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GLAST Large Area Telescope (LAT). GLAST Burst Monitor (GBM). GLAST GeV Astronomy in a Multiwavelength Context Jonathan F. Ormes NASA Goddard Space Flight Center GLAST Large Area Telescope Collaboration [email protected]

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GLAST Large Area Telescope (LAT)

GLAST Burst Monitor (GBM)


GeV Astronomy in a Multiwavelength Context

Jonathan F. Ormes

NASA Goddard Space Flight Center

GLAST Large Area Telescope Collaboration

[email protected]

Special thanks to Dave Thompson and Steve Ritz for providing most of this material


Multiwavelength observations are essential for GLAST science

Both previous observations and theoretical considerations show that gamma-ray sources are usually broad-band objects.

GLAST will address many important questions:

What is going on around black holes? How do Nature’s most powerful accelerators work? (are these engines really black holes?)

What are the unidentified sources found by EGRET?

What is the origin of the diffuse background?

What is the high energy behavior of gamma ray bursts?

What else out there is shining gamma rays? Are there further surprises in the poorly measured energy region?

When did galaxies form?

GLAST operations will contribute to a wide range of cooperative, multiwavelength observations.


Coordinated observations

Most of our science depends on coordinated observations: science





Unidentified sources

Discovery: finding and understanding new phenomena

Learning from experience

Coordinated Observations

Pulsars rotating neutron stars
Pulsars – Rotating Neutron Stars science

  • Science Topics

  • Neutron star population studies.

  • Location and nature of particle acceleration and interaction (model testing).

  • Physics in extreme magnetic and electric fields.

  • Matter state at high densities.

  • Relativistic effects.

Except for the pulsations themselves, time variability is not significant for pulsars. Simultaneous multiwavelength observations are not essential.

Agn multiwavelength variety
AGN – Multiwavelength Variety science

Radio Optical X-ray Gamma ray

  • Science Topics

  • Location and nature of particle acceleration and interaction in jets.

  • Confirmation of unified models.

  • Cosmological probes using high-energy cutoff due to absorption by Extragalactic Background Light.

  • Contribution to the diffuse background.

Fossati’s summary of blazar Spectral Energy Distributions

Due to variability on short time scales, AGN require simultaneous multiwavelength observations for maximum scientific return.

A few additional remarks on multiwavelength agn observations

Measure spectral energy distributions science

model fits can tell us (in the context of the models!) some of the features and parameters of the system, if error analysis (both statistical and systematic) is understood.

Leverage complementary capabilities

Gamma spatial resolution isn’t great, but we can tell time well (especially from ground-based observatories).

Use radio: take advantage of superior spatial resolution. By measuring flare time lags between radio and gamma, can get an indication of where emission is taking place.

Time lags relative to other wavelengths also can tell us the size of the emission region (again, in the context of models).

Physics with sources. Use optical, radio, x-ray: need follow-up measurements to ID sources and measure redshifts.

enables EBL studies, luminosity function determination, evolution studies, early Universe probes (especially 1-50 GeV observatories). Work for 100’s or 1000’s of new sources.

A Few Additional Remarks on Multiwavelength AGN Observations

Agn challenge

Supermassive BH systems shine magnificently in gammas, but what physics are we learning?

Are we just measuring the weather?

That’s interesting, but can we learn more about the holes themselves? (e.g., find a measure of the hole mass, spin and do a population survey; study GR effects, etc.)

AGN Challenge

from Sikora, Begelman, and Rees (1994),

shown in Greg Madejski’s talk

Agn multiwavelength variability
AGN – Multiwavelength Variability what physics are we learning?


Gamma rays






  • Strength and phasing of flaring at different wavelengths is a powerful tool for modeling emission.

  • Also need observations before and after a flare to be sure it is the same flare.

  • Test universality of the idea that high states have flatter spectra.

Supernova remnants origin of cosmic rays
Supernova Remnants – Origin of Cosmic Rays? what physics are we learning?

