GLAST Science and Opportunities

Seattle AAS Meeting, January 2007

Enhancing GLAST Science Through Complementary Radio Observations

Jim UlvestadPaper 176.02

2Acknowledgments

• Slides from Greg Taylor, Sean Dougherty• Stanford group (Romani, Sowards-Emmerd, Healey)

and others for collaborative VLA programs

3Outline

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

4Guiding 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?

5IDs 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.?

6Radio 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

7IDs 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)

8CRATES Source Distribution

• Flat-spectrum sources, CLASS + VLA + ATCA (Healey et al. 2007)

11,000 flat-spectrum sources, |b|>10 deg., S > 65 mJy

9A 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

10Hypothetical Targeted VLA Survey

5 GHz

1.4 GHz

11

Gamma-Ray Emission Mechanisms for Blazars

GLAST will detect thousands of gamma-ray blazars that

can only be resolved by VLBI techniques

12Sub-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?

13Requirements 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

14VLBA

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

15Sample 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

16VLBA 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

17Which Jets will be Detected by GLAST?

Helmboldt et al. 2007

18

• VLBA observations have enabled an orbit solution

Colliding Wind Binary, WR 140

• 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

EGRET (100MeV – 20 GeV)

From Benaglia & Romero (2003)

WR140 lies in 3EG J2022+4317 Error Box

• Is WR140 a gamma-ray source?– Are CWBs gamma-

ray sources?

• What should we expect at high energies?

20WR140 Emission at phase 0.8 (from fits to radio data)

Radio ASCA GLAST

21Predicted 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

22Radio 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