Chimera_VOalerts

• Responsable: William Schoenell [email protected], Javier Gorosabel [email protected]

Project Description

Build a module which responds to Gamma Ray Burst events from a VOEvent Broker. Alerts are generated by Gamma Ray space observatories (satellites) and broadcasted via VOEvent protocol.


The project consist in two parts:

• Part 1: VOEvent daemon

A VOEvent Broker (twisted + comet) which runs as a daemon verifying the content of the VOEvents. As input, it haves a set of xpath filters and a plugin which calls chimera when one of those filters are detected.

• Part 2: chimera controller module

Receives an VOEventlib object with the filtered event and the filter name which it corresponds. Then, execute a set of actions on chimera (mostly on scheduler) to treat the action associated to this filter.

Basic workflow

GCN <--> Comet --> Chimera Plugin (filters) --(if match)--> Chimera-voevent (filter+VOEvent obj) --> scheduler

Chimera .config sample

controller:
  - type: VOEvent
  - filter_file: /home/wiliam/.chimera/grb_filters.xpath
  - actions_file:  /home/wiliam/.chimera/grb_actions.txt

Broker filter event

This example filters all packet with type == 97. To learn more about packet types, see GCN on links section.

( //What/Param[@name="Packet_Type" and @value="97"] )

A good xpath testbed can be found on xpath links section.

Chimera action file sample

All we need here is:

• RA(J2000)
• dec(J2000)
• Error box size
• Time since GRB occurence

Depending on the camera readout time we might want to include windowing. A 1k x 1k Fov should be more than enough for Swift alerts (ID=97). For Fermi we would need the whole Fov.

RA and DEC should be used to estimate the Galactic Av in the direction of the GRB. If Av is > 2.5 mag we should skip the activation. The observations should be conducted in the Sloan i-band filter.

The typical exposure time would be ~10 seconds for the first frames and ~180s for the last ones. A first trial would consist of an observations of ~1 hour. It will depend on the read-out noise of the CCD. If the CCD has a neglectable read-out noise we would go for short exposure and the co-add. If the read-out noise is high (i.e. > 15 e-) we probably will have to expose larger and sacrifice temporal resolution in the i-band lightcurve.

The action file will map each filter to a scheduler-like file:

filterGRB: /home/william/.chimera/filterGRB.sched

where filterGRB.sched could be a file like:

#type    name  N*(f1:t1:n1, f2:t2:n2, ......)
OBJECT  obj1  2*(V:7, R:6:2, B:5:2)
OBJECT  obj2  2*(V:7, R:6:2, B:5:2)

or include also binning:

#type    name  N*(f1:t1:n1:b1, f2:t2:n2:b2, ......)
OBJECT  obj1  2*(V:7, R:6:2, B:5:2:500x500)
OBJECT  obj2  2*(V:7, R:6:2, B:5:2:250x250)

In these cases, RA, DEC and EPOCH will came from VOEvent.

Twisted+Comet installation and configuration

Comet depends on: twisted (versions >= 11.1.0), lxml (versions >= 2.3) and ipaddr-py. Chimera-plugin depends on: VOEventlib http://lib.skyalert.org/VOEventLib/

Links

VOEvent
http://www.ivoa.net/internal/IVOA/IvoaVOEvent/voevent_v2.html - VOEvent spec v2.0
http://ivoa.net/internal/IVOA/IvoaVOEvent/

GCN - Gamma-ray Coordinates Network
http://gcn.gsfc.nasa.gov/admin/voevent_version20_available.txt - VOTable v2.0 announcement
http://gcn.gsfc.nasa.gov/sock_pkt_def_doc.html - GCN packet definition

Comet VOEvent Broker
https://github.com/jdswinbank/Comet
http://comet.transientskp.org/

twisted
http://twistedmatrix.com/trac/

xpath
http://www.whitebeam.org/library/guide/TechNotes/xpathtestbed.rhtm - xpath testbed