Gamma-ray Burst 050826

(All information courtesy of the instrument teams.)

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Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 26 Aug 05 06:19:14 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     152113,   Seg_Num: 0
GRB_RA:           87.729d {+05h 50m 55s} (J2000),
                  87.800d {+05h 51m 12s} (current),
                  87.101d {+05h 48m 24s} (1950)
GRB_DEC:          -2.680d {-02d 40' 46"} (J2000),
                  -2.679d {-02d 40' 42"} (current),
                  -2.692d {-02d 41' 31"} (1950)
GRB_ERROR:       4.00 [arcmin radius, statistical only]
GRB_INTEN:       30879 [cnts]    Image_Peak=533 [image_cnts]
TRIGGER_DUR:     8.192 [sec] 
TRIGGER_INDEX:   490     E_range: 25-100 keV
BKG_INTEN:       221667 [cnts]
BKG_TIME:        22600.00 SOD {06:16:40.00} UT
BKG_DUR:         64 [sec]
GRB_DATE:        13608 TJD;   238 DOY;   05/08/26
GRB_TIME:        22690.28 SOD {06:18:10.28} UT
GRB_PHI:          52.20 [deg]
GRB_THETA:        17.68 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     12.44 [sigma]
IMAGE_SIGNIF:    8.16 [sigma]
MERIT_PARAMS:     +1  +0  +0  +4  +2  +3  +0  +0 -36  +1 
SUN_POSTN:       155.06d {+10h 20m 14s}  +10.36d {+10d 21' 35"}
SUN_DIST:         68.20 [deg]
MOON_POSTN:       55.75d {+03h 43m 00s}  +23.39d {+23d 23' 42"}
MOON_DIST:        40.67 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      208.35,-14.68 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       87.47,-26.10 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Coordinates.  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.

red DSS finding chart ps-file

GCN/SWIFT NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 26 Aug 05 06:20:07 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     152113,   Seg_Num: 0
POINT_RA:         87.735d {+05h 50m 56s} (J2000)
POINT_DEC:        -2.678d {-02d 40' 39"} (J2000)
GRB_DATE:        13608 TJD;   238 DOY;   05/08/26
GRB_TIME:        22796.53 SOD {06:19:56.53} UT
COUNTS:          201    Min_needed= 20
STD_DEV:         0.00   Max_StdDev_for_Good=28.44 [arcsec]
PH2_ITER:        4    Max_iter_allowed= 4
ERROR_CODE:      2
COMMENTS:        SWIFT-XRT Nack Position.  
COMMENTS:        Algorithm did not converge; too many interations.

GCN/SWIFT NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 26 Aug 05 06:22:06 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     152113,   Seg_Num: 0
GRB_RA:           87.729d {+05h 50m 55s} (J2000),
                  87.800d {+05h 51m 12s} (current),
                  87.101d {+05h 48m 24s} (1950)
GRB_DEC:          -2.680d {-02d 40' 46"} (J2000),
                  -2.679d {-02d 40' 42"} (current),
                  -2.692d {-02d 41' 31"} (1950)
GRB_DATE:        13608 TJD;   238 DOY;   05/08/26
GRB_TIME:        22690.28 SOD {06:18:10.28} UT
TRIGGER_INDEX:   490
GRB_PHI:          52.20 [deg]
GRB_THETA:        17.68 [deg]
DELTA_TIME:      65498.00 [sec]
TRIGGER_DUR:     8.192 [sec] 
LC_URL:          sw00152113000msb.lc
SUN_POSTN:       155.06d {+10h 20m 14s}  +10.36d {+10d 21' 35"}
SUN_DIST:         68.20 [deg]
MOON_POSTN:       55.75d {+03h 43m 00s}  +23.39d {+23d 23' 42"}
MOON_DIST:        40.67 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      208.35,-14.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       87.47,-26.10 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-BAT GRB Lightcurve.  
COMMENTS:           
COMMENTS:        The next comments were copied from the BAT_POS Notice:  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.