  • Science Topics

  • Electron v. proton acceleration in SNR.

  • Interactions with interstellar medium.

  • Upper limit of SNR acceleration of cosmic rays.

Multi-component model of SNR W44 by De Jager and Mastichiadis (1997). Components include synchrotron, thermal X-ray, pulsar wind nebula, relativistic bremsstrahlung, and inverse Compton.

Time scale for variability is long; therefore simultaneity is not critical for multiwavelength observations.

Unidentified sources
Unidentified Sources what physics are we learning?

Spectrum of 3EG J1835+5918 compared to that of Geminga, indicating a probable isolated neutron star (Halpern et al., Reimer et al. )

  • Science Topics

  • Discovery science.

  • New sources or new insight about known objects.

  • Nature of non-blazar transients.

Spectrum of 3EG J1714-3857/SNR RXJ1713-3946. With the limited multiwavelength coverage, no simple model explains the source (Reimer and Pohl).

For transients or other variable unidentified gamma-ray sources, having simultaneous observations may be the only viable means of positive identification.

Some lessons learned from cgro
Some Lessons Learned from CGRO what physics are we learning?

No Real Surprises Here

  • Observers at other wavelengths seem very helpful with “service observations”, as long as the observing time needed is relatively small.

  • Organizing a true multiwavelength campaign, especially for extended observations, is VERY difficult.

  • Relying on a few “friends” to carry out coordinated observations is risky (ground conditions vary).

  • We were most successful in just announcing a target of interest to a large group and then seeing who was able to collect data.

  • AGN flares seemed to be more easily seen first in gamma rays; these could prove to be a useful trigger for a coordinated campaign.

  • Unidentified gamma-ray sources are far less interesting than known objects to observers at other wavelengths (largely due to position uncertainties).

Gamma ray observatories
Gamma-ray Observatories what physics are we learning?

Complementary capabilities

ground-based space-based


angular resolution good fair good

duty cycle low high high

area large large small

field of view small large large+can reorient

energy resolution good fair good, w/ smaller systematic


limiting factor background photon statistics

The next-generation ground-based and space-based gamma-ray telescopes are well matched.

Gamma ray observatories1
Gamma-ray Observatories what physics are we learning?


Glast mission operating plan
GLAST Mission Operating Plan what physics are we learning?

GLAST is considered a facility.

A User’s Group will be formed to help the SWG

determine the optimal scientific operations of the facility.

  • Working Concept for GLAST Operations

  • The first year will be an all-sky survey.Unlike CGRO, the survey will be carried out primarily in a scanning mode, keeping the instruments always pointed away from the Earth (which is bright in gamma rays). This approach takes maximum advantage of the large fields of view of the LAT and the GBM, allowing a full sky survey on short (day) timescales.

  • After the first year, the scientific program will be determined by peer-reviewed proposals. Proposals can request pointed observations, based on scientific requirements. A pointed observation can obtain about 3 times as many photons from a source per unit time as the scanning mode. Target of Opportunity proposals can also be included.

Constraints on GLAST Operations:Essentially none!

Any non-occulted source can be observed at any time.

Mission repointing plan for bursts
Mission Repointing Plan for Bursts what physics are we learning?

  • Summary of plan

  • During all-sky scanning operations, detection of a sufficiently significant burst will cause the observatory to interrupt the scanning operation autonomously and to remain pointed at the burst region during all non-occulted viewing time for a period of 5 hours (TBR). There are two cases:

1. The burst occurs within the LAT FOV.

If the burst is bright enough that an on-board analysis provides >90% certainty that a burst occurred within the LAT FOV, the observatory will slew to keep the burst direction within 30 degrees (TBR) of the LAT z axis during >80% of the entire non-occulted viewing period (neglecting SAA effects). Such events are estimated to occur approximately once per week.

Only if the burst is exceptionally bright, the observatory will slew to bring the burst direction within 30 degrees (TBR) of the LAT z axis during >80% of the entire non-occulted viewing period (neglecting SAA effects). Such events are likely to occur a few times per year.

