GRB 040903
GCN Circular 2690
Subject
Possible GRB 040903 detected with INTEGRAL
Date
2004-09-03T19:23:25Z (21 years ago)
From
Diego Gotz at IASF-CNR <diego@mi.iasf.cnr.it>
D. Gotz, S. Mereghetti (IASF-Milano) and N. Mowlavi (ISDC) on behalf of
the IBAS Localization Team report:
The off-line analysis of IBAS Alert # 1972 reveals a possible GRB of the
duration of 10 s detected in the 15-60 keV energy range. Its coordinates
are (J2000)
R.A. = 18h 03m 22s
Dec. = -25deg 15' 23''
with an uncertainty of 2.5 arcmin (90% c.l.).
Considering the location close to the Galactic Center and the soft
spectrum, we cannot exclude that this burst is due to a new galactic
source. Further analysis is underway.
GCN Circular 2691
Subject
Possible GRB 040903 - further analysis
Date
2004-09-03T19:52:45Z (21 years ago)
From
Diego Gotz at IASF-CNR <diego@mi.iasf.cnr.it>
D. Gotz and S. Mereghetti (IASF-Milano) report:
The burst time is 18:17:55 UTC. Its peak flux (over 1 s) in the 20-200 keV
band is ~0.4 ph/cmsq/s (2E-8 erg/cmsq/s).
We note that inside the error box of the refined position (GCN 2690),
there are 3 galactic sources (although never detected at these energies
before):
1RXS J180326.2-251556 18 03 26.20 -25 15 56.0
HD 164679 18 03 26.43 -25 15 59.4
IRC -30347 18 03 14.5 -25 14 23
This message can be cited.
GCN Circular 2692
Subject
ROTSE-III Rapid Response to possible GRB 040903 (INTEGRAL #1972)
Date
2004-09-03T21:32:31Z (21 years ago)
From
Don Smith at U michigan <dasmith@rotse2.physics.lsa.umich.edu>
Smith, D. A., Yost, S. A., & Rykoff, E. S. report on behalf of the ROTSE
collaboration:
ROTSE-IIIc at the H.E.S.S. site in Namibia responded automatically to the
INTEGRAL wakeup alert #1972. The first exposure began at 18:18:34.6 (UTC),
approximately 8 s after the alert time stamp and 40 s after the burst time
reported by Gotz & Mereghetti (GCN Circ. 2691). The ROTSE-IIIc system
automatically scheduled a series of exposures: 10 five-second images, 10
twenty-second images, and then a long series of sixty-second exposures. As of
this writing, we have analyzed 82 images, and find no evidence for any variable
source within the updated offline error circle that is not in the USNO A2.0
catalog. We estimate our unfiltered limiting magnitude to be roughly 15.1 in
the first two images, and then varying between 15.7 and 16.5 for all subsequent
images. The field is extremely crowded relative to the ROTSE-IIIc PSF, which
greatly reduces sensitivity. Co-adding ten frames does not significantly
improve the upper limits.
GCN Circular 2695
Subject
GRB 040903 - INTEGRAL data analysis
Date
2004-09-07T07:19:17Z (21 years ago)
From
Diego Gotz at IASF-CNR <diego@mi.iasf.cnr.it>
D. Gotz, S. Mereghetti (IASF-Milano), N. Produit and N. Mowlavi (ISDC)
report:
The analysis of INTEGRAL data reveal no presistent source at the position
of 040903 (Gotz et al., GCN 2690) with a 3 sigma upper limit of 10 mCrab.
Due to its soft spectrum, we conclude that the burst is either an X-Ray
Flash or, due to its location in the Galactic Bulge region, a hard and
powerful type I X-ray burst from a new transient source.
This message can be cited.
GCN Circular 2697
Subject
GRB040903, REM near-IR observation
Date
2004-09-07T12:51:21Z (21 years ago)
From
Vincenzo Testa at INAF/Astro. Obs. of Rome <testa@mporzio.astro.it>
V. Testa (INAF-OAR), S. Covino (INAF-OAB), L.A.Antonelli (INAF-OAR),
F.M.Zerbi (INAF-OAB), G. Chincarini(Univ. Milano Bicocca, INAF-OAB)
on behalf of the REM/ROSS team report
The robotic telescope REM observed the field of GRB040903 (IBAS #alert 1972,
Gotz et al., GCN 2690) with the IR camera REMIR in the filter H starting on
Sept. 03 at UT 22:58, 4.67 hrs after the first INTEGRAL alert.
