyman-alpha break if the redshift
is z~4.5 to 5.

Further analysis is ongoing.

D. Malesani (DARK), A. A. Djupvik, J. Niemela (NOT), J. P. U. Fynbo 
(DARK), report on behalf of a larger collaboration:

We observed the field of GRB 080320 (Grupe et al., GCN 7473
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 ) with the 
Nordic Optical Telescope. R-band observations were carried out with the 
StanCam instrument, with mean time 2008 March 20.254 UT (1.47 hr after 
the GRB).

We do not detect any object at the position of the afterglow reported by 
Tanvir et al. (GCN 7488
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 ) nor inside the XRT error circle (Goad et al., 
GCN 7479
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 ). Our limiting magnitude is R=22 (based on USNO-B1), consistent 
with the nearly-simultaneous measurement of Tanvir et al. (GCNs 7480
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 , 7488
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 ).

Adria C. Updike, Brian C. Donehew, Ian Oliver, and Dieter H. Hartmann
(Clemson University) report:

We used the Kitt Peak 2.1m telescope and the FLAMINGOS instrument in NIR
imaging mode to obtain J-band exposures of the field of GRB 080320 (GCN
7473
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 , Grupe et al.). In 80 minutes of stacked exposures, we marginally
detect the
afterglow (GCN 7488
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 , Tanvir et al.) at J ~ 20 (using a 2MASS comparison
star located at RA=11:50:47.4, Dec=+57:10:07.41).  The midtime of the
stacked exposures was ~3 hours after the trigger.  Further analysis is
ongoing.

This message may be cited.

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

The robotic 0.6-m Super-LOTIS telescope began observing the error box
of GRB 080320 (Swift Trigger 306858, Grupe et al. GCN 7473
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 ) at
04:38:34.3 UT, 56.3 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 any variable sources or afterglow candidates within
the refined XRT error box (Goad et al. GCN 7479
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 ) or at the location of
the OT candidate (Tanvir et al. GCN 7488
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 , Updike et al. GCN 7491
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 ) in
any of our single exposures or combined exposures to the following
3-sigma limiting magnitudes:

t_start (UT)    t_end (UT)     exp t (s)     t_start-t_0 (s)    Limit
       coadd?
----------------------------------------------------------------------------------------------------------
04:38:34.3     04:38:44.3     10.0           56.3                R > 17.7      N
04:39:59.3     04:40:19.3     20.0           141.3              R > 18.3      N
04:42:13.7     04:43:13.7     60.0           275.7              R > 19.0      N
04:38:34.3     04:39:52.6     50.0           56.3                R > 18.7      Y
04:39:59.3     04:42:07.0     100.0         141.3               R > 19.4      Y
04:42:13.7     04:47:41.5     300.0         275.7               R > 20.0      Y

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


The XRT began observing the field of GRB 080320 (trigger=306858; Grupe 
et al.,
GCN Circ 7473
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 ) at 04:40:29.4 UT, 171.0 seconds after
the BAT trigger.

The astrometrically corrected X-ray position (using the XRT-UVOT 
alignment and
matching UVOT field sources to the USNO-B1 catalogue) is: RA, Dec = 
177.7353,
+57.1574 which is equivalent to:

RA (J2000):  11 50 56.46
Dec (J2000): +57 09 26.8

with an uncertainty of 1.4 arcsec (radius, 90% confidence).


The 0.3-10 keV X-ray light curve starts with three flares up to 12 
counts/s.
The afterglow decays very fast and started to flatten at the end of the 
first orbit
about 1000 s after the burst. The light curve is currently decaying with a
shallow decay slope of 0.63 +/- 0.05.

The spectrum of the Photon Counting data of the first three orbits
can be well fitted by an absorbed single powerlaw with a photon
index Gamma = 1.96 +/- 0.20 and column density of (6.9 +/- 4.0)e20 cm-2
This is slightly in excess of the Galactic column density of 1.35e20 
cm-2 in this direction.
Using this spectrum we estimated a count rate to flux conversion of
 1 count/s converts to 4.22e-11 ergs/cm2/s.

If the underlying powerlaw decay continues as is, we predict an XRT 
count rate
of 0.026 counts/s at T+24 hours or 1.1e-12 ergs/s/cm2.

K. McLean (GSFC/UMD), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC),
E. Fenimore (LANL), N. Gehrels (GSFC), D. Grupe (PSU),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL),
A. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), 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-119 to T+183 sec from the telemetry downlinks,
we report further analysis of BAT GRB 080320 (trigger #306858)
(Grupe, et al., GCN Circ. 7473
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 ).  The BAT ground-calculated position is
RA, Dec = 177.763, 57.162 deg, which is 
   RA(J2000)  =  11h 51m 03.1s 
   Dec(J2000) = +57d 09' 42.6" 
with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 93%.
 
The mask-weighted light curve shows a FRED peak starting at ~T-5 sec,
peaking at ~T+0, and ending at ~T+35 sec.  There a possible (3 sigma)
precursor peak at ~T-55 sec with a width of about 5 sec.
T90 (15-350 keV) is 14 +- 2 sec (estimated error including systematics).
 
The time-averaged spectrum from T-1.7 to T+13.8 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.70 +- 0.22.  The fluence in the 15-150 keV band is 2.7 +- 0.4 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.15 sec in the 15-150 keV band
is 0.6 +- 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/306858/BA/

A. Melandri (Liverpool JMU), A. Gomboc (Ljubljana), C. Guidorzi
(INAF-OAB), R.J. Smith, I.A. Steele, C.G. Mundell, D.F. Bersier, M.F. 
Bode, M.J. Burgdorf, S. Kobayashi, C.J. Mottram (Liverpool JMU),
P. O'Brien, N. Bannister, N. Tanvir (U. Leicester) report on behalf of 
larger GRB collaboration :


On 2008 March 20 (06:00:59UT) we observed the field of GRB 080320
(trigger=306858, Grupe et al. GCN 7473
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 ) with the Faulkes Telescope
North. Observations constited of 10x300s exposures acquired using the
SDSS-i' filter.

In our coadded frame we do not detect any source inside the refined XRT
error box (Goad et al. GCN 7479
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 ) or at the position of the faint infrared
afterglow reported by Tanvir et al. (GCN 7488
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 ) and Updike et al. (GCN
7491
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 ), down to the limiting magnitude reported below.


Telescope        Filter  DT_mean[min]  Exposure(s)    M_lim (3-sigma)

----------------------------------------------------------------------
Faulkes North      i'       108.4         3000         20.4
----------------------------------------------------------------------