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GRB 090813

GCN Circular 9781

Subject
GRB 090813: Swift detection of a burst
Date
2009-08-13T04:26:12Z (16 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
J. R. Cummings (NASA/UMBC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
C. Gronwall (PSU), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL),
M. Stamatikos (OSU/NASA/GSFC) and T. N. Ukwatta (GSFC/GWU) report on
behalf of the Swift Team:

At 04:10:43 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090813 (trigger=359884).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 227.017, +88.573 which is 
   RA(J2000) = 15h 08m 04s
   Dec(J2000) = +88d 34' 21"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows two peaks
with a duration of about 8 sec.  The peak count rate
was ~9000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 04:12:01.7 UT, 78.7 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 225.8016, +88.5687 which is equivalent to:
   RA(J2000)  = 15h 03m 12.38s
   Dec(J2000) = +88d 34' 07.3"
with an uncertainty of 6.1 arcseconds (radius, 90% containment). This
location is 110 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. 

The initial flux in the 2.5 s image was 6.26e-10 erg cm^-2 s^-1 (0.2-10
keV). 


UVOT took a finding chart exposure of 150 seconds with the White filter
starting 87 seconds after the BAT trigger. No credible 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 19.6 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
0.17. 




Burst Advocate for this burst is J. R. Cummings (jayc AT milkyway.gsfc.nasa.gov). 
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.)

GCN Circular 9782

Subject
GRB 090813: optical candidate from 1.23m CAHA telescope
Date
2009-08-13T05:01:48Z (16 years ago)
From
Javier Gorosabel at IAA-CSIC <jgu@iaa.es>
J. Gorosabel, V. Terron, M. Fernandez, P. Kubanek, M. Jelinek, A.J.
Castro-Tirado (IAA-CSIC), on behalf of a larger collaboration, report;

We have  carried out  I-band observations of  the XRT position  of GRB
090813  (GCN  9781) with  the  1.23m  telescope  of Calar  Alto.   The 
observations started  at 04:18  UT (437 s  after the GRB  trigger). We
detect an object  with a rough magnitude of I~17 coincident with the XRT
position  no present  on the  DSS. We propose  that object  as the optical
afterglow of GRB 090813.

GCN Circular 9783

Subject
GRB 090813: P60 Optical Afterglow Confirmation
Date
2009-08-13T05:25:55Z (16 years ago)
From
S. Bradley Cenko at Caltech <cenko@srl.caltech.edu>
S. B. Cenko (Caltech) reports on behalf of a larger collaboration:

We have imaged the field of GRB090813 (Cummings et al., GCN 9781) with the
automated Palomar 60 inch telescope.  Observations were taken in the Sloan
r', i', and z' filters beginning at approximately 4:12 UT (~ 2 minutes
after the burst).

Inside the XRT error circle we find a fading point source with coordinates
(J2000.0):

   RA: 15:03:08.48
   Dec: +88:34:05.5

with an estimated error of ~ 0.3" in each coordinate.  Presumably this is
the same source identified by Gorosabel et al. (GCN 9782).

With reference to several USNO-B1 sources in the field, we measure the
following I-band magnitudes for the afterglow:

UT (mid-point)     Exposure (s)       Magnitude
----------------------------------------------------------------
04:15:47           60                 17.8
04:20:33           60                 18.2

Further observations are planned.

GCN Circular 9784

Subject
GRB 090813: Liverpool Telescope afterglow confirmation
Date
2009-08-13T06:17:10Z (16 years ago)
From
James Smith at ARI,Liverpool John Moors U <rjs@astro.livjm.ac.uk>
R.J. Smith, I.A. Steele, Z. Cano (Liverpool JMU), C. Guidorzi (U.
Ferrara),  C.G. Mundell, A. Melandri, S. Kobayashi, C.J. Mottram,
D.F. Bersier,  (Liverpool JMU), A. Gomboc (U. Ljubljana), report on behalf 
of a large collaboration:

On 2009 August 13 at 04:13:40.8 UT the 2-m Liverpool Telescope
automatically began observing the Swift GRB 090813 (Cummings et al.,
GCN Circ. 9781) using the r' and i' filters. We confirm the detection by 
Gorosabel et al (GCN 9782) and Cenko et al (GCN 9783) of an optical 
counterpart to the XRT source. We measure a position of 15:03:05.9 
88:34:05.5 J2000 with an uncertainty of 1arcsec and further, confirm the 
OT is fading. Ths position is 1 arcsec from and therefore conssitent from 
that reported by Cenko et al (GCN 9783).


