- GCN/BACODINE POSITION NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Sat 25 Dec 10 18:56:17 UT
NOTICE_TYPE: Swift-BAT GRB Position
TRIGGER_NUM: 441015, Seg_Num: 0
GRB_RA: 0.234d {+00h 00m 56s} (J2000),
0.375d {+00h 01m 30s} (current),
359.594d {+23h 58m 23s} (1950)
GRB_DEC: +44.602d {+44d 36' 06"} (J2000),
+44.663d {+44d 39' 46"} (current),
+44.323d {+44d 19' 24"} (1950)
GRB_ERROR: 3.00 [arcmin radius, statistical only]
GRB_INTEN: 0 [cnts] Image_Peak=7159 [image_cnts]
TRIGGER_DUR: 1088.000 [sec] (=18.1 [min])
TRIGGER_INDEX: 20000 E_range: 15-50 keV
BKG_INTEN: 0 [cnts]
BKG_TIME: 0.00 SOD {00:00:00.00} UT
BKG_DUR: 0 [sec]
GRB_DATE: 15555 TJD; 359 DOY; 10/12/25
GRB_TIME: 67065.50 SOD {18:37:45.50} UT
GRB_PHI: -40.15 [deg]
GRB_THETA: 22.85 [deg]
SOLN_STATUS: 0x13
RATE_SIGNIF: 0.00 [sigma]
IMAGE_SIGNIF: 8.06 [sigma]
MERIT_PARAMS: +1 +0 +0 +5 +1 -2 +0 +0 +23 +0
SUN_POSTN: 274.22d {+18h 16m 53s} -23.38d {-23d 22' 49"}
SUN_DIST: 103.60 [deg] Sun_angle= -5.7 [hr] (East of Sun)
MOON_POSTN: 152.43d {+10h 09m 43s} +6.53d {+06d 32' 05"}
MOON_DIST: 122.97 [deg]
MOON_ILLUM: 76 [%]
GAL_COORDS: 113.55,-17.35 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 21.61, 40.02 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS: SWIFT-BAT GRB Coordinates.
COMMENTS: This is an image trigger. (The RATE_SIGNIF & BKG_{INTEN, TIME, DUR} are undefined.)
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: This trigger occurred at longitude,latitude = 37.82,20.24 [deg].
- red DSS finding chart
ps-file
- GCN NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Sat 25 Dec 10 18:59:17 UT
NOTICE_TYPE: Swift-BAT GRB Lightcurve
TRIGGER_NUM: 441015, Seg_Num: 0
GRB_RA: 0.234d {+00h 00m 56s} (J2000),
0.375d {+00h 01m 30s} (current),
359.594d {+23h 58m 23s} (1950)
GRB_DEC: +44.602d {+44d 36' 06"} (J2000),
+44.663d {+44d 39' 46"} (current),
+44.323d {+44d 19' 24"} (1950)
GRB_DATE: 15555 TJD; 359 DOY; 10/12/25
GRB_TIME: 67065.50 SOD {18:37:45.50} UT
TRIGGER_INDEX: 20000
GRB_PHI: -40.15 [deg]
GRB_THETA: 22.85 [deg]
DELTA_TIME: 0.00 [sec]
TRIGGER_DUR: 1088.000 [sec] (=18.1 [min])
SOLN_STATUS: 0x13
RATE_SIGNIF: 0.00 [sigma]
IMAGE_SIGNIF: 8.06 [sigma]
LC_URL: sw00441015000msb.lc
SUN_POSTN: 274.22d {+18h 16m 53s} -23.38d {-23d 22' 49"}
SUN_DIST: 103.60 [deg] Sun_angle= -5.7 [hr] (East of Sun)
MOON_POSTN: 152.46d {+10h 09m 49s} +6.52d {+06d 31' 22"}
MOON_DIST: 122.99 [deg]
MOON_ILLUM: 76 [%]
GAL_COORDS: 113.55,-17.35 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 21.61, 40.02 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS: SWIFT-BAT GRB Lightcurve.
COMMENTS:
COMMENTS: The next comments were copied from the BAT_POS Notice:
COMMENTS: This is an image 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: This trigger occurred at longitude,latitude = 37.82,20.24 [deg].
COMMENTS: This lightcurve contains more than 50 illegal values -- probably an empty lightcurve.
COMMENTS: So the FITS file will have empty/missing rows -- possibly all rows will be missing.
COMMENTS: One explanation is a long Image-trigger(>~10min); another is corrupted tlm.
- GCN NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Sat 25 Dec 10 19:01:21 UT
NOTICE_TYPE: Swift-XRT Position
TRIGGER_NUM: 441015, Seg_Num: 0
GRB_RA: 0.1992d {+00h 00m 47.80s} (J2000),
0.3402d {+00h 01m 21.64s} (current),
359.5593d {+23h 58m 14.22s} (1950)
GRB_DEC: +44.6017d {+44d 36' 06.1"} (J2000),
+44.6628d {+44d 39' 46.2"} (current),
+44.3233d {+44d 19' 23.8"} (1950)
GRB_ERROR: 5.1 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN: 2.36e-09 [erg/cm2/sec]
GRB_SIGNIF: 8.83 [sigma]
IMG_START_DATE: 15555 TJD; 359 DOY; 10/12/25
IMG_START_TIME: 68448.54 SOD {19:00:48.54} UT, 1383.0 [sec] since BAT Trigger Time
TAM[0-3]: 327.61 237.26 261.44 243.53
AMPLIFIER: 2
WAVEFORM: 134
SUN_POSTN: 274.22d {+18h 16m 54s} -23.38d {-23d 22' 49"}
SUN_DIST: 103.58 [deg] Sun_angle= -5.7 [hr] (East of Sun)
MOON_POSTN: 152.48d {+10h 09m 54s} +6.51d {+06d 30' 53"}
MOON_DIST: 123.02 [deg]
MOON_ILLUM: 76 [%]
GAL_COORDS: 113.52,-17.34 [deg] galactic lon,lat of the burst
ECL_COORDS: 21.58, 40.03 [deg] ecliptic lon,lat of the burst
COMMENTS: SWIFT-XRT Coordinates.
COMMENTS: The XRT position is 1.49 arcmin from the BAT position.
