GRB 070306

A.O. Jaunsen (Univ. Oslo), C.C. Thoene, J.P.U. Fynbo, J. Hjorth (DARK/ 
NBI),
P. Vreeswijk (ESO) report on behalf of a larger collaboration.

We observed the field of GRB 070306 (Pandey et al., GCN 6169
Loading...
 
  & GCN  
Report 38.1)
with the ESO/VLT equipped with FORS2. Observations started on 2007  
Mar 08.11 UT
(about 34 hr after the GRB) and three 1800-s spectra were acquired  
with the
300V grism covering a wavelength range of 3500-9500A.

The spectrum consists of a largely featureless continuum from about  
4000-9400A
with the exception of an apparent emission line at ~9310A. The  
emission-line
is very close to the prominent telluric skyline at 9313A, but is seen  
in each
of the three individual spectra. The lack of other detected lines in the
observed wavelength range suggests that the emission line is due to  
[O II] at
a red-shift of z=1.497. It should be cautioned, however, that this  
host galaxy
appears to be highly reddened (as already noted by Rol et al., GCN  
6174
Loading...
 
 ), which
could have an unforeseen suppression-effect on the bluer part of the  
spectrum.

We acknowledge the excellent support from the ESO/Paranal staff.

S.Maeno, E.Sonoda, R.Hara, H.Tanaka, K.Tanaka, T.Matsumura, M.Yamauchi
(University of Miyazaki)


We have observed the field covering the error region of
GRB 070306 (GCN 6169
Loading...
 
 ) with the unfiltered CCD camera on
the 30-cm telescope at University of Miyazaki.
The observation was started from 16:43:36 UT on Mar. 6
(128 s after the trigger).

We have compared our data of 30 sec exposures
with the USNO-A2.0 catalog.
There is no new source at the XRT position(GCN 6172
Loading...
 
 ).

The upper limit is as follows:
--------------------------------------------------------------
Start(UT)       End(UT)     Num. of frames      Limit (mag.)    
--------------------------------------------------------------
16:43:36        16:44:06        1               ~15.8
16:45:24        16:59:40        9               ~17.0
---------------------------------------------------------------

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
070306 (GCN 6169
Loading...
 
 ) at a frequency of 8.46 GHz on 2007 March 8th at 5.22 
UT. The GRB is undetected and the 2-sigma upper limit on the peak radio 
flux at the SWIFT-XRT position (GCN 6172
Loading...
 
 ) is 60 uJy (rms 30 uJy). 

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

D. Malesani (DARK/NBI), A.O. Jaunsen (Univ. Oslo), C.C. Thoene, J. Hjorth
(DARK/NBI), D. Paraficz (NOT), E. Leitet, and B. Caldwell (Univ. Uppsala),
report on behalf of a larger collaboration:

We observed the field of GRB 070306 (Pandey et al., GCN 6169
Loading...
 
 ) with the NOT
equipped with StanCam. Imaging was carried out in the I filter, starting
on Mar 6.946 UT (6 hr after the GRB), with a seeing of 1". The object
visible in the SDSS (SDSS J095223.31+102855.4) and reported by Rol et al.
(GCN 6174
Loading...
 
 ) and Levan et al. (GCN 6176
Loading...
 
 ) is seen in our images.

Preliminary photometry calibrated against the SDSS i-band magnitudes (Cool
et al., GCN 6170
Loading...
 
 ) provides i(AB) = 22.65+-0.30 (mean time Mar 6.954 UT).
This is consistent, within the large errors, with the value measured in
the SDSS for this object:  i(AB) = 22.8+-0.4, and indicates little
contribution from the afterglow in the I band at the epoch of our
observation.

Comparison with the magnitudes reported by Rol et al. (GCN 6174
Loading...
 
 ) further
suggests that either the host galaxy, or the afterglow, or both, are quite
red.

Using the X-ray flux at 6 hr from Nat Butler's web page
(http://astro.berkeley.edu/~nat/swift/00263361/bat_xrt.jpg; see also Page
et al., GCN 6172
Loading...
 
