GRB 090401B

M. Suzuki, M. Ohno, M. Kokubun, T. Takahashi (ISAS/JAXA),
N. Kodaka, W. Iwakiri, M. Tashiro, Y. Terada, Y. Urata, A. Endo,
K. Onda, K. Morigami, T. Sugasahara (Saitama U.), T. Enoto,
K. Nakazawa, K. Makishima (Univ. of Tokyo), S. Sugita, K. Yamaoka
(Aoyama Gakuin U.), Y. E. Nakagawa, T. Tamagawa (RIKEN), T. Uehara,
T. Takahashi, Y. Fukazawa, C. Kira, Y. Hanabata (Hiroshima U.),
E. Sonoda, M. Yamauchi, H. Tanaka, R. Hara, N. Ohmori, K. Kono,
H. Hayashi (Univ. of Miyazaki), S. Hong (Nihon U.), N. Vasquez
(Tokyo Tech.), on behalf of the Suzaku WAM team, report:

The bright long GRB 090401B (Swift/BAT trigger #348152; Schady et al. 
GCN 9066
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 ; Stamatikos et al., GCN 9068
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 ) triggered the Suzaku Wide-band 
All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV 
at 08:35:24.504 UT (=T0).

The observed light curve shows a multi-peaked structure
lasting from T0+0s to T0+10s with a duration (T90) of about 9 seconds. 
The fluence in 100 - 1000 keV was 2.56 (-0.11,+0.09) x 10^-5 erg/cm^2. 
The 1-s peak flux measured from T0+7s was 21.6 (-1.5,+1.3) photons/cm^2/s
in the same energy range.

Preliminary result shows that the time-averaged spectrum from T0+0s to
T0+10s is well fitted by a single power-law with a photon index
of 2.22 (-0.09,+0.10) (chi^2/d.o.f = 24.9/25).

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

The light curves for this burst are available at:
 http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html

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

The long bright GRB 090401B (Swift-BAT trigger #348152: Schady et al., 
GCN 9066
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 ; Stamatikos et al., GCN 9068
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 ) triggered Konus-Wind at 
T0=30922.964 s UT (08:35:22.964).

The burst light curve shows a multipeaked structure with a duration of
~11 s. There is a hint of an extended soft emission.

As observed by Konus-Wind the burst
had a fluence of 6.25(-0.75, +0.78)x10^-5 erg/cm2,
and a 16-ms peak flux measured from T0+6.576 s
of 4.63(-0.86, +0.87)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst
(from T0 to T0+16.996 s) is well fitted (in the 20 keV - 10 MeV
range) by GRB (Band) model for which:
the low-energy photon index alpha = -0.78(-0.09, +0.11),
the high energy photon index beta = -2.14(-0.23, +0.15),
the peak energy Ep = 409(-60, +66) keV (chi2 = 61.8/85 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.ru/LEA/GRBs/GRB090401_T30922/

S.M. Hu, L.P. Xin, W.K. Zheng, Y.L. Qiu, J.Y. Wei,
j. Wang, J.S. Deng and J.Y. Hu on behalf of EAFON report:

We have observed GRB 090401B (Schady et al., GCN
9066
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 ; Schady & Oates, GCN 9067
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 , GCN 9074
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 )
with Xinglong TNT telescope from Apr.1, 11:25:22(UT),
3.37 hr after the burst. After combined 9*300s R
band images, no new source was found in our combined
image. The 3 sigma upper limits was obtained
to be R=19.9 mag at the mean time of 2.71 hr after 
the trigger, with the calibration to USNO-B1.0 R2 magnitude.

This message may be cited.

For more information about Xinglong GRBs Follow-up
observations, please visit the website:
http://www.xinglong-naoc.org/grb/

Poonam Chandra (RMC) 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 090401B (GCN 9066
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 ) at a frequency of 8.46 GHz on 2009 Apr. 02.15
UT. The GRB radio afterglow is undetected at the Swift-UVOT position 
(GCN 9067
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 ). The three-sigma flux density of the GRB afterglow at the
Swift UVOT position is 138 uJy.

