GRB 050826
GCN Circular 3884
Subject
GRB050826: Swift-BAT detection of a long burst
Date
2005-08-26T07:02:02Z (20 years ago)
From
Craig Markwardt at NASA/GSFC/UMD <craigm@milkyway.gsfc.nasa.gov>
V. Mangano (INAF-IASF), L. Barbier (GSFC), A. Blustin (UCL-MSSL),
D. Burrows (PSU), J. Cummings (GSFC), S. Hunsberger (PSU),
C. Markwardt (GSFC/UMD), D. Morris (PSU), K. Page (U. Leicester),
D. Palmer (LANL),
on behalf of the Swift team:
At 06:18:10 UT, Swift-BAT triggered and located GRB 050826
(trigger=152113). The spacecraft slewed immediately. The BAT
on-board calculated location is RA,Dec 87.729, -2.680 {+05h 50m 55s,
-02d 40' 46"} (J2000), with an uncertainty of 3 arcmin (radius, 90%
containment, stat+sys). The BAT light curve shows two peaks (T+10
sec and T+30 sec) with a total duration of 45 sec. The peak count
rate was ~800 counts/sec (15-350 keV), at ~10 sec after the trigger.
Observations by the Swift X-Ray Telescope (XRT) began at 06:19:56 UT
(106 seconds after the BAT trigger) with the XRT in the auto
state. The on-board detection algorithm failed to find a centroid,
suggesting a very faint source. More information will be available
around 11:00 UT, after the next Malindi pass.
The UVOT began observing the field of GRB 050826 at 06:19:55 UT, 105 s
after the BAT trigger. The UVOT image covers the whole of the 3
arcmin BAT error circle. A comparison of the parameterised UVOT
finding chart, based on a 100 sec V-band image, with the DSS image
reveals no new source brighter than ~19th mag.
GCN Circular 3885
Subject
GRB 050826: Swift XRT position
Date
2005-08-26T13:35:41Z (20 years ago)
From
David Morris at PSU/Swift-XRT <morris@astro.psu.edu>
V. Mangano (INAF-IASF), J. Racusin (PSU), D. Morris (PSU), D. N. Burrows
(PSU) report on behalf of the Swift XRT team:
We have analysed the ground data from GRB 050826 (BAT Trigger #152113).
We find a previously uncatalogued, fading x-ray source at the following
coordinates:
RA(J2000): 05:51:01.3
Dec(J2000): -02:38:37.8
with an uncertainty of 8 arcseconds radius (90% containment). This
position is 2.7 arcminutes from the BAT position reported in GCN 3884
(Mangano et al).
GCN Circular 3887
Subject
GRB050826: Swift/UVOT early upper limits
Date
2005-08-26T20:18:52Z (20 years ago)
From
Alexander Blustin at MSSL-UCL <ajb@mssl.ucl.ac.uk>
A. J. Blustin (UCL-MSSL), V. Mangano (INAF-IASF),
F. Marshall (GSFC), M. Ajello (MPE), M. Trippico (GSFC-SSAI),
N. Gehrels (GSFC) on behalf of the Swift/UVOT team
The Swift/UVOT began observing the field of GRB050826 at
06:19:55 UT, 105 s after the BAT trigger (Mangano et al.,
GCN 3884). No new source with respect to the DSS image was
detected in the 100 s V-band UVOT Image down to a 3-sigma
upper limit (in the XRT error circle: Mangano et al., GCN
3885) of 17.9 mag.
There was also no optical/UV counterpart detected in summed
images from all filters, down to the following 3-sigma magnitude
upper limits:
Filter T_range (s) Exp (s) 3sig UL
V 105-6545 777 19.4
B 251-16450 1857 21.2
U 236-12331 823 19.0
UVW1 223-11570 968 19.7
UVM2 209-10662 968 19.3
UVW2 266-17318 1818 20.3
Where T_range is the time range post-trigger over which the
summed images were accumulated and Exp is the total exposure time
of the summed image. The magnitude upper limits are not corrected
for extinction.
These magnitudes are based on preliminary zero-points, measured
in orbit, and will require refinement with further calibration.
GCN Circular 3888
Subject
GRB 050826: BAT refined analysis
Date
2005-08-26T21:17:04Z (20 years ago)
From
Craig Markwardt at NASA/GSFC/UMD <craigm@milkyway.gsfc.nasa.gov>
C. Markwardt (GSFC/UMD), L. Barbier (GSFC), S. Barthelmy (GSFC),
J. Cummings (GSFC/NRC), D. Hullinger (GSFC/UMD), E. Fenimore (LANL),
N. Gehrels (GSFC), H. Krimm (GSFC/USRA), T. McMahon (Langston U.),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC),
G. Sato (ISAS), J. Tueller (GSFC), N. White (GSFC)
on behalf of the Swift-BAT team:
Using the full data set, we report further analysis of Swift-BAT
GRB 050826 (trigger # 152113) (Mangano, et al., GCN 3884). The
ground-analysis position is RA,Dec 87.772, -2.667 (J2000) with
an uncertainty of 2.1 arcmin (radius, 90%, stat+sys). This is
2.7 arcmin from the onboard position and 1.7 arcmin from the XRT
position reported by Mangano et al. in GCN Circ. 3885.
