////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6189
SUBJECT: GRB 070311: a long GRB detected by INTEGRAL
DATE:    07/03/11 03:06:14 GMT
FROM:    Sandro Mereghetti at IASF/CNR  <sandro@iasf-milano.inaf.it>

S.Mereghetti, A.Paizis (IASF-Milano), D.Gotz (CEA-Saclay), I.Kreykenbohm, 
N.Mowlavi, M. Beck (ISDC, Versoix), and J. Borkowski (CAMK, Torun) on 
behalf of the IBAS Localization Team report:

A GRB lasting about 50 s has been detected by IBAS in IBIS/ISGRI data on 
March 11 at 01:52:50 UT

The coordinates (J2000)  are:
RA = 87.5411 deg   
DEC = 3.3748 deg

with an uncertainty of 2.5 arcmin (90% c.l.).

Preliminary analysis of the IBIS data indicates a peak flux of 0.9 
photons/cmq s (20-200 keV, 1 s integration time) and a fluence of 2x10e-6 
erg/cmq

A plot of the light curve will be posted at

http://ibas.mi.iasf.cnr.it/IBAS_Results.html

This message can be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6190
SUBJECT: GRB 070311: REM candidate afterglow
DATE:    07/03/11 03:09:52 GMT
FROM:    Stefano Covino at Brera Astronomical Observatory  <stefano.covino@poste.it>

S. Covino, L.A. Antonelli, L. Calzoletti, S. Campana, G. Chincarini,  
M.L. Conciatore, S. Cutini, P. D'Avanzo, V. D'Elia, F. Dalessio, F.  
Fiore, D. Fugazza, P. Goldoni, D. Guetta, C. Guidorzi, G.L. Israel,  
D. Malesani, A. Melandri, E. Meurs, S. Piranomonte, D. Rizzuto, L.  
Stella, G. Stratta, G. Tagliaferri, G. Tosti, V. Testa, S. Vergani,  
V. Vitali report on behalf of the REM team:

We observed the field of the GRB 070311 (Mereghetti et al. GCN 6189)  
with the robotic 60-cm REM telescope located at La Silla (Chile). A  
set of observations was performed automatically in the optical and  
near infrared filters (V, R, I and J, H, K, z) starting on 2007 March  
11 at 01:53:45 UT, 43 s after the Integral trigger and 51 s after the  
GRB  time.

Preliminary analysis of the whole dataset shows a possible transient  
source at coordinate:

RA: 05:50:08.21
DEC: 03:22:30.3

The approximate magnitude about 3 minutes after the burst time was H  
~ 14.3.

Further observations are in progress.

This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6191
SUBJECT: GRB 070311: PAIRITEL confirmation of variability of REM candidate 
DATE:    07/03/11 03:47:25 GMT
FROM:    Josh Bloom at UC Berkeley  <jbloom@astron.berkeley.edu>

J. S. Bloom (UC Berkeley) reports:

We analyzed the stack of images of the field of GRB 070311  
(Mereghetti et al. GCN 6189) obtained with the 1.3m PAIRITEL project  
starting 2007-03-11 02:07:17 UTC (494 second total). The source noted  
as a possible afterglow by Covino et al. (GCN 6190) is well detected  
in J and H band. A comparison to 2MASS yields a preliminary H-band  
magnitude of H=17.0 +/- 0.1.  This is 2.7 magnitudes fainter and ~14  
minutes later than the REM detection. As such, we confirm that the  
source noted by Covino et al. is indeed the afterglow of GRB 070311.

This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6192
SUBJECT: GRB 070311: Swift-XRT refined analysis
DATE:    07/03/11 12:41:53 GMT
FROM:    Cristiano Guidorzi at INAF-OAB  <cristiano.guidorzi@brera.inaf.it>

C. Guidorzi, P. Romano, S. Vergani and A. Moretti (Uni-Bicocca and OAB)
report on behalf of the Swift-XRT team:

We have analysed the first two orbits of Swift-XRT data obtained for the
GRB 070311 detected by INTEGRAL (Mereghetti et al., GCN Circ. 6189),
which includes 4.2 ks of Photon Counting (PC) mode data, beginning
7000 s after the burst trigger time.
Using the PC data we found a fading source at the position of
RA, Dec = 87.5351, 3.3750, which is equivalent to

RA(J2000)  =  05 50 08.43
Dec(J2000) = +03 22 30.0

with an estimated error radius of 3.8 arcsec (90% confidence). This lies
3.3 arcsec from the optical afterglow discovered by REM (Covino et al.,
GCN Circ. 6190) and confirmed by PAIRITEL (Bloom et al., GCN Circ. 6191).

