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GRB 090727

GCN Circular 9718

Subject
GRB 090727: Swift detection of a burst
Date
2009-07-27T22:59:22Z (16 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
P. A. Evans (U Leicester), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
M. M. Chester (PSU), S. T. Holland (CRESST/USRA/GSFC),
N. P. M. Kuin (MSSL), C. B. Markwardt (CRESST/GSFC/UMD),
K. L. Page (U Leicester), A. Rowlinson (U Leicester),
M. H. Siegel (PSU), M. A. Stark (PSU) and T. N. Ukwatta (GSFC/GWU)
report on behalf of the Swift Team:

At 22:42:18 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090727 (trigger=358520).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 315.972, +64.916 which is 
   RA(J2000) = 21h 03m 53s
   Dec(J2000) = +64d 54' 58"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single peak
with a duration of about 25 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 22:43:46.0 UT, 87.9 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 315.96139, 64.92438 which is equivalent
to:
   RA(J2000)  = 21h 03m 50.73s
   Dec(J2000) = +64d 55' 27.8"
with an uncertainty of 4.0 arcseconds (radius, 90% containment). This
location is 34 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
2.48e+21 cm^-2 (Kalberla et al. 2005). 


UVOT took a finding chart exposure of nominal 150 seconds with the White filter
starting 91 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. Data from the 2.7'x2.7' sub-image are
not available at this time. 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 0.54. 




Burst Advocate for this burst is P. A. Evans (pae9 AT star.le.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.)

GCN Circular 9719

Subject
GRB 090727: Liverpool Telescope possible OT candidate
Date
2009-07-28T02:19:38Z (16 years ago)
From
James Smith at ARI,Liverpool John Moors U <rjs@astro.livjm.ac.uk>
R.J. Smith, C.G. Mundell (Liverpool JMU) on behalf of a large 
collaboration report:

The 2-m Liverpool Telescope robotically reacted to GRB 090727 (SWIFT 
trigger 358520, Evans et al, GCN Circ. 9718), starting observing at 
22:44:59UTC. A source which is not visible in the digitized sky survey is 
detected in both SDSS r' and i' filters at position 21:03:50.6 +64:55:30 
J2000. This lies within the XRT error circle reported by Evans et al, GCN 
Circ. 9718. The approximate magnitude, calibrated with respect to nearby 
USNOB stars is R=21.3 +/- 0.2 and I = 20.2 +/- 0.2. The target is slightly 
crowded by brighter stellar sources and analysis is ongoing to determine 
if the OT candidate is fading.

GCN Circular 9721

Subject
GRB 090727: Enhanced Swift-XRT position
Date
2009-07-28T09:53:03Z (16 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 5314 s of XRT Photon Counting mode data and 7 UVOT
images for GRB 090727, 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 = 315.96078, +64.92481 which is equivalent
to:

RA (J2000): 21h 03m 50.59s
Dec (J2000): +64d 55' 29.3"

with an uncertainty of 1.6 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 9722

Subject
GRB 090727: Liverpool Telescope Afterglow Confirmation and Optical Flare
Date
2009-07-28T10:35:59Z (16 years ago)
From
Carole Mundell at ARI, JMU,Liverpool <cgm@astro.livjm.ac.uk>
R.J. Smith, C.G. Mundell, I.A. Steele,  A. Melandri, S. Kobayashi, C.J.
Mottram, D.F. Bersier, Z. Cano (Liverpool JMU), A. Gomboc (Ljubljana), C.
Guidorzi (INAF-OAB) report:

"Further analysis of the optical light curves of the uncatalogued optical 
source, at RA(J2000)=21:03:50.6, Dec(J2000)= +64:55:30, reported by Smith 
& Mundell (GCN Circ. 9719) show significant variability and confirm this 
object as the optical afterglow of GRB 090727 (SWIFT trigger 358520, 
Evans et al, GCN Circ. 9718; Goad et al. GCN Circ. 9721).