- GCN NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Sat 25 Dec 10 19:01:32 UT
NOTICE_TYPE: Swift-XRT Image
TRIGGER_NUM: 441015, Seg_Num: 0
GRB_RA: 0.1992d {+00h 00m 47.8s} (J2000),
0.3402d {+00h 01m 21.6s} (current),
359.5593d {+23h 58m 14.2s} (1950)
GRB_DEC: +44.6017d {+44d 36' 06.1"} (J2000),
+44.6628d {+44d 39' 46.2"} (current),
+44.3233d {+44d 19' 23.8"} (1950)
GRB_ERROR: 5.0 [arcsec, radius, statistical plus systematic]
GRB_INTEN: 78 [cnts]
IMG_START_DATE: 15555 TJD; 359 DOY; 10/12/25
IMG_START_TIME: 68448.54 SOD {19:00:48.54} UT, 1383.0 [sec] since BAT Trigger Time
CENTROID_X: 214.21, raw= 214 [pixels]
CENTROID_Y: 368.48, raw= 368 [pixels]
ROLL: 250.31 [deg]
GAIN: 1
MODE: 3, Long Image mode
WAVEFORM: 134
EXPO_TIME: 2.50 [sec]
GRB_POS_XRT_Y: 166.16
GRB_POS_XRT_Z: -207.64
IMAGE_URL: sw00441015000msxps_rw.img
SUN_POSTN: 274.22d {+18h 16m 54s} -23.38d {-23d 22' 49"}
SUN_DIST: 103.58 [deg] Sun_angle= -5.7 [hr] (East of Sun)
MOON_POSTN: 152.48d {+10h 09m 54s} +6.51d {+06d 30' 50"}
MOON_DIST: 123.02 [deg]
MOON_ILLUM: 76 [%]
GAL_COORDS: 113.52,-17.34 [deg] galactic lon,lat of the burst
ECL_COORDS: 21.58, 40.03 [deg] ecliptic lon,lat of the burst
COMMENTS: SWIFT-XRT Image.
- GCN NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Sat 25 Dec 10 19:01:43 UT
NOTICE_TYPE: Swift-XRT Processed Image
TRIGGER_NUM: 441015, Seg_Num: 0
GRB_RA: 0.1992d {+00h 00m 47.8s} (J2000),
0.3402d {+00h 01m 21.6s} (current),
359.5593d {+23h 58m 14.2s} (1950)
GRB_DEC: +44.6017d {+44d 36' 06.1"} (J2000),
+44.6628d {+44d 39' 46.2"} (current),
+44.3233d {+44d 19' 23.8"} (1950)
GRB_ERROR: 5.0 [arcsec, radius, statistical plus systematic]
GRB_INTEN: 78 [cnts]
IMG_START_DATE: 15555 TJD; 359 DOY; 10/12/25
IMG_START_TIME: 68448.54 SOD {19:00:48.54} UT, 1383.0 [sec] since BAT Trigger Time
CENTROID_X: 214.21, raw= 214 [pixels]
CENTROID_Y: 368.48, raw= 368 [pixels]
ROLL: 250.31 [deg]
GAIN: 1
MODE: 3, Long Image mode
WAVEFORM: 134
EXPO_TIME: 2.50 [sec]
GRB_POS_XRT_Y: 166.16
GRB_POS_XRT_Z: -207.64
IMAGE_URL: sw00441015000msxps_rw.img
SUN_POSTN: 274.22d {+18h 16m 54s} -23.38d {-23d 22' 49"}
SUN_DIST: 103.58 [deg] Sun_angle= -5.7 [hr] (East of Sun)
MOON_POSTN: 152.48d {+10h 09m 55s} +6.51d {+06d 30' 48"}
MOON_DIST: 123.03 [deg]
MOON_ILLUM: 76 [%]
GAL_COORDS: 113.52,-17.34 [deg] galactic lon,lat of the burst
ECL_COORDS: 21.58, 40.03 [deg] ecliptic lon,lat of the burst
COMMENTS: SWIFT-XRT Processed Image.
- GCN Circular #11493
J. L. Racusin (NASA/GSFC), A. P. Beardmore (U Leicester),
S. Campana (INAF-OAB), M. M. Chester (PSU),
J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC),
J. M. Gelbord (PSU), S. T. Holland (CRESST/USRA/GSFC),
J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA),
O. M. Littlejohns (U Leicester), K. L. Page (U Leicester),
B. Sbarufatti (INAF-OAB/IASFPA) and M. H. Siegel (PSU) report on
behalf of the Swift Team:
At 18:37:45 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 101225A (trigger=441015). Swift slewed immediately to the burst.
However, given that this was a 1088-second image trigger, the time from the
trigger time (at the start of the image interval) to the XRT observation is
over 23 minutes. The BAT on-board calculated location is
RA, Dec 0.234, +44.602 which is
RA(J2000) = 00h 00m 56s
Dec(J2000) = +44d 36' 06"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). Since this was an image trigger, the
currently available BAT light curve does not show significant structure.
The XRT began observing the field at 19:00:48.5 UT, 1383.0 seconds
after the BAT trigger. XRT found a bright, uncatalogued X-ray source
located at RA, Dec 0.1992, +44.6017 which is equivalent to:
RA(J2000) = 00h 00m 47.80s
Dec(J2000) = +44d 36' 06.1"
with an uncertainty of 5.1 arcseconds (radius, 90% containment). This
location is 89 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.
UVOT data products have not been received at this time.
The BAT trigger was an unusually long image trigger. Due to the
relative proximity to the Galactic plane (l=113.55,b=-17.35), and lack
of fading information from XRT at this time, we are unsure if this
trigger is a GRB or transient. We will report as more information is
available.
Burst Advocate for this burst is J. L. Racusin (judith.racusin AT 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 #11494
M. Andreev, A. Sergeev (Terskol Branch of Institute of Astronomy),
A.Pozanenko (IKI) on behalf of larger GRB follow up collaboration report:
We observed the field of the Swift trigger 441015 = GRB 101225A? (Racusin
et al, GCN 11493) with Zeiss-600 telescope of Mt.Terskol observatory.
In the XRT error circle (Racusin et al, GCN 11493) we do not detect any
sources down to R=21.5 (3 sigma):
UT (mid time), Exposure, Filter, ULimit
19:46 21 x 120s R 21.5
The combined image can be found at
http://grb.eam.ru/Swift_441015/Trigger_441015_Zeiss600.jpg
- GCN Circular #11495
D. Xu (Weizmann Inst.), I. Ilyin (AIP), J.P.U. Fynbo (DARK/NBI) report
on behalf of a larger collaboration:
We observed the field of GRB 101225A (Racusin et al., GCN 11493) at
the Nordic Optical Telescope (NOT) equipped with StanCam. We obtained
3x300 s exposures in each of the V, R, and I filters, starting at
20:10:33.5 UT, 25/12/2010 (i.e., 1.54681 hrs after the BAT trigger).
Within the XRT error circle only one optical source is detected in our
images in each filter at coordinates
(RA,Dec)(J2000.0) = (00:00:47.5, +44:36:02.4)
(error-radius: 0.7 arcsec)
This source lies on the southwestern border of the Swift/XRT error
circle and not apparently extended. We found R=22.1+/-0.1 mag
(calibrated with nearby USNO B1 stars) at 20:13:3.5 UT (i.e., 1.58847
hrs after the BAT trigger).
Further NOT observation is undergoing in order to check the brightness
variation of this source.
- GCN Circular #11496
D. Xu (Weizmann Inst.), I. Ilyin (AIP), J.P.U. Fynbo (DARK/NBI) report
on behalf of a larger collaboration:
We continued to observe the field of GRB 101225A (Racusin et al., GCN
11493) at the Nordic Optical Telescope (NOT) equipped with StanCam. We
obtained 2x300 s exposures in each of the R and I filters, starting at
23:57:30.9 UT, 25/12/2010 (i.e., 5.32942 hrs after the BAT trigger).
