Gamma-ray Burst 050421

(All information courtesy of the instrument teams.)

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Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 21 Apr 05 04:12:50 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     115135,   Seg_Num: 0
GRB_RA:          307.241d {+20h 28m 58s} (J2000),
                 307.229d {+20h 28m 55s} (current),
                 307.352d {+20h 29m 24s} (1950)
GRB_DEC:         +73.665d {+73d 39' 54"} (J2000),
                 +73.683d {+73d 40' 59"} (current),
                 +73.496d {+73d 29' 47"} (1950)
GRB_ERROR:       4.00 [arcmin radius, statistical only]
GRB_INTEN:       22529 [cnts]    Peak=379 [cnts/sec]
TRIGGER_DUR:     5.504 [sec]
TRIGGER_INDEX:   476     E_range: 25-100 keV
BKG_INTEN:       182684 [cnts]
BKG_TIME:        15040.00 SOD {04:10:40.00} UT
BKG_DUR:         48 [sec]
GRB_DATE:        13481 TJD;   111 DOY;   05/04/21
GRB_TIME:        15111.61 SOD {04:11:51.61} UT
GRB_PHI:           4.01 [deg]
GRB_THETA:        25.36 [deg]
SOLN_STATUS:     0x83
RATE_SIGNIF:     9.84 [sigma]
IMAGE_SIGNIF:    6.00 [sigma]
MERIT_PARAMS:     +1  +0  +0  +2  +2  +0  +0  +0 -23  +1 
SUN_POSTN:        29.03d {+01h 56m 06s}  +11.88d {+11d 52' 45"}
SUN_DIST:         76.30 [deg]
MOON_POSTN:      173.72d {+11h 34m 53s}   +5.72d {+05d 43' 23"}
MOON_DIST:        95.55 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      107.16, 19.53 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       46.01, 75.82 [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.  
COMMENTS:        Since the IMAGE_SIGNIF is less than 7 sigma, this is a questionable detection.

red DSS finding chart ps-file

GCN/SWIFT NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 21 Apr 05 04:14:14 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     115135,   Seg_Num: 0
GRB_RA:          307.2530d {+20h 29m 01s} (J2000),
                 307.2408d {+20h 28m 58s} (current),
                 307.3633d {+20h 29m 27s} (1950)
GRB_DEC:         +73.6528d {+73d 39' 10"} (J2000),
                 +73.6707d {+73d 40' 14"} (current),
                 +73.4840d {+73d 29' 03"} (1950)
GRB_ERROR:       5.8 [arcsec radius, statistical plus systematic]
GRB_INTEN:       2962.15 [arb]
GRB_SIGNIF:      6.63 [sigma]
GRB_DATE:        13481 TJD;   111 DOY;   05/04/21
GRB_TIME:        15222.32 SOD {04:13:42.32} UT
TAM[0-3]:        327.61 237.19 261.32 242.39
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:        29.03d {+01h 56m 06s}  +11.88d {+11d 52' 46"}
SUN_DIST:         76.30 [deg]
MOON_POSTN:      173.73d {+11h 34m 56s}   +5.72d {+05d 42' 56"}
MOON_DIST:        95.57 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      107.15, 19.52 [deg] galactic lon,lat of the burst
ECL_COORDS:       45.95, 75.81 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        WARNING: XRT alignment calibration is on-going, and there may be  
COMMENTS:        residual systematic offsets of several arcseconds not accounted for yet  
COMMENTS:        by our on-board position determination algorithm.  We have increased  
COMMENTS:        the estimated error circle radius to take this into account.

GCN/SWIFT NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 21 Apr 05 04:16:11 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     115135,   Seg_Num: 0
GRB_RA:          307.241d {+20h 28m 58s} (J2000),
                 307.229d {+20h 28m 55s} (current),
                 307.352d {+20h 29m 24s} (1950)
GRB_DEC:         +73.665d {+73d 39' 54"} (J2000),
                 +73.683d {+73d 40' 59"} (current),
                 +73.496d {+73d 29' 47"} (1950)
GRB_DATE:        13481 TJD;   111 DOY;   05/04/21
GRB_TIME:        15111.61 SOD {04:11:51.61} UT
TRIGGER_INDEX:   476
GRB_PHI:           4.01 [deg]
GRB_THETA:        25.36 [deg]
DELTA_TIME:      65465.00 [sec]
LC_URL:          sw00115135000msb.lc
SUN_POSTN:        29.03d {+01h 56m 06s}  +11.88d {+11d 52' 45"}
SUN_DIST:         76.30 [deg]
MOON_POSTN:      173.72d {+11h 34m 53s}   +5.72d {+05d 43' 23"}
MOON_DIST:        95.55 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      107.16, 19.53 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       46.01, 75.82 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-BAT GRB Lightcurve.  
COMMENTS:        This does not match any source in the ground catalog.