The XRT light-curve can be fit with a single power law with index of
1.9  0.4 from 7 ks to 14 ks after the burst.

The PC photon spectrum can be modelled by a power-law of Gamma=1.6 +/- 0.2,
with a total absorbing column fixed to the Galactic value of 2.6x10^^21 
cm^-2
in this direction. Alternatively, if the absorbing column is left free 
to vary,
we find Gamma=1.9 +/- 0.4 and a column density of (3.8 +/- 1.6)x1021 cm^-2
(90% confidence).

The mean observed (unabsorbed) flux over 0.3-10 keV over this period
is 3.9e-12 (4.9e-12) erg cm^-2 s^-1.

If the decay continues with the same rate as above, the count rate is
predicted to be 1.1e-3 count s^-1 at 24 hours. This corresponds to an
observed flux of 6.5e-14 erg cm^-2 s^-1 (over 0.3-10 keV), with the
unabsorbed value being 7.9e-14 erg cm^-2 s^-1, using the spectral fit to
the PC data.

This circular is an official product of the XRT team.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6193
SUBJECT: GRB 070311: MITSuME Okayama Optical Observation
DATE:    07/03/11 14:26:37 GMT
FROM:    Michitoshi Yoshida at Okayama Astrophysical Obs  <yoshida@oao.nao.ac.jp>

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

We performed optical imaging observation (g', Rc, and Ic) of the 
field of GRB 070311 (Mereghetti et al. GCN 6189) with 50cm MITSuME
telescope at Okayama Astrophysical Observatory from UT 10:11 to 
UT 12:03 on Mar.11 2007.

We coadded 76 CCD frames for each band. Exposure time of each frame
is 1 minute. We made flux calibration using USNO B1.0 catalg. No 
new source was found around the position of the IR source reported
by Covino et al. (GCN 6190) and the XRT source reported by Guidorzi
(GCN 6192).  Three sigma limiting magnitudes of our observation are
listed below. 

----------------------------------------------------
band   mid-UT          exp.time       upper limit 
g'     Mar. 11 11:07   76 x 1 min.    20.7 mag
Rc     Mar. 11 11:07   76 x 1 min.    21.0 mag
Ic     Mar. 11 11:07   76 x 1 min.    19.2 mag
----------------------------------------------------

////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6194
SUBJECT: GRB 070311: Swift/UVOT Upper Limits
DATE:    07/03/11 14:59:18 GMT
FROM:    Stephen Holland at USRA/NASA/GSFC/SSC  <sholland@milkyway.gsfc.nasa.gov>

S. T. Holland (CRESST/USRA/GSFC) reports on behalf of the Swift UVOT
team:

      Swift/UVOT observed the field of GRB 070311 (Mereghetti, et
al. 2007, GCN Circ. 6189) starting 7004 s after the INTEGRAL/IBAS
trigger.  UVOT did not detect any source at the location of the
infrared afterglow (Covino, et al. 2007, GCN Circ. 6190), relative to
the DSS, down to the following 3 sigma upper limits.

