GRB 130408A

A. Y. Lien (NASA/GSFC/ORAU), W. H. Baumgartner (GSFC/UMBC),
D. N. Burrows (PSU), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU),
D. Malesani (DARK/NBI), V. Mangano (INAF-IASFPA),
C. Pagani (U Leicester), K. L. Page (U Leicester) and
D. M. Palmer (LANL) report on behalf of the Swift Team:

At 21:51:38 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130408A (trigger=553132).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 134.401, -32.361 which is 
   RA(J2000) = 08h 57m 36s
   Dec(J2000) = -32d 21' 37"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 12 sec.  The peak count rate
was ~3914 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 21:54:08.6 UT, 149.9 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 134.40809, -32.36136 which is
equivalent to:
   RA(J2000)  = 08h 57m 37.94s
   Dec(J2000) = -32d 21' 40.9"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 21 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at http://www.swift.ac.uk/sper.  We
cannot determine whether the source is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 1.98
x 10^21 cm^-2 (Kalberla et al. 2005). 

UVOT data analysis is not available at this time. 

Burst Advocate for this burst is A. Y. Lien (yarleen AT gmail.com). 
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.)

A. Melandri (INAF-OAB), J. Japelj (U. Ljubljana), F.J. Virgili(LJMU),  
C.G. Mundell (LJMU) report:

The 2-m Liverpool Telescope robotically followed up GRB130408A (Swift  
trigger 553132, Lien et al., GCN 14361
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 ) 19.42 min after the GRB  
trigger time observing with SLOAN-gri filters.

The automatic LT-TRAP procedure detected an uncatalogued fading source  
candidate at:

RA=08:57:37.30
Dec=-32:21:38.90    (J2000)

with magnitude R~16.5 mag (vs USNOB1) ~20 min after the burst trigger.  
The object is clearly fading in all filters and we suggest this is the  
optical afterglow of GRB130408A.

Observations and analysis are ongoing.

M. H. Siegel (PSU) and A. Y. Lien (NASA/GSFC/ORAU) report on behalf
of the UVOT team:

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 155 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
 RA(J2000)  =	08:57:37.30 = 134.40540
 DEC(J2000) = -32:21:38.9  = -32.36081
with a 90%-confidence error radius of about 0.5 arc sec. This position is 8.4
arc sec. from the center of the XRT error circle. The estimated magnitude is
16.82 with a 1-sigma error of about  0.04. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.26.

V. Sudilovsky (MPE Garching), A. Nicuesa Guelbenzu (TLS Tautenburg) and
J.Greiner (MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 130408A (Swift trigger 553132; Lien et al.,
GCN 14361
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 ) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,
PASP 120, 405) mounted at the 2.2 m MPG/ESO telescope at La Silla
Observatory (Chile).

Observations started at 23:22 UT on April 8th, 1.5 hrs after the GRB
trigger. They were performed at an average seeing of 1.0 and at an average
airmass of 1.0.

Based integrations of 260s in the optical and 240s in the NIR taken at a
mid-time of UT 23:34, we detect the variable source reported by Melandri
et al. (GCN 14362
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 ) and Siegel & Lien (GCN 14363
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 ), with preliminary
magnitudes (all AB):

g' = 21.0 +- 0.1,
r' = 19.7 +- 0.1,
i' = 19.1 +- 0.1,
z' = 18.8 +- 0.1,
J = 18.0 +- 0.1,
H = 17.8 +- 0.1, and
K > 17.0.

The large r-g color implies a redshift of z>3. Observations are ongoing.

Given magnitudes are calibrated against GROND zeropoints in g'r'i'z' and
2MASS field stars in JHK. They are not corrected for the Galactic
foreground extinction corresponding to a reddening of E_(B-V)= 0.26 mag in
the direction of the burst (Schlegel et al. 1998).

J. Hjorth (DARK), A. Melandri (INAF-OAB), D. Malesani (DARK), 
T. Kruehler (DARK), and D. Xu (DARK) report on behalf of a 
larger collaboration:

We observed the afterglow of GRB 130408A (Lien et al. GCN 14361
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 ; 
Melandri et al. GCN 14362
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 ; Siegel et al. GCN 14363
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 ) with the 
X-shooter spectrograph on the ESO VLT, beginning approximately 
1 h 55 min after the BAT trigger.  