Mid Time     Delay from BAT   Total Exp  Filter     Mag
(UT)	     trigger (min)      (s)
----------------------------------------------------------
04:13:45.8      3.05		10	R	19.36 +/- 0.13
04:18:11.9      7.48		120	R	19.90 +/- 0.05
04:20:58.2     10.25		120	I	18.11 +/- 0.02
----------------------------------------------------------

Both astrometry and photometry is calibrated and quoted with respect
to USNO-B.

Further observations are ongoing.

GCN Circular 9785

Subject
GRB 090813: Enhanced Swift-XRT position
Date
2009-08-13T11:51:40Z (16 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 615 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 090813, 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 = 225.77887, +88.56795 which is equivalent
to:

RA (J2000): 15h 03m 6.93s
Dec (J2000): +88d 34' 04.6"

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.

GCN Circular 9786

Subject
GRB090813: Swift/UVOT upper limits
Date
2009-08-13T13:16:46Z (16 years ago)
From
Patricia Schady at MSSL/Swift <ps@mssl.ucl.ac.uk>
P. Schady (MSSL-UCL) and J.R. Cummings (NASA/UMBC) report on behalf of the 
Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 090813 88s 
after the BAT trigger (Cummings et al., GCN Circ 9781). No new source is 
detected within the XRT error circle or at the optical position reported 
by Cenko (GCN Circ. 9783) in any of the individual or combined UVOT 
filters.

The 3-sigma upper limits of detected a source at the position of the 
optical afterglow reported by Cenko (GCN Circ. 9783) in the first white 
band finding chart (fc) observation, and in consecutive coadded 
observations for each of the UVOT filters are as follows:

Filter  T_start(s)  T_stop(s)  Exp(s)  Mag 3-sig UL
wh (fc)    88         237      147       > 20.55
wh         581        1894     264       > 21.35
vv         631        1943     156       > 19.39
bb         556        1869     136       > 20.29
uu         300        2017     382       > 20.44
w1         681        1992     156       > 19.73
m2         656        1967     156       > 19.41
w2         607        1919     156       > 19.83

The values quoted above are not corrected for the Galactic extinction due 
to the large reddening of E(B-V) = 0.17 in the direction of the burst 
(Schlegel et al., 1998). The photometry is on the UVOT photometric system 
described in Poole et al. (2008, MNRAS, 383, 627).

GCN Circular 9787

Subject
Konus-Wind observations of GRB090813
Date
2009-08-13T13:30:59Z (16 years ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
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:

GRB 090813 (Swift trigger=359884: Cummings et al., GCN 9781)
triggered Konus-Wind at T0=15041.925 s UT (04:10:41.925)

The burst started with a double-peaked structure with a
duration of ~2 s.
Another, softer peak, with a duration of ~1.5 s,
was observed at T0 + 6s.

The Konus-Wind light curves of this GRB are available at
http://www.ioffe.ru/LEA/GRBs/GRB090813_T15041/

As observed by Konus-Wind the burst had
a fluence of 2.4(-0.4,+0.5)x10-6 erg/cm2, and
a 64-ms peak flux, measured from T0,
of 3.3(-0.6,+0.7)x10-6 erg/cm2/s
(both in the 20 keV - 1 MeV energy range).

The time-integrated spectrum of the burst (from T0 to T0+8.448 s)
is well fitted (in the 20 keV - 1 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -1.37(-0.28,+0.35),
and Ep = 104(-23,+41)keV (chi2 = 58/61 dof).

Fitting by GRB (Band) model yields to the same alpha and Ep values
with the high energy photon index beta < -9.

The spectrum at the maximum count rate, measured from T0 to T0+0.256 s,
is well fitted (in the 20 keV - 1 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.85(-0.29,+0.34),
and Ep = 195(-43,+71)keV (chi2 = 20/23 dof).

