GRB 040812
GCN Circular 2655
Subject
GRB 040812: Second epoch CXO Observations
Date
2004-08-25T01:53:25Z (21 years ago)
From
Chryssa Kouveliotou at MSFC <chryssa.kouveliotou-1@nasa.gov>
S. Patel (USRA/NSSTC), C. Kouveliotou (NASA/MSFC,NSSTC), S. Mereghetti,
D. Gotz (IASF-Milano), N. Lund, J. Chenevez (Danish Space Research
Institute), P. Ubertini (IASF-Rome), A. Levan (U. Leicester),
E. van den Heuvel (University of Amsterdam), K. Hurley (UCB), report on
behalf of a larger Integral team:
We observed with Chandra/ACIS-S the error box of the Integral GRB 040812
(Gotz et al. 2004, GCN 2640) for a second time starting on 2004-08-22 9:55
UT,
approximately 10 days after the trigger for 10 ks. We have compared the
sources reported in our earlier GCN on the first CXO observation (Patel et
al., 2004, GCN 2648) with the second CXO image, applying a SNR>2 selection
threshold. The results are shown in the Table below.
No. RA Dec Counts(1)* SNR Counts(2) SNR
1 16 26 0.47 -44 41 22.6 9 2.8 -- --
2 16 26 2.25 -44 43 49.4 57 6.9 38 5.4
3 16 26 6.48 -44 43 20.8 10 2.9 10 2.7
4 16 26 8.44 -44 41 25.2 33 5.0 33 5.2
5 16 26 1.71 -44 43 27.9 -- --- 16 3.7
*0.5-8.0 keV band
All coordinates are given in J2000.
We do not detect source #1 above SNR=2.0; a search in the corresponding
error
region in the second epoch CXO image reveals 5 net counts at this location.
We
conclude that there is no significant variation in that source within
statistics. Source #2 decayed with an index of approximately 0.6 between the
two CXO observations; this source, thus, seems to be most likely the
candidate
of the GRB 040812 afterglow, as also pointed out by Campana et al. 2004
(GCN 2649). Finally, a new source (#5) appeared within the IBIS error box;
inspection of the first image reveals 3 net counts at this location,
indicating a variable source.
We detect two of the radio sources (#2 and #4) reported by Ishwara Chandra
et al. 2004 (GCN # 2653) at the same flux level in both CXO observations.
We are grateful to the Chandra Science Data Center for processing the
data rapidly and in particular to Harvey Tananbaum and Andrea Prestwich
for approving this DDT observation.
GCN Circular 2650
Subject
GRB 040812: Optical counterparts of CXO sources
Date
2004-08-18T17:45:40Z (21 years ago)
From
Edo Berger at Caltech <ejb@astro.caltech.edu>
E. Berger (Carnegie Observatories) reports on behalf of a larger
collaboration:
"We inspected the positions of Chandra sources CXO 1-7 (GCN #2648),
detected in the error circle of GRB 040812 (GCN #2640), in our Keck LRIS
and Las Campanas Du Pont 2.5-m I-band images (GCN #2645):
CXO# RA Dec Counterpart?
---------------------------------------------------
1 16 26 00.47 -44 41 22.6 star
2 16 26 02.25 -44 43 49.4 ---- *
3 16 26 06.48 -44 43 20.8 star
4 16 26 08.44 -44 41 25.2 none **
5 16 25 54.65 -44 42 49.4 star/galaxy
6 16 25 58.73 -44 41 47.0 star/galaxy
7 16 26 1.21 -44 42 46.6 star
* CXO-2 is located about 20" away from a very bright star, and this
position is saturated in all of our images
** CXO-4 is located about 2" away from a galaxy/star
In addition, none of the optical counterparts (excluding CXO-2) exhibit
any significant variability either between the two Keck epochs (taken 47
and 104 minutes after the burst) or between the Keck and LCO observations
(taken 1.75 days after the burst)."