Filter  t_start(s)  t_stop(s)  Exp(s)  Mag 3-sig UL

     V      7618       7818      197        19.5
     B      7004       7203      197        20.5
     U      8232       8432      197        20.1
   UVW1     8027       8227      197        20.0
   UVM2     7822       8022      197        20.0
   UVW2     7414       7613      197        20.3

These upper limits are not corrected for the Galactic extinction,
corresponding to a reddening of E_{B-V} = 0.76 mag (Schlegel et
al. 1998), in the direction of this burst.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6195
SUBJECT: GRB 070311: MDM Optical Detection
DATE:    07/03/11 19:03:12 GMT
FROM:    Jules Halpern at Columbia U.  <jules@astro.columbia.edu>

J. P. Halpern & E. Armstrong (Columbia U.) report on behalf
of the MDM Observatory GRB follow-up team.

"We acquired R-band observations of INTEGRAL GRB 070311
(Mereghetti et al., GCN 6189) using the MDM 1.3m telescope
on Mar. 11 02:44-03:28 UT.  The IR afterglow discovered by
Covino et al. (GCN 6190) and confirmed by Bloom (GCN 6191)
is well detected in our images.  In an uncalibrated image,
we measure a preliminary magnitude of R = 21.12 +/- 0.09
at a mean time of 02:47 UT, or 54 minutes post-burst.  This
is with respect to a comparison star with USNO-B1.0 magnitude
R2=16.67 at (J2000) 05:50:11.83, +03:22:25.2.

This message may be cited"

////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6196
SUBJECT: GRB 070311: P60 Observations
DATE:    07/03/11 20:15:25 GMT
FROM:    S. Bradley Cenko at Caltech  <cenko@srl.caltech.edu>

S. B. Cenko (Caltech) reports on behalf of a larger collaboration:

We have imaged the field of GRB070311 (Mereghetti et al., GCN 6189) with
the automated Palomar 60-inch telescope.  Observations were taken in the
i' filter at a mean epoch of approximately 3:05 11 March UT (~ 72 minutes
after the burst).  We detect a faint source at the position of the NIR
afterglow (Covino et al., GCN 6190).  Using several USNO-B objects in the
field, we measure a magnitude of I ~ 21.5.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6197
SUBJECT: GRB070311: FRAM early follow-up limit
DATE:    07/03/11 20:23:49 GMT
FROM:    Martin Jelinek at Inst.Astrophys.Andalucia,Granada  <mates@iaa.es>

Martin Jelnek, Petr Kubnek (IAA Granada, Spain) and
Michael Prouza (Columbia University New York, USA and FZU Praha, Czech Rep.)
on behalf of the FRAM team, coordinated by FZU Praha, Czech Rep.

report

"The wide field camera of the FRAM telescope, located 
at Pierre Auger observatory in Malargue, Argentina,
followed the INTEGRAL GRB 070311 (Mereghetti et al. GCN
6189, Guidorzi et al. GCN 6192, Covino et al. GCN 6190,
trigger #4166).

20s R-band (lambda_eff = 640nm) images were obtained 
starting 46.8s after the GRB (32s after receiving the
notification).

We do not detect any new source down to the limiting
magnitude R=~15.0."

this message may be cited

-- 
Martin Jelinek, +420602105255, +34617840945, sirrah.cz/mates
       Instituto de Astrofisica de Andalucia, Granada

# vim:set ai et sts=8 tw=60:

////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6198
SUBJECT: GRB 070311: RAPTOR Detection of Optical Emission
DATE:    07/03/12 04:03:22 GMT
FROM:    James Wren at LANL  <jwren@nis.lanl.gov>

J. Wren, W.T. Vestrand, P.R. Wozniak, R. White, J. Pergande
of Los Alamos National Laboratory report:
 
Our Raptor telescopes responded to Integral trigger 6146
(Mereghetti et al., GCN 6189) at 01:53:16.10 UT, 26.1 s after
the trigger and 5.9 s after receiving the GCN packet.  We detected
optical emission from the IR counterpart reported by Covino et al.
(GCN 6190) and confirmed by Bloom et al. (GCN 6191).  Due to
twilight conditions we did not detect the optical counterpart while
the gamma-rays were still being detected by Integral (3-sigma
limiting magnitude R~15.5).  As the twilight period ended we detected
the counterpart at magnitude 17.8 +/- 0.2 in a 40 s image stack with
a mid-exposure time of 01:55:22.7 UT.  Subsequent image stacks show
fading of the counterpart.  Our unfiltered magnitudes were calibrated
using the R-band magnitudes from the USNO B1.0 catalog.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6199
SUBJECT: GRB 070311: MDM Optical Follow-up
DATE:    07/03/12 16:59:07 GMT
FROM:    Jules Halpern at Columbia U.  <jules@astro.columbia.edu>