GCN/SWIFT NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 21 Apr 05 04:16:56 UT
NOTICE_TYPE:     Swift-XRT Lightcurve
TRIGGER_NUM:     115135,   Seg_Num: 0
POINT_RA:        307.216d {+20h 28m 52s} (J2000)
POINT_DEC:       +73.668d {+73d 40' 05"} (J2000)
LC_START_DATE:   13481 TJD;   111 DOY;   05/04/21
LC_START_TIME:   15225.11 SOD {04:13:45.11} UT
LC_STOP_DATE:    13481 TJD;   111 DOY;   05/04/21
LC_STOP_TIME:    15402.30 SOD {04:16:42.30} UT
LC_LIVE_TIME:    173.59 [sec], 98.0%
DELTA_TIME:      86222.81 [sec]
N_BINS:          100
TERM_COND:       0
LC_URL:          sw00115135000msx.lc
SUN_POSTN:        29.03d {+01h 56m 06s}  +11.88d {+11d 52' 46"}
SUN_DIST:         76.31 [deg]
MOON_POSTN:      173.74d {+11h 34m 56s}   +5.72d {+05d 42' 55"}
MOON_DIST:        95.55 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      107.16, 19.53 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       46.02, 75.82 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-XRT Lightcurve.

GCN notice #3296
L. Barbier (GSFC), D. Palmer (LANL), D. Burrows (PSU), A. Blustin (MSSL), C. Markwardt (GSFC/UMd), N. Gehrels (GSFC), P. Roming (PSU)
At 04:11:52 UT, the Swift Burst Alert Telescope (BAT) triggered and located on-board GRB050421 (trigger # 115135). The BAT on-board calculated location is RA, Dec 307.241, +73.665 (20:28:58, 73:39:54) (J2000) with an uncertainty of 4 arcmin (radius, 3-sigma, including estimated systematic uncertainty). The BAT light curve showed a weak, multipeak structure with a duration of about 10 seconds. The peak count rate was measured by BAT to be 1000 counts/sec in the 15 - 350 keV band.
The Swift spacecraft slewed promptly onto the BAT position and observations by the Swift X-Ray Telescope (XRT) began at 04:13:42 UT with the XRT in the auto state. An uncatalogued X-ray source was detected at the following position: RA, Dec 307.2542, +73.6528 (20:29:01, 73:39:10) (J2000) with an uncertainty of 5 arcsec (radius). This is 46 arcsec from the BAT position reported above.
The Swift Ultra-Violet/Optical Telescope (UVOT) began observations 112 seconds after the burst at 04:13:44 UT. Information on UVOT observations will be published in the next GCN.
GCN notice #3297
A. de Ugarte Postigo (IAA-CSIC), J. Furnes, R. Corradi (ING, La Palma), M. Jelinek, J. Gorosabel and A. J. Castro-Tirado (IAA-CSIC Granada),
report:
"Following the detection by SWIFT/BAT of GRB 050421 (Barbier et al. GCN Circ. 3296), we started observations at the 2.5m Isaac Newton Telescope at Observatorio del Roque de los Muchachos in La Palma. The first 120-s image (in the Sloan i-band filter), started on Apr 21.1858 UT (i.e. 15.7 min after the event). We do not see any object within the reported SWIFT/XRT position. Further analysis of additional i-band images is in progress."
This message can be quoted.
GCN notice #3298
M. Jelinek, A. J. Castro-Tirado, J. Gorosabel, A. de Ugarte Postigo=20 (IAA-CSIC Granada), P. Kubanek, R. Hudec (Astronomical Institute of the Academy of Sciences,=20 Ondrejov), T. J. Mateo Sanguino (Universidad de Huelva), T. Soria, R. Fern=E1ndez=20 (EELM-CSIC, M=E1laga) and J. Fabregat (Universidad de Valencia)
report:
"The BOOTES-2 very wide field camera, located at the Estaci=F3n=20 Experimental de La Mayora (EELM-CSIC) in M=E1laga, observed the region of= =20 the sky containing the SWIFT/BAT error box for GRB 050421 (Barbier et al. GCN 3296) as part of its routine=20 observing schedule. A 30 s exposure started at 04:12:00 UT (8 s after the onset of the 10 s long=20 burst), with the previous frame starting at 04:11:00 UT. A limiting (unfiltered) magnitude of 9.0=20 is derived for any prompt optical flash arising from this event."
This message can be quoted.
GCN notice #3299
S. Bradley Cenko and Derek B. Fox (Caltech) report on behalf of the Caltech-NRAO-GRB collaboration:
We have imaged the field of GRB050421 (GCN #3296) with the automated Palomar 60-inch telescope. Observations consisted of 17 x 120 s images in the Kron R band, taken at a mean epoch of 08:50 UT (~ 4.6 hours after the burst). We find no sources in the XRT error circle reported in GCN #3296. Our 3.0-sigma limiting magnitude, estimated by comparison with several stars from the Guide Star Catalog, is approximately R < 22.0.
GCN notice #3300