Within the first 100 mins, the optical light curve shows an early-time 
flare, peaking at r'=19.4 mag, followed by a plateau and break - features 
that are the same as suggested by the partially sampled XRT light curve.

Observations are ongoing."

GCN Circular 9723

Subject
GRB 090727: Swift-XRT refined analysis
Date
2009-07-28T11:30:11Z (16 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
P. A. Evans (U Leicester) reports on behalf of the Swift-XRT team:

We have analysed 11 ks of XRT data for GRB 090727 (Evans et al. GCN
Circ. 9718), from 91 s to 29.2 ks after the BAT trigger. The data
comprise 40 s in Windowed Timing (WT) mode from T+260 s to T+300 s,
with  the remainder in Photon Counting (PC) mode. The enhanced XRT
position for this burst was given by Goad et al. (GCN. Circ 9721).

The XRT initially observed the GRB for only 210 s before slewing away,
and the data in this interval are dominated by a flare, making it
impossible to determine the underlying decay rate. Fitting only the data
from the second snapshot onwards (beginning at T+3.9 ks) we find a
power-law decay with an index of alpha=0.73 (+/-0.19).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.60 (+0.20, -0.14). The
best-fitting absorption column is consistent with the Galactic value of
2.5 x 10^21 cm^-2  (Kalberla et al. 2005).

If the light curve continues to decay with a power-law decay index of
0.73, the count rate at T+24 hours will be 0.0043 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.3 x
10^-13 (2.9 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00358520.

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

GCN Circular 9724

Subject
GRB 090727: Swift-BAT refined analysis
Date
2009-07-28T12:00:35Z (16 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
C. B. Markwardt (GSFC/UMD), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), P. A. Evans (U Leicester), E. E. Fenimore (LANL),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), D. M. Palmer (LANL),
A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-240 to T+962 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 090727 (trigger #358520)
(Evans, et al., GCN Circ. 9718).  The BAT ground-calculated position is
RA, Dec = 315.917, 64.937 deg, which is 
   RA(J2000)  =  21h 03m 40.0s 
   Dec(J2000) = +64d 56' 12.7" 
with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 83%.
 
The mask-weighted light curve shows an initial FRED-like peak starting at
~T-5 sec, peaking at ~T_zero, and ending at ~T+20 sec.  The second, weaker,
peak starts at ~T+130 to ~T+150 sec.  The third peak starts at ~T+180 sec,
peaks at ~T+270 sec, and ends at ~T+320 sec.  This third peak corresponds
to the flare mentioned in Circ 9723 (Evans).  T90 (15-350 keV) is 302 +- 23 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-1.3 to T+318.9 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.24 +- 0.24.  The fluence in the 15-150 keV band is 1.4 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+0.12 sec in the 15-150 keV band
is 0.5 +- 0.1 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/358520/BA/

GCN Circular 9728

Subject
GRB 090727: I-band observations from 1.23m CAHA
Date
2009-07-28T17:56:59Z (16 years ago)
From
Javier Gorosabel at IAA-CSIC <jgu@iaa.es>
J. Gorosabel (IAA-CSIC, Spain), N. Huelamo (LAEFF-CAB/INTA-CSIC, Spain),
M. Fernandez (IAA-CSIC, Spain), M. Jelinek (IAA-CSIC, Spain), P. Kubanek
(IAA-CSIC, Spain), A. de Ugarte Postigo (OAB-INAF, Italy), A.J.
Castro-Tirado (IAA-CSIC, Spain), R.J. Smith (JMU, Liverpool, UK), C.G.
Mundell (JMU, Liverpool, UK), on behalf of a larger collaboration, report:

"We carried out I-band observations of the GRB 090727 XRT optical
afterglow (Smith et al. GCN Circ. 9719; GCN Circ. 9722) with the 1.23m
Calar Alto telescope. The observations were carried out on July
27.9646-28.0063 UT (0.45-1.45 hours post GRB) with an exposure time of
3600s. Very preliminary photometry yields I ~ 19.4 (Vega system) for the
afterglow, against USNO B1.0 star with I=18.72 placed at (RA_J2000,
DEC_J2000) = (21:03:49.099, +64:55:58.23)."