 ), we can measure a limit on the broad-band spectral index
beta_OX < 0.2 at 6 hr after the GRB. According to the criterion by
Jakobsson et al. (2004, ApJ, 617, L21), this burst is classified as dark.
The detection of the relatively bright host in the SDSS g filter and the
presence of a large absorbing column in the X-ray spectrum (Page et al.,
GCN 6172
Loading...
 
 ; Grupe et al. 2007, AJ, in press; astro-ph/0612104) imply the
redshift is not very large. Therefore this afterglow was likely suffering
significant dust extinction.

M. De Pasquale, S.B. Pandey (MSSL/UCL) report on the behalf of
the Swift UVOT team:

  Swift/UVOT observed the field of GRB070306 (Pandey et al. 2007, GCN 6169
Loading...
 
 )
starting 146s after the trigger with the settling expsoure.

  UVOT did not find any source inside the refined XRT error circle
(Page et al. 2007, GCN  6172
Loading...
 
 ), down to the following 3 sigma upper
limits in the White filter finding exposure and in the coadded
frames in all filters:


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

Wh_find      162      262       98         19.8

V            267    11158     1259         20.5
B            745     6257      403         21.5
U            721     6053      413         21.0
W1           697     5848      236         19.0
M2           673     5633      236         18.7
W2           773     6651      397         19.5
Wh           162     6462      512         20.7

These upper limits are not corrected for the small Galactic extinction,
corresponding to a reddening of E(B-V)=0.03 (Schlegel et al. 1998), 
towards the direction of this burst.

A.  Levan  (Warwick),  E.  Rol  (Leicester),  N.  Tanvir  (Leicester),
M. Schirmer (ING) and A.J. Castro-Tirado (IAA-CSIC Granada), on behalf
of a larger collaboration, report:

We have  re-observed  the location of GRB 070306  (Pandey et al., GCNC
6169) with  WHT+LIRIS, in  K-band. Observations  started at  00:39 UT,
7.97  hours after the  trigger.  Comparison  with our  previous K-band
observation  (Rol et  al., GCNC  6174) shows  the  suggested candidate
afterglow  to  have increased  in  brightness  by  about a  magnitude,
confirming it  to be variable and  the near infrared  afterglow of GRB
070306. Further observations are strongly encouraged.

[GCN OPS NOTE(07mar07): Per author's request, the typo in the Subject
was changed from "070603" to "070306".]

The error region of GRB 070306 (Pandey et al. GCN 6169
Loading...
 
 ; Page et
al. GCN 6172
Loading...
 
 ; Barthelmy et al. 6173) was observed with the ART-3a and
ART-3b under the partly cloudy condition.

 The imaging started at 2007 March 6, 16:43:00 UT (92 s after the
trigger) in Ic band (ART-3a), and at 16:43:24 UT (116 s after the trigger)
in J band (ART-3b). We do not detect neither optical nor near infrared
counterpart for the IR afterglow candidate (Rol et al. GCN
6174
Loading...
 
 ). From the useful data sets, we derive the following 3 sigma upper
limits for any new source within the XRT error region (GCN 6172
Loading...
 
 ),
relative to USNO-B1.0 I2 or 2MASS J magnitudes.

-----------------------------------------
StartUT         Filter  Limit   Exposure
=========================================
16:52:28        Ic      17.3    60s x 7
16:48:28        J       13.3    20s x 121
=========================================

E. Rol (Leicester), A. Levan (Warwick), N. Tanvir (Leicester), M.
Schirmer (ING), A.J. Castro-Tirado (IAA-CSIC Granada), on behalf of 
a larger collaboration, report:

"We observed the location of GRB 070306 (Pandey et al. GCNC 6169) using 
the 4.2m WHT (+LIRIS) in the JHK bands beginning at 19:57 UT, roughly 
3.27 hours after the burst. Within the X-ray localisation of Page et al. 
(GCNC 6172) we find a single source, which is also present in the SDSS 
pre-observations of the field (Cool et al. GCNC 6170). The location of 
this source is

RA:  09:52:23.31 (J2000)
DEC: +10:28:55.26 (J2000)

with errors of 0.3" in each coordinate.