2. The burst occurs outside the LAT FOV.

After six months, this strategy will be re-evaluated. In particular, the brightness criterion for case 2 and the stare time will be revisited, based on what has been learned about the late high-energy emission of bursts.

Glast mission data plans
GLAST Mission Data Plans what physics are we learning?

  • Working Concept for GLAST Data

  • During the all-sky survey.The LAT team will use the early data for instrument calibration and preparation of an initial source catalog. At the end of the survey, all the data will be made public. The LAT team and the GLAST Science Support Center will be developing user-friendly software to enable all types of standard analysis.

  • After the first year. All data (Level 1 – gamma ray events and sensitivity) will be made public. Guest Investigator proposals will be awarded for scientific ideas, not images or other data. Use of data will be handled on an honor system. No data will be proprietary. The GLAST Science Support Center will be providing users access to the data and software tools.

  • At all times, data from transient sources, including burst data from the GBM, will be made public immediately, in order to facilitate multiwavelength observations. On-board processing will produce alerts for bursts within seconds.

Challenges for multiwavelength observations 1
Challenges for Multiwavelength Observations (1) what physics are we learning?

The large GLAST field of view changes the situation, even compared to CGRO

  • GLAST can monitor the sky for variable sources.

    • Especially in scanning mode, but even if pointed, GLAST will see a large fraction of the sky with good sensitivity every day. GLAST can serve as a trigger for observations at other wavelengths. Flaring sources probably require some processing on the ground and will require a day or more (depending on intensity) for quicklook recognition. How the GLAST instrument teams communicate this information is under discussion. Proposals include a Web site showing bright sources, updated regularly.

    • Bursts will give an on-board trigger that can be sent immediately to the ground. The current plan is to use the GCN.

Challenges for multiwavelength observations 2
Challenges for Multiwavelength Observations (2) what physics are we learning?

  • Selecting the sources for multiwavelength study will rely largely on other wavelengths.

    • Availability of telescope time, coordinated plans, and observational constraints will limit the number and choice of sources. The GLAST science teams want to cooperate in multiwavelength programs with the broadest coverage. The LAT team is encouraging small optical observatories and even amateurs to help monitor sufficiently bright sources. We will try to support ongoing programs that contribute to multiwavelength studies.

The GLAST Telescope Network

The Whole Earth Blazar Telescope

The Whole Year Blazar Telescope

Challenges for multiwavelength observations 3
Challenges for Multiwavelength Observations (3) what physics are we learning?

  • We need multiwavelength observation programs for non-flaring sources.

    • The broad-band shape of the spectrum is often critical in determining the nature of an unidentified source.

    • The fluctuation (power density) spectrum is an important part of understanding flares.

    • Determining blazar radio properties and redshifts is important, since GLAST expects to detect many blazars that are not yet identified as such. The proposed VLBA Imaging and Polarimetry Survey program could be extremely valuable.

    • Monitoring of pulsars is important. The Parkes radio telescope in the southern hemisphere and several northern telescopes, perhaps including SETI’s Allen Telescope Array are important.

Maximizing the science will require cooperation among many instruments at all wavelengths.

Exciting times are ahead
Exciting Times Are Ahead! what physics are we learning?


    • Running! Outriggers complete, transient notification system.


    • Running!


    • Building prototype. Northern hemisphere, array capabilities, great co-located optical opportunities

  • HESS

    • Building and commissioning phase 1. Southern hemisphere, array capabilities


    • Building. Simultaneous optical monitoring to 18m w/ dedicated and integrated 80cm-100cm telescope planned. Observing w/ INTEGRAL planned.

Exciting times are ahead1
Exciting Times Are Ahead! what physics are we learning?


    • Launch in 2003. Multi-wavelength. Primary mission is burst science (>100/year, GCN alerts, locations), plus hard x-ray survey, sky monitor.


