GCN Circular 3141
Subject
GRB050319, color indices
Date
2005-03-25T10:50:15Z (20 years ago)
From
Rene Hudec at AIO <rhudec@asu.cas.cz>
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<> V. Simon, R. Hudec (Astronomical Institute AV CR, Ondrejov, Czech
Republic) and G. Pizzichini, N. Masetti (INAF/IASF Bologna, Italy) report:
<>
We have determined the color indices of the optical afterglow (OA) of
GRB050319 in its very early phase from the available data (GCN 3124,
3129). The interpolation method described in Simon et al. (2001, A&A,
377, 450) was used. Since the Swift UVOT magnitudes need a confirmation
of their calibration, we determined the indices separately for UVOT and
ground-based observations. The indices of the OA from UVOT are:
t-To=0.0044 d: B-V=0.68; 0.0119: -0.10; 0.0625: 0.85; 0.1968: 0.64,
while those of the ground-based observations (GCN 3124) are: t-To(d)=
0.331 d: B-R=0.73; 0.448: 1.12. The typical error of these indices is
about 0.10 mag.
The Galactic reddening E(B-V)=0.011, determined from the maps by
Schlegel et al. (1998, ApJ, 500, 525), is comparable to the errors
of the measurements.
We note that the variations in B-V, with a peak at t-To=0.01 days,
are caused by a plateau in B while the V magnitude was already
steadily decreasing. The last two measurements from UVOT can
suggest that B-V reached the value roughly consistent with the
typical one for the ensemble of 23 OAs, defined by Simon et al.
(2001; 2004, AIP Conf. Proc., Vol.727, p.487), not later than at
t-To=0.06 days.
The indices of the OA of GRB050319 for t-To > 0.06 days thus appear
to be plausibly consistent with the mean values of the ensemble
(B-V)o=0.45+/-0.15, (B-R)o=0.86+/-0.17. This suggests that the shape
of the spectrum of the afterglow of GRB050319 is similar to the other
afterglows and that its intrinsic reddening (that is inside the host
galaxy) must be again small (Simon et al. 2001; 2004, AIP Conf.
Proc., Vol.727, p.487). Also the redshift of GRB050319 z=3.24 (GCN
3136) suggests that this GRB appears to be another member of the
above-mentioned ensemble of the OAs with z < 3.5.
The search for the host galaxy and the determination of its type
are also encouraged.
This message may be cited.
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<pre style="text-align: justify;"><tt>
<o:p></o:p></tt></pre>
<tt><> V. Simon, R. Hudec (Astronomical Institute AV CR, Ondrejov,
Czech <o:p></o:p></></tt>
<pre style="text-align: justify;"><tt>Republic) and G. Pizzichini, N. Masetti (INAF/IASF Bologna, Italy) report:
<o:p></o:p></tt></pre>
<tt><><span style=""><br>
</span><o:p></o:p>We have determined the color indices of the optical
afterglow (OA) of <o:p></o:p></></tt>
<pre style="text-align: justify;"><tt>GRB050319 in its very early phase from the available data (GCN 3124, <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>3129). The interpolation method described in Simon et al. (2001, A&A, <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>377, 450) was used. Since the Swift UVOT magnitudes need a confirmation <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>of their calibration, we determined the indices separately for UVOT and <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>ground-based observations. The indices of the OA from UVOT are: <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>t-To=0.0044 d: B-V=0.68; 0.0119: -0.10; 0.0625: 0.85; 0.1968: 0.64, <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>while those of the ground-based observations (GCN 3124) are: t-To(d)=<o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>0.331 d: B-R=0.73; 0.448: 1.12. The typical error of these indices is <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>about 0.10 mag. <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt><o:p> </o:p></tt></pre>
<pre style="text-align: justify;"><tt>The Galactic reddening E(B-V)=0.011, determined from the maps by <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>Schlegel et al. (1998, ApJ, 500, 525), is comparable to the errors <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>of the measurements. <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt><span style=""> </span><o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>We note that the variations in B-V, with a peak at t-To=0.01 days, <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>are caused by a plateau in B while the V magnitude was already <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>steadily decreasing. The last two measurements from UVOT can <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>suggest that B-V reached the value roughly consistent with the <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>typical one for the ensemble of 23 OAs, defined by Simon et al. <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>(2001; 2004, AIP Conf. Proc., Vol.727, p.487), not later than at <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>t-To=0.06 days.<o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt> <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>The indices of the OA of GRB050319 for t-To > 0.06 days thus appear <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>to be plausibly consistent with the mean values of the ensemble <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>(B-V)o=0.45+/-0.15, (B-R)o=0.86+/-0.17. This suggests that the shape <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>of the spectrum of the afterglow of GRB050319 is similar to the other <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>afterglows and that its intrinsic reddening (that is inside the host <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>galaxy) must be again small (Simon et al. 2001; 2004, AIP Conf. <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>Proc., Vol.727, p.487). Also the redshift of GRB050319 z=3.24 (GCN <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>3136) suggests that this GRB appears to be another member of the <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>above-mentioned ensemble of the OAs with z < 3.5. <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>The search for the host galaxy and the determination of its type <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>are also encouraged. <o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt><span style=""> </span><o:p></o:p></tt></pre>
<pre style="text-align: justify;"><tt>This message may be cited.</tt><o:p></o:p></pre>
<pre style="text-align: justify;"> <o:p></o:p></pre>
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fn:Rene Hudec
n:Hudec;Rene
org:Astronomical Institute, CZ-251 65 Ondrejov, Czech Republic;High Energy Astrophysics Group
adr:;;Observatory Ondrejov;Ondrejov;;CZ-251 65;Czech Republic
email;internet:rhudec@asu.cas.cz
tel;work:00420 323 620128
tel;fax:00420 323 620263
tel;home:00420 323 649011
tel;cell:00420 737 137396
url:http://www.asu.cas.cz
version:2.1
end:vcard
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