The optical source detected in our previous images (Xu et al., GCN
11495) is still present in the new stacked images for both R and I
filters. We found m(R)=22.6+/-0.2 mag at 00:06:03 UT, 26/12/2010
(i.e., 5.47167 hrs after the BAT trigger), which shows that this
object has decreased 0.5 mag in the R filter between the two epochs
with a mean power-law decay index \alpha~0.4. The magnitude in the I
filter, m(I)=21.6+/-0.2, largely remains unchanged.
We thus conclude that this optical source is likely the afterglow of
GRB 101225A. And further observation is encouraged.
- GCN Circular #11497
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester)
report on behalf of the Swift-XRT team.
Using 6262 s of XRT Photon Counting mode data and 15 UVOT
images for GRB 101225A, 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 = 0.19778, +44.60027 which is equivalent
to:
RA (J2000): 00h 00m 47.47s
Dec (J2000): +44d 36' 01.0"
with an uncertainty of 1.4 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, MNRAS, 397, 1177).
This circular was automatically generated, and is an official product of the
Swift-XRT team.
- GCN Circular #11498
K.L. Page (U. Leicester) and J. L. Racusin (NASA/GSFC) report on behalf
of the Swift-XRT team:
We have analysed 13 ks of XRT data for possible GRB 101225A (Racusin et
al., GCN Circ. 11493), from 1.4 ks to 35.6 ks after the BAT trigger.
The data comprise 2.7 ks in Windowed Timing (WT) mode with the
remainder in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Evans et al. (GCN. Circ 11497).
The light curve shows substantial structure, but the underlying
continuum can be modelled with a broken power-law decay. The initial
decay index is alpha= 1.108 (+/-0.011). At T+21682 s the decay steepens
to an alpha of 5.93 (+/-0.30).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.71 (+/-0.04). The
best-fitting absorption column is 1.78 (+/-0.11) x 10^21 cm^-2, in
excess of the Galactic value of 7.9 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 1.96 (+/-0.06) and a
best-fitting absorption column of 1.58 (+0.16, -0.15) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 4.1 x 10^-11 (5.6 x 10^-11) erg cm^-2
count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.58 (+0.16, -0.15) x 10^21 cm^-2
Galactic foreground: 7.9 x 10^20 cm^-2
Excess significance: 17.1 sigma
Photon index: 1.96 (+/-0.06)
If the light curve continues to decay with a power-law decay index of
5.59, the count rate at T+24 hours will be 0.0007 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.7 x
10^-14 (3.7 x 10^-14) erg cm^-2 s^-1.
We note that this is the brightest afterglow that the XRT has ever
observed at a few thousand seconds after the trigger.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00441015.
This circular is an official product of the Swift-XRT team.
- GCN Circular #11499
M. H. Siegel (PSU) and J. L. Racusin (NASA/GSFC)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 101225A
1387 s after the BAT trigger (Racusion et al., GCN Circ. 11493). We
find
a marginal detection in the later data consistent with the enhanced
XRT position (Evans et al., GCN Circ. 11497). Preliminary 3-sigma upper
limits and magnitudes using the UVOT photometric system
(Poole et al. 2008, MNRAS, 383, 627) for the exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
V 1387 1705 58 >19.11
V 5572 29944 2601 >21.40
B 1485 1655 38 >19.84
B 5161 28991 3933 21.73+-0.29
U 1460 1630 38 >19.35
U 4955 7534 507 >20.68
UVW1 1435 1754 58 >19.25
UVW1 5982 7413 393 20.58+-0.37
UVM2 1410 1729 58 >18.74
UVM2 5777 7208 393 20.12+-0.34
UVW2 1512 1680 38 >18.82
UVW2 5367 6798 393 19.67+-0.22
UVW2 11650 12550 885 20.35+-0.22
UVW2 17470 18370 885 19.62+-0.15
UVW2 23218 29897 1771 20.10+-0.14
The values quoted above are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.10 in the direction of the burst
(Schlegel et al. 1998).
- GCN Circular #11500
D. M. Palmer (LANL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), J. L. Racusin (NASA/GSFC),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (OSU),
J. Tueller (GSFC), T. N. Ukwatta (GWU) (i.e. the Swift-BAT team):
Using the data set from T-131 to T+1366 sec from the recent telemetry downlink,
we report further analysis of Swift/BAT GRB 101225A (trigger #441015)
(Racusin, et al., GCN Circ. 11493). The BAT ground-calculated position is
RA, Dec = 0.2037, +44.5739 deg which is
RA(J2000) = 00h 00m 48.9s Dec(J2000) = +44d 34' 26.0"
with an uncertainty of 3.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 85%.
The mask-tagged light curve shows that the GRB entered the BAT field of view at
~T-80 sec during a pre-planned slew. The flux slowly declined after this point
and then increased at about T+600 seconds. There were less significant
fluctuations until the end of the event data at about T+1300. T90 (15-350 keV)
is 1088.0 +- 20.0 sec (estimated error including systematics).
The time-averaged spectrum from T+0 to T+963 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.82 +- 0.32. The fluence in the 15-150 keV band is 1.9 +- 0.4 x 10-6 erg/cm2.
The 1-sec peak photon flux measured from T+0.00 sec in the 15-150 keV band
is 0.0 +- 0.0 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/441015/BA/
- GCN Circular #11501
S. Campana (INAF-OAB), S. Covino (INAF-OAB),
J.L. Racusin (NASA/GSFC) and K. L. Page (U Leicester)
report on behalf of the Swift Team:
GRB 101225A was detected by Swift BAT as an image trigger (Racusin
al. 2010, GCN 11493). Swift XRT started observing 1383 s after the
trigger observing the main event. The afterglow is very bright and
the XRT remained in the Windowed Timing (WT) mode for two consecutive
orbits. Within each orbit the spectrum remain constant as judged from
the hardness ratio and from the power law photon index.
We extract the XRT spectra for each of the first two orbits, separately.
We then fit the two spectra within XSPEC using the model
tbabs * ztbabs * (cutoff), keeping the same absorption pattern and leaving
free the cutoff power-law model for the two spectra (the cutoff power-law
model provides much better results in terms of column density evaluation
with respect to a simple power-law model when small spectral variations
are present).
We assume a Galactic column density of 7.9x10^20 cm-2 (Kalberla et al.
2005, A&A 440 775) and we allow for a 30% uncertainty in the fit. We
binned the spectra to 50 counts per energy bin and used the latest (v12)
response matrix. The detection in the UVW2 filter by UVOT (Siegel &
Racusin 2010, GCN 11499) constrains the redshift to be <1.4.
The fit with the cutoff power-law is relatively good with a reduced
chi^2 of 1.13 (508 dof).
Motivated by the similarities with GRB 060218 (extremely long duration,
soft prompt-emission spectrum, bright smoothly decaying X-ray afterglow
light curve, UV detection with optical non-detection), we fit the X-ray
spectrum including a blackbody component.