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

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

We observed the field of GRB 090401B (Schady et al. GCN 9066
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 )
with optical three color (g', Rc and Ic) CCD camera attached to
the MITSuME 50cm telescope of Okayama Astrophysical Observatory.
We did not detect the optical afterglow reported by Schady and
Oates (GCN 9067
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 ; GCN 9074
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 ). 3-sigma upper limits to our
observation are listed below. We used GSC2.3 catalog for flux
calibration.

       Mid-UT         T(s)   EXP(s)      g'      Rc     Ic
-------------------------------------------------------------
2009-04-01 10:43:51   7706     660     >18.2   >18.1  >17.6
-------------------------------------------------------------

K.Kono, K.Noda, E.Sonoda, N.Ohmori, H.hayasi, 
A.Daikyuji, Y.Nisioka, M.Yamauchi
(University of Miyazaki)

 We have observed the field covering the error circle of
GRB090401B (Swift trigger 348152, GCN 9066
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 , Schady et al.) 
with the unfiltered CCD camera on the 30-cm telescope 
at University of Miyazaki.
The observation was started 10:47:10 UT, about 1.8 hr
after the Swift trigger time.
We have compared our data of 30 sec exposures
with the USNO-A2.0 catalog,
There is no new source at the reported position.
(GCN 9068
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 , Stamatikos et al. GCN 9070
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 , Osborne et al. )

the upper limits are as follows:
--------------------------------------------------------------
Start(UT)   End(UT)    Num. of frames    Limit (mag.)
--------------------------------------------------------------
11:41:47    11:42:17          1            16.8
11:41:47    12:32:21         43            17.7
---------------------------------------------------------------

D. Malesani, J.P.U. Fynbo (DARK/NBI), J. Heidt (Heidelberg), T. Liimets 
(Tartu Observatory), T. Pursimo (NOT), and P. Jakobsson (Univ. Iceland), 
report on behalf of a larger collaboration:

We observed the optical afterglow of GRB 090401B (Schady et al., GCN 
9066
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 ; Schady & Oates, GCN 9067
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 ), also detected by AGILE (Moretti et al., 
GCN 9069
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 ; Giuliani et al., GCN 9075
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 ). Observations were carried out in 
the R band with the Nordic Optical Telescope, starting on April 1.870 
UT, 12.3 hr after the GRB.

In a single 300 s exposure, the afterglow is clearly detected, with a 
magnitude R ~ 22.2 +- 0.1, referred to USNO-B1 stars in the neighbourhood.

We acknowledge excellent support from the NOT visiting observers and staff.

P. Schady (MSSL-UCL) and S.R.Oates (MSSL-UCL) reports on behalf of the 
Swift/UVOT team:

Swift UVOT began settled exposures of GRB090401B (Schady et al, GCN 9066
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 ) 
82 s after the burst trigger, and detected a bright optical transient at 
the position reported in by Schady et al. (GCN 9067
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 ), consistent with the 
enhanced XRT error circle (Osborne et al, GCN 9070
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 ).

The source is detected in the white, v, b and u filter, but not in any of 
UV filters, placing an upper limit on the redshift of z < 3. We note that 
the afterglow lies close to a known source, which may be contaminating our 
phometry. The light curve decays steeply at early times at a rate of 
alpha_1~1.5, and then breaks at ~T+440s to a slope of alpha_2~0.7.

Using 2.5arcsec aperture, the magnitudes and 3 sigma upper limits to our 
observations our reported below:

Filt    T_start (s)  T_stop (s)  Exp (s)  Mag/3-sig UL
white      82           232       147     16.83+/-0.02
white      874          1024      147     19.14+/-0.08
v          623          1248      78      18.31+/-0.20
v          4753         4953      197     19.10+/-0.25
b          549          1346      58      19.48+/-0.26
b          5573         5773      197     20.39+/-0.28
u          293          543       246     17.99+/-0.07
u          698          1312      58      18.67+/-0.22
uvw1       672          1297      78        > 19.42
uvm2       647          1272      78        > 18.99
uvw2       599          1387      78        > 19.39