Preliminary photometry implies K=17.9 +/- 0.1. Compared to the measured SDSS 
magnitudes this implies r-K~5. This is unusually red for a GRB host
galaxy and may indicate a contribution from the IR afterglow. Further
observations will be necessary to ascertain any variability."

S. D. Barthelmy (GSFC), L. Barbier (GSFC), J. Cummings (GSFC/UMBC),
E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), D. Palmer (LANL), S. B. Pandey (UCL-MSSL),
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-240 to T+962 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 070306 (trigger #263361)
(Pandy, et al., GCN Circ. 6169
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 148.097, +10.477 deg which is 
   RA(J2000)  = 09h 52m 23.3s 
   Dec(J2000) = 10d 28' 37.2" 
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 28%.
 
The mask-weighted lightcurve shows a small precursor peak starting
at T-120 through T-105 sec.  Then a second pulse (of equal amplitude)
starting at ~T-15 sec and exponentially decaying back to background
at ~T+50 sec.  Then a much larger peak starting at ~T+75 sec,
exponentially rising to a peak at T+98 sec, end then exponentially
decaying to background at ~T+220 sec.  T90 (15-350 keV) is 210 +- 10 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-118.8 to T+186.5 is best fit by a
simple power-law model.  The power law index of the time-averaged
spectrum is 1.72 +- 0.10.  The fluence in the 15-150 keV band is
5.5 +- 0.3 x 10^-6 erg/cm2.  The 1-sec peak photon flux measured
from T+98.27 sec in the 15-150 keV band is 4.2 +- 0.2 ph/cm2/sec.
All the quoted errors are at the 90% confidence level.

K.L. Page (U. Leicester) and S.B. Pandey (UCL-MSSL) report on behalf of 
the Swift-XRT team:

We have analysed the first three orbits of Swift-XRT data obtained for GRB
070306 (Pandey et al., GCN Circ. 6169
Loading...
 
 ), which includes 156 s of Windowed
Timing (WT) data and 3.3 ks of Photon Counting (PC) mode data. Using the
PC data we derive a refined position of RA, Dec = 148.0974, 10.4820, which
is equivalent to

RA(J2000)  =  09 52 23.39
Dec(J2000) = +10 28 55.3

with an estimated error radius of 3.6 arcsec (90% confidence). This lies
67 arcsec and 3.3 arcsec from the onboard BAT and XRT positions given in
GCN Circ. 6169
Loading...
 
 , respectively.

The XRT light-curve initially decays between ~155 and 165 seconds after
the trigger, followed by a small increase in count rate until 180 seconds;  
after this time, the curve shows a steep decay, with alpha_1 = 6.3 +/- 0.2
until 411 +/- 17 seconds post-trigger, at which point the decay flattens
to alpha_2 = 0.22 +/- 0.08. All error bars are at the 90% confidence
level. Note that Swift triggered on a precursor; if T0 for the light-curve
fits were to be referenced to the main peak of the burst, around 100
seconds later, this initial decay would not be so steep.

The WT spectrum can be modelled by a power-law of Gamma = 2.29 +/- 0.05,
with a total absorbing column of 3.9x10^21 cm^-2, compared to the Galactic
column of 2.94x10^20 cm^-2 in this direction. This value of NH was
calculated from the later PC data (Gamma = 2.14 +/- 0.17), when the
spectral evolution apparent during the initial steep decay has ceased. The
mean observed (unabsorbed) flux over 0.3-10 keV for this WT spectrum is
1.73e-9 (3.48e-9) erg cm^-2 s^-1.

If the decay continues with a slope of alpha = 0.22, the count rate is
predicted to be 0.21 count s^-1 at 24 hours. This corresponds to an
observed flux of 1.0e-11 erg cm^-2 s^-1 (over 0.3-10 keV), with the 
unabsorbed value being 1.9e-11 erg cm^-2 s^-1, using the spectral fit to 
the PC data.

