glast science and opportunities seattle aas meeting, january 2007 enhancing glast science through...

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