The above magnitudes have not been corrected for the Galactic extinction 
corresponding to E(B-V) = 0.67 (Schlegel et al 1998). The photometry is on 
the UVOT flight system described in Poole et al (2008, MNRAS, 383,627)

A.Giuliani (INAF/IASF Milan), S.Cutini, C. Pittori (ASDC)
E. Moretti, F.Longo, G.Barbiellini, E.Vallazza (INFN Trieste),
M. Marisaldi, A. Bulgarelli, F. Gianotti, M. Trifoglio, G. Di Cocco,  
C. Labanti,
F. Fuschino, M. Galli, (INAF/IASF Bologna),
A. Chen, S. Mereghetti, F. Perotti, P. Caraveo (INAF/IASF Milan),
E. Del Monte, I. Donnarumma, Y.
Evangelista, M. Feroci, L. Pacciani, P. Soffitta, E. Costa,
F. Lazzarotto, I. Lapshov, M. Rapisarda(INAF/IASF Rome), A. Pellizzoni,
M. Pilia (INAF/OA Cagliari), S. Vercellone (INAF/IASF Palermo),
M. Tavani, G. Pucella,
F. D'Ammando, V.Vittorini, A. Argan, A. Trois, G. Piano, S. Sabatini
(INAF/IASF Rome), P. Picozza, A. Morselli (INFN Roma-2), M. Prest
(Universita`
dell'Insubria), P.Lipari, D. Zanello (INFN Roma-1), A.Rappoldi,  
P.Cattaneo
(INFN Pavia) and P. Giommi,  P. Santolamazza,
F.Verrecchia (ASDC) and L. Salotti (ASI), on behalf of the AGILE Team,
report:

A more refined analysis of the AGILE-GRID (Gamma-Ray Imaging  
Detector) data of
GRB 090401B (Moretti et al. GCN 9069
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 ) confirms the gamma-ray  
detection of the
GRB  at energies above 30 MeV with a statistical significance larger  
than 4
for a 10-second integration after trigger.

Fluence estimate for a 10 second integration is 0.038+/-0.011 ph/cm2
(above 30 MeV).
The GRB 090401B gamma-ray spectrum appears to be relatively hard.

An estimate of fluence in the 500 keV - 10 MeV range, as
derived from MCAL data, is (1.6 +/- 0.5)e-5 erg/cm2 in the same time  
interval.

This message may be cited.

P. Schady (MSSL-UCL) and S.R.Oates (MSSL-UCL) reports on behalf of the 
Swift/UVOT team:

Swift UVOT began settled exposures of GRB090401B (Schady et al, GCN 9066
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 ) 
82 s after the burst trigger, and detected a bright optical transient at 
the position reported in by Schady et al. (GCN 9067
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 ), consistent with the 
enhanced XRT error circle (Osborne et al, GCN 9070
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 ).

The source is detected in the white, v, b and u filter, but not in any of 
UV filters, placing an upper limit on the redshift of z < 3. We note that 
the afterglow lies close to a known source, which may be contaminating our 
phometry. The light curve decays steeply at early times at a rate of 
alpha_1~1.5, and then breaks at ~T+440s to a slope of alpha_2~0.7.

Using 2.5arcsec aperture, the magnitudes and 3 sigma upper
limits to our observations our reported below:

Filt    T_start (s)  T_stop (s)  Exp (s)  Mag/3-sig UL
white      82           232       147     16.83+/-0.02
white      874          1024      147     19.14+/-0.08
v          623          1248      78      18.31+/-0.20
v          4753         4953      197     19.10+/-0.25
b          549          1346      58      19.48+/-0.26
b          5573         5773      197     20.39+/-0.28
u          293          543       246     17.99+/-0.07
u          698          1312      58      18.67+/-0.22
uvw1       672          1297      78        > 19.42
uvm2       647          1272      78        > 18.99
uvw2       599          1387      78        > 19.39

The above magnitudes have not been corrected for the Galactic extinction 
corresponding to E(B-V) = 0.67 (Schlegel et al 1998). The photometry is on 
the UVOT flight system described in Poole et al (2008, MNRAS, 383,627)