GCN Circular 2648
Subject
CXO observation of GRB 040812
Date
2004-08-18T15:27:41Z (21 years ago)
From
Peter Woods at UAH/MSFC <peter.woods@msfc.nasa.gov>
S. Patel (USRA/NSSTC), C. Kouveliotou (NASA/MSFC,NSSTC), S. Mereghetti,
D. Gotz (IASF-Milano), N. Lund, J. Chenevez (Danish Space Research
Institute), P. Ubertini (IASF-Rome), E. van den Heuvel (University of
Amsterdam), K. Hurley (UCB), report on behalf of a larger Integral team:
We observed with Chandra/ACIS-S the error box of the Integral GRB 040812
(Gotz et al. 2004, GCN 2640). The observation started at 2004-08-17
7:08:22 UT, approximately 5 days after the trigger, and lasted for 10
ks. We find 4 sources above SNR=2.6 within a 2' radius (90% c.l.)
centered at the refined Integral/IBIS location (RA=246.50, DEC=-44.70).
No. RA Dec Counts* SNR
1 16 26 0.47 -44 41 22.6 9 2.8
2 16 26 2.25 -44 43 49.4 57 6.9
3 16 26 6.48 -44 43 20.8 10 2.9
4 16 26 8.44 -44 41 25.2 33 5.0
*0.5-8.0 keV band
Within the Jem-X error region centered at RA=16:25:55.0, Dec=-44:42:40
(1.7' preliminary error radius) which is consistent with the IBIS
location, we detect no source above SNR=2.6. Our source detection
method found 3 sources above SNR=1.7 in this region as given below.
These sources become more significant when we increase the search
energy band to 0.1-10 keV.
No. RA Dec Counts* SNR
5 16 25 54.65 -44 42 49.4 6 1.9
6 16 25 58.73 -44 41 47.0 4 1.9
7 16 26 1.21 -44 42 46.6 4 1.9
*0.5-8.0 keV band
All coordinates are given in J2000.
None of these sources exhibits significant variability within the 10ks
observation. No X-ray source was found at the position of the radio
source reported by Soderberg et al (2004, GCN 2643). At this point we
cannot identify any of these sources as the counterpart of GRB040812,
and we strongly encourage searches for optical variability. Another
planned 10 ks Chandra DDT observation may reveal the GRB counterpart.
We are grateful to the Chandra Science Data Center for processing the
data rapidly and in particular to Harvey Tananbaum and Andrea Prestwich
for approving this DDT observation.
GCN Circular 2645
Subject
GRB 040812: Keck and LCO optical observations
Date
2004-08-14T22:59:59Z (21 years ago)
From
Edo Berger at Caltech <ejb@astro.caltech.edu>
E. Berger (Carnegie Observatories), D.B. Fox, S.R. Kulkarni (Caltech),
Wojtek Krzeminski and Mario Hamuy (Las Campanas Observatory, Carnegie)
report on behalf of a larger collaboration:
"We imaged the 2-arcmin error circle of GRB 040812 (GCN #2640) with the
Low-Resolution Imaging Spectrometer on the Keck-I telescope 47 and 104
minutes after the burst, and with the Du Pont 2.5-m telescope at Las
Campanas Observatory (LCO) 1.75 days after the burst. All observations
were taken in the I-band (Galactic extinction, A_I~2.3 mag). Within the
8-arcsec radius error cirle of the VLA source detected by Soderberg (GCN
#2643) we find several sources, but none exhibit significant variability
either between the two Keck epochs or between the Keck and LCO
observations. Visual comparison of the two Keck epochs do not reveal the
presence of a strongly fading source within the entire 2-arcmin INTEGRAL
error circle."