J. P. Halpern & E. Armstrong (Columbia U.) report on behalf
of the MDM Observatory GRB follow-up team.

"We observed the afterglow of INTEGRAL GRB 070311 in the
R band for a second night using the MDM 1.3m telescope.
A combined 8x600 s image with mid-epoch Mar. 12 03:33 UT
yields R = 23.05 +/- 0.10 using the same comparison star
as in GCN 6195.  The corresponding power-law decay index
is -0.53 between 0.9 and 25.7 hours.  The seeing was ~1.7".
There is possible evidence for emission extending ~1.5"
to the west of the OT.  If so, it may contribute to the
shallow decay index.

MDM images are posted at

http://www.astro.columbia.edu/~jules/grb/070311/

This message may be cited"

////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6201
SUBJECT: GRB 070311: SARA upper limit
DATE:    07/03/12 19:23:54 GMT
FROM:    Adria C. Updike at Clemson U  <aupdike@clemson.edu>

A. C. Updike, D. H. Hartmann (Clemson University) and Todd Hillwig (Valparaiso University) report on behalf of the Clemson GRB Follow-Up Team:


The .9m SARA telescope began imaging the field of INTEGRAL GRB 070311
(Mereghetti et al., GCN 6189) 1 hour and 10 minutes after the trigger.  The 
observations were comprised of 180-second and 60-second exposures in the R band.  
After stacking one hour's worth of exposures, we do not detect the afterglow 
(Covino et al. GCN 6190) to a limiting magnitude of 19.6 based
on calibration to 10 field stars from USNO B1.0 R2.

We thank Jules Halpern for providing a finding chart based on MDM observations.


The Clemson University GRB Response Site may be found at:
http://people.clemson.edu/~kgarime/burst/index.php

The SARA Homepage can be found at:
http://saraobservatory.org

This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6203
SUBJECT: GRB 070311: Optical Brightening
DATE:    07/03/13 16:23:43 GMT
FROM:    Jules Halpern at Columbia U.  <jules@astro.columbia.edu>

J. P. Halpern & E. Armstrong (Columbia U.) report on behalf
of the MDM Observatory GRB follow-up team:

"We observed the afterglow of INTEGRAL GRB 070311 in the
R band on the third consecutive night using the MDM 1.3m
telescope.  A combined 7x600 s image with mid-epoch
Mar. 13 03:10 UT shows that the OT has brightened by 0.88
mag since the previous night, reported in GCN 6199.
We measure R = 22.17 +/- 0.06 at 49.3 hours post burst,
using the same comparison star as in GCN 6195.
Considering that this location suffers 2.0 magnitudes of
Galactic extinction in the R band, it is possible that this
burst is at low redshift, and that the brightening represents
the onset of a supernova.  Spectroscopy to determine its
redshift and to search for a supernova are urged, as well
as continued photometry.

MDM images are posted at

http://www.astro.columbia.edu/~jules/grb/070311/

This message may be cited."


////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6204
SUBJECT: GRB 070311: Optical observation.
DATE:    07/03/13 23:54:45 GMT
FROM:    Giuseppe Greco at U Bologna  <giuseppe.greco2@studio.unibo.it>

G. Greco (Bologna University), F. Terra (Second University of
Roma "Tor Vergata"), C. Bartolini, A. Guarnieri, A. Piccioni
(Bologna University), G. Pizzichini (INAF/IASF Bologna),
D. Nanni (INAF/OAR and Second University of Rome "Tor Vergata"),
G. Clementini (Bologna University), S. Galleti, 
S. Bernabei (Bologna Observatory) report:

We observed the field of GRB 070311 (Mereghetti et al. GCN 6189)
with the 152 cm Loiano telescope in the Rc band in clear sky conditions. 
One 1800 sec exposure was obtained, significantly deeper than the 
DSS catalogue. The afterglow found by Covino et al.(GCN 6190) 
is detected with R = 22.3+/0.2 based on the NOMAD catalog. 
Our obsevation was done on 2007 March 13.792 UT middle exposure time.