GCN Circular 9731

Subject
GRB 090727: Swift/UVOT Upper Limits
Date
2009-07-29T02:00:58Z (16 years ago)
From
Margaret Chester at PSU <chester@astro.psu.edu>
M.M. Chester (PSU) and P. A. Evans (U Leicester) report on behalf of the 
Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 090727
92 s after the BAT trigger (Evans et al., GCN Circ. 9718).  We do not find 
any new source at the position of the XRT afterglow (Goad et al., GCN Circ. 
9721). Preliminary 3-sigma upper limits for the white finding chart and the 
co-added images, using the UVOT photometric system (Poole et al. 2008, 
MNRAS, 383, 627), are:

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

white_FC            92          241          147         >20.6
white               92         5987          541         >21.5
v                 4760        57429         3737         >21.1
b                 4145        46543         1752         >21.3
u                 3939        52323         4261         >21.8
w1                5171        51651         4625         >22.1
m2                4965        57845         4989         >22.3
w2                4556        56519         3825         >21.7

The values quoted above are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.54 in the direction of the burst
(Schlegel et al. 1998).

GCN Circular 9733

Subject
GRB 090727: optical observations
Date
2009-07-29T12:31:34Z (16 years ago)
From
Vladimir Sokolov at SAO RAS <sokolov@sao.ru>
A. Moskvitin, A. Valeev, T. Fatkhullin,
O. Sholukhova & S. Fabrika (SAO-RAS Niznijh Arkhyz, Russia),
on behalf of a larger colaboration, report:

We observed the GRB090727 optical afterglow (Smith et al. GCN Circ. 9719,
GCN Circ. 9722; J. Gorosabel et al. GCN Circ 9728 ) with the SAO RAS 6-m
telescope in Caucasus. The observations were carried out in the R band 
with a total exposure of 158 sec. The weather was cloudy with a sufficient
atmospheric extinction. We estimated the brightness of the object as
R = 21.53 +/- 0.17 at the middle epoch of 23:21:12 27 July 2009 UT
(2334 sec after the trigger). Calibration was done aganist 10 USNO B1.0 
stars.

This message may be cited.

GCN Circular 9735

Subject
GRB 090727: GRT Optical Observation
Date
2009-07-29T19:19:45Z (16 years ago)
From
Takanori Sakamoto at NASA/GSFC <takanori@milkyway.gsfc.nasa.gov>
T. Sakamoto (UMBC/GSFC), D. Donato (ORAU/GSFC), N. Gehrels (GSFC),
T. Okajima (JHU/GSFC), T.N. Ukwatta (GWU/GSFC), Y. Urata (NCU),
C.A. Wallace (FGCU)

We observed the field of GRB 090727 detected by Swift
(trigger #358520; Evans et al., GCN Circ. 9718) with the 14-inch
Goddard Robotic Telescope (GRT) located at the Goddard Geophysical
and Astronomical Observatory (http://cddisa.gsfc.nasa.gov/ggao/).

77 set of 30 sec exposures (excluding the bad quality images) were 
taken in the R filter starting from July 28 01:57:45 (UT) about 
3.2 hours after the trigger and stopped on July 28 02:40:50 (UT).  
We do not detect the optical afterglow (Smith et al., GCN Circ. 
9719; Gorosabel et al., GCN Circ. 9728; Moskvitin et al., GCN Circ. 
9733) both in the individual images and the combined image.  The 
estimated three sigma upper limit of the combined image (total 
exposure of 2310 sec) is ~16.6 mag using the USNO-B1 catalog.

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