    • Launch in 2006. Satellite capabilities, large GO program planned, GTN underway, GCN alerts.

  • Cross-calibration and overlap between ground-based and space-based measurements

  • Optical monitoring campaigns being organized


  • The promise of neutrinos.

    • Amanda II preliminary limit for Mkn501 approaching optimistic models (factor ~10 improvement over AMANDA B10). Putting performance parameters on the same footing (Aeff w/ energy). what physics are we learning?

Glast project master schedule
GLAST Project Master Schedule what physics are we learning?

  • Instrument preliminary Design Reviews completed

  • Spacecraft contractor selected: Spectrum-Astro

    • S/C PDR March 2003

    • S/C CDR fall 2003

  • Critical Design Reviews for instruments will be April or May this year

  • Instrument deliveries in 2005

    • GBM spring

    • LAT summer

  • Launch in 2006

    • September (“God willin’ and the creek don’t rise.”)

Guest investigator program
Guest Investigator Program what physics are we learning?

  • GI program starts during the survey

    • 10-15 GIs

  • Will grow to ~100 Guest Investigations funded by NASA each year.

  • GLAST Fellows program

  • Continue Interdisciplinary Scientist (IDS) Program

    C. Dermer (NRL) - non-thermal universe

    B. Dingus (Wisconsin) - transients

    M. Pohl (Ruhr U.) - diffuse galactic

    S. Thorsett (UCSC) - pulsars

  • Program of Education and Public Outreach continues throughout the mission

Transient policy
Transient policy what physics are we learning?

  • The GLAST instrument teams have the duty to release data on transient gamma ray sources to the community as soon as practical. The decisions on which data are to be released will be based on advice from scientists analyzing the data and an evaluation of the scientific interest that the data might generate. They will follow the general guidelines suggested below:

  • 1) Gamma-ray bursts: All data on gamma-ray bursts that trigger either the LAT or GBM will be released. The prompt data release will include direction, fluence estimate and other key information about the burst immediately on discovery. Individual photon data and technical information for their analysis will be released as soon as practical.

  • 2) Blazars and some other sources of high interest: 10-20 pre-selected sources from the 3rd EGRET catalog will be monitored continuously and the fluxes and spectral characteristics will be posted on a publicly accessible web site. Another 10-20 scientifically interesting sources will be added to this list during the survey. The list will include some known or newly discovered AGN selected to be of special interest by the TeV and other communities as well as galactic sources of special interest discovered during the survey.

  • 3) New transients: The community will be notified when a newly discovered source goes above an adjustable flux level of about (2-5) x 10-6 photons (> 100 MeV) per cm2 s for the first time; the flux level is to be adjusted to set the release rate to about 1-2 per week. A source exhibiting unusual behavior that is detectable on sub-day timescales, such as a spectral state change or a large flux derivative while the source is at elevated flux levels, will also trigger an alert to the community.

Multi wavelength campaigns
Multi-wavelength campaigns what physics are we learning?

  • Science requires broad band (radio to gamma-rays) study of these celestial sources. Therefore, following the survey, the observing program will be determined entirely by the astronomical and high energy physics communities based on proposals submitted.

    • LAT and GBM team members can compete, but cannot win additional funding.

    • Non-US investigators may apply

    • Selection is based on peer reviewed proposals.

  • The community will interface to the GLAST data through the GLAST Science Support Center.

    • SSC mirror sites in Italy (LAT and GBM may have others)

Glast science requires multi wavelength approach
GLAST science requires multi-wavelength approach what physics are we learning?

In the MeV range and above, sources are non-thermal

 produced by interactions of energetic particles

  • Nature rarely produces mono-energetic particle beams. Broad range of particle energies leads to a broad range of photon energies.

    • Example: po production

  • Charged particles rarely interact by only one process. Different processes radiate in different energy bands.

    • Example: synchrotron-Compton processes

  • High-energy particles, as they lose energy, can radiate in lower-energy bands.

