Polarimetric monitoring of Blazars at San Pedro Martir

A beetle at SPM 84cm telescope at SPM Sunset at SPM

1. The project

The long-term project "Polarimetric monitoring of Blazars at San Pedro Martir" started in July 2008. It will run initially for 3 years and will make efficient use of the 84cm telescope at San Pedro Martir . Currently, a dozen scientists from Mexico, the US and Europe are involved of the project. The PI is J. Heidt..

2. Scientific motivation

Numerous multiwavelength campaigns from the observational side as well as theoretical modeling on the other have largely improved our understanding of how the central engine of Blazars - presumably a supermassive Black Hole - and their associated relativistic jets work. Still, many details are an open issue such as the exact mechanism of how the supermassive Black Hole is feeded, how material is transported into its relativistic jets as well as the onset and evolution of shocks within the jets. Especially the latter are of high interest since they are most likely responsible for the strong variability observed across the entire wavelength range accessible nowadays from ground and space in this class of active galactic nuclei.
One of the major surprises in the last decade was the detection of (variable) radiation of Blazars at highest energies thanks to e.g. EGRET, INTEGRAL , MAGIC, or HESS. With continuing upgrades of the MAGIC and HESS telescopes as well as due to the unprecedented sensitivity of Agile, GLAST or SWIFT numerous Blazars are expected not only to be detected at highest energies but the temporal evolution of their radiation to be observed.
Of particular interest in these observations is the interplay between the (variable) radiation observed at low-frequencies (due to Synchrotron radiation) and at high-frequencies (most likely inverse-Compton radiation). Several models have been developed which are able to explain the temporal evolution in both frequency domains and will now be tested. This requires, however, support from ground-based telescopes in the optical as a test for the Synchrotron branch.
Optical observations of Blazars are routinely carried out since more than a decade on a large number of observatories (see a compilation of the most active observatories at the WEBT page). However, the observations are traditionally carried out by means of flux measurements only, which allows to investigate e.g. the energy budget in these sources. Largely neglected has been the potential of determining the properties of the sources in polarized light. This is a powerful tool, to e.g. determine strength and orientation of magnetic fields giving rise to the variable synchrotron radiation. Only few programs are currently conducted in this direction as e.g. the polarization monitoring on OJ 287, the MAPcat program (PI. I. Agudo) or the one carried out in Alan Marscher/Svetlana Jorstads group.

3. Observations and scientific projects

The observations will be carried out with the 84 cm telescope + POLIMA at San Pedro Martir. Since POLIMA has currently only a rotatable polarization foil available to carry out polarization measurements (with the hope to move to a calcite system in the near future) our observations are currently strongly influenced by the presence of moonlight and/or cirrus/clouds. Thus our observations are currently carried out on a monthly basis always during 7n runs centered on new moon.
Throughout the year a set of ~ 35 sources will be observed. They are divided in groups of "brighter" and "fainter" sources (for more information see the target list). The "brighter" sources are observed each night when observable, the "fainter" sources only 1-2 times per run. The main scientific projects are:
  • Determine statistically the duty cycle (variability in total and polarized light, changes/stability of polarization angle etc.) on timescales of days on a long-term basis and compare them with other properties of the sources. This will be done for the "bright" sources.
  • Monitor the sources as part of the GASP = The GLAST - AGILE Support Program and to set an alert in case of unexpected high activity of one of the sources.
  • Participate in multi-lambda campaigns initiated due to high activity of one of the GASP-sources (or others).

4. Further information

The Team

Target & polarization standard list

Hints for the observations

Lightcurves based on San Pedro Martir data

Publications based on or including project data

Travel hints

Internal area (user restricted)


Maintained by Jochen Heidt
Last modified: 3.7.2009