GCN/SWIFT NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 26 Aug 05 06:22:50 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     152113,   Seg_Num: 0
POINT_RA:         87.735d {+05h 50m 56s} (J2000)
POINT_DEC:        -2.678d {-02d 40' 39"} (J2000)
POINT_ROLL:      77.751d
GRB_DATE:        13608 TJD;   238 DOY;   05/08/26
GRB_TIME:        22795.09 SOD {06:19:55.09} UT
FILTER:          3, V
BKG_MEAN:        1061570777
N_STARS:         1435
X_OFFSET:        1514 [pixels]
Y_OFFSET:        40 [pixels]
X_MAX:           476 [pixels]
Y_MAX:           555 [pixels]
DET_THRESH:      8
PHOTO_THRESH:    3
SL_URL:          sw00152113000msufc.fits
SUN_POSTN:       155.06d {+10h 20m 14s}  +10.36d {+10d 21' 34"}
SUN_DIST:         68.19 [deg]
MOON_POSTN:       55.77d {+03h 43m 04s}  +23.40d {+23d 23' 58"}
MOON_DIST:        40.66 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      208.35,-14.67 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       87.48,-26.10 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN/SWIFT NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 26 Aug 05 06:23:28 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     152113,   Seg_Num: 0
POINT_RA:         87.735d {+05h 50m 56s} (J2000)
POINT_DEC:        -2.678d {-02d 40' 39"} (J2000)
POINT_ROLL:      77.751d
GRB_DATE:        13608 TJD;   238 DOY;   05/08/26
GRB_TIME:        22795.09 SOD {06:19:55.09} UT
FILTER:          3, V
BKG_MEAN:        1061570777
N_STARS:         1435
X_OFFSET:        1514 [pixels]
Y_OFFSET:        40 [pixels]
X_MAX:           476 [pixels]
Y_MAX:           555 [pixels]
DET_THRESH:      8
PHOTO_THRESH:    3
SL_URL:          sw00152113000msufc.fits
SUN_POSTN:       155.06d {+10h 20m 14s}  +10.36d {+10d 21' 34"}
SUN_DIST:         68.19 [deg]
MOON_POSTN:       55.77d {+03h 43m 04s}  +23.40d {+23d 23' 58"}
MOON_DIST:        40.66 [deg]
MOON_ILLUM:      54 [%]
GAL_COORDS:      208.35,-14.67 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       87.48,-26.10 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.

GCN notice #3884
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 notice #3885
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 notice #3887
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 notice #3888
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 notice #3889
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 notice #3891
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 notice #3898
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
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
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."
1006.3560 from 21 Jun 10
Emily M. Levesque et al.: The Host Galaxies of Gamma-Ray Bursts II: A Mass-Metallicity Relation for Long-Duration Gamma-Ray Burst Host Galaxies
We present a statistically robust mass-metallicity (M-Z) relation for long-duration gamma-ray burst (LGRB) host galaxies at z < 1. By comparing the LGRB host M-Z relation to samples representative of the general star-forming galaxy population, we conclude that LGRBs occur in host galaxies with lower metallicities than the general population, and that this trend extends to z ~ 1, with an average offset of -0.50 +/- 0.19 from the M-Z relation for star-forming galaxies. Our sample in this work includes new spectroscopic data for 6 LGRB host galaxies obtained at the Keck and Magellan telescopes, as well as 2 new host galaxies from the literature. Combined with data from our previous work, this yields a total sample of 6 LGRB host galaxies at z < 0.3 and 10 host galaxies at 0.3 < z < 1. We have determined a number of interstellar medium properties for our host galaxies using optical emission-line diagnostics, including metallicity, ionization parameter, young stellar population age, and star formation rate. Across our full sample of 16 LGRB hosts we find an average metallicity of log(O/H) + 12 = 8.4 +/- 0.3. Notably, we also measure a comparatively high metallicity of log(O/H) + 12 = 8.83 +/- 0.1 for the z = 0.296 host galaxy of GRB 050826. We also determine stellar masses (M*) for our LGRB host galaxy sample, finding a mean stellar mass of log(M*/Msun) = 9.25 (+0.19,-0.23).

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Jochen Greiner, last update: 21-Jun-2010 [Disclaimer]