The fit improves considerably (and the cutoff energy goes well above the
XRT energy band, becoming unimportant for both spectra).
The new fit provides a reduced chi^2 of 1.07 (504 dof), based on an F-test
the addition of the blackbody component improves the fit by 4.2 sigma.
In the intrinsic column density vs. redshift plane there is just one
deep minimum hinting for a redshift z=0.07^+0.13_-0.04 (90% confidence
level) and an intrinsic column density N_H(z)=(1.5^+0.5_-0.2)x10^21 cm^-2.
The power law component shows a small softening from the first to the
second orbit, with a photon index around 2.2-2.4.
The blackbody component is hot with a temperature of ~1 keV, consistent
among the two observations. The blackbody radius decreases from the first
observation to the second from ~2x10^10 cm to ~0.6x10^10 cm.
Ground-based optical follow-up observations are strongly encouraged in order
to get spectroscopic confirmation for the redshift estimate and, eventually,
to monitor the coming out of a supernova.
- GCN Circular #11502
K. Wiersema, N. Tanvir (Leicester) and A. Levan (Warwick) report:
We observed the afterglow of GRB 101225A (Racusin et al. GCN 11493; Xu et al.
GCN 11496) with the 4.2m William Herschel Telescope.
We used the ACAM instrument to obtain imaging in r and i filters, and low
resolution spectroscopy.
The afterglow is clearly detected in individual images of 300 second
exposure, at R=22.8 +/- 0.2 mag (uncertainties are dominated by scatter in
USNO-B star magnitudes), at 28.2 hrs after burst. The source appears
pointlike, in the 1.1 arcsecond seeing conditions. We note that this
magnitude compared with the Xu et al value (GCN 11496) implies a very
shallow decay.
We obtained two low resolution spectra immediately following the imaging,
each with 1200 second exposure time. Continuum emission is detected
in the 5000 - 9300 A range, but no significant emission or absorption
lines are detected. Detection of continuum up to 5000 A gives a formal
constraint on the redshift of z<3.1.
At the redshift estimated by Campana et al. (GCN 11501) we would expect to
detect emission lines in the ACAM spectra (e.g. Balmer lines, [O III]),
implying that the spectrum is either strongly dominated by the afterglow
(the host is faint) or that the emission lines are redshifted into
wavelength areas dominated by strong skylines.
We thank Ovidiu Vaduvescu for excellent support.
- GCN Circular #11503
C. C. Thoene, J. Gorosabel, S. Guziy, P. Kub�nek, A. J. Castro-Tirado
(IAA-CSIC), A. de Ugarte Postigo (DARK-NBI) and D. Xu (Weizmann Institute)
report:
"We observed the afterglow of the "Christmas burst" GRB 101225A (GCN
11493, Racusin et al.) on Dec. 26, starting 18:49 UT (1.008 days after the
burst onset) with the 1.23m telescope at the Spanish-German Calar Alto
Observatory in Southern Spain. Observations were obtained in V, R and I
with total exposure times of 21x180s, 19x180s and 17x180s respectively.
From the stacked images we obtain the following preliminary magnitudes for
the optical afterglow (GCN 11495, Xu et al.) based on calibrations with
Landolt standard stars taken immediately after the observations:
V = 23.1
R = 22.2
I = 21.3
with errors of about 0.2 mag.
This would imply that the afterglow has rebrightened after the first day
(GCNs 11495 and 11496, Xu et al.) and, considering the possible low
redshift of the GRB from the bright X-ray afterglow (GCN 11501, Campana et
al.), this could be due to the onset of the accompanying SN, similar to
the case of GRB 060218 (Campana et al. 2006). It is more significant if we
consider the fast decay that is observed in X-rays (GCN 11498 Page et
al.).
We note that the magnitude reported by Wiersema et al. (GCN 11502) shows a
shallow decay at a similar epoch, implying that there could be a problem
of cross calibration of the different photometries or a non smooth
behavior. In any case the evolution of the optical light curve would be
rather flat, compared to other GRB light curves.
Further follow up observations are planned."
- GCN Circular #11504
J. R. Cummings (GSFC/UMBC) and T. Sakamoto (GSFC/UMBC)
on behalf of the Swift-BAT team:
We report further results of BAT observations of GRB 101225A (Racusin, et al.,
GCN Circ. 11493).
The most intense emission observed by BAT from GRB 101225A in the 14-50 keV range
occurred from T+1372 to T+1672 seconds, later than previously reported (Palmer,
et al. GCN circ #11500). The source was not in the BAT field of view from T-4500
to T-100 sec, from T+1088 to T+1372 sec, and from T+1758 to T+4936 sec. There was
no detectable emission prior to T-4500 sec, and the burst appears to have started
sometime before the source entered the BAT field of view at T-100 sec.
The spectrum from T+1372 to T+1672 seconds is similar to the earlier report, with
a single power law photon index of 1.87 +- 0.21. The total fluence was greater,
possibly much greater, than 3 x 10^-6 ergs/cm^2 or about 1.6 times the fluence
reported earlier.
BAT detection of extremely long emission is similar to that of GRB 060218 and
GRB 100316D (both spectroscopically confirmed SN-GRBs).
- GCN Circular #11505
M. Serino, T. Mihara, Y.E. Nakagawa, M. Sugizaki,
T. Yamamoto, T. Sootome, M. Matsuoka (RIKEN),
N. Kawai, M. Morii, K. Sugimori, R. Usui (Tokyo Tech),
K. Kawasaki, S. Ueno, H. Tomida, M. Kohama, M. Ishikawa (JAXA),
A. Yoshida, K. Yamaoka, S. Nakahira (AGU),
H. Tsunemi, M. Kimura (Osaka U.), H. Negoro, M. Nakajima
H. Ozawa, F. Suwa (Nihon U.), Y. Ueda, N. Isobe,
S. Eguchi, K. Hiroi (Kyoto U.), A. Daikyuji (Miyazaki U.),
K. Yamazaki, A. Uzawa, T. Matsumura (Chuo U.),
report on behalf of the MAXI team:
MAXI/GSC observed the field of the Swift trigger 441015 = GRB 101225A
(Racusin et al, GCN 11493) before and after the trigger time.
The transit times (UT) and the observed fluxes in 2-10 keV energy band are
15:51 (T-9988s) -19 +- 11 mCrab
17:23 (T-4483s) 20 +- 13 mCrab
18:54 (T+1002s) 20 +- 15 mCrab
20:05 (T+5218s) 11 +- 9 mCrab
23:08 (T+16209s) 2 +- 7 mCrab
All the quoted uncertainties are 1-sigma statistical errors.
Note that the third transit occurred within the 1088-second Swift image trigger interval. While it is not statistically significant, there appears be a weak X-ray enhancement at the location of the Swift trigger position during or near the BAT detection times (Cummings and Sakamoto, GCN 11504).