    • Contrast: non-thermal X-ray source can have high-energy cutoff

      Due to variability on short time scales, AGN require simultaneous multiwavelength observations for maximum scientific return.

      For other science, the time scale for variability is long (e.g. SNR, plereons); therefore simultaneity is not critical for multiwavelength observations.

      For transients or other variable unidentified gamma-ray sources, having simultaneous observations may be the only viable means of positive identification.

Data release policies
Data release policies what physics are we learning?

  • All-sky survey during the first year.

    • LAT team to produce a point source catalog and an all sky map; formal release 90 days following completion of the survey.

  • Transient source locations are made public immediately with photon data (light curves, improved positions, etc.) to follow as practical.

    • During first year photon data to include warning that the data may be unverified and uncalibrated

    • Best efforts to release preliminary catalogs in time for AOs

      • The first 3 months of observations will be delivered at 6 months

      • The full 12 months of observations will be delivered 1 month after the end of the sky survey

  • Guest investigators may propose for source studies, associated theory or key projects

    • Data from these sources of interest are made available immediately to the GIs.

  • Following the survey, it is being proposed that all GLAST data will be made public immediately.

    • Comments on this policy may be sent to [email protected] or [email protected]

    • We plan to conduct workshops on how to propose for and how to the use the tools to analyze the GLAST data

Some lessons learned from cgro agn 1
Some Lessons Learned from CGRO - AGN (1) what physics are we learning?

Notes from Bob Hartman/Dave Thompson

  • Even in the optical, it is difficult to get light curves over several weeks for more than 1-3 objects at a time.

  • For most blazars, the peak of the synchrotron bump is in the far IR, corresponding to a Compton peak in the GeV range.  It would be very useful to be able to correlate those, but there are essentially no observing resources there.  We got no real help from ISO. SIRTF has capability out to 160 m but is likely to be oversubscribed.

  • Except for the brightest blazars, X-ray observations require focusing instruments. However, the big focusing instruments (e.g. Chandra, XMM) are generally hugely oversubscribed and very inflexible.  We got some good support at times from ASCA, BeppoSAX, and RXTE, but they will all be gone by 2007. Astro-E2 may help.

  • Most of the X-ray telescopes need to have the target near 90 degrees from the Sun.  This means that the ground-based observers, (optical, TeV, etc.) must observe in poor conditions, if it is possible at all. Swift may be a big help.

  • INTEGRAL, Swift, and perhaps EXIST will provide the hard X-ray coverage in the GLAST era that was offered by COMPTEL and OSSE in the CGRO time frame, although the medium-energy gamma-ray range (10-30 MeV) will be open.

Some lessons learned from cgro agn 2
Some Lessons Learned from CGRO - AGN (2) what physics are we learning?

  • We had very good radio support from U. Michigan (5, 8, 15 GHz) and Metsahovi (Finland; 22, 37 GHz). However, both of those programs have funding problems. We might be able to influence that (had some success while CGRO was active).

  • At higher radio frequencies (90-600 GHz, the instruments are largely dedicated to topics like star formation, etc.  We have a few friends in key places, but there is no possibility for monitoring at intervals less than ~1 month.

  • The capabilities for VLBI observations at frequencies up to and beyond 100 GHz are improving rapidly.  This allows resolution much closer to the nucleus, and better correlation of blob ejections with gamma flares. This will only get better.

  • The situation is improving in the optical with the increase in the number of 0.5-1 meter automated telescopes.  However, for monitoring bright flares on timescales <1 day, the observers and instruments are largely concentrated in Europe and NA.  The Whole Earth Blazar Telescope and the Whole Year Blazar Telescope (WEBT; WYBT; Mattox; Villata, et al.) are valuable approaches to organizing this.

  • For bright objects and flares, the amateur astronomy community can make valuable contributions.  With a small amount of financial aid (filters, maybe some CCDs), they could be much more valuable.  They are a dedicated bunch - some of them make as many blazar observations as the professionals. The GLAST Telescope Network (GTN) involves them.