Transcript MW Update

Multiwavelength Challenges in the Fermi Era
Dave Thompson
Fermi Gamma-ray Space Telescope
Large Area Telescope Multiwavelength Coordinator
Outline
1. Introduction - The Multiwavelength Revolution
2. Multiwavelength Opportunities
3. Some Challenges for Multiwavelength Studies
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A Revolution? Why?
Simple literature search using NASA ADS.
Search for the word “Multiwavelength” in titles.
1976
0
1986
2
1996
58
2006
97
Many astrophysicists have come to recognize
the value of multiwavelength research.
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One Reason – Communication
1977 – 111 computers on ARPANET, forerunner of the
Internet. Most information exchange was on paper.
1981 – First IBM PC
1983 – TCP/IP protocol; SENDMAIL program started;
e-mail became practical.
1988 – NSFNET backbone upgraded to 1.5 Mbps
1990 – Tim Berners-Lee and the first Web server
1993 – Mosaic Web browser
1999 - Wi-Fi (IEEE 802.11standard) wireless
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Another Reason – Facilities
The situation across the spectrum in 1982 – 27 yrs ago:
Radio telescopes – VLA open 2 years, no VLBA
Sub-mm – just getting started
IR – no satellites (IRAS 1983), detectors limited
Optical – largest telescopes: Hale 5 m, Soviet 6 m, few
CCDs
UV – IUE (a bright spot)
X-ray – Hakucho Japanese satellite
Gamma-ray – COS-B turned off in that year
TeV – Whipple Observatory just getting started
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Gamma-ray Facilities: More Numerous, More Capable
Swift
Fermi
INTEGRAL
CANGAROO
MAGIC
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ARGO-YBJ
Milagro/HAWC
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H.E.S.S.
VERITAS
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Multiwavelength Opportunities:
The Gamma-ray Perspective
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Some Multiwavelength Successes
1. Gamma-ray bursts - LAT and GBM, plus others,
including redshift measurements in optical.
2. Pulsars, both using radio and X-ray data and
providing information to radio observers
3. AGN studies - especially ATel flare reports, MW
correlations and spectral studies.
4. Binaries - timing and spectral comparisons with Xray and TeV.
5. New source classes - including starburst galaxies,
narrow line Seyfert quasars.
6. Diffuse radiation (and associated dark matter
searches) - models built on MW data.
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PSR J1741-2054 - radio pulsar found from
gamma-ray timing
Fermi LAT point source -> Swift X-ray source gave better
position -> LAT timing discovered the gamma-ray
pulsations -> Radio telescopes found the radio pulsar
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PMN J0948+0022 - A new source type
A Spectral Energy
Distribution using
simultaneous data
provides evidence
that this narrowline Seyfert 1 is
similar to the
gamma-ray blazars.
Work led by Luigi
Foschini
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Independent MW groups using public LAT Data
3C454.3
Bonning et
al. 2008
We can
expect
more such
work now
that the
data are
public.
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Multiwavelength Challenges:
What Can Be Done?
1. Time can be an enemy (Patrizia Caraveo’s talk
later today)
2. Too many sources to get enough
Multiwavelength coverage?
3. Deciding whether to work with an instrument
team
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The Challenge of Time
GRBs are so bright that they can be
seen by on-board processing, but
flares require ground analysis.
Some flares, however can be as
short as one day.
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Two LAT Unidentified Fast Transients
High confidence
>10 sigma
3EG J0903-3531
Preliminary 68%
error circles 0.12
deg, 0.07 deg
Fermi J0910-5041
Daily rates
- counts (E>200 MeV)
within 2 deg radius
- exposure corrected
- scaled to
background rate
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Q. How quickly can the LAT team tell if a source is flaring?
A. At least half a day before an Automated Science
Processing (ASP) run is done. ASP reports are
generated every six hours.