A. Rowlinson (U. Leicester) and P. Schady (MSSL-UCL) report on behalf of
the Swift-XRT team:

We have analysed 3.7 ks of XRT data for GRB 090401B (Schady et al. GCN
Circ. 9066
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 ), from 79 s to 7.2 ks after the BAT trigger. The data
comprise 1.3 ks in Windowed Timing (WT) mode and 2.4ks in Photon
Counting (PC) mode. The enhanced XRT position for this burst was given
by Osborne et al. (GCN. Circ 9070). The light curve can be modelled with
an initial power-law decay with an index of alpha=1.145 (+/-0.020),
followed by a break at T+474 s to an alpha of 1.409 (+0.028, -0.026).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.736 (+/-0.026). The
best-fitting absorption column is 3.68 (+/-0.12) x 10^21 cm^-2, in
excess of the Galactic value of 2.3 x 10^21 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 2.13 (+/-0.11) and a
best-fitting absorption column of 4.4 (+0.5, -0.4) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 4.5 x 10^-11 (8.4 x 10^-11) erg cm^-2
count^-1.

If the light curve continues to decay with a power-law decay index of
1.409, the count rate at T+24 hours will be 0.017 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.7 x
10^-13 (1.4 x 10^-12) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00348152.

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

[GCN OPS NOTE(02apr09):  Per author's request, the typo in the Subject line
of "080401B" was changed to "090401B".]

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

Using 2409 s of XRT Photon Counting mode data and 5 UVOT
images for GRB 090401B, 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 = 95.08773, -8.97244 which is equivalent
to:

RA (J2000): 06h 20m 21.06s
Dec (J2000): -08d 58' 20.8"

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) and Evans
et al. (2009, arXiv:0812.3662).

This circular was automatically generated, and is an official product of the
Swift-XRT team.

E. Moretti, F. Longo, G. Barbiellini, E. Vallazza (INFN Trieste),  
A. Giuliani (INAF/IASF Milan), S. Cutini, C. Pittori (ASDC),
A. Chen, S. Mereghetti, F. Perotti, P. Caraveo (INAF/IASF Milan),
E. Del Monte, I. Donnarumma, Y. Evangelista, M. Feroci, L. Pacciani,
P. Soffitta, E. Costa, F. Lazzarotto, I. Lapshov, M. Rapisarda 
(INAF/IASF Rome), A. Pellizzoni, M. Pilia (INAF/OA Cagliari), 
S. Vercellone (INAF/IASF Palermo), A. Bulgarelli, F. Gianotti, 
M. Trifoglio, G. Di Cocco, C. Labanti, F. Fuschino, M. Marisaldi, 
M. Galli, (INAF/IASF Bologna), M. Tavani, G. Pucella, F. D'Ammando, 
V. Vittorini, A. Argan, A. Trois, G. Piano, S. Sabatini (INAF/IASF Rome), 
P. Picozza, A. Morselli (INFN Roma-2), M. Prest (Universita` 
dell'Insubria), P. Lipari, D. Zanello (INFN Roma-1), A.Rappoldi, 
P. Cattaneo (INFN Pavia) and P. Giommi, P. Santolamazza
F.Verrecchia (ASDC) and L. Salotti (ASI), on behalf of the AGILE Team, 
report:

The gamma ray burst 090401B (Schady et al. GCN 9066
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  & 9067) occurred 
in the field of view of AGILE, approximately 41 deg off-axis. 
This 12-s long event was triggered and localized in one dimension by 
SuperAGILE. It was detected also by the AGILE/ACS and MCAL, with 
significant detection above 2.8 MeV.
  
A preliminary analysis of the Gamma-Ray Imaging Detector (GRID) data
in temporal and spatial coincidence with the GRB shows a significant 
excess of gamma-ray events above 30 MeV at the location of the event.

A more detailed analysis of the AGILE-GRID data is in progress.
More observations of this interesting burst are strongly encouraged.
 
This message may be cited.

