GRB 060312

D. Grupe (PSU), S. Barthelmy (GSFC), D. Burrows (PSU),
N. Gehrels (GSFC), S. Hunsberger (PSU), C. Pagani (PSU),
D. Palmer (LANL)
on behalf of the Swift team:

At 01:36:12 UT, the Swift Burst Alert Telescope (BAT) triggered
and located GRB 060312 (trigger=201391).  Swift slewed immediately
to the burst. The BAT on-board calculated location is
RA,Dec 45.768, +12.820 {03h 03m 04s, +12d 49' 12"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 30 sec.  The peak count rate
was 1300 counts/sec (15-350 keV), at ~6 sec after the trigger.

The XRT began observing the burst position at 01:37:03 UT (51 s after
the BAT trigger).  The XRT found a bright, uncataloged, fading source
located at
RA(J2000) = 3h 03m 06.1s
Dec(J2000) = +12d 50' 04"
with an uncertainty of 5.0 arcseconds (90% confidence radius).
This is 58 arcseconds from the BAT position.  The initial flux
was 1.8E-9 ergs/cm2/s.

The UVOT is currently in a state where it is unable to take data.

B. E. Schaefer (Louisiana State), F. Yuan (U Mich), S.A. Yost (U Mich), R. 
Quimby (U Texas), report on behalf of the ROTSE collaboration:

ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB
060312 (Swift trigger 201391; D. Grupe et al. 2005, GCN 4859
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 ), producing
images beginning 6.0 s after the GCN notice time. An automated response
took the first image at 01:36:33.0 UT, 20.3 s after the burst trigger. We
took 10 5-sec, 10 20-sec and 74 60-sec eposures; with ongoing imaging. The
first 25 images were taken with moderate twilight and thin clouds, but
after this there appears to be no problem with the sky conditions. These
unfiltered images are calibrated relative to USNO A2.0 (R).

Comparison to the DSS (second epoch) reveals no new sources within the 
3-sigma error circle, for both single images and coadding into sets of 10; 
the field is not crowded. In particular, we see no source at the location 
of the XRT fading transient (Grupe et al. 2005). Individual images have 
limiting magnitudes ranging from 14.4-17.5; we set the following specific 
limits.

start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd?
--------------------------------------------------------------------
01:36:33.0 01:36:38.0 5 14.6 20.3 N
01:47:39.9 01:52:22.2 282 17.1 687.2 Y
01:57:23.3 02:02:06.5 283 18.3 1270.6 Y

Subject: GRB 060312: Swift XRT team refined analysis

Dirk Grupe (PSU), David N. Burrows (PSU), Claudio Pagani (PSU), on behalf
of the Swift XRT team:


We report on the analysis of the first three orbits of X-ray data of the
Swift discovered GRB 060312.
The XRT began observing the field of GRB 060312 01:36:12 UT, 51 seconds
after the BAT trigger. The following refined position was obtained:

RA(J2000) =  03h 03m 06.12s
Dec(J2000)= =12d 50' 03.5"

with an estimated uncertainty of 3.7 arcsec (90% containment). This is 0.5
arcsec from the XRT position given in GCN 4859
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  (Grupe et al.), and
87 arcsec from the BAT position reported in the same circular.

The X-ray spectrum of the Windowed Timing (WT) data can be fitted by a
single absorbed power low with a photon index Gamma=2.17+/-0.10 and an
absorption column density NH=(2.3+/_0.3)e21 cm-2. This column density is
above the Galactic value (1.4e21; Dickey & Lockman 1990) and suggests
that the burst is intrinsically absorbed. The photon counting (pc) mode
data are consistent with this result.


The light curve shows several flares in the first orbit. The underlying
afterglow decay slope withing the first 10 ks after the burst is
alpha=0.60+/-0.13. Assuming this decay slope the prediction for the flux
24 hours after the trigger is 4e-13 ergs/s/cm2.


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

H. Krimm (GSFC/USRA), L. Barbier (GSFC), S. Barthelmy (GSFC),
J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC),
D. Grupe (PSU), D. Hullinger (BYU-Idaho), C. Markwardt (GSFC/UMD), 
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC),
G. Sato (ISAS), J. Tueller (GSFC)
on behalf of the Swift-BAT team:

Using the data set from T-300 to T+302 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 060312 (trigger #201391)
(Grupe, et al., GCN 4859
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 ).  The BAT ground-calculated position is RA,Dec =
45.777,+12.825 deg {3h 3m 6.5s,+12d 49' 29.6"} (J2000) +- 0.9 arcmin,
(radius, sys+stat, 90% containment).  The partial coding was 100%.
 
The mask-weighted lightcurve shows two main peaks at T-27 and T+7 sec.
The first peak starts at T-35 sec and the second ends at ~T+30 sec.
T90 (15-350 keV) is 43 +- 3 sec (estimated error including systematics).
 
The time-averaged spectrum from T-29.4 to T+22.0 is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.35 +- 0.34, 
and Epeak of 62.8 +- 21.5 keV (chi squared 46.33 for 56 d.o.f.).  
For this model the total fluence in the 15-150 keV band is
1.8 +- 0.1 x 10^-06 erg/cm2 and the 1-sec peak flux measured from
T+5.63 sec in the 15-150 keV band is 1.5 +- 0.1 ph/cm2/sec.  
A fit to a simple power law gives a photon index of 1.85 +- 0.08
(chi squared 52.99 for 57 d.o.f.).  All the quoted errors are at the 90%
confidence level.

S. D. Hunsberger (PSU), D. Grupe (PSU), and F. Marshall (GSFC)
on behalf of the Swift UVOT team:

The UVOT took a finding chart exposure of 200 seconds with the
V filter starting 14.4 hours after the BAT trigger. No afterglow
candidate has been found in the 2.7'x2.7' sub-image which
covers 100% of the XRT error circle. The 3-sigma UL at the
XRT position is 0.9 cps or 18.0 mag. No correction has
been made for the expected extinction of about 0.6 magnitudes.