- GCN Circular #11506
S. B. Cenko (UC Berkeley) reports on behalf of a larger collaboration:
We have imaged the field of GRB101225A (Racusin et al., GCN 11493) with
the automated Palomar 60 inch telescope. Images were obtained in the
Sloan r' and i' filters on 2010 December 28 beginning at 01:49 UT (~ 55.2
hours after the BAT trigger time).
We detect a faint source at the location of the optical afterglow (Xu et
al., GCN 11495) in both filters. Using a set of nearby sources from the
USNO-B1 catalog for reference, we measure the following magnitudes for the
source at this time: R = 22.8 +/- 0.2; I = 22.3 +/- 0.2.
Our R-band measurement is consistent with that found by Wiersema et al
(GCN 11502) at t ~ 28 hours, but fainter (in both R and I) than the values
reported by Thoene at al (GCN 11503) at a similar time. In either case,
we find no evidence for a re-brightening as of yet, as would be expected
for the emergence of supernova emission from a nearby event like
GRB060218/SN2006aj.
- GCN Circular #11507
R. Chornock, G. H. Marion, G. Narayan, E. Berger, and A. M. Soderberg
(Harvard/CfA) report:
We obtained spectroscopy of the optical source (Xu et al., GCN 11495; Xu
et al., GCN 11496; Siegel et al., GCN 11499; Wiersema et al., 11502;
Thoene et al., 11503; Cenko et al., 11506) associated with GRB 101225A
(Racusin et al., GCN 11493) using the Blue Channel Spectrograph on the
6.5-m MMT. Two 2400 s observations starting on December 29.1 UT covered
the spectral range 3175-8385 Angstroms. The source has a smooth blue
continuum and no clear emission or absorption features associated with a
host galaxy are detected in our spectra, similar to the findings of
Wiersema et al. (GCN 11502). In addition, the continuum has no obvious
broad undulations or evidence for line blanketing shortward of 4000
Angstroms, such as would be expected if the spectral features of a
supernova were emerging. The spectrum is well fit by a power law of the
form F_nu ~ constant * nu^(0.4), which is bluer than typical afterglow
spectra, which typically scale as F_nu ~ nu^(-0.6).
- GCN Circular #11508
D. Xu (Weizmann Inst.), P. Hakala (Turku U.), J.P.U. Fynbo (DARK/NBI)
report on behalf of a larger collaboration:
We imaged the filed of GRB(or XRF) 101225A (Racusin et al., GCN 11493)
at the Nordic Optical Telescope (NOT) equipped with either StanCam or
ALFOSC in B, V, R, and I filters. The R-band optical afterglow (Xu et
al., GCN 11495) light curve was found decaying very slowly from
m(R)=22.6 +/- 0.2 at 5.47167 hrs after the BAT trigger to m(R)=22.8
+/- 0.2 at 55.2 hrs after the BAT trigger (Xu et al., GCN 11496;
Wiersema et al., GCN 11502; Thoene et al., GCN 11503; Cenko, GCN
11506).
Two 450 s R-band images were obtained with NOT/ALFOSC, starting at
21:50:46.9 UT, 30/12/2010 (i.e., 123.217 hrs after the BAT trigger)
under the conditions of seeing ~1". The afterglow was clearly detected
in the stacked image, largely pointlike, and had m(R)=23.3+/-0.2. This
indicates that R-band afterglow is now decaying faster compared with
its behavior during the past days, and that the host hasn't dominated
the brightness, being consistent with the featureless spectroscopy
(Wiersema et al., GCN 11502; Chornock et al., 11507).
- GCN Circular #11519
D. Xu (Weizmann Inst.), D. Malesani, J.P.U. Fynbo, J. Hjorth
(DARK/NBI), P. Jakobsson (U. Iceland), T. Augusteijn (NOT), report on
behalf of a larger collaboration:
We imaged the field of GRB 101225A (Racusin et al., GCN 11493) at the
Nordic Optical Telescope (NOT) equipped with ALFOSC. We obtained 6x600
s R-band images with a good seeing ~0.7" and little cloud cover.
Observations started at 20:55:25 UT on 2011 Jan 4 (i.e., 10.1 days
after the BAT trigger).
The optical counterpart of the burst (Xu et al., GCN 11495) has faded
further and it is detected in the stacked image with R = 24.1+/-0.1,
calibrated against the USNO-B1 star #1345-0000324. The object is now
significantly extended along the northwest-southeast direction,
indicating a significant contribution from the underlying host galaxy.
Further observations are encouraged, especially in the NIR.
- GCN Circular #11522
D. Xu, A. Gal-Yam (WIS), J. P. U. Fynbo (DARK/NBI), report on behalf
of a large collaboration:
Spectroscopy of the host galaxy of GRB 101225A (Racusin et al., GCN
11493; Xu et al. GCN 11519) was carried out at the 10m Keck-I
telescope equipped with the Low Resolution Imaging Spectrometer (LRIS)
around 10 UT, 6th Jan. 2011, with a good seeing ~0.7". A 900s spectrum
was obtained and it consists of a red and a blue channels, covering
~3200-5500 A and ~5000-8200 A, respectively. The spectrum has a low
signal-to-noise ration and the trace is best detected in the red
channel. Three weak emission lines are found at a common redshift of
z=0.40, considered as Hbeta (4861 AA), and the O III (4960 AA, 5007
AA).
Isotropic energy: >~ 7.8+/-1.6 x10^50 erg, using the BAT fluence
(Palmer et al., GCN 11500)
The absence of evidence for an emerging SN at the above redshift
suggests that GRB 101225A is a SN-less or SN-weak long GRB event.
Further deep spectroscopic observations are encouraged.
- GCN Circular #11550
Dale A. Frail (NRAO) reports on behalf of a larger collaboration:
"We observed GRB 101225A (GCN#s 11494, 11497, 11498, 11499, 11500)
with the Expanded Very Large Array (EVLA) on 2011 January 6.99 UT using
the C-band wide receiver (frequency range 4-8 GHz).
No significant radio signal is detected at the enhanced Swift-XRT
position (GCN 11497) at frequencies of 4.5 and 7.9 GHz and at 3-sigma
levels of 42 uJy and 30 uJy, respectively.
No further observations are planned.
- GCN Circular #11563
J. P. U. Fynbo (DARK/NBI), D. Xu (WIS) report on behalf of a larger
collaboration:
We re-analyzed the 900s low signal-to-noise spectrum reported in our
previous GCN #11522. We found that the brightest of the three weak
emission features is due to bad removal of a cosmic ray hit. The two
other features are close to sky emission lines. We thus conclude that
the reported redshift of z=0.4 in GCN #11522 for this event is not
secure and may be wrong. Deep spectroscopic observations from 8-10 m
telescopes are strongly encouraged. We apologize for the confusing
this report may have caused.
We also continued photometric follow-ups of the optical counterpart of
GRB 101225A at NOT, and obtained 6x600 s R-band images on Jan. 9 with
a good seeing ~0.65". The object decayed to m(R)=24.5+/-0.2 compared
to m(R)=24.1+/-0.1 on Jan. 5 in GCN #11519. However, this time it was
largely pointlike, which is at odds with being found
significantly extended along the northwest-southeast direction on Jan.