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

GCN Circular 9788

Subject
GRB 090813, Swift-BAT refined analysis
Date
2009-08-13T13:55:52Z (16 years ago)
From
Jay R. Cummings at NASA/GSFC/Swift <james.r.cummings@nasa.gov>
J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (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),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):

Using the data set from T-60 to T+243 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 090813 (trigger #359884)
(GRB 090813, Cummings et al., GCN Circ. 9781). The BAT
ground-calculated position is RA, Dec = 225.065, 88.571 deg which is
RA(J2000) = 15h 00m 15.6s
Dec(J2000) = +88d 34' 15.8"
with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 18%.

The mask weighted lightcurve had three main spikes, at T+0, T+1 and
T+6.5 sec, each with a duration of about 1 sec. T90 (15-350 keV) was
7.1 +- 0.6 sec (estimated error including systematics). The three
spikes were progressively softer.

The time-averaged spectrum from T-0.8 to T+7.3 sec is best fit by a
simple power-law model. The power law index of the time-averaged
spectrum is 1.69 +- 0.12. The fluence in the 15-150 keV band is 1.3 +-
0.1 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T-0.04 sec
in the 15-150 keV band is 8.5 +- 0.6 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/359884/BA/

GCN Circular 9790

Subject
GRB 090813: Swift-XRT refined analysis
Date
2009-08-13T15:43:56Z (16 years ago)
From
Andy Beardmore at U Leicester <apb@star.le.ac.uk>
A. P. Beardmore (U. Leicester) and J. R. Cummings (NASA/UMBC) report
on behalf of the Swift-XRT team:

We have analysed 8.8 ks of XRT data for GRB 090813 (Cummings et
al., GCN Circ. 9781), from 84 s to 19.3 ks after the BAT trigger. The
data span four orbits, comprising 810 s in Windowed Timing (WT) mode
with the remainder in Photon Counting (PC) mode. The enhanced XRT
position for this burst was given by Osborne et al. (GCN. Circ 9785).

The X-ray light curve initially follows a shallow decay, with a decay 
index of 0.22 +/ 0.10, before steepening to an index of 1.15 +/- 0.03 at 
about 450 s after the trigger.

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.10 +/- 0.07. The
best-fitting absorption column is (2.23 +0.20 -0.19) x 10^21 cm^-2, in
excess of the Galactic value of 6.3 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 2.00 +0.11 -0.10 and
a best-fitting absorption column of (2.3 +/- 0.3) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 4.3 x 10^-11 (6.4 x 10^-11) erg cm^-2
count^-1.

If the light curve continues to decay with a power-law decay index of
1.15, the estimated count rate at T+24 hours will be 0.016 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of
6.9 x 10^-13 (1.0x 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/00359884.

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

GCN Circular 9792

Subject
GRB 090813: Fermi GBM observation
Date
2009-08-13T16:48:15Z (16 years ago)
From
Andreas von Kienlin at MPE <azk@mpe.mpg.de>
A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: 

"At 04:10:42.59 UT on 13 August 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090813 (trigger 271829444  / 090813174), which 
was also detected by the SWIFT-BAT (Cummings et al. 2009, GCN 9781)
and Konus/Wind (Golenetskii et al., 2009, GCN Circular 9787).
The GBM on-ground location is consistent with the Swift position.
 
The angle from the Fermi LAT boresight is 35.3 degrees.

This burst was also independently detected by INTEGRAL SPI-ACS.

The GBM light curve consists of two separate pulses with a 
duration (T90) of about 9 s (8-1000 keV). The time-averaged 
spectrum from T0-0.256 s to T0+8.960 s is well fit by a 
power law function with an exponential high energy cutoff. 
The power law index is -1.43 +/- 0.08 an the cutoff energy, 
parameterized as Epeak, is 161 +/- 26 keV
(chi squared 495 for 480 d.o.f.).

The event fluence (8-1000 keV) in this time interval is 
(3.5 +/- 0.2)E-06 erg/cm^2. The 1.024-sec peak photon flux measured 
starting from T0+0.512 s in the 8-1000 keV band 
is 14.4 +/- 0.5 ph/s/cm^2.