•
•
GPS
msec
Large Area Telescope
& GBM
DELTA
7920H
-
• Telemetry 1 kbps
•
Fermi Spacecraft
TDRSS SN
S & Ku
•
•
S
•
GN
•
Schedules
Mission Operations
Center (MOC)
GRB
Coordination
Network (GCN)
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LAT Instrument
Science
Operations Center
Science
Support Center
Schedules
Alerts
White Sands
HEASARC
GBM Instrument
Operations Center
Data, Command Loads
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What is the LAT Team Doing?
The LAT team intends to continue quicklook work
The LAT Flare Advocates review data daily and put out ATels for
“breaking news.” The LAT team has sent out 45 ATels.
No outside group seems likely to want to set up the infrastructure
needed for such analysis. Similar situation for Burst Advocates.
This group also generates the Fermi Blog,
http://fermisky.blogspot.com/
The public light curves for bright sources are generated
automatically. 41 sources are now being tracked, and new ones
are being added regularly. That work will continue.
All these exercises are advertisements of
multiwavelength opportunities for the community.
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The Challenge of Too Much Data
“We've
gone from
data-starved to data-rich!”
Alan Marscher, Sept. 2009
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The Gamma-ray Sky in Celestial Coordinates
How do we choose from the many sources for multiwavelength study?
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How long should we observe a source?
PKS 1510-089
from the public
LAT data.
100 days of data
shows a bright
flare and some
low-level
emission. Let’s
write a paper right?
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Radio Monitoring
AGN studies (http://pulsar.sternwarte.uni-erlangen.de/radiogamma/)
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Optical/IR Monitoring
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New Multiwavelength Opportunities
Congratulations to the MAXI team!
The Japanese MAXI all-sky X-ray monitor is now in operation on
the International Space Station, with sensitivity of a few
mCrab in a few days. The plan is to make results public.
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New Multiwavelength Opportunities
Planck and Herschel are now in orbit, and WISE is at
Vandenburg for a December launch
Following the end of the cryogenic part of the Spitzer mission, these
satellites are the primary source of long-wavelength observations
from space. Planck and WISE will observe the full sky every six
months.
AKARI
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The Challenge of Choosing
Collaborators
With all the LAT data and some of the
AGILE data public, when should MW
observers consider working with the
instrument teams (who tend to be big
and a bit cumbersome as partners)?
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Simple Cases
Published or
public data are
OK for broadbrush science
topics, such as
broadband
SEDs or light
Tavecchio et al 2009
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curves for bright
sources.
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Simple Cases
The Fermi
Science
Support
Center
provides
software and
instructions
as well as
the Fermi
data.
Particularly for bright sources away from the Galactic
Plane, source detection and construction of simple
spectra are designed to be straightforward.
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Where Things Get Complicated
There are important caveats about analysis of Fermi
LAT data. Ignoring these can lead to misleading or
incorrect results.
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Where Things Get Complicated
• The diffuse Galactic emission is bright and highly
structured (see Stan Hunter’s talk). The diffuse model
supplied by the LAT team has recently been updated
and is likely to continue to evolve. Separating weaker
sources from the diffuse Galactic emission is nontrivial.
• The LAT Instrument Response Functions (IRFs) have
significant uncertainties at energies near 100 MeV and
a non-negligible charged particle background at
energies above 10 GeV. Improvements in the IRFs are
expected but are not imminent.
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Some Occasions to Think about Contacting
the Instrument Team
• If you are searching for a source that is not in the LAT
catalog, then it is probably weak enough that a simple
analysis will not be adequate.
• If you need a detailed energy spectrum or are looking
for particular spectral features, especially at very low or
very high energies, the LAT team has experience with
non-standard analysis.
• If you are trying to analyze the Galactic Center region,
you are strongly advised not to go it alone!
• If you are interested in the most complete
multiwavelength coverage, consider contacting the LAT
team. We have many cooperating groups across the
spectrum who may be interested in working with you
(even if you don’t include the LAT team).
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Summary
• With the public release of LAT and AGILE
data, opportunities for multiwavelength
studies of the gamma-ray sky are growing.
• Particular challenges in this new era
include the need for quick responses, the
difficulty of getting enough coverage for the
many sources that are seen, and the question
of whether to work with an instrument team.
• Communication continues to be a key to
multiwavelength success.
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