5. The decay in brightness and the variation in morphology indicates
that the underlying host galaxy, if any, still hasn't dominated the
optical counterpart.
Further photometric and spectroscopic observations are underway.
- GCN Circular #11564
N.R. Tanvir (U. Leicester), A.J. Levan (U. Warwick), J.P.U. Fynbo,
D. Malesani, J. Hjorth (DARK/NBI), A. Gal-Yam (Weizmann Inst.)
K. Wiersema, P.A. Evans (U. Leicester) & D.F. Bersier (Liverpool JMU)
report:
We observed the location of GRB 101225A (Racusin et al. GCN 11493; Xu
et al.=C2=A0 GCN 11495) using HST/ACS on 2011 Jan 13 beginning at 00:25 U=
T,
approximately 18 days post-burst.=C2=A0 Images were obtained in the F606W
and F435W filters.=C2=A0 Contrary to the claim in Xu et al. (GCN 11519), =
we
find no evidence for extension in either image, and thus no indication
of a host galaxy.=C2=A0 We do, however, find the colour of the optical
transient is now quite red with an (AB) colour of F435W-F606W=3D1.6,
confirming the reddening trend from the initially very blue colour
(Chornock et al. GCN 11507).=C2=A0 The magnitude (F606W(AB)=3D24.6) is
consistent with a continuing post-break power-law decline in the
R-band with a slope t^-1.
We note that if this event is at a redshift as low as z=3D0.07, as
suggested by an analysis of the X-ray data (Campana et al.=C2=A0 GCN
11501), then any host galaxy beneath the transient would have to be
both very faint (less than about M_R=3D-12) and compact not to be seen
in the HST images.
We thank the STScI staff for rapidly implementing these observations.
- GCN Circular #11568
C. C. Thoene, S. Guizy, A. Castro-Tirado, J. Gorosabel (IAA-CSIC) and A.
de Ugarte Postigo (DARK/NBI) report:
We observed the optical counterpart of GRB 101225A (the Christmas burst,
GCN 11493, Racusin et al.) with OSIRIS at the 10.4m GTC on Dec. 27,
starting at 21:20 UT (51h after the trigger). We obtained 2 exposures of
1800s using grism R300B.
The combined and flux-calibrated spectrum shows a smooth, very blue
continuum without any absorption of emission features, consistent with the
spectral observations from WHT (GCN 11502, Wiersema et al.), MMT (GCN
11507, Chornock et al.) and Keck/LRIS (GCN 11563, Fynbo et al.) at
different times after the trigger. The continuum is well fitted using a
power law with F(nu) = nu^(0.9+/-0.5).
Considering the very flat optical light curve, the apparent color changes
in the optical SED, the shape of the X-ray spectrum (GCN 11501, Campana et
al.) and the lack of a host galaxy (GCN 11564, Tanvir et al.), we think
that this object might not be a GRB but rather a compact object from the
MW or the local group. Further follow-up is encouraged to determine the
nature of this peculiar object.
- GCN Circular #11570
N.R. Tanvir, P.A. Evans, O.M. Littlejohns (U. Leicester), A.J. Levan (U. =
Warwick)
report:
In light of the continuing uncertainty about the nature of GRB 101225A,
we performed a search for any periodic signal in the BAT and XRT light cu=
rves
for this event.=C2=A0 In neither case do we find any significant periods =
in the data: from
~0.01 Hz (100 s periods) to ~100 Hz (0.01 s periods) in the case of BAT (=
data from
50-900 s post-trigger), and from ~0.004 Hz (250 s periods) to ~1 Hz in XR=
T (2nd orbit
data).
- GCN Report 314.1
GCN_Report 314.1 has been posted:
http://gcn.gsfc.nasa.gov/reports/report_314_1.pdf
by J.L. Racusin
at NASA/GSFC
titled: "Final report on Swift Observations of GRB 101225A"
- GCN Circular #11594
Won-Kee Park, Myungshin Im, Changsu Choi (Seoul National Univ.),
Hyeonju Jeong, Juhee Lim, and Soojong Pak (Kyung Hee Univ.)
The field of GRB 101225A was observed with CQUEAN, an optical
CCD camera attached at the 2.1m telescope at McDonald Observatory,
USA. The observation was carried out from 01:16:23 UT, Dec. 26, 2010,
with i, r, z, and Y filters, with exposures of 3 * 300 secs for each
band.
The afterglow was clearly visible on i and r-band images at
the same position reported by Xu et al.(GCN 11495). We obtained
the preliminary magnitude of the afterglow on the stacked i-band
image calibrated with the neighboring USNO B-1.0 stars:
R = 22.60 +- 0.19 at 01:42:47 UT. Further analysis of the data is
ongoing.
- GCN Circular #11642
A.J. Levan (U. Warwick), N.R. Tanvir (U. Leicester) report for a
larger collaboration:
We obtained imaging of GRB 101225A (Racusin et al. GCN 11493) with
GMOS on Gemini North on 5 Feb 2011. At this epoch we obtained a
total of 2400s in a narrow band H-alpha filter (centered a z~0) and
900s in the r-band.
The afterglow is weakly detected in the H-alpha image, but not in the
contemporaneous r-band imaging. This suggests substantial spectral
evolution from the early-time spectroscopy (Chornock et al. GCN
11507), and that line emission is now contributing significantly
to the emission between 6000-7000A.
Given the absence of any host galaxy, and the extremely unusual
characteristics of this event, the most natural explanation is that
we are detecting Ha at z~0 from some class of high-energy
transient. If that is the case, three possible locations seem most
likely:
(a) it could be a source within the Milky Way, sufficiently far
away that the progenitor was undetected in prior imaging,
(b) it could be in the far halo of M31 at a distance of at least
~115 kpc
(c) it could be associated with the distant Local Group dwarf
spheroidal galaxy Andromeda XVIII, which itself is located ~1.4 Mpc
from us, but is only ~12 kpc from the line of sight to 101225A.
We note that the early optical and X-ray emission (in particular
the ratio of the two) remain extremely unusual for known Galactic
transients.
We thank the staff of Gemini North for the rapid and effective
execution of these observations.
- GCN Circular #11751
GRB 101225A, the review of the sky area in plate archives
V.V. Golovnya, L.M. Kizyun, L.K. Pakuliak (Main Astro Obs, Kyiv)
report:
We have undertaken the review of the sky area of GRB 101225A
(P.A. Evans et al., GCN 11497) on astronegatives, collected
in Ukrainian NAS Main astronomical observatory plate archive
(1976-1996). All the plates with the possible object appearance
are digitized using Microtek ScanMaker 9800XL TMA flatbed scanner
and have been placed into Golosiiv Plate Archive database DBGPA
with open access to them. No any object has been found in the
point with the mentioned coordinates of GRB.
