GRB 070328

C. B. Markwardt (GSFC/UMD), M. M. Chester (PSU),
J. R. Cummings (NASA/UMBC), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), J. A. Kennea (PSU), H. A. Krimm (GSFC/USRA),
F. E. Marshall (NASA/GSFC), C. Pagani (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL),
M. Stamatikos (NASA/ORAU) and E. Troja (INAF-IASFPA) report on behalf
of the Swift Team:

At 03:53:53 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070328 (trigger=272773).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 65.117, -34.069 which is 
   RA(J2000) = 04h 20m 28s
   Dec(J2000) = -34d 04' 07"
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 70 sec.  The peak count rate
was ~8000 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 03:55:21 UT, 88 seconds after the
BAT trigger. XRT found a bright, fading X-ray source located at
RA, Dec 65.1160, -34.0646 which is
   RA(J2000)  =  04h 20m 27.8s
   Dec(J2000) = -34d 03' 52.5"
with an uncertainty of 4.7 arcseconds (radius, 90% containment). 
This location is 16 arcseconds from the BAT on-board position,
within the BAT error circle. The initial flux in the 2.5s image
was 2.6e-09 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 98 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 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
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
0.04.

M. Stamatikos (GSFC/ORAU), L. Barbier (GSFC), S. D. Barthelmy (GSFC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL),
A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS),
J. Tueller (GSFC)
on behalf of the Swift-BAT team:
 
Using the data set from T-120 to T+183 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 070328 (trigger
#272773) (Markwardt et al., GCN Circ. 6224
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 ).  The BAT
ground-calculated position is RA, Dec = 65.110, -34.077 deg which is
   RA(J2000) = 4h 20m 26.4s 
   Dec(J2000) = -34d 4' 38.9" 
with an uncertainty of 0.6 arcmin, (radius, sys+stat, 90%
containment).  The partial coding was 60%.

The mask weighted light curve shows a burst profile which consists
of a rise starting at T-10, multiple spikes peaking between T+0
and T+22, and a gradual decay detected out to T+140.  T90 (15-350 keV)
is 69 +- 5 sec (estimated error including systematics).
 
The time-averaged spectrum from T-8.5 to T+133 is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.26 +- 0.04.  The fluence in the 15-150 keV band is 8.9 +- 0.2 x
10^-6 erg/cm2.  The 1-sec peak photon flux measured from T+0.78 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. Nakazawa (ISAS/JAXA), T. Murakami (Kanazawa U.),
M. Tashiro (Saitama U.), D. Yonetoku (Kanazawa U.),
Y. Nakagawa (Aoyama Gakuin U.), S. Yokota (Kanazawa U.), Y. Kodama (Kanazawa U.),
Y. Maeda (ISAS/JAXA), H. Murakami (ISAS/JAXA), S. Maeno (Miyazaki U.), N. Yamasaki (ISAS/JAXA)
M. Namiki (Osaka U.), E. Sonoda (Miyazaki U.) and K. Mitsuda (ISAS/JAXA) on behald of the Suzaku team

We will start the follow-up observation of GRB 070328 (Markwardt et al., GCN 6224
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 ) 
immediately (from around 07:20 on 28 March 2007 UT),
with the Suzaku narrow field instruments (XIS and HXD). 
The observation will continue for about 28 hours.

P.A. Evans, A.P. Beardmore, M.R. Goad, K.L. Page, R.L.C. Starling, L.G.
Tyler (U. Leicester) and C.B. Markwardt (GSFC/UMD) report on behalf of
the Swift/XRT team:

We have analysed the first two orbits of Swift-XRT data obtained for GRB
070328 (Markwardt et al., GCN Circ 6224
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 ) which includes 1.3 ks of
Windowed Timing (WT) mode data and 2.2 ks of Photon Counting  (PC) mode
data. Using the PC mode data we find the following astrometrically
corrected XRT refined position (by matching the UVOT images with the
USNO-B1 catalogue): RA, Dec = 65.1150, -34.0668 deg, which is equivalent to:

RA(J2000)  = 04 20 27.60
Dec(J2000) = -34 04 00.4

with an estimated error radius of 2.31 arcsec (90% confidence). This
lies 39.7 and 8.4 arcsec from the refined BAT and onboard XRT positions
given in GCN Circs. 6225
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  and 6224
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  respectively.

The XRT light curve begins 95 s after the trigger, and decays as a
power-law with alpha1=1.33 +0.25/-0.12 until 184 +10/-20 s after the
trigger. At this point the decay shallows to alpha2=0.28 +/-0.06. This
shallow decay continues until 629 +33/-27 s after the trigger, when the
lightcurve breaks again to alpha3=1.34 +/-0.03. All errors are quoted at
the 90% confidence level.

The WT spectrum can be modelled with a power-law of Gamma=2.22 +/-0.03
with a total absorbing column of 2.6 +/-0.4x10^21 cm-2, compared to the
Galactic value of 2.1x10^20 cm^-2. The PC mode data give almost
identical values, however with larger errors as there are less counts in
the spectrum.

If the decay continues with a slope of alpha=1.34 the count-rate at 24
hours post-trigger is predicted to be 0.029 counts s^-1. This
corresponds to an observed (unabsorbed) 0.3-10 keV flux of 2.74e-12
(4.96e-12) erg cm^-2 s^-1 .

