Identification of very high energy gamma ray sources
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Identification of Very high energy gamma-ray sources. Introduction into the problem Status of the identifications Summary. Outline:. During the first 2 years of operation of H.E.S.S. more than 15 (initially) unidentified gamma-ray sources were found

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Identification of Very high energy gamma-ray sources

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Identification of very high energy gamma ray sources

Identification of Very high energy gamma-ray sources

  • Introduction into the problem

  • Status of the identifications

  • Summary

Outline:


Unidentified sources

During the first 2 years of operation of H.E.S.S. more than 15 (initially) unidentified gamma-ray sources were found

Mostly found in the Galactic plane survey, but also some serendipitous discoveries in targeted observations on known sources

Common properties of these sources:

Positioned along the plane

Most of the sources (at least) slightly extended

Energy spectra generally hard (Photon index ~ 2.2)

Unidentified sources

e.g. Kookaburra region

H.E.S.S. plane survey


Identifying the sources

Necessary for a firm identification: counterpart at other wavebands

Step 1: Positional agreement. Good angular resolution helps against source confusion.

Step 2: Viable gamma-ray emission mechanism of the positional counterpart

Step 3: Consistent multi-wavelength picture

Additionally: if extended - morphological match

VHE gamma-astronomy in fortunate situation of “few” sources. For GLAST detailed case-by-case MWL studies for all sources is impossible.

  • Possible sources:

  • SNRs

  • Pulsars and PWN

  • Microquasars and binaries

  • Molecular clouds

  • Background AGN

  • Others?

The Crab Nebula

  • Possible sources:

  • SNRs

  • Pulsars and PWN

  • Microquasars and binaries

  • Molecular clouds

  • Background AGN

  • Others?

~ 0.1deg per event

The Crab Nebula

EGRET

  • Most importantwavebands:

    • Radio

    • X-rays

  • Timing information (periodicity or variability) can provide final proof

H.E.S.S

  • Most importantwavebands:

    • Radio

    • X-rays

  • Timing information (periodicity or variability) can provide final proof

EGRET

H.E.S.S

~ 0.1deg per event

Identifying the sources


Status of identification

Position

Emission

MWL

Status of identification

  • Following the scheme outlined before try to categorise the sources in the following scheme:

    • CAT A: Perfect match (all items fulfilled plus morphological match for extended sources)

    • CAT B: Inconsistency in positional / morphological match

    • CAT C: Inconsistency in multiwavelength picture

    • CAT D: No match


A perfect match

Position

Emission

MWL

A: Perfect match

  • Extended Objects with (perfect) morphological matchto other wavebands (e.g. X-rays)

    • Association beyond doubt.

    • Associations with shell-type SNRs and with X-ray plerions

    • Gather MWL data to understand the emission mechanism

    • Probably not the typical objects for GLAST due to worse PSF

MSH 15-52

RX J1713.7-3946

Vela X

RX J0852.0-4622


A perfect match1

Position

Emission

MWL

A: Perfect match

MSH 15-52

  • Extended Objects with (perfect) morphological matchto other wavebands (e.g. X-rays)

  • Point-like objects - One counterpart candidate

    • Error on reconstructed position vs distance to the object.

    • Final proof from correlated variability (if exists) or periodicity.

    • Gather MWL data to understand the emission mechanism

    • GLAST likely to find sources of this category

RX J0852.0-4622

RX J1713.7-3946

Vela X

LS 5039

G0.9-0.1


A perfect match2

Position

Emission

MWL

A: Perfect match

MSH 15-52

  • Extended Objects with (perfect) morphological matchto other wavebands (e.g. X-rays)

  • Point-like objects – One counterpart candidate

  • Not quite perfect: Point-like objects – Source confusion

    • Arcmin angular resolution, Galactic Center still confused region

    • Only really identifiable via correlated variability in other wavebands

    • GLAST will be heavily facing this problem in the Galactic plane

RX J0852.0-4622

RX J1713.7-3946

Vela X

LS 5039

G0.9-0.1

VHE  - H.E.S.S.

Radio 90 cm - VLA

Sgr A*

Sgr A East


B problems in position morphology

Position

Emission

MWL

XMM 2-10 keV

B: Problems in position/morphology

  • H.E.S.S. sees several “offset” PWN, aroundenergetic pulsars, often with X-ray PWN.

    • Archetypal example: HESS J1825-137

      • Same morphology but vastly differentspatial scales for X-rays and g-rays

      • Reason could be different coolingtimescales for e- emitting synchrotron X-rays emitting IC gamma-rays

      • Energy dependent morphology in gamma-raysaway from pulsar position supports this picture

    • Here we can construct a plausible emission mechanism explaining the MWL data, but no direct morphological match

H.E.S.S. 0.25-30 TeV

3’


C inconsistency in mwl picture

Position

Emission

MWL

C: Inconsistency in MWL picture

  • Example: HESS J1813-178

    • Detected in plane survey, initially unidentified

    • Shortly afterwards reports on a coincidentunidentified non-thermal strongly absorbedASCA and an INTEGRAL source

    • Radio (VLA) data show shell-like structure.Another shell-type SNR emitting g-rays?

  • XMM data show no shell but rather an extended object. Maybe another compositeSNR, but g-rays (most) probably not from shell.


D unidentified

Position

Emission

MWL

D: Unidentified

  • The first example: HEGRA sourceTeV J2032+4131 in Cygnus region

  • Another one: HESS J1303-631

    • No counterpart so far, recentlyalso no counterpart in a 5 ks Chandra exposure.

    • Claims of an associated GRB remnant …

  • There are more of these objects. Currently obtaining XMM/Chandra/Suzaku data in a case-by-case effort.

  • Still a long way to go …


The status so far

Position

Emission

MWL

The status so far …


Summary

Position

Emission

MWL

Summary

  • Categorise sources according to their identification status

  • Clearly gathering good MWL data is the way to go to identify the H.E.S.S. unidentified sources.

  • What will we learn for GLAST:

    • Individual identification is very tedious, even with arcmin resolution

    • Positional match does not suffice

    • We need another approach than case-by-case MWL studies

    • Nevertheless we will heavily depend on MWL catalogues for population studies


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