The list of plates is given in the table:
YYYYMMDD UT Plates Exp. LimMag
19850815 00:26:01 GUA040C000702A 16.0 16.15
19841212 16:51:23 GUA040C000587 16.0 15.35
19840827 23:46:55 GUA040C000468A 16.0 15.35
19930923 21:33:33 GUA040C002237 18.0 15.35
19840827 23:12:28 GUA040C000467A 16.0 16.10
19840905 22:33:06 GUA040C000491 18.0 16.35
19850815 00:02:05 GUA040C000701 16.0 16.15
19871024 19:40:17 GUA040C001153A 18.0 15.35
19840809 01:08:44 GUA040C000441 16.0 14.10
19840905 22:58:22 GUA040C000492A 18.0 16.55
Plates: the plate's identifier in GUA040C archive of DWA
(D/F=400/2000, M=103"/mm)
of the Ukrainian NAS Main Astro obs in Kyiv
(Marsden's number - 83)[1].
Exp. - Duration of the maximum exposure (minutes).
LimMag - Limited V mag, derived in the 15 minutes area around the
location given in P.A. Evans et al., GCN 11497:
RA (J2000): 00h 00m 47.47s, Dec (J2000): +44d 36' 01.0".
The preview images of 10 areas together with
the 15 min.of arc area from SkyMap can be found in
http://gua.db.ukr-vo.org/img/grb/101225A/index.html
The images with full resolution are available via e-mail on demand.
References:
1.L.Pakuliak DATABASE of GOLOSIIV PLATE ARCHIVE (DBGPA V2.0),
http://gua.db.ukr-vo.org
- GCN Circular #11752
GRB 101225A, the review of the sky area in plate archives
V.V. Golovnya, L.M. Kizyun, L.K. Pakuliak (Main Astro Obs, Kyiv)
report:
We have undertaken the review of the sky area of GRB 101225A
(P.A. Evans et al., GCN 11497) on astronegatives, collected
in Ukrainian NAS Main astronomical observatory plate archive
(1976-1996). All the plates with the possible object appearance
are digitized using Microtek ScanMaker 9800XL TMA flatbed scanner
and have been placed into Golosiiv Plate Archive database DBGPA
with open access to them. No any object has been found in the
point with the mentioned coordinates of GRB.
The list of plates is given in the table:
YYYYMMDD UT Plates Exp. LimMag
19850815 00:26:01 GUA040C000702A 16.0 16.15
19841212 16:51:23 GUA040C000587 16.0 15.35
19840827 23:46:55 GUA040C000468A 16.0 15.35
19930923 21:33:33 GUA040C002237 18.0 15.35
19840827 23:12:28 GUA040C000467A 16.0 16.10
19840905 22:33:06 GUA040C000491 18.0 16.35
19850815 00:02:05 GUA040C000701 16.0 16.15
19871024 19:40:17 GUA040C001153A 18.0 15.35
19840809 01:08:44 GUA040C000441 16.0 14.10
19840905 22:58:22 GUA040C000492A 18.0 16.55
Plates: the plate's identifier in GUA040C archive of DWA
(D/F=400/2000, M=103"/mm)
of the Ukrainian NAS Main Astro obs in Kyiv
(Marsden's number - 83)[1].
Exp. - Duration of the maximum exposure (minutes).
LimMag - Limited V mag, derived in the 15 minutes area around the
location given in P.A. Evans et al., GCN 11497:
RA (J2000): 00h 00m 47.47s, Dec (J2000): +44d 36' 01.0".
The preview images of 10 areas together with
the 15 min.of arc area from SkyMap can be found in
http://gua.db.ukr-vo.org/img/grb/101225A/index.html
The images with full resolution are available via e-mail on demand.
References:
1.L.Pakuliak DATABASE of GOLOSIIV PLATE ARCHIVE (DBGPA V2.0),
http://gua.db.ukr-vo.org
- GCN Circular #11770
A. Zauderer, E. Berger, and W. Fong (Harvard) report:
We observed the position of the Christmas GRB 101225A for 32 minutes
with the EVLA at a frequency of 5 GHz on 2010 December 30.03, less than
five days after the burst (GCN 11493). We find no significant radio
source at the XRT position (GCN 11497) to a 3-sigma upper limit of 60
microJy.
We thank the EVLA staff for their support of these observations over the
holidays.
- GCN Circular #11819
N. R. Tanvir (U. Leicester) and A. J. Levan (U. Warwick) report:
We have re-reduced and re-analysed more thoroughly the imaging reported
in GCN 11642. While it remains the case that the optical transient is
detected in the H-alpha narrow-band filter, and at best marginally present
in the r-band, the significance of the excess H-alpha detection is reduced.
Within the associated errors the revised photometry is broadly consistent
with the red colour of the transient at this time (the narrow-band filter
being
somewhat redward of the central wavelength of the r-band filter), and hence,
the data do not require significant line emission. This argument for a z~0
origin is therefore weakened.
- 1105.3015 from 17 May 11
C.C. Thöne et al.: An unusual stellar death on Christmas Day
Massive stars can end their lives in many different ways. Long Gamma-Ray Bursts (GRBs) are the most dramatic examples, releasing
ultra-relativistic ejecta that produce non-thermal emission when interacting with the surrounding medium (Zhang et al. 2004). Usually, those
events are accompanied by a supernova (SN) (Woosley et al. 2006). In a few low-redshift GRB-SNe we could observe the actual breakout of the
shock front from the surface of the star (Campana et al. 2006). Here we present GRB 101225A, a very peculiar event at a distance of 1.6 Gpc. A
bright X-ray transient with a thermal component and an unusual optical counterpart followed an exceptionally long gamma-ray event. During the
first 10 days, the optical emission evolved as an expanding, cooling blackbody with a large initial radius, after which a faint SN was
observed. The absence of a normal GRB afterglow implies that some dense material, likely ejected by the progenitor star, completely thermalized
the high-energy emission. A possible progenitor is a helium star/neutron star binary which underwent a common envelope phase, expelling its
hydrogen envelope prior to the explosion. The final merging process created a GRB-like event where we observe the shock breakout of the
secondary star before the high-energy emission gets thermalized in the collision with the previously expelled shell, until finally the emission
from the SN itself takes over. GRB 101225A defines a new, rare type of blackbody-dominated GRB which explodes in a dense environment created by
the progenitor system itself.
- 1112.0018 from 2 Dec 11
S. Campana et al.: A minor body falling onto a neutron star as an explanation for the unusual gamma-ray burst GRB 101225A
G. Ghisellini, A. Melandri, E. Pian, R. Salvaterra, G. Cusumano, V. D'Elia, D. Fugazza, E. Palazzi, B. Sbarufatti, S. D. Vergani
The tidal disruption of a solar mass star around a supermassive black hole has been extensively studied analytically and numerically. In these
events the star develops into an elongated banana-shaped structure. After completing an eccentric orbit, the bound debris fall onto the black
hole, forming an accretion disk and emitting radiation. The same process may occur on planetary scales, if a minor body orbits too close to its
star. In the Solar System, comets fall directly onto our Sun or onto planets. If the star is a compact object, the minor body can become
tidally disrupted. Indeed, one of the first mechanisms invoked to produce strong gamma-ray emission involved accretion of comets onto neutron
stars in our Galaxy. Here we report that the peculiarities of the `Christmas' gamma-ray burst (GRB 101225A) can be explained by a tidal
disruption event of a minor body around a Galactic isolated neutron star. This result would indicate either that minor bodies can be captured
by compact stellar remnants more frequently than it occurs in our Solar System or that minor body formation is relatively easy around
millisecond radio pulsars. A peculiar Supernova associated to a GRB may provide an alternative explanation.