D. Fugazza (INAF-OABr), L.A. Antonelli, V. Testa (INAF-OAR), L. Di Fabrizio, G. Tessicini (INAF-TNG), and D. Malesani (SISSA), report on behalf of a larger collaboration:
We imaged the field of GRB 050421 (Barbier et al., GCN 3296) with the Italian 3.6m TNG. Observations were carried out under moderate observing conditions (seeing ~0.8"), just before the dawn. Exposures were acquired in the K filter, for a total integration time of 20 min, starting on Apr 21.2313 UT (mean time Apr 21.2453 UT, 1.7 h after the GRB).
We find no sources within the XRT error circle, down to a limiting magnitude K = 18.6 (3 sigma).
This message can be cited.
GCN notice #3301
O. Godet, M. Goad, K. Page, J. Osborne (U. Leicester), D. N. Burrows (PSU), N. Gehrels (NASA/GSFC) report on behalf of the Swift XRT team:
We have analyzed the Swift XRT data from the first orbit observation of GRB 050421. The refined coordinates are:
```
RA(J2000) = 20h 29m 01.75s
Dec(J2000) = +73d 39' 17.4"
```
This position is 40 arcseconds from the BAT position given in GCN 3296 (Barbier et al 2005). We estimate a total uncertainty of 5 arcseconds radius (90% containment). We note that this refined position is 8.1 arcseconds from the XRT position reported in GCN 3296. Optical observers should re-check their images for sources in the new error circle.
Our 0.2-10 keV light curve covers the interval 116-591 sec after the BAT trigger. It is well-fit with a broken powerlaw with initial slope of 0.9 +1.1/-1.6 breaking to a steeper slope of 3.3 +0.6/-0.3 after 147 +/-10 sec. All errors are 90% confidence. A single power law decline is not a good fit to the data.
A preliminary spectral fit to the WT mode data gives a power law photon index of 1.23 +0.37/-0.34 (error at 90% confidence level) in the 0.3-10 keV band, assuming Galactic absorption (1.44 E21 cm^-2) and a possible excess in the absorption of 6 +4/-3 E21 cm^-2. The unabsorbed 0.3-10 keV flux is 8.5E-10 erg cm^-2 s^-1 in the interval 116-171 sec after the BAT trigger.
GCN notice #3302
The field of GRB050421 (GCN 3296, using the updated position in GCN 3301) was observed with the Ryle Telescope in Cambridge at 15 GHz from 08:37 to 12:12 UT on 2005 Apr 21 (4h25m to 8h after the trigger). The angular resolution is 25".
A formal measure of the flux density at the position in GCN 3301 is 0.59 mJy with an rms noise 0.27 mJy, and is therefore not a convincing detection.
This message is quotable.
Guy Pooley, Astrophysics, Cavendish Laboratory
GCN notice #3303
V. Testa, L.A. Antonelli (INAF-OAR), D. Fugazza (INAF-OABr), L. Di Fabrizio, G. Tessicini (INAF-TNG), and D. Malesani (SISSA), report on behalf of a larger collaboration:
After the revision of the XRT position (Godet et al., GCN 3301) of the X-ray afterglow of GRB 050421 (Barbier et al., GCN 3296), we re-examined our TNG K-band images (Fugazza et al., GCN 3300).
We find no sources within the revised XRT error box down to the 3-sigma limit K > 18.6.
This message can be cited.
GCN notice #3304
E.S. Rykoff (U Mich), S.A. Yost (U Mich), H. Swan (U Mich) report on behalf of the ROTSE collaboration:
ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB 050421 (Swift trigger 115135), producing images beginning 9.7 s after the GCN notice time. An automated response took the first image at 04:12:58.8 UT, 67.2 s after the burst, under good conditions. These observations were affected by the bright moon. We took 10 5-sec, and 350 20-sec eposures. These unfiltered images are calibrated relative to USNO A2.0 (R).
Comparison to the DSS (second epoch) reveals no new sources within the 3-sigma BAT error circle including the 3-sigma XRT error circle (GCN 3301). Individual images have limiting magnitudes ranging from 16.49-17.34. In particular, we set a limit of magnitude 16.49 in a single 5 s exposure, starting 67.1 s after the burst. Coadding images into sets of 10 reveals no new sources down to limits of 17.8 (t0+61.7s - t0+130.7s) and 18.4 (t0+144s - t0+431s)
GCN notice #3305
T. Sakamoto (GSFC/NRC), L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (UMD), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), T. Mitani (ISAS), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS), M. Suzuki (Saitama), J. Tueller (GSFC), on behalf of the Swift/BAT team:
At 04:11:52 UT Swift-BAT detected GRB 050421 (trigger=115135) (GCN Circ 3296, Barbier et al.). The refined BAT ground position is (RA,Dec) = 307.306, +73.665, [deg; J2000] +- 3.4 arcmin, (95% containment). The partial coding was 91%.
The light curve has a FRED structure with a rise in < 1 second and a decay in ~10 seconds. T90 (15-350 keV) is (10.3 +- 2) seconds (estimated error including systematics).
The photon index of the time-averaged spectrum is 1.7 +-0.4. The fluence in the 15-350 keV band is (1.8 +- 0.7 ) x 10^-7 erg/cm2. The 1-s peak photon flux measured from T0+1.4 seconds in the 15-350 keV band and is (0.5 +- 0.1) ph/cm2/s. All the quoted errors are at the 90% confidence level.
GCN notice #3306
J. S. Bloom (UCB) reports on behalf of a larger collaboration:
"We observed the field of GRB 050421 (GCN 3296, GCN 3301) with the PAIRITEL 1.3m on Mt. Hopkins over several epochs. In a 502 sec exposure beginning on 2005-04-21 11:23:45 UT, we find a faint source in J,H,Ks, consistent with XRT position, located at:
```
  RA   20:29:00.94
  DEC +73:39.19.2  (J2000; uncertainty ~ 0.5 arcsec)
```
We have not checked the variability of this source so its identification as the afterglow cannot be confirmed at this time. We note that there is also a JHKs source just outside the XRT 5 arcsec error radius at (end figures): 02.01, 22.3."
This message may be cited.
GCN notice #3307
A. Blustin (MSSL), L. Barbier (GSFC), K. McGowan (MSSL), P. Roming (PSU), M. De Pasquale (MSSL), S. T. Holland (GSFC), N. Gehrels (GSFC), K. Mason (MSSL), J. Nousek (PSU), on behalf of the Swift UVOT team
Starting with the data taken ~245s after the BAT trigger (Barbier et al., GCN 3296) we have co-added the early time data of GRB 050421 in each of the Ultra-Violet/Optical Telescope (UVOT) V, B and U bands. The co-added images are made up of 9 x 10s exposures. No source is detected within the revised XRT error circle (Godet et al., GCN 3301) in any of the bands; we estimate the five sigma magnitude upper limits from the co-added images to be:
Filter Upper limit
```
V      17.5
B      19.1
U      18.8
```
The magnitudes are based on preliminary zero-points, measured in orbit, and will require refinement with further calibration.
This message may be cited.
GCN notice #3308
A. M. Soderberg (Caltech) and D. A. Frail (NRAO) report on behalf of the Caltech-NRAO-Carnegie GRB Collaboration:
"We observed the field centered on the BAT position of the Swift burst GRB 050421 (GCN#3296) using the VLA at a frequency of 8.46 GHz on Apr 21.62 UT (t ~ 0.4 days after the burst). We do not detect any radio sources within the XRT error circle (GCN#3301). We place a 2-sigma detection limit of 34 uJy on the field."
GCN notice #3309
A. M. Soderberg (Caltech) and D. A. Frail (NRAO) report on behalf of the Caltech-NRAO-Carnegie GRB Collaboration:
"We observed the field centered on the BAT position of the Swift burst GRB 050421 (GCN#3296) using the VLA at a frequency of 8.46 GHz on Apr 21.62 UT (t ~ 0.4 days after the burst). We do not detect any radio sources within the XRT error circle (GCN#3301). We place a 2-sigma detection limit of 34 uJy on the field."
GCN notice #3310
C. Blake and J. S. Bloom report on behalf of a larger collaboration:
"Following further analysis of ~2000 seconds of J,H,Ks observations of the field of GRB 050421 (GCN 3296, GCN 3301) with the PAIRITEL 1.3m on Mt. Hopkins we cannot confirm variability in the source reported in GCN 3306. Furthermore, analysis of our full J,H,Ks data set from UT April 21 does not reveal any sources detected at >3 sigma within the XRT error-circle."
This message may be cited.
GCN notice #3313
P.A. Price (IfA), T. Minezaki (U. Tokyo), L. Cowie (IfA) and Y. Yoshii (U. Tokyo) report on behalf of the UH-MAGNUM GRB collaboration:
We observed the XRT position of GRB 050421 (Godet et al., GCN #3301) with the automated MAGNUM telescope + MIP dual-beam optical-NIR imager, commencing at April 21.57 UTC (9.4 hours after the GRB). We obtained 9x60 sec images in JHK, reaching limiting magnitudes of J ~ 20.3 mag, H ~ 19 mag, K ~ 18.6 mag (from comparison with a single 2MASS star). We do not detect any afterglow candidate in the XRT error circle.
This message may be cited.

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Jochen Greiner, last update: 22-Apr-2005 [Disclaimer]