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

F.E. Marshall (NASA/GSFC) and C.B. Markwardt (GSFC/UMD) report 
on behalf of the Swift UVOT team:

      Swift/UVOT began its initial finding chart exposure of the 
field of GRB 070328 (Markwardt et al. 2007, GCN Circ. 6224
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 ) 
98 s after the Swift/BAT trigger. No afterglow candidate is seen 
in the refined XRT error region (Evans et al. 2007, GCN Circ. 6227
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 )
in any of the early UVOT exposures. Three-sigma upper limits
for the initial finding chart exposure and for the total exposure
for each of the UVOT filters are provided below. The times
in the table are from the Swift/BAT trigger.

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

   WHITE      98        198       98        19.6
   WHITE      98       6984      567        21.1
     V        79      11988     1721        20.7
     B       682       6823      397        20.8
     U       657       6619      429        20.4
   UVW1      634       6414      432        20.7
   UVM2      609      12770     1197        21.6
   UVW2      711      11076     1101        21.5

These upper limits are not corrected for extinction.
The Galactic reddening in the direction of the burst is 
E_{B-V} = 0.04 mag (Schlegel et al. 1998).

S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, and
T. Cline on behalf of the Konus-Wind team report:

The long GRB 070328 (Swift-BAT trigger #272773:
Markwardt et al., GCN 6224
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 ; Stamatikos et al., GCN 6225
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 ),
triggered Konus-Wind at T0=14029.993 s UT (03:53:49.993).

The Konus-Wind light curve shows multipeaked structure
with a duration of ~45 s, followed by a weak tail
marginally seen up to T-T0~130 s in the 70-300 keV band.
As observed by Konus-Wind the burst
had a fluence of 5.95(-0.76, +1.06)x10^-5 erg/cm2,
and the 256-ms peak flux measured from T0+1.808 s
4.57(-0.91, +1.07)x10^-6 erg/cm2/s
(both in the 20 keV - 6 MeV energy range).

The time-integrated spectrum of the burst
(from T0 to T0+41.216 s) is well fitted (in the 20 keV - 6 MeV range)
by GRBM (Band) model for which:
the low-energy photon index is alpha = -0.99(-0.11, +0.13),
the high energy photon index beta = -1.99(-0.40, +0.18),
the peak energy Ep = 496(-117, +172) keV (chi2 = 80/77 dof).
Fitting by a power law with exponential cutoff model:
dN/dE ~ E^(-alpha) * exp(-(2-alpha)*E/Ep)
yields alpha = 1.09 +/- 0.08,
and Ep = 688(-119, +173) keV (chi2 = 88/78 dof).

All the quoted errors are at the 90% confidence level.

The Konus-Wind light curve of this GRB is available
at http://www.ioffe.rssi.ru/LEA/GRBs/GRB070328_T14029/

A. Pelangeon & J-L. Atteia (LATT-OMP) report:

We have used the spectral parameters obtained for the most intense part
of GRB 070328 -- from T0 to T-T0 ~22 sec, Konus time (V. Pal'shin, Ioffe 
Inst.,
private communication) -- observed by Konus-Wind (Golenetskii et al., 
GCNC 6230)
to compute the spectral pseudo-redshift** of this burst detected by 
SWIFT-BAT
(Markwardt et al., GCNC 6224; Stamatikos et al., GCNC 6225).

We find a pseudo-redshift pz= 2.75 +/- 0.95

We thank V. Pal'shin for having kindly performed the spectrum analysis
of the most intense part and providing us the spectral parameters.


** cf. http://www.ast.obs-mip.fr/grb/pz

S. Hong (Nihon U.), K. Yamaoka, Y.E. Nakagawa, S. Sugita (Aoyama Gakuin U.), 
M. Ohno, T. Takahashi, T. Asano, T. Uehara, Y. Fukazawa (Hiroshima U.), 
Y. Urata, M. Tashiro, K. Abe, K. Onda, Y. Sato, M. Suzuki (Saitama U.), 
T. Enoto, R. Miyawaki, K. Makishima (Univ. of Tokyo), 
M. Suzuki, T. Tamagawa, Y. Terada (RIKEN), 
K. Nakazawa, M. Kokubun, T. Takahashi (ISAS/JAXA), 
E. Sonoda, M. Yamauchi (Univ. of Miyazaki), 
on behalf of the Suzaku WAM team report:

The bright, long GRB 070328 (Markwardt et al., GCN 6224
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 ;
Stamatikos et al., GCN 6225
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 ) triggered the Suzaku Wide-band All-sky
Monitor (WAM), which covers the energy range of 50 keV - 5 MeV, at
03:53:46 UT(=T0).  The light curve shows multiple separate pulses with
the T90 duration of about 38 seconds. The fluence in 100 keV - 3 MeV
was 4.42 (-1.65, +0.54) x 10^-5 erg/cm^2, while the 1-s peak flux
measured from T0+8 was 4.28 (-2.95, +0.18) photons/cm^2/s in the same
energy range.

Preliminary result shows that the time-averaged spectrum from T0+1 to 
 T0+39 is described with a Band model as follows:

 the low-energy photon index alpha : -1.00 (-0.18, 0.21),
 the high-energy photon index beta : -1.89 (-0.43, 0.20),
 the Break energy E0 :       959 (-343, 664) keV,
 and the peak energy Epeak : 959 (-453, 1005) keV (chi^2/dof = 33.2/22).

Fitting by a power law with exponential cutoff model:

  dN/dE ~  E^{-alpha} * exp(-(2-alpha)*E/Epeak)
  alpha       1.17 (-0.15 +0.14), and
  Epeak       1126 (-426, +868) keV (chi^2/dof = 37.6/23).

All the quoted errors are at statistical 90% confidence level, while
systematic errors are not included. 

The WAM light curve of this event is available at
http://www.astro.isas.ac.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html