The image, in which the comparison stars are marked, has been 
posted in our public directory from where it can be retrieved 
by sftp using 
hostname: ermione.bo.astro.it
username: publicGRB
password: GRB_bo.
directory: GRB070311



////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6206
SUBJECT: GRB 070311: Tautenburg sees afterglow fading
DATE:    07/03/14 22:09:44 GMT
FROM:    Alexander Kann at TLS Tautenburg  <kann@tls-tautenburg.de>

D. A. Kann, R. Filgas & C. Hoegner (TLS Tautenburg) report:

We observed the position of the optical/NIR afterglow (Covino et al., GCN 
6190, Bloom, GCN 6191, Halpern & Armstrong, GCN 6195) of GRB 070311 
(Mereghetti et al., GCN 6189) with the 1.34m Schmidt Telescope of the 
Thueringer Landessternwarte Tautenburg. Observing conditions were good but 
the image depth was affected by light pollution.

We obtained 6 x 600 sec images with the Rc filter. Observation midtime was 
March 14.80113 UT, which is 3.72277 days after the GRB.

At the position of the GRB afterglow, we detect a very faint source at the 
limit of the image (which is Rc > 23.4, 2 sigma). Using the same USNO 
comparison star that Halpern & Armstrong (GCN 6195) use, we derive the 
following magnitude:

dt (days)	Rc mag	dmag

3.72277		23.35	0.37

We caution that the detection is marginal and may not represent a real 
source. On the other hand, it is clear that the afterglow has faded, 
probably around one magnitude, between the rebrightening seen by Halpern & 
Armstrong (GCN 6203) and Greco et al. (GCN 6204). Thus, we conclude that 
it is probably not a low redshift GRB exhibiting the early rise of SN 
emission.

Still, the rebrightening is interesting and further deep photometric 
follow-up is warranted. No further observations are planned at TLS as we 
will not be able to reach deeper limiting magnitudes for this object.

This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6207
SUBJECT: VLA observation of GRB 070311
DATE:    07/03/15 05:41:53 GMT
FROM:    Poonam Chandra at U Virginia/NRAO  <pc8s@virginia.edu>

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
070311 (GCN 6191) at a frequency of 8.46 GHz on 2007 March 15th at 4.23
UT. The GRB is undetected and the peak radio flux at the SWIFT-XRT
position (GCN 6192) is 21+/-51 uJy.


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

////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6208
SUBJECT: GRB 070311: MDM Optical Monitoring
DATE:    07/03/15 05:43:48 GMT
FROM:    Jules Halpern at Columbia U.  <jules@astro.columbia.edu>

J. P. Halpern & E. Armstrong (Columbia U.) report on behalf
of the MDM Observatory GRB follow-up team:

"We observed the afterglow of INTEGRAL GRB 070311 in the
R band on the fourth and fifth consecutive nights using
the MDM 1.3m telescope.  The new results are summarized
as follows (using the comparison star from GCN 6195):

       -----------------------------------------
       Date(UT)  t-t0(days) Exposure R(mag) +/-
       -----------------------------------------
       Mar 14.15    3.07     7x600s  22.65  0.07
       Mar 15.14    4.06     9x600s  23.62  0.13
       -----------------------------------------

These magnitudes are in agreement with observations of
Greco et al. (GCN 6204) and Kann, Filgas, & Hoegner
GCN (6206), which together show that the rebrightening
we reported in GCN 6203 peaked on day 2.  The afterglow
is now fading rapidly.

The lastest MDM images are posted at

http://www.astro.columbia.edu/~jules/grb/070311/

This message may be cited"


////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6209
SUBJECT: GRB 070311: Late Central Engine Activity Optical Flare??
DATE:    07/03/15 06:54:08 GMT
FROM:    Alexander Kann at TLS Tautenburg  <kann@tls-tautenburg.de>

D. A. Kann (TLS Tautenburg) reports:

I wish to point out the possibility of the strong optical rebrightening 
(Halpern & Armstrong, GCN 6203) of the afterglow of GRB 070311 
(Mereghetti et al., GCN 6189) being due to a very late reactivation of the 
central engine.