The light curve shows a peak with a FRED structure lasting until T+14,
a second 4-sec peak centered at T+18, and possible lower-energy peaks
at T+34 sec and T+52 sec. The main part of the burst is weak and hard
in the BAT energy range. T90 is 35 +- 8 sec. Fitting a simple power
law over the interval from T+1 to T+36 sec, the photon index is
1.2 +/- 0.3 with a fluence of 4.3 +/- 0.7 x 10^-7 erg/cm^2 in the
15-150 keV band (90% c.l). The peak flux in a 1-second wide window
starting at T+1 sec is 0.42 +/- 0.12 ph/cm^2/sec (15-150 keV).
GCN Circular 3889
Subject
GRB 050826: Swift XRT preliminary analysis results
Date
2005-08-26T21:31:23Z (20 years ago)
From
Milvia Capalbi at ISAC/ASDC <capalbi@asdc.asi.it>
V. Mangano (INAF-IASF), D. Morris (PSU), D. Burrows (PSU),
J. Kennea (PSU), L. Angelini (GSFC-JHU), N. White (GSFC)
report on behalf of the Swift XRT team:
We have analyzed the Swift XRT data from the first
observation of GRB 050826 (four orbits).
The new refined coordinates are:
RA(J2000) = 05h 51m 01.3s Dec(J2000) = -02:38:41.9
with an uncertainty of 6 arcseconds radius (90% containment).
This position is 2.6 arcmin from the BAT position given
in GCN 3384 (Mangano et al 2005a) and consistent with
the previously distributed coodinates given in GCN 3385
(Mangano et al 2005b).
The 0.2-10 keV light curve in Photon Counting (PC) mode
starts 114.97 seconds from the BAT trigger.
The light curve shows a single power law decay with slope
-1.16 +/- 0.07 (90% confidence level).
A preliminary spectral fit to the first orbit PC data
gives a spectral power law photon index of 2.0 +/- 0.4
in the [0.2-10] keV band, with an absorption column
of 8e21 cm^2, in excess of the Galactic value (2e21 cm^2).
The average (in the time range 100-700 seconds from trigger)
estimated unabsorbed 0.5-10 keV flux is then
6.9E-11 erg cm-2 s-1.
The predicted flux at T=24 h after the trigger is
at the level of 7.0e-14 erg cm-2 s-1 (or 1.0e-3 counts/s).
GCN Circular 3891
Subject
GRB 050826: Optical Candidate
Date
2005-08-27T12:09:34Z (20 years ago)
From
Jules Halpern at Columbia U. <jules@astro.columbia.edu>
J. P. Halpern (Columbia U.) reports on behalf of the MDM Observatory
GRB follow-up team:
"I observed the error box of GRB 050826 (Swift trigger #152113, GCN #3884)
in the R band with the MDM 1.3m telescope for 75 minutes on each of two
consecutive nights. A fading object not visible on the Digitized Sky
Survey is present at coordinates
(J2000) 05:51:01.59, -02:38:35.4 (+/- 1")
which is 8" from the revised Swift XRT position (error radius 6", GCN #3889).
The epochs and magnitudes are:
---------------------------------------------------
Date(UT) Time(UT) t-t0(hours) R(mag)
---------------------------------------------------
Aug. 26 10:42-11:57 4.40- 5.65 21.0 +/- 0.2
Aug. 27 10:43-11:58 28.42-29.67 21.6 +/- 0.2
---------------------------------------------------
The indicated errors are systematic at this stage of the analysis,
but the difference between the two observations is not affected by
systematics. Improvements in precision of position and magnitudes
will be forthcoming from these data. These preliminary magnitudes
should not be used in formal analyses.
I also note that this location suffers from significant Galactic extinction,
E(B-V)=0.59, A(R)=1.57, according to Schlegel et al. (1998)."
GCN Circular 3898
Subject
GRB 050826 : Lulin R band observation
Date
2005-08-28T13:52:10Z (20 years ago)
From
Kuiyun Huang at IANCU <d919003@astro.ncu.edu.tw>
H.T. Lee, H.F. Huang, F.Y. Huang, K.Y. Huang, W.H. Ip (NCU),
Y. Urata(RIKEN), Y. Qiu (BAO), Y.Q. Lou (THCA) on behalf of EAFON
report:
"We have observed the error region of GRB 050826 (Mangano et al., GCN
2884) using 1-m telescope at Lulin Observatory, Taiwan. The R band
observations are started at 20.36 UT (~ 14.1 hours after the burst). No
source was found around the position of XRT (Mangano et al., GCN 3889)
and the optical candidate ( Halpern et al.,GCN2891) at our co-add
image (300s x 7). The limiting magnitude is R~ 20.3 compared with
USNOB1.0 stars.