A Band function fits the spectrum equally well (chi squared 492 
for 479 d.o.f.) with Epeak= 95 +/- 30 keV, alpha = -1.25 +/- 0.18 
and beta = -2.0 +/- 0.1. 

The spectral analysis results presented above are preliminary; 
final results will be published in the GBM GRB Catalog."

GCN Circular 9798

Subject
GRB 090813: correction to GCN 9787
Date
2009-08-14T10:57:53Z (16 years ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
D. Frederiks, on behalf of Konus-Wind team, report:

The correct upper limit for the high energy spectral index (beta)
for the GRB (Band) model fit to Konus-Wind time integrated spectrum
of GRB 090813 is -2.23 (90% confidence level, 20-1000 keV range).

GCN Circular 9811

Subject
GRB 090813: CrAO optical obsevations
Date
2009-08-15T09:29:00Z (16 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
A. Volnova (SAI MSU), E. Pavlenko, O. Antoniuk, V. Rumyantsev (CrAO), A. 
Pozanenko (IKI)  report on behalf of larger GRB follow-up collaboration:

We observed the field of the Swift GRB 090813 (Cummings et al. GCN 9781) 
starting (UT) Aug. 13 23:57:26 with Shajn telescope of  CrAO under favorable 
weather condition and seeing ~1.6".
At the place of optical afterglow (Gorosabel et al. GCN 9782; Cenko et al. 
GCN 9783; Smith et al. GCN 9784) we detect a source which appears slightly 
E-W extended.

Preliminary photometry of the source in a combined image based on  USNO-B1.0 
star (RA(J2000)=15:02:47.99, Dec(J2000)=88:31:41.4) assuming R= 14.23 is 
following:

T0+     Filter, Exposure, mag.,     err.
(d)             (s)

0.8440   R       57x60     20.50 +/-0.06

Observations will be continued.

GCN Circular 9817

Subject
GRB 090813: Suzaku WAM observation of the prompt emission
Date
2009-08-17T09:43:52Z (16 years ago)
From
Takeshi Uehara at Hiroshima U <uehara@hirax7.hepl.hiroshima-u.ac.jp>
GRB 090813: Suzaku WAM observation of the prompt emission

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

The long, GRB 090813 
(Swift/BAT trigger #359884 ; Cummings et al., GCN 9781; 
Fermi GBM trigger #271829444 ) 
triggered the Suzaku Wide-band  All-sky Monitor (WAM) 
which covers an energy range of 50 keV - 5 MeV at 04:10:43.2 UT (=T0). 
The observed light curve shows a double-peaked structure 
lasting from T0-0.8s to T0+1.2s followed by a long weak tail seen up
to T0+6.8s with a duration (T90) of about 7.6 seconds. 
The fluence in 100 - 1000 keV was 1.70 (-0.51, +0.61) 10^-6 erg/cm^2. 
The 1-s peak flux measured from T0-0.2s was 2.77 (-0.40, +0.35) 
photons/cm^2/s in the same  energy range.

Preliminary result shows that the time-averaged spectrum from T0-0.8s to 
T0+6.8s is well fitted by a single power-law with a photon index 
of 1.80 (-0.30, +0.40) (chi^2/d.o.f = 7.6/8).
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

GCN Circular 9820

Subject
GRB 090813: I-band observations from 1.5m OSN telescope
Date
2009-08-17T15:09:25Z (16 years ago)
From
Javier Gorosabel at IAA-CSIC <jgu@iaa.es>
J. Gorosabel (IAA-CSIC), A. de Ugarte Postigo (INAF-OAB), A. Sota (IAA- 
CSIC),  S. Guziy (IAA-CSIC),  M. Jelinek (IAA-CSIC), P. Kubanek (IAA- 
CSIC & IPL Univ. Valencia), A.J. Castro-Tirado (IAA-CSIC), report;

We performed I-band observations of the GRB 090813 optical afterglow  
(Gorosabel et al. GCN 9782; Cenko et al. GCN 9783; Smith et al. GCN  
9784) with the 1.5m telescope of Observatorio de Sierra Nevada. The  
observations were carried on Aug 13.8979 - 13.9667 UT with a total  
exposure time of 4950 seconds. No object brigther than I = 21.9 was  
detected at the afterglow position.

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