This circular is an official product of the XRT team.

M. Uemura, A. Arai, and T. Uehara (Hiroshima Univ.), 
report on behalf of the KANATA GRB team:

  We took optical and IR images of the field of GRB070306 (GCN 6169
Loading...
 
 ) at 
16:57-17:18 UT 6 Mar. using TRISPEC attached to the KANATA 
1.5-m telescope at Higashi-Hiroshima Observatory, Japan.  
The observation was performed with a bad seeing under strong wind.  
We obtained 10 sets of Rc, J, and Ks-band images with a 123, 120, 
and 96-s exposure time, respectively.  
The images were calibrated with neighbor stars in the USNO A2.0 and 
2MASS catalog.

We cannot significantly detect the optical and IR afterglows at 
the XRT position reported in GCN 6169
Loading...
 
 . 
The limit magnitudes are below:   

UT                       Limit mag     Exp. Time
Mar. 6.71383             Rc > 20.3    123 * 10
Mar. 6.71378             J  > 17.3    120 * 10
Mar. 6.71363             Ks > 15.1     96 * 10

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 GRB070306
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/GRB070306

We supply FITS images in each of the 5 SDSS bands of a 8'x8' region  
centered
on the GRB position (ra=148.082 (09:52:19.7), dec=10.4710 (10:28:15.6);
Swift-BAT TRIGGER 263361), 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 GRB070306_sdss.calstar.dat, we report photometry and  
astrometry
of 266 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 GRB070306_sdss.objects_flux.dat and
GRB070306_sdss.objects_magnitudes.dat, we report photometry of 458
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 GRB070306_sdss.objects_flux.dat are in nanomaggies
while the magnitudes listed in GRB070306_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=0.148 mag, A_g=0.109 mag,  
A_r =
0.079 mag, A_i=0.060 mag, and A_z=0.042 mag.

The file GRB070306_sdss.spectro.dat contains a list of the 4 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. (2006, ApJS, 162, 38), when using the data or
referring to the technical documentation.

S. B. Pandey (UCL-MSSL), S. D. Barthelmy (GSFC),
J. R. Cummings (NASA/UMBC), M. De Pasquale (UCL-MSSL),
N. Gehrels (NASA/GSFC), O. Godet (U Leicester),
S. T. Holland (CRESST/GSFC/USRA), S. Immler (GSFC/USRA),
J. A. Kennea (PSU), H. A. Krimm (GSFC/USRA),
V. Mangano (INAF-IASFPA), C. B. Markwardt (GSFC/UMD),
F. E. Marshall (NASA/GSFC), A. Moretti (INAF-OAB), C. Pagani (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL), A. M. Parsons (GSFC),
T. Sakamoto (NASA/ORAU), B. Sbarufatti (INAF-IASFPA),
M. Stamatikos (NASA/ORAU), E. Troja (INAF-IASFPA) and
H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team:

At 16:41:28 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070306 (trigger=263361).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 148.082, +10.471 which is 
   RA(J2000)  =  09h 52m 20s
   Dec(J2000) = +10d 28' 17"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  We did not receive a BAT lightcurve down TDRSS
so we can not say anything about its shape.  However, this 12 second 
trigger does have a strong image significance, and as such, the 
reliability is high. 

The XRT began observing the field at 16:44:01 UT, 153 seconds after the
BAT trigger. XRT found a bright, fading and uncatalogued X-ray source
located at RA, Dec 148.0980, +10.4827 which is
   RA(J2000)  =  09h 52m 23.5s
   Dec(J2000) =  10d 28' 57.7"
with an uncertainty of 6.1 arcseconds (radius, 90% containment). 
This location is 71 arcseconds from the BAT on-board position,
within the BAT error circle. The initial flux in the 0.1s image
was 1.3e-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 162 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 3-sigma upper limit is about 19.8 mag. 
The 8'x8' region for the list of sources generated on-board also 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
0.03.