Taking R Band detections (Wren et al., GCN 6198; Halpern & Armstrong, GCN 
6195, GCN 6199, GCN 6203, GCN 6208; Greco et al., GCN 6204, Kann, Filgas 
& Hoegner, GCN 6206), I find that the first three data points (from RAPTOR 
and MDM, up to a day after the GRB) are already not fit well by a single 
power law (alpha = 0.67, chi^2/d.o.f. = 30). Fitting only the first two 
points from the first hour, I find alpha = 1, and a peak magnitude of the 
rebrightening of at least 3.34 magnitudes above the extrapolation of the 
early decay.

This situation is similar to the powerful rebrightening seen for GRB 
050721 (Antonelli et al., A&A, 456, 509).

Fitting only the data points after the peak of the rebrightening (beyond 
2.7 days) I find alpha = 3.17 +/- 0.11, which is steeper than the typical 
alpha_2 = p decay seen for post-jet-break afterglows.

On the other hand, the situation is very similar to the giant X-ray flares 
seen in Swift afterglows (e.g. Burrows et al., Science, 309, 1833), which 
also often exhibit hard-to-soft evolution. Happening two days after the 
GRB, one could expect such a giant flare to have a peak energy in the 
optical range. There is also possibly a contemporaneous flare followed by 
a steep decay detected in the X-rays, as can be seen in the light curve 
posted on Nat Butler's page:

http://astro.berkeley.edu/~nat/swift/00020052/bat_xrt.jpg

While this is not conclusive evidence that this flare is due to late 
central engine activity, further deep optical monitoring of this burst is 
strongly warranted.

I thank Jules Halpern and Nat Butler for discussions.

This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6219
SUBJECT: GRB 070311, deep optical photometry
DATE:    07/03/20 19:00:21 GMT
FROM:    Peter Garnavich at U of Notre Dame  <pgarnavi@nd.edu>

X. Dai (Ohio State), P. Garnavich (Notre Dame), R. Pogge (Ohio State),
J. Hill (LBTO/UAz), X. Fan (U Ariz), J. Prieto, K. Z. Stanek (Ohio State),
R. M. Wagner (LBTO/OSU), J. Rhoads (Ariz State), E. Egami, J. Bechtold,
S. Herbert-Fort (UAz) report:

The Large Binocular Telescope (LBT) imaged the position of the GRB 070311
afterglow (Mereghetti et al, GCN 6189; Covino et al. GCN 6190) with the
LBC-blue CCD camera (http//lbc.mporzio.astro.it) and 8.4-m SX mirror on
2007 March 17.14 (UT). Ten dithered, 200 second exposures were obtained
with the Sloan-r filter in 0.65" seeing. After combining the images, the
afterglow is clearly detected. No obvious GRB host galaxy is visible. The
field is filled with clouds of faint emission due to the low Galactic
latitude of the region.

The comparison star used by Halpern & Armstrong (GCN 6195; star "A"
with USNO-B1.0 R2=16.67 mag) is heavily saturated in the LBT data,
so we obtained short exposure images of the field with LBC-blue to
calibrate a fainter star ("B") at 5:50:10.341, 03:23:02.58 (J2000).
The difference in brightness between star A and B is 2.62+/-0.01 mag.
in Sloan-r and this is confirmed with R-band images taken at MDM
(E. Armstrong, private communication). From point-spread-function fitting
photometry, the afterglow is 5.44+/-0.06 mag fainter than comparison
star B or at a brightness of R2=16.67+2.62+5.44= 24.73+/-0.06 mag.

The brightness of the afterglow 6.0 days after the GRB suggests that it
has continued a very steep decline after its optical flare
(Halpern & Armstrong GCN 6203). The afterglow has not resumed the shallow
decay it followed on the first day after the GRB. A late flare
occurring just before the break resembles GRB 000301c (Garnavich, Loeb &
Stanek 2000, ApJ, 544, 11; Rhoads & Fruchter 2001, ApJ 546, 117)
and GRB 060526 (Dai et al. 2006, astro-ph/0609269).