This message may be cited."
GCN Circular 4749
Subject
GRB 050826: Optical Afterglow and Host Galaxy
Date
2006-02-12T01:53:14Z (19 years ago)
From
Jules Halpern at Columbia U. <jules@astro.columbia.edu>
J. P. Halpern (Columbia U.) and N. Mirabal (U. Michigan) report
on behalf of the MDM Observatory GRB follow-up team:
"Follow-up observations summarized here support our original
suggestion in GCN 3891 of an optical afterglow for the Swift
GRB 050826 (GCN 3884, 3888), and indicate the presence of a
relatively bright host galaxy for this long burst.
First, the Swift XRT position of the afterglow, which was
originally determined to lie 8" from the optical candidate
with an 90% uncertainty radius of 6" (GCN 3889, 3891), was
subsequently refined (as were all XRT positions). In the
revised catalog of Moretti et al. (astro-ph/0511604), the
XRT position falls only 3.1" from the optical position,
consistent with the improved 3.4" X-ray uncertainty.
---------------------------------------------------
R.A. (2000) Dec. (2000) +/- (")
---------------------------------------------------
Swift XRT 05 51 01.49 -02 38 38.6 3.4
MDM 1.3m OT 05 51 01.58 -02 38 35.8 0.5
MDM 2.4m host 05 51 01.59 -02 38 36.2 0.5
---------------------------------------------------
Second, image subtraction among observations obtained on three
consecutive nights on the MDM 1.3m reveals a point-like OT on
the first night only, and shows that the light is dominated by
the host galaxy on the second and third nights. The OT is offset
~0.4" to the north of the brightest part of the galaxy.
------------------------------------------------------
MDM 1.3m
------------------------------------------------------
Date(UT) Time(UT) t-t0(hours) Diff OT R(mag)
------------------------------------------------------
Aug. 26 10:42-11:57 4.40- 5.65 22.23 +/- 0.15
Aug. 27 10:43-11:58 28.42-29.67 > 22.8
Aug. 28 11:03-11:57 52.75-53.65
------------------------------------------------------
MDM 2.4m Host R(mag)
------------------------------------------------------
Dec. 25 21.67 +/- 0.05
------------------------------------------------------
Third, using the MDM 2.4m, RETROCAM imager, and SDSS r' filter
on 2005 Dec. 25, a bright core and irregular extension of the
presumed host galaxy are clearly resolved in seeing of 1".
The host magnitude listed above is measured in a 1.8" radius.
Optical magnitudes were calibrated with Landolt standard stars,
and positions were derived with respect to the USNO B1.0 catalog.
The MDM images are posted at
http://www.astro.columbia.edu/~jules/grb/050826/
Spectroscopy and deeper imaging are needed to measure the redshift
and star-forming properties of the presumed host galaxy.
This message may be cited."
GCN Circular 5982
Subject
GRB 050826: MDM Redshift
Date
2006-12-25T04:34:34Z (18 years ago)
From
Jules Halpern at Columbia U. <jules@astro.columbia.edu>
J. P. Halpern & N. Mirabal (Columbia U.) report on behalf of the
MDM Observatory GRB follow-up team:
"Previously, we reported the detection of the optical afterglow of
Swift GRB 050826 within a relatively bright, irregular galaxy of
R=21.67, or R=20.1 when corrected for Galactic extinction.
Image subtraction was used to separate the OT contribution
from the host galaxy. See GCNs 3891 and 4749 for details.
On 2006 Dec. 24 UT, we obtained three 1-hour, low-resolution spectra
of the host galaxy using the Boller & Chivens CCD Spectrograph (CCDS)
on the MDM 2.4m telescope. Acquisition was by blind offset. Narrow
emission lines corresponding to [O II] 3727 and [O III] 4959,5007
are seen in the individual exposures. Their line strengths are
characteristic of a high-excitation starburst, similar to other
hosts of long bursts. From the summed spectrum, we derive a redshift
of z=0.297+/-0.001.
The Swift BAT fluence of 4.3x10^-7 erg/cm^2 in the 15-150 keV band
(Markwardt et al., GCN 3888) then corresponds to an isotropic
energy release of 9x10^49 erg using standard cosmological parameters.
This example illustrates the role of image subtraction in completing
the census of low-luminosity GRBs in nearby galaxies.
This message may be cited."