We detect damped Ly-alpha absorption, Ly-alpha forest, the 
Lyman break, and numerous metal lines consistent with 
a redshift of 3.758.

We thank Maria Teresa Ruiz, Avril Day-Jones, Cedric Ledoux,
Leo Rivas, Alex Correa, and Lorenzo Monaco for conducting
the observations.

N. R. Tanvir (U. Leicester), A. Cucchiara (UCSC/UCO Lick Observatory)
and S. B. Cenko (UC Berkeley) report on behalf of a larger collaboration:

We observed the afterglow of GRB 130408A (Lien et al. GCN 14361
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 ,
Melandri et al. GCN 14362
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 , Siegel et al. GCN 14363
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 ) with the GMOS-S
spectrograph on Gemini-S, beginning approximately 1 hr 56 mins after
the BAT trigger.  The integration was 4x600s and the wavelength
covered approximately 3950-6700A.

We detect numerous lines, including Lyman alpha, beta, gamma,
SII1250, SII1253, CII/CII*1260, SiII*1264, OI1302, SiII/OI*1304, SiII*1309,
CII/CII* 1334/1335, SiIV1394/1402 at a common redshift of z=3.757.

We thank D. Krogsrud for performing the observation.

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

Using 573 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 130408A, 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 = 134.40543, -32.36089 which is equivalent
to:

RA (J2000): 08h 57m 37.30s
Dec (J2000): -32d 21' 39.2"

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, MNRAS, 397, 1177).

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

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

The long-duration GRB 130408A
(Swift/BAT trigger=553132: Lien et al., GCN 14361
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 )
triggered Konus-Wind at T0=78701.184s UT (21:51:41.194)

The light curve shows a bright pulse from ~T0-0.5 to ~T0+5 s
followed by a much weaker emission pulse peaked around ~T0+12;
a total duration of the burst is ~15 s.
The emission is seen up to several MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB130408_T78701/

As observed by Konus-Wind, the burst
had a fluence of (1.2 � 0.2)x10-5 erg/cm2,
and a 64-ms peak flux, measured from T0+3.328s,
of (5.2 � 0.5)x10-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+16.640 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.4 � 0.2,
the high energy photon index beta = -2.3 � 0.2,
the peak energy Ep = 211 � 29 keV,
chi2 = 99.4/97 dof.

The spectrum at the maximum count rate (measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.70 � 0.15,
the high energy photon index beta = -2.3 � 0.3,
the peak energy Ep = 272 � 40 keV,
chi2 = 87.7/99 dof.

Assuming redshift z=3.758 (Hjorth et al., GCN 14365
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 ; Tanvir et al., GCN 14366
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 ),
and a standard cosmology (H_0=70 km/s/Mpc, Omega_M=0.3, Omega_\Lambda=0.7),
we estimate the following cosmological rest-frame parameters of the prompt
gamma-ray emission:
- the isotropic equivalent energy release E_iso = (3.3 � 0.6)x10^53 erg;
- the peak luminosity L_iso = (5.5 � 0.5)x10^53 erg/s;
- the peak energy of the time-integrated spectrum Ep_rest = 1.00 � 0.14 MeV.

All the quoted results are preliminary.

V. D'Elia (ASDC), A. Maselli  (INAF-IASFPA), V. Mangano (INAF-IASFPA),
J.A. Kennea (PSU), M.C. Stroh (PSU), D.N. Burrows (PSU), A.P. Beardmore
(U. Leicester), P.A. Evans (U. Leicester), B.P. Gompertz (U. Leicester)
and A.Y. Lien report on behalf of the Swift-XRT team:

We have analysed 6.2 ks of XRT data for GRB 130408A (Lien  et al. GCN
Circ. 14361
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 ),  from 134 s to 28.6 ks after the	BAT trigger. The data
comprise 28 s in Windowed Timing (WT) mode (the first 9 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Beardmore
et al. (GCN. Circ 14367).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=0.39 (+0.06, -0.07). At T+3999 s  the
decay steepens to an alpha of 8.0 (+0.0, -3.0) before breaking again at
T+4518 s to a final decay with index alpha=0.97 (+0.14, -0.15).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.00 (+0.08, -0.07). The
best-fitting absorption column is  consistent with the Galactic value
of 2.0 x 10^21 cm^-2 (Kalberla et al. 2005). The counts to observed
(unabsorbed) 0.3-10 keV flux conversion factor deduced from this
spectrum  is 3.9 x 10^-11 (5.6 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 2.0 x 10^21 cm^-2
Intrinsic column:    0 (+4.9, -0) x 10^21 cm^-2 at z=3.758
Photon index:	     2.00 (+0.08, -0.07)

If the light curve continues to decay with a power-law decay index of
0.97, the count rate at T+24 hours will be 0.020 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.8 x
10^-13 (1.1 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/00553132.

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

A. Breeveld (MSSL/UCL) and A. Y. Lien (NASA/GSFC/ORAU) report on behalf 
of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 130408A 
134 s after the BAT trigger (Lien et al., GCN Circ. 14361
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 ). A bright but 
rapidly fading source is detected in the initial exposures (Siegel and 
Lien, GCN Circ. 14363
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 ) with a position consistent with detections by 
Melandri et al., (GCN Circ., 14362), Sudilovsky et al., (GCN Circ., 
14364) and Beardmore et al., (GCN Circ. 14367
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 ).

The preliminary UVOT position is:
  RA(J2000)  =    08:57:37.30 = 134.40540
  DEC(J2000) =   -32:21:38.9  = -32.36081
with a 90%-confidence error radius of about 0.5 arc sec.

Preliminary detections and 3-sigma upper limits using the UVOT 
photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for 
the early and summed exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white              156          305      147.4          16.80 � 0.05
white             3708         3900      189.2          20.29 � 0.22
white             6083        10367      924.3          21.99 � 0.35
v                  134          145       10.1          15.75 � 0.15
v                 4201         4400      196.7          19.61 � 0.35
b                 3503         6078      393.2          >20.84
u                  313         5872      236.2          >20.55
uvw1              4611         4752      139.0          >19.82
uvm2              4405         4605      196.6          >19.75
uvw2              3996        21851     1748.0          >21.56

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.258 in the direction of 
the burst (Schlegel et al. 1998).

H. Dereli (UNS-CNRS-OCA), A. Klotz (IRAP-CNRS-OMP),
D. Macpherson (UWA/ICRAR), D. Coward (UWA),
B. Gendre (IRAP-CNRS-OMP), M. Boer, K. Siellez, O. Bardho (UNS-CNRS-OCA),
A. Williams (PO-UWA), R. Martin (PO-UWA)

We imaged the field of GRB 130408A detected by SWIFT
(trigger 553132) with the Zadko robotic telescope (D=100cm)
located at the observatory - Gingin, Australia.

The observations started 13.99h after the GRB trigger.
The elevation of the field increased from
87.5 degrees above horizon and weather conditions
were good.

The co addition of the six images filtered C, g, r
gives one image with an equivalent exposure time
of 540s. We did not detected the afteglow
mentioned in Melandri et al. (GCNC 14362):

t0+13.99h to t0+14.56h : Rlim = 20.5

The limiting magnitude of the zadko image is R~20.5.

Magnitudes were estimated with the nearby NOMAD1
stars and are not corrected for galactic
dust extinction.

[GNC OPS NOTE(17apr13):  Per athor's request, the GRB name
was changed from "1130408A" to "130408A".]

W. H. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), A. Y. Lien (NASA/GSFC/ORAU),
C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC),
G. Sato (ISAS), M. Stamatikos (OSU), J. Tueller (GSFC),
T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):

Using the data set from T-240 to T+960 sec from the recent telemetry 
downlink, we report further analysis of BAT GRB 130408A (trigger 
#553132) (Lien, et al., GCN Circ. 14361
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 ).  The BAT ground-calculated 
position is
RA, Dec = 134.398, -32.363 deg which is
    RA(J2000)  =  08h 57m 35.5s
    Dec(J2000) = -32d 21' 45.9"
with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment). 
The partial coding was 6%.

T90 (15-350 keV) is 28 +- 13 sec (estimated error including 
systematics).  The mask weighted light curve has a main FRED-like 
component with a rise time of about 2 sec and decline of 5 sec, peaking 
at time T+1 sec, followed by a smaller peak at T+12 sec.  There is 
possible low-level emission out to about T+33 sec.