The light curve of 070311 is available at:
http://www.astronomy.ohio-state.edu/~xinyu/grb/070311.jpg
and uses photometry from GCNs 6198 (Wren et al. 2007), 6195
(Halpern & Armstrong 2007), 6199 (Halpern & Armstrong 2007), 6203 (Halpern
& Armstrong 2007), 6204 (Greco et al. 2007), 6206 (Kann et al. 2007), 6208
(Halpern & Armstrong 2007).

The LBT image is available at:
http://www.nd.edu/~pgarnavi/grb070311/LBT_grb070311.jpg
and a wide-field view is at:
http://www.nd.edu/~pgarnavi/grb070311/LBT_grb070311_clr.jpg

We thank Eve Armstrong for providing MDM images to calibrate
fainter comparison stars.

The LBT is an international collaboration between institutions in the
U.S.A., Italy and Germany. LBT Corporation partners are The Universities
of Arizona; Italy's Istituto Nazionale di Astrofisica; Germany's LBT
Beteiligungsgesellschaft representing the Max-Planck Society, the
Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State
University and The Research Corporation, which represents The
University of Notre Dame, University of Minnesota and University of
Virginia.

This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  6245
SUBJECT: GRB 070311, deep optical photometry
DATE:    07/04/04 19:37:04 GMT
FROM:    Peter Garnavich at U of Notre Dame  <pgarnavi@nd.edu>

P. Garnavich (Notre Dame), X. Dai,  R. Pogge (Ohio State),
J. Hill (LBTO/UAz), X. Fan (U Ariz), J. Prieto, K. Z. Stanek (Ohio State),
R. M. Wagner (LBTO/OSU), J. Rhoads (Ariz State), E. Egami, J. Bechtold,
S. Herbert-Fort (U Ariz) report:

The Large Binocular Telescope (LBT) imaged the position of the GRB 070311
afterglow (Mereghetti et al, GCN 6189; Covino et al. GCN 6190;
Dai et al. GCN 6219) with the LBC-blue CCD camera
(http//lbc.mporzio.astro.it) and 8.4-m SX mirror on 2007 March 20.13 (UT).
Fifteen dithered, 200 second exposures were obtained with the
Sloan-r filter in 0.8" seeing. After combining the images, the
afterglow is still clearly detected. Using the same calibration as
Dai et al. (GCN 6219), we estimate the brightness of the afterglow
to be R2=25.42+/-0.12 mag at 9.0 days after the burst.

The new LBT image shows evidence of a faint host galaxy 1.8" to
the west of the GRB afterglow. After subtracting the afterglow
using DAOPHOT (Stetson 1987, PASP, 99, 191) we estimate the host
brightness at R2=25.5+/-0.2 mag in a 1.1" radius aperture.

The LBT photometry 9 days after the burst shows a continued
decay from the optical flare, but the rate of fading is not as
steep. The afterglow may be approaching a more typical
post-break decay index. The light curve of 070311 is available at:
http://www.astronomy.ohio-state.edu/~xinyu/grb/070311.jpg
and uses photometry from GCNs 6198 (Wren et al. 2007), 6195
(Halpern & Armstrong 2007), 6199 (Halpern & Armstrong 2007), 6203 (Halpern
& Armstrong 2007), 6204 (Greco et al. 2007), 6206 (Kann et al. 2007), 6208
(Halpern & Armstrong 2007), 6219 (Dai et al. 2007).


The LBT is an international collaboration among institutions in the
United States, Italy and Germany. The LBT Corporation partners are:
*  The University of Arizona on behalf of the Arizona university system
*  Istituto Nazionale di Astrofisica, Italy
*  LBT Beteiligungsgesellschaft, Germany, representing the Max Planck
Society, the Astrophysical Institute Potsdam, and Heidelberg University
*  The Ohio State University
*  The Research Corporation, on behalf of The University of Notre Dame,
University of Minnesota and University of Virginia


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