Presentation on theme: "Gamma-Rays and Blazars More Work for Variable Star Observers Gordon G. Spear Sonoma State University."— Presentation transcript:
Gamma-Rays and Blazars More Work for Variable Star Observers Gordon G. Spear Sonoma State University
What are Gamma-rays? n Just photons, but with very high energies n Photons with energies billions of times greater than visible light photons n Natural sources of Gamma-rays n Man made sources of Gamma-rays n Gamma-rays from space
How are Gamma-rays characterized? n Gamma-rays are characterized by the energy of individual photons. n Energies generally measured in MeV and GeV (millions and billions of eV). n Infrared photons have energies on the order of eV. n One erg is about 600 billion eV. n The erg and the mosquito?
Compton GRO and EGRET n Compton Gamma Ray Observatory (CGRO) n Launched in 1991 n Re-entered Earth atmosphere in 2000 n Energetic Gamma Ray Experiment Telescope (EGRET) n First all-sky survey in energy range 30 MeV to 10 GeV
The Objects in the Gamma-Ray Sky n Milky Way glow from cosmic ray interactions with dust n Point sources in the Milky Way are Gamma-ray pulsars (SNRs) n Point sources outside the Milky Way are AGNs n Some point sources remain unidentified
GLAST and the LAT n Gamma-ray Large Area Space Telescope (GLAST) n Substantial increases in sensitivity, energy range, and resolution over GRO n GLAST Burst Monitor (GBM) n Large Area Telescope (LAT) n Scheduled for launch in 2006 n 5 year mission design, expected 10 year useful lifetime n One year all-sky survey followed by pointed observations
AGNs n Active Galactic Nuclei n Extragalactic objects that are more luminous than normal galaxies n The nucleus can be 10 to 100 times brighter than an entire normal galaxy n The underlying galaxy can appear relatively normal (when it can be seen) n Many different types or sub-classes
Some Categories of AGNs n Seyfert Galaxies –Sy 1, Sy2 n Radio Galaxies –Narrow Line Radio Galaxies (NLRG... FR I, FR II) –Broad Line Radio Galaxies (BLRG) n Quasars –Broad Absorption Line Quasars (BALQ) –Steep Spectrum Radio Quasars (SSRQ) –Flat Spectrum Radio Quasars (FSRQ) n Blazars n Optically Violent Variables (OVV)
General Characteristics of AGNs n Extragalactic n More luminous than normal galaxies n Generally point sources (stellar appearance) n Some exhibit jets n Bright in X-rays and Gamma-rays n All exhibit variability at some level!
AGN Unification n All AGN are manifestations of the same physical phenomenon n This phenomenon is the accretion disk and jets associated with a supermassive black hole n The different appearances are simply due to the orientation of the jets and disk to our line of sight
Voyage into an AGN A Simulation n Starts 100s of Mpc away from AGN n Underlying galaxy is a spiral (20000 stars) n The AGN engine has been switched off n Size scale changes by 10 orders of magnitude
The Blazars n The blazars appear to be AGN for which the jets are pointing directly at us. n We are looking directly down the throat of the dragon! n Spectra (SEDs) have bright compton peak in addition to the typical AGN synchrotron peak. n These are the only prominent point sources in the Gamma-ray sky. (Gamma loud) n Beams of particles moving at relativistic speeds produce intense beams of Gamma- rays. n These are the most variable of the AGNs.
AGN Variability? n All AGNs appear to be variable at some level n The emission lines vary in strength n The continuum levels vary in brightness n Variability has been documented over decades, years, months, weeks, days, and even hours
Characteristics of AGN Variability n Periodicity has NOT been convincingly demonstrated! n Slow, longterm irregular changes n Outbursts (flares) and declines n General increase in variability for shorter wavelengths (higher energy photons) n General increase in variability for longer time scales n Apparent increase in variability with luminosity n Apparent increase in variability with redshift
AGN Variability Data n Available observations –Longterm (few per year) –Intraday (few per week) –Microvariability (many per hour) n Lightcurve classification –Outbursts –Declines –Outbursts and declines n The blazars –Most variable of the AGNs –Amplitudes to 4 magnitudes or more –Can exhibit detectable variations from night-to- night and within a night
Observing Techniques for AGNs n Just like variable stars! n Visual observations can detect outbursts and declines. n CCD images which include a photometric sequence can be measured. (BVRI filters preferred) n Robotic telescope systems can be extremely efficient, consistent, and productive.
Opportunities Provided by GLAST n Detect the Gamma-rays that are directly produced by the supermassive black hole engine. n Provide data to evaluate various theories of jet production. n Detect and measure several thousand new Gamma-loud blazars. n Provide for true multi-wavelength blazar and AGN surveillance.
Enter the GTN n GLAST Telescope Network (GTN) n Collaboration of observatories and observers to obtain observations of AGNs n Professional astronomers, amateur astronomers, students n Establish base line variability and coordinate multi-wavelength campaigns n Provide fundamental scientific data that will support and complement the GLAST mission
The Goals for the GTN n Establish base-line activity levels and behavior for gamma-loud blazars n Coordinate multi-wavelength campaigns (eventually include GLAST) n Establish and maintain data archive of blazar images n Establish and maintain database of brightness data (like the AAVSO database?) n Distribute announcements about blazar activity (a GCN for blazars?) n Encourage participation by professionals, amateurs, and students; establish mentoring relationships
Participants in the GTN will... n Contribute a minimum of 1-2 observations each month n Participate in coordinated campaigns 1-2 times each year –intraday campaigns –microvariability campaigns n Have access to data in the GTN archives n Contribute to improved understanding of blazar energy production (supermassive black holes, relativistic jets) n Contribute to the success of the GLAST mission
AAVSO Contributions n GTN partner n Add bright Gamma-loud AGNs (blazars) to AAVSO object list n Monitor program AGNs for outbursts and other activity and provide notification to interested parties n Introduce and mentor new observers to the process of variable star observation n Establish robotic observatories for use by AAVSO members, students, and schools