The time-averaged spectrum from T-0.1 to T+33.5 sec is best fit by a 
simple power-law model.  The power law index of the time-averaged 
spectrum is 1.28 +- 0.26.  The fluence in the 15-150 keV band is 2.3 +- 
0.4 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+1.12 sec 
in the 15-150 keV band is 4.9 +- 1.0 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/553132/BA/

B. E. Cobb (GWU), reports:

Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
obtained optical/IR imaging of the error region of GRB 130408A
(GCN 14361
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 , Lien et al.)  over several epochs (with mid-exposure
times of 2013-04-09 00:30 UT, 02:15 UT, 03:41 UT and 2013-04-11
02:24 UT). For each epoch, several dithered images were obtained with
total summed exposure times of 15 min in V and I and 12 min in J
and K.  For the final epoch, total exposure times were 36 min in I
and 30 min in J.

The fading afterglow of GRB 130408A (e.g. GCN 14362
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 , Melandri et al.;
GCN 14363
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 , Siegel et al.; GCN 14364
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 , Sudilovsky et al.) was detected
with the following magnitudes (or 3-sigma limits):

mid-exposure
time
(hours)           I mag             J mag            K mag
2.64611         18.8 +/- 0.1    17.8 +/- 0.1     > 16.1
4.38444         19.6 +/- 0.1    18.6 +/- 0.2    16.8 +/- 0.2
5.82472         20.0 +/- 0.1    18.6 +/- 0.2     > 17.2
52.53694        > 21.5            > 19.6            ...

(Optical photometry is calibrated against USNO-B1.0 stars
and IR photometry is calibrated against 2MASS stars in the field.)

Between about 2.6 hrs and 5.8 hrs post-burst, the GRB afterglow fades
with a decay rate of approximately alpha = 1.4 (where afterglow flux is
proportional to t^-alpha).

A. Trotter, N. Frank, A. LaCluyze, D. Reichart, J. Haislip, K. Ivarsen, J. 
Moore, H. T. Cromartie, R. Egger, A. Foster, M. Nysewander, A. Oza, E. 
Speckhard, and J. A. Crain report:

Skynet began observing the field of GRB130408A (Swift trigger 553132, GCN 
14361
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 ) in BVRI beginning ~93 minutes after the burst using four of the 
PROMPT telescopes located at CTIO in Chile. A fading source is detected at 
the enhanced position reported by the Swift-XRT team (GCN 14367
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 .)

A preliminary light curve of the first two night's data from PROMPT can be 
found at: http://skynet.unc.edu/grb/grb130408a.png

K. Takaki, M. Ohno, T. Kawano, R. Nakamura, S. Furui, Y. Fukazawa
(Hiroshima U.),
M. Tashiro, Y. Terada, T. Yasuda, Y. Ishida, H. Ueno, S. Sugimoto(Saitama
U.),
K. Yamaoka (Nagoya U.), M. Yamauchi, M. Akiyama, N. Ohmori (Univ. of
Miyazaki),
S. Sugita (Ehime U.), Y. E. Nakagawa, M. Kokubun,
T. Takahashi (ISAS/JAXA), W. Iwakiri(RIKEN), Y. Hanabata (ICRR), Y. Urata
(NCU), K. Nakazawa, K. Makishima (Univ. of Tokyo) on behalf of the Suzaku
WAM team, report:

The long GRB 130408A (Lien et al., GCN14361
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 ) triggered by the
Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range of
50 keV - 5 MeV at 21:51:38 UT (=T0).

The observed light curve shows a single peak starting at T0-2s, ending
at T0+5s with a duration (T90) of about 7 seconds.
The fluence in 100 - 1000 keV was 7.18(+0.06/-0.15) x 10^-6 erg/cm^2.
The 1-s peak flux measured from T0s was 5.42(+1.37/-2.27) photons/cm^2/s
in the same energy range.

Preliminary result shows that the time-averaged spectrum from T0-2s to
T0+5s is well fitted by a single power-law with a photon index of
2.32 (+0.41/-0.34) (chi2/d.o.f = 12.19/13).

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

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