Fast dissemination of GRB afterglow information

Patrizia Ferrero 3rd Integral Bart Work Shop Chocerady - November 1-3, 2004

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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 soimportant 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 aren’t!!

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 featuresFiltersNumber of observationsCalibrations


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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.

bright OT with a slow decay

different filters (B,V,Rc,Ic)

a lot of observations


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OT features, Filters and Number of observations: GRB with OT

bright OT with a rapid decay

different filters (B,V,Rc,Ic)

few data

faint OT

Rc and Ic filters

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 Henden’s 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 - IIThe 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-BGSC 2.2 vs USNO-BUSNO-A2.0 USNO-B1.0 GSC 2.2

Total Object

526,230,8811,042,618,261

455,851,237

Magnitude Limit

O=21E=20

V=21F=18.5J=19.5V=19.5

Astrometry Errors

0.25” 0.2” 0.3”

PhotometryErrors

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 F<20.5 & J<22.


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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 Rc=18, when it was localized, we have few optical data because it was “obscured” by the famous GRB030329.


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ConclusionsOur 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 Thank You for

YourYour

Attention !!!Attention !!!

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Fast dissemination of GRB afterglow information