This message may be cited
GCN Circular 2644
Subject
GRB 040812: Keck and LCO observations
Date
2004-08-14T22:43:57Z (21 years ago)
From
Edo Berger at Caltech <ejb@astro.caltech.edu>
E. Berger (Carnegie Observatories), D.B. Fox, S.R. Kulkarni (Caltech),
Wojtek Krzeminski and Mario Hamuy (Las Campanas Observatory, Carnegie)
report on behalf of a larger collaboration:
"We imaged the 2-arcmin error circle of GRB 040812 (GCN #2640) with the
Low-Resolution Imaging Spectrometer on the Keck-I telescope 47 and 104
minutes after the burst, and with the Du Pont 2.5-m telescope at Las
Campanas Observatory (LCO) 1.75 days after the burst. All observations
were taken in the I-band (Galactic extinction, A_I~2.3 mag). Within the
8-arcsec radius error cirle of the VLA source detected by Soderberg (GCN
#2643) we find several sources, but none exhibit significant variability
either between the two Keck epochs or between the Keck and LCO
observations. Visual comparison of the two Keck epochs do not reveal the
presence of a strongly fading source within the entire 2-arcmin INTEGRAL
error circle."
This message may be cited
GCN Circular 2643
Subject
GRB 040812: radio observations
Date
2004-08-14T22:27:47Z (21 years ago)
From
Alicia Soderberg at Caltech <ams@astro.caltech.edu>
A. M. Soderberg (Caltech) reports on behalf of a larger
Caltech/NRAO/Carnegie collaboration:
"We have observed the error box of GRB 040812 (GCN 2640) with the Very
Large Array on 2004 August 14.15 UT (t ~ 2 days since burst). At 8.5
GHz we detect a 0.45 mJy source at location:
RA: 16:26:08.5 Dec: -44:41:04.0 (J2000)
with a positional uncertainty of 8 arcsec (radius). The source is
also detected at 4.9 GHz with a flux density of 0.79 mJy giving
a spectral index of beta ~ -1 between the two observing bands.
This spectral index is inconsistent with those measured for
early radio afterglows.
No other sources are detected within the error box with
a 2 sigma detection limit of 0.14 and 0.16 mJy at 4.9 and 8.5
GHz, respectively.
Further observations are planned."
GCN Circular 2642
Subject
GRB040812, optical/IR observations
Date
2004-08-13T18:06:44Z (21 years ago)
From
Charles Bailyn at Yale/Astro <bailyn@astro.yale.edu>
B. E. Cobb and C. D. Bailyn (Yale), part of the larger SMARTS
consortium, report:
Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
obtained optical/IR imaging of the error region of GRB 040812
(Gotz et al. GCN 2640) beginning ~18.4 hours post-burst
(2004-08-13 00:25 UT). Optical imaging in B,V,R and I has a
field of view of 6'x6' and, therefore, covers the entire GRB
error circle. IR imaging in J, H, K and Y has a smaller field
of view and covers a region totalling 3 square arcminutes in
the middle of the quoted error region. Several dithered images
were obtained in each filter, with total summed exposure times
of 180s in each of BRIYJK and 120s in each of H and V.
Preliminary visual comparison of the optical images to the SDSS
and the IR images to 2MASS frames does not reveal any new sources
to the limit of the comparison frames.
GCN Circular 2640
Subject
GRB 040812: a long GRB detected by INTEGRAL
Date
2004-08-12T06:52:50Z (21 years ago)
From
Diego Gotz at IASF-CNR <diego@mi.iasf.cnr.it>
D. Gotz, S. Mereghetti (IASF, Milano), N. Mowlavi, M. Beck, J.Borkowsk
(ISDC) on behalf of the IBAS Localization Team report:
A 20 s long GRB has been detected with the INTEGRAL Burst Alert System
(IBAS) on August 12 at 06:01:50 UT. The GRB has been detected with
IBIS/ISGRI in the 15-200 keV band (IBAS Alert # 1901)
Its coordinates (J2000) are:
R.A. 16h 26m 05s
Dec. -44deg 42' 32''
with an uncertainty of 2 arcmin (90% c.l. radius)
The preliminary peak flux in the 20-200 keV range is about 0.6
photons/cmsq/s (5E-8 erg/cmsq/s) (1 s integration time).
A preliminary spectral analysis inidcates that this event is X-ray rich.
This message can be cited.