Enhancing GLAST Science Through Complementary Radio Observations

1. Enhancing GLAST Science Through Complementary Radio Observations Jim Ulvestad Paper 176.02

2. Acknowledgments • Slides from Greg Taylor, Sean Dougherty • Stanford group (Romani, Sowards-Emmerd, Healey) and others for collaborative VLA programs

3. Outline • Guiding Principles • IDs of New Source Classes • IDs of Individual Sources • Examples: Blazars, Colliding Wind Binaries

4. Guiding Principles • Radio observations should be driven by peer-reviewed science, and by maximizing the combined science outputs of the GLAST mission and the radio telescopes • Selection of radio telescopes should be governed by those that are uniquely required for the complementary GLAST science • Radio telescope facilities must balance GLAST science carefully with the rest of their science portfolio • Bureaucratic headaches and double-jeopardy for proposers and observers should be minimized • Question: How does one secure GLAST-supporting data (e.g., pulsar timing) that do not represent exciting science from the radio observatory alone?

5. IDs of New Source Classes • EGRET detected approximately 271 individual gamma-ray sources (3EG, Hartman et al. 1999) • Only about 1/3 had high-confidence identifications in 3EG • Many unidentified sources at both low and high galactic latitudes • Two primary identified classes were blazars and pulsars • GLAST will detect ~104 individual sources • How can radio observations be used to (help) identify new classes of sources, such as LLAGNs, supernova remnants, microquasars, etc.?

6. Radio Catalogs and New Source Classes • Correlative studies between gamma-ray error boxes and sources of high/medium/low/absent radio flux density • Large-area radio catalogs at moderately low frequencies of 1-5 GHz (e.g., FIRST, NVSS, SUMSS, Parkes, GB6) • Optical IDs/classifications are incomplete • Most have poor resolution, and catalogs are not contemporaneous • Radio surveys of particular classes of sources • Unbiased radio surveys of particular object classes are rare • Excellent approach may be to use classes of sources identified in SDSS (e.g., SDSS quasars), and look for correlations with the radio fluxes/powers in the individual classes

7. IDs of Individual Sources • Very promising avenue for radio observations AFTER source classes are identified • Likely correlation of gamma-ray detection/fluence with radio flux density • Figure of Merit approach developed over last several years has worked very well for blazars (Sowards-Emmerd et al. 2004)

8. CRATES Source Distribution • Flat-spectrum sources, CLASS + VLA + ATCA (Healey et al. 2007) 11,000 flat-spectrum sources, |b|>10 deg., S > 65 mJy

9. A Possible VLA Approach to Identifying Counterparts • Scaling from NVSS, an all-sky VLA 8.4 GHz survey would require approximately 3,000 * (8.4/1.4)2 = 108,000 hr, or 15-18 years of observing! • However, one could carry out a targeted survey of 5,000 GLAST source fields at the rate of 1,000 fields per day • Total observing time of 120 hr • Simultaneous 1.4 and 5 GHz observations with 12 antennas each, for 30 seconds on target, in A configuration of VLA • RMS noise = 0.5 mJy in each band • Resolution ~ 2 arcsec, field of view ~ 9 arcmin

10. Hypothetical Targeted VLA Survey 1.4 GHz 5 GHz

11. Gamma-Ray Emission Mechanisms for Blazars GLAST will detect thousands of gamma-ray blazars that can only be resolved by VLBI techniques

12. Sub-Milliarcsecond Imaging of Blazar Jets • How do gamma-ray flares relate to changing structures in blazar radio jets? Which comes first? • What is the origin of the gamma rays? Internal or External Compton? • There are hints that EGRET blazers are faster (Jorstad et al 2001) and more strongly polarized (Lister & Homan 2005) • Do we have the observational tools to image jets on the appropriate length scales and time scales?

13. Requirements for Imaging Blazar Jets • High-frequency capability (> 20 GHz) to image jets where they are optically thin • Full-polarization imaging • Dynamic scheduling for response to gamma-ray flares at any time of year, and for repeated reliable observations • Sub-milliarcsecond resolution to detect changes on time scales of days to months • Only the VLBA meets these requirements

14. VLBA • High Sensitivity Array (add VLA, GBT, Effelsberg) may be desirable for LLAGNs, TeV blazars

15. Sample Jet Evolution Imaged with VLBA • Monthly VLBA imaging of radio galaxy 3C 120 at 22 GHz (Gomez et al. 2000) • What were the gamma rays doing during this period? • Desire imaging on time scales of weeks or less for z~0.5

16. VLBA Imaging Polarimetry Survey (VIPS) • 1127 sources, S > 85 mJy, 65 >  > 20 deg., |b| > 10 deg., at 5 GHz • First-epoch VLBA observations in 2006 • Helmboldt et al. 2007, astro-ph/0611459 • Identifications and redshifts from SDSS, HET, Palomar, Keck, … • Goals: • Characterize GLAST sources (pre-launch) • Study evolution of radio sources • Probe AGN environments • Find binary supermassive black holes http://www.phys.unm.edu/~gbtaylor/VIPS

17. Which Jets will be Detected by GLAST? Helmboldt et al. 2007

18. Colliding Wind Binary, WR 140 • VLBA observations have enabled an orbit solution • Distance – NOT based on stellar parameters! • Distance = 1.85 +/- 0.16 kpc • O supergiant • All important system parms now defined!!! • Stellar types • Distance • All orbit parameters (including inclination) • ALL VERY IMPORTANT to modelling Dougherty, Pittard et al. 2005, 2006

19. WR140 lies in 3EG J2022+4317 Error Box EGRET (100MeV – 20 GeV) • Is WR140 a gamma-ray source? • Are CWBs gamma-ray sources? • What should we expect at high energies? From Benaglia & Romero (2003)

20. GLAST WR140 Emission at phase 0.8 (from fits to radio data) Radio ASCA

21. Predicted Luminosities and Fluxes at Phase 0.8 • GLAST 5σ sensitivity at E > 100 MeV for a 2-yr all-sky survey is 1.6 x 10-9 ph s-1 cm-2 (should detect WR140 with GLAST) • High-energy observations are critical to establishing some model parameters

22. Radio Observatories • NRAO: VLA, VLBA, GBT; eventually EVLA & ALMA • Rapid Response and Large Proposal processes • Existing surveys (NVSS, FIRST, VIPS, MOJAVE, etc.) • Non-NRAO telescopes • European VLBI Network (3 sessions/yr, 2-3 weeks) • University Radio Observatories • History of rapid response science with CARMA • Arecibo, at frequencies below 10 GHz • Australia Telescope Compact Array, or LBA