Due to the poor weather conditions only one set of five 1s dithered images,
for a total exposure time of 5s, was acquired. The acquisition and image
preprocessing were done automatically. The photometry was calibrated with
a subset of the 2MASS catalog.
Off-line analysis revealed no evident new sources, compared to the 2MASS
catalog, within the error circle of INTEGRAL.
The detection upper limit (3 sigma) is H=15.2 and the extinction in the area
is A_H=2.56.
This message can be cited.
GCN Circular 2699
Subject
GRB040903 - A XRF?
Date
2004-09-09T11:22:45Z (21 years ago)
From
Erik Kuulkers at ESA/ESTEC-Integral(ISOC) <ekuulker@rssd.esa.int>
E. Kuulkers (ESA/ESTEC), D. Gotz, S. Mereghetti (IASF-Milano), P. Goldoni, A. Goldwurm
(CEA/Saclay) and S. Brandt (DSRI, Copenhagen)
report:
Prompted by the message (GCN #2695) that the possible GRB 040903 (GCN #2690, #2691)
discovered by IBAS might be either a X-ray flash (XRF) or a type I X-ray burst (XRB),
we further investigated this event.
The inital light curve of GRB 040903 shows basically two peaks, which is
reminiscent to that seen in hard X-ray light curves of strong photospheric radius
expansion XRBs from, e.g., 4U 1812-12 (see Cocchi et al. 2000, A&A 357, 527).
Also, both the GRB and XRBs reach peak intensities a few seconds after the
start of the events. We compared in more detail the temporal and spectral behaviour
of GRB 040903 with that of XRBs from 4U 1812-12, both as seen with the IBIS/ISGRI
instrument onboard INTEGRAL. The XRBs we focussed on were observed on 2003 April 25 and 27.
The 20-100 keV GRB spectrum integrated over the burst can be well fit by
a power-law model with a photon index of 2.9 +/- 0.4 (1 sigma error;
Chi^2_red = 0.6 for 16 dof), although a black-body model cannot be formally
ruled out (Chi^2_red = 1.1 for 16 dof). The latter model gives for the effective
temperature a value of kT = 6.9 +/- 1.5 keV, which is significantly higher than
the maximum value reached during any XRB (~3 keV).
The 20-100 keV spectrum of the XRB integrated over the burst can be well fit
by a black-body model with effective temperature kT = 2.9 +/- 0.3
(Chi^2_red = 0.5 for 5 dof), whereas a power-law model provides a rather bad fit
(Chi^2_red = 1.6 for 5 dof).
We used three energy bands to investigate the temporal behaviour at a time resolution
of 1 sec: 13-26 keV, 26-60 keV and 60-500 keV. The main differences between GRB 040903
and the XRBs are the following. The GRB is clearly seen in the 13-26 keV and 26-60 keV
bands, whereas the XRBs are only seen in the 13-26 keV band. During the first peak
of the GRB the event is harder with respect to the second peak, whereas the XRB
is soft during both peaks (as well as in between).
The light curves (and the hardness curve, i.e., the ratio of the counts in the 26-60 keV
band to that of the counts in the 13-26 keV band, versus time) can be retrieved from
ftp://astro.estec.esa.nl/pub/ekuulker/4u1812-12.ps and
ftp://astro.estec.esa.nl/pub/ekuulker/grb040903.ps.
Given that
1) GRB 040903 is significantly harder than the XRBs from 4U 1812-12,
2) the spectral evolution of the GRB is unlike that seen for the XRBs, but more common for
GRBs (and XRFs),
3) the integrated spectrum of the GRB is consistent with being due to power-law emission,
but not with black-body emission as expected during XRBs,
4) the GRB is not significantly detected above ~60 keV,
we favour GRB 040903 being a XRF.
This message can be cited.