Fast dissemination of GRB afterglow information

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Fast dissemination of GRB afterglow information

• Patrizia Ferrero
• (IASF-BO, OACT Universita di Teramo)

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Our collaboration

• Patrizia Ferrero
• (IASF-BO, OACT Universita di Teramo)
• Corrado Bartolini, Adriano Guarnieri,
• Adalberto Piccioni
• (Universita di Bologna)
• Graziella Pizzichini
• (IASF-BO)

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The GRB Coordinates Network (GCN)
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• The GCN was originally developed at NASA/MSFC as
  BACODINE under Scott Barthelmy to support BATSE
  positions/identifications
• Now at NASA/GSFC, still under Scott Barthelmy,
  it distributes near real time GRB positions from
  active satellites as well as reports of follow-up
  observations by ground based observers
• http//gcn.gsfc.nasa.gov/

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Why are GCN Circulars so important to us?

• They give us information about the OT (optical
  transient)
• localization and position
• magnitude
• the time of the optical decay
• essential data to plan other observations.

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But are GCN data always so complete, exhaustive
and precise?
The answer is they arent!! We have to remember
that they are preliminary data, that it is not
mandatory for observers to issue a GCN as soon as
they obtain data and that issued data are no
longer private, but public.
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In some cases data are abundant in different
filters, in other cases they are relatively
scarce. The quality and the quantity of the GCN
data are determined by several factors, which
could be summarized in this way
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• OT features
• Filters
• Number of observations
• Calibrations

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OT features, Filters and Number of observations

• The situation is different for
• GRB with optical afterglow
• GRB without optical afterglow

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OT features, Filters and Number of observations
GRB with OT
The kind of optical afterglow would be
fundamental for the choice of filter and the
amount of observations.
different filters (B,V,Rc,Ic)
bright OT with a slow decay
a lot of observations
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OT features, Filters and Number of observations
GRB with OT
different filters (B,V,Rc,Ic)
bright OT with a rapid decay
few data
Rc and Ic filters
faint OT
few observations
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GRB021004 light curves in several filters
(data from GCN)
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GRB030226 light curves in different filters
(data from GCN)
A rapid decay could explain the lack of more
optical data.
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• A lot of multiband data could be useful
• to trace the GRB light curves
• to locate on them the point of break
• to analyse the color indices and to confirm the
  studies of them made by Simon et al. 2001.

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OT features, Filters and Number of observations
GRB without OT
In the case of GRB without detected optical
afterglow, we have usually upper limits
(sometimes in different bands) and few
observations. An example.....
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GRB030416 upper limits in different filters
(data from GCN)
Here, in spite of the lack of the OT, the
observers attempted to give magnitude limits in
four filters.
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Calibrations
When a GRB event occurs, all of us are wainting
for Hendens precise photometry to calibrate our
data. However, at least at the beginning of data
release, we must do without it and choice a
system which to refer to. USNOA.2, USNOB.1 or
something else?
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The Guide Star Catalog - II

• The GSC2.2 is an all-sky catalog based on 1
  resolution scans of the photographic Sky Survey
  plates, at two epochs and three bandpasses, from
  the Palomar and UK Schmidt telescopes (DSS).
• The GSC2.2 is a joint project of the Space
  Telescope Science Institute and the Osservatorio
  Astronomico di Torino.

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GSC 2.2 vs USNO-B
USNO-A2.0 USNO-B1.0 GSC 2.2
Total Object 526,230,881 1,042,618,261 455,851,237
Magnitude Limit O21 E20 V21 F18.5 J19.5 V19.5
Astrometry Errors 0.25 0.2 0.3
Photometry Errors 0.2-0.4 mag 0.3 mag 0.1-0.2 mag
In the future GSC-2.3 with 997,028,547 objects
and mag limit Flt20.5 Jlt22.
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GRB021004 Rc light curves with different
calibrations (data from GCN)
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GRB030329 Rc light curves with different
calibrations (data from GCN)
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In other cases it is a matter of bad luck. For
example....
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GRB030328 light curves of the orphan GRB
(data from GCN)
Although it had about Rc18, when it was
localized, we have few optical data because it
was obscured by the famous GRB030329.
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Conclusions

• Our conclusions are fairly simple and could be
  easily anticipated. It would be very helpful and
  productive, in order to obtain the best set of
  data
• to have, at least, early estimates of OT
  magnitudes in several filters,
• to converge as soon as possible on the same
  calibration system or to define some precise
  rules in order to choice it,
• to plan and to share the task of following the
  OTs with multifilter photometry between different
  observatories.

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• Thank You for
• Your
• Attention !!!