XRF 040812
GCN Circular 2656
Subject
XRF040812: possible afterglow second Chandra observation
Date
2004-08-25T08:53:50Z (21 years ago)
Edited On
2025-09-09T18:36:48Z (a month ago)
From
Sergio Campana at INAF-OAB <campana@merate.mi.astro.it>
Edited By
courey.elliott@gmail.com
S. Campana and A. Moretti (INAF-Osservatorio astronomico di Brera) report on
behalf of a larger team:
"We analyzed the second Chandra ACIS-S observation of the XRF040812
(Gotz et
al. 2004, GCN 2640). We carried out spectral analysis of our previous
afterglow candidate (CXOJ162602.3-444349, Campana & Moretti GCN 2649,
see also
Patel et al. GCN 2648, 2655). The source is still very hard with a power law
photon index of 0.9+/-0.6 (fixing the column density to the Galactic
value of
5.3x10^21 cm-2 and using Cash statistics in the XSPEC fit). The spectrum is
slightly softer than in the first observation (Campana & Moretti GCN
2649). The unabsorbed 0.5-10 keV source flux is 9.30x10^-14 erg cm-2 s-1 a
factor of ~3 lower than in the previous Chandra observation. A constant
temporal evolution is not consistent with the data at a ~4.5 sigma level. A
power law decay describes better the temporal evolution with a time decay as
t^-1.4(+/-0.6) (90% confidence level, note that this is different from the
Patel et al. GCN 2655, since we fitted the flux evolution and not the counts
evolution)."
This message can be cited.
GCN Circular 2653
Subject
XRF040812: GMRT observations
Date
2004-08-24T10:48:05Z (21 years ago)
Edited On
2025-09-09T18:36:46Z (a month ago)
From
D. Bhattacharya at Raman Research Inst. <dipankar@rri.res.in>
Edited By
courey.elliott@gmail.com
C.H. Ishwara Chandra and A.P. Rao (National Centre for Radio Astrophysics,
Pune, India), L. Resmi and D. Bhattacharya (Raman Research Institute,
Bangalore, India) report:
We imaged the XRF040812 field at 1280 MHz on Aug 16, 2004 using the
Giant Metrewave Radio Telescope. The following previously uncatalogued
sources were detected within a 15' field of view centered at the
position of the VLA source reported by Soderberg et al (2004, GCN 2643).
No. RA (J2000) Dec (J2000) flux (mJy)
1. 16 26 08.404 -44 41 27.2 0.8
2. 16 26 15.674 -44 43 56.2 2.5
3. 16 26 13.025 -44 47 08.8 1.9
4. 16 26 08.795 -44 47 46.0 1.0
5. 16 26 09.448 -44 47 51.0 1.9
Typical astrometric uncertainties in the above coordinates are
expected to be better than an arcsec, but ionospheric refraction due to
low elevation could introduce a systematic shift up to 2 arc sec.
All sources except no. 5 are point sources. Source no. 5 shows extended
emission.
We note that source no. 1 in the above list is within 2 arc sec
of source no. 4 in the list of Chandra sources reported by Patel
et al (2004, GCN 2648), and could be coincident with it.
No detectable emission was found at the location of the VLA source
(GCN 2643).
At present we are unable to determine the extent of variability,
if any, of the above sources.
This message may be cited.
GCN Circular 2651
Subject
XRF 040812: optical observation at VLT
Date
2004-08-18T20:19:37Z (21 years ago)
Edited On
2025-09-09T18:36:45Z (a month ago)
From
Daniele Malesani at SISSA-ISAS,Trieste,Italy <malesani@sissa.it>
Edited By
courey.elliott@gmail.com
P. D'Avanzo, A. Cucchiara, G. Tagliaferri, D. Malesani, D. Fugazza, S.
Covino, S. Campana, on behalf of a larger collaboration, report
We observed the field of XRF 040812 (Gotz et al. GCN 2640) with the
ESO-VLT on Aug 12.9795 UT (~17.5 hours after the GRB) and Aug 13.9844 UT
(~41.5 hours after the GRB). Observations were performed in the I-band,
under good observing conditions.
Ten 1-minute exposures were taken in both nights. The seeing was 1.1" on
Aug 12 and 0.8" on Aug 13. We estimate the limiting magnitude to be I ~ 24.
To avoid saturation from the bright star close to the center of the field,
we had to place on occulting bar, which hides 9% of the error box.
We briefly report about the Chandra X-ray sources (Patel et al. GCN 1648).
Source #1, #3 and #7 are visible in the DSS, as well as in our images.
Source #2 (see also Campana & Moretti, GCN 1649) is not detected in the
DSS and, moreover, in our images it is falling just behind the occulting
bar.
Source #4 is close (~1.5"), but not coincident, with a faint source in the
VLT images, not visible in the DSS.
Source #5, #6 are visible in our images but not in the DSS.
None of the counterparts of the Chandra sources shows any significant
variability. Moreover we don't have evidence of candidates in the whole
Integral error-box (Gotz et al. GCN 2640), in particular at the radio
position (Soderberg GCN 2643).
PSF-matched photometry was performed with DAOPHOT and image subtraction
with ISIS.
We thank the ESO staff at Paranal for carefully performing the
observations.
This message may be cited.
GCN Circular 2649
Subject
XRF040812: possible afterglow
Date
2004-08-18T15:57:39Z (21 years ago)
Edited On
2025-09-09T18:36:41Z (a month ago)
From
Sergio Campana at INAF-OAB <campana@merate.mi.astro.it>
Edited By
courey.elliott@gmail.com
S. Campana and A. Moretti (INAF-Osservatorio di Brera) report:
"We analyzed the Chandra ACIS-S data of the XRF040812 (Gotz et al. 2004,
GCN 2640) region. We carried out spectral analysis of the second source
(CXOJ162602.3-444349) in the Patel et al. (2004, GCN 2648), the only one
with a sizable number of counts. The source is extremely hard with a
photon index of 0.1+\-0.6 (90% confidence level), fixing the column
density to the Galactic value of 5.3x10^21 cm-2. Leaving free the column
density the error on the photon index increases to 0.1_(-1.0)^(+1.5).
This hard photon index is typical of GRB X-ray afterglows. The
unabsorbed 0.5-10 keV source flux is 2.53E-13 erg cm-2 s-1. The
following Chandra observation (August 22, 2004) will allow to assess
the afterglow nature of CXOJ162608.4-444125."
We acknowledge the extraordinary effort by the CXC in providing rapid
processing of this challenging data-set, thereby enabling this report.
This message can be cited.