- 1302.2352 from 12 Feb 13
A.J. Levan et al.: A new population of ultra-long duration gamma-ray bursts
We present comprehensive multiwavelength observations of three gamma-ray bursts (GRBs) with durations of several thousand seconds. We
demonstrate that these events are extragalactic transients; in particular we resolve the long-standing conundrum of the distance of GRB 101225A
(the "Christmas-day burst"), finding it to have a redshift z=0.847, and showing that two apparently similar events (GRB 111209A and GRB
121027A) lie at z=0.677 and z=1.773 respectively. The systems show extremely unusual X-ray and optical lightcurves, very different from
classical GRBs, with long lasting highly variable X-ray emission and optical light curves that exhibit little correlation with the behaviour
seen in the X-ray. Their host galaxies are faint, compact, and highly star forming dwarf galaxies, typical of "blue compact galaxies". We
propose that these bursts are the prototypes of a hitherto largely unrecognized population of ultra-long GRBs, that while observationally
difficult to detect may be astrophysically relatively common. The long durations may naturally be explained by the engine driven explosions of
stars of much larger radii than normally considered for GRB progenitors which are thought to have compact Wolf-Rayet progenitor stars. However,
we cannot unambiguously identify supernova signatures within their light curves or spectra. We also consider the alternative possibility that
they arise from the tidal disruption of stars by supermassive black holes.
- 1307.5061 from 19 Jul 13
Daisuke Nakauchi et al.: Blue Supergiant Model for Ultra-Long Gamma-Ray Burst with Superluminous-Supernova-Like Bump
Long GRBs (LGRBs) have typical duration of $\sim 30\ {\rm s}$ and some of them are associated with hypernovae, like Type Ic SN 1998bw.
Wolf-Rayet stars are the most plausible LGRB progenitors, since the free-fall time of the envelope is consistent with the duration, and the
natural outcome of the progenitor is a Type Ic SN. While a new population of ultra-long GRBs (ULGRBs), GRB 111209A, GRB 101225A, and GRB
121027A, has a duration of $\sim 10^4$ s, two of them are accompanied by superluminous-supernova (SLSN) like bumps, which are $\lesssim 10$
times brighter than typical hypernovae. Wolf-Rayet progenitors cannot explain ULGRBs because of too long duration and too bright SN-like bump.
A blue supergiant (BSG) progenitor model, however, can explain the duration of ULGRBs. Moreover, SLSN-like bump can be attributed to the
so-called cocoon-fireball photospheric emissions (CFPEs). Since a large cocoon is inevitably produced during the relativistic jet piercing
though the BSG envelope, this component can be a smoking-gun evidence of BSG model for ULGRBs. In this paper, we examine u, g, r, i, and J-band
light curves of three ULGRBs and demonstrate that they can be fitted quite well by our BSG model with the appropriate choices of the jet
opening angle and the number density of the ambient gas. In addition, we predict that for 121027A, SLSN-like bump could have been observed for
$\sim 20 \mbox{-} 80$ days after the burst. We also propose that some SLSNe might be CFPEs of off-axis ULGRBs without visible prompt emission.
- 1408.1305 from 7 Aug 14
Carlos F. Cuesta-Martínez et al.: Numerical models of black body dominated GRBs: I. Hydrodynamics and the origin of the thermal emission
We extend an existing theoretical model to explain the class of Black-Body Dominated GRBs, namely long lasting events characterized by the
presence of a notable thermal component trailing the GRB prompt emission, and a rather weak traditional afterglow. GRB 101225A, the Christmas
Burst (CB), is a prototype of such class. It has been suggested that BBD-GRBs could result from the merger of a binary system formed by a
neutron star and the Helium core of a main sequence star. We have modeled the propagation of ultrarelativistic jets through the environment
left behind the merger by means of detailed relativistic hydrodynamic numerical simulations. In this paper, the output of our numerical models
is further postprocessed to obtain the (thermal) radiative signature of the resulting outflow. The complete (thermal and non-thermal) output of
our models is considered in a companion contribution. Here, we outline the most relevant dynamical details of the jet propagation and connect
them to the generation of thermal radiation in GRB events akin to that of the CB. A comprehensive parameter study of the jet/environment
interaction has been performed and synthetic light curves are confronted with the observational data. The thermal emission in our models
originates from the interaction between the jet and the Hydrogen envelope ejected during the neutron star / He core merger. We find that the
lack of a classical afterglow and the accompanying thermal emission in BBD-GRBs can be explained by the interaction of an ultrarelativistic jet
with a toroidally shaped ejecta whose axis coincides with the binary rotation axis. We obtain that the spectral inversion and reddening
happening at about 2 days in the CB can be related to the time at which the massive shell ejected in an early phase of the common-envelope
evolution of the progenitor system is completely ablated by the ultrarelativistic jet.
- 1408.1814 from 11 Aug 14
Carlos F. Cuesta-Martínez et al.: Numerical models of black body dominated GRBs: II. Emission properties
We extend an existing theoretical model to explain the class of Black-Body Dominated (BBD) gamma-ray bursts (GRBs), long lasting events
characterized by the presence of a significant thermal component trailing the GRB prompt emission, and also by an absence of a traditional
afterglow. GRB 101225A, the Christmas Burst, is a prototype of such class. It has been suggested that BBD-GRBs could be observed after a merger
in a binary system consisting of a neutron star and a Helium core of a main sequence star. Using detailed relativistic hydrodynamic numerical
simulations we model the propagation of ultrarelativistic jets through the environments created by such mergers. In this paper we focus on
explaining the emission properties of the jet evolution computing the whole radiative signature (both thermal and non-thermal) of the jet
dynamical evolution. A comprehensive parameter study of the jet/environment interaction has been performed and synthetic spectra and light
curves are compared with the observational data. The lack of a classical afterglow and the presence of thermal emission in BBD-GRBs are
consistent with the interaction of an ultrarelativistic jet with a toroidally shaped ejecta whose axis coincides with the binary system
rotation axis. We find that the non-thermal (synchrotron) emission of the forward shock of the jet is dominant during the early phases of the
evolution, during which that shock is still moderately relativistic. The contribution of the reverse shock is of the same magnitude than that
of the forward shock during the first 80 minutes after the GRB. Later, it quickly fades because the jet/environment interaction chocks the
ultrarelativistic jet beam and effectively dumps the reverse shock.
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