M. Stamatikos (GSFC/ORAU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL),
A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS),
P. Schady (MSSL-UCL), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+914 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090401B (trigger #348152)
(Schady, et al., GCN Circ. 9066
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 ).  The BAT ground-calculated position is
RA, Dec = 95.095, -8.963 deg, which is 
   RA(J2000)  =  06h 20m 22.7s 
   Dec(J2000) = -08d 57' 47.1" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 67%.
 
The mask-weighted light curve shows several FRED-like peaks with the first
starting at ~T-0.4 sec.  The brightest peak is at ~T+7 sec with a long
exponential tail out to ~T+600 sec.  T90 (15-350 keV) is 183 +- 39 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-0.1 to T+326.1 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.37 +- 0.05.  The fluence in the 15-150 keV band is 1.0 +- 0.0 x 10^-5 erg/cm2.
The 1-sec peak photon flux measured from T+6.49 sec in the 15-150 keV band
is 23.1 +- 0.5 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/348152/BA/

P.Schady (MSSL-UCL) and S.R.Oates report on behalf of the Swift/UVOT  
team

Following from the tentative UVOT afterglow detection of GRB090401B  
reported in Schady et al. (GCN 9066
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 ), we here report a fading by over  
two magnitudes between the two UVOT white finding charts, taken 792s  
apart at the following position

RA (J2000) = 06:20:21.11 (95.08775deg)
Dec (J2000) = -08:58:19.5 (-8.97199deg)

with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence),  
suggesting this to be the optical afterglow of GRB090401B. This  
position falls on a known source, making absolute magnitudes and a  
precise localisation difficult at this stage, and further data will be  
required in order to carry out source subtraction.

The values quoted above are not corrected for the Galactic extinction  
due to the reddening of E(B-V)  = 0.67 in the direction of the burst  
(Schlegel et al. 1998). All photometry is on the UVOT photometry  
system described in Poole et al. (2008, MNRAS, 383, 627).

P. Schady (MSSL-UCL), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), O. Godet (U Leicester),
H. A. Krimm (CRESST/GSFC/USRA), J. Mao (INAF-OAB),
P. T. O'Brien (U Leicester), S. R. Oates (UCL-MSSL),
J. P. Osborne (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), A. M. Parsons (GSFC), P. Romano (INAF-IASFPA),
B. A. Rowlinson (U Leicester) and H. Ziaeepour (UCL-MSSL) report on
behalf of the Swift Team:

At 08:35:25 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090401B (trigger=348152).  The BAT on-board calculated 
location is RA, Dec 95.101d, -8.963d which is 
   RA(J2000)  =  06h 20m 24s
   Dec(J2000) = -8d 57' 47"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows at least four
overlapping peaks with a total duration of ~20 seconds. 
The peak count rate was ~55,000 counts/sec (15-350 keV), at ~8 sec
after the trigger. 

The XRT began observing the field at 08:36:37.9 UT, 73.2 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 95.0889, -8.9734 which is equivalent to:
   RA(J2000)  = 06h 20m 21.33s
   Dec(J2000) = -08d 58' 24.2"
with an uncertainty of 4.7 arcseconds (radius, 90% containment). This
location is 57 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

UVOT took a finding chart exposure of 150 seconds with the White      
filter  starting 81 seconds after the BAT trigger. No credible      
afterglow candidate has  been found in the automatic analysis. The   
2.7'x2.7' sub-image covers 100% of  the XRT error circle. The typical 
3-sigma upper limit has been about 19.6 mag, although we note that 
there are two bright known sources within the XRT error circle that  
 may be confusing source detection. One of these sources appears to   
be brighter and slightly offset from the DSS position, suggesting the
possible detection of the optical afterglow. However, we shall need
more data to check for any variability. The coverage of the XRT error
circle by the  8'x8' region for the list of  sources generated
on-board is uncertain because the large number of sources  filled the
available telemetry. No correction has been made for the expected 
extinction   corresponding to E(B-V) of 0.67. 

Burst Advocate for this burst is P. Schady (ps AT mssl.ucl.ac.uk). 
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.)