GAMMA-RAY OBSERVATIONS OF THE ORION MOLECULAR CLOUDS WITH THE FERMI LARGE AREA TELESCOPE
Markus Ackermann
,
Marco Ajello
,
A. Allafort
,
E. Antolini
,
Luca Baldini
,
Jean Ballet
(1)
,
Guido Barbiellini
,
D. Bastieri
,
K. Bechtol
,
R. Bellazzini
,
B. Berenji
,
R. D. Blandford
,
E. D. Bloom
,
E. Bonamente
,
A. W. Borgland
,
E. Bottacini
,
T. J. Brandt
(2)
,
J. Bregeon
,
M. Brigida
,
Pascal Bruel
(3)
,
R. Buehler
,
S. Buson
,
G. A. Caliandro
,
R. A. Cameron
,
P. A. Caraveo
,
C. Cecchi
,
A. Chekhtman
,
J. Chiang
,
S. Ciprini
,
R. Claus
,
J. Cohen-Tanugi
(4)
,
J. Conrad
,
F. d'Ammando
,
A. de Angelis
,
F. de Palma
,
C. D. Dermer
,
E. Do Couto E Silva
,
P. S. Drell
,
A. Drlica-Wagner
,
T. Enoto
,
L. Falletti
,
C. Favuzzi
,
S. J. Fegan
(3)
,
E. C. Ferrara
,
W. B. Focke
,
Y. Fukazawa
,
Y. Fukui
,
P. Fusco
,
F. Gargano
,
D. Gasparrini
,
S. Germani
,
N. Giglietto
,
F. Giordano
,
M. Giroletti
,
T. Glanzman
,
G. Godfrey
,
S. Guiriec
,
D. Hadasch
,
Y. Hanabata
,
A. K. Harding
,
M. Hayashida
,
K. Hayashi
,
D. Horan
(3)
,
X. Hou
(5)
,
R. E. Hughes
,
M. S. Jackson
,
G. J 'Ohannesson
,
A. S. Johnson
,
T. Kamae
,
H. Katagiri
,
J. Kataoka
,
M. Kerr
,
Jürgen Knödlseder
(2)
,
M. Kuss
,
J. Lande
(2)
,
S. Larsson
,
S.-H. Lee
,
F. Longo
,
F. Loparco
,
M. N. Lovellette
,
P. Lubrano
,
K. Makishima
,
M. N. Mazziotta
,
J. Mehault
(4)
,
W. Mitthumsiri
,
A. A. Moiseev
,
C. Monte
,
M. E. Monzani
,
A. Morselli
,
I. V. Moskalenko
,
S. Murgia
,
T. Nakamori
,
M. Naumann-Godo
,
S. Nishino
,
J. P. Norris
,
E. Nuss
(4)
,
M. Ohno
,
T. Ohsugi
,
A. Okumura
,
M. Orienti
,
E. Orlando
,
J. F. Ormes
,
M. Ozaki
,
D. Paneque
,
J. H. Panetta
,
D. Parent
,
V. Pelassa
(4)
,
M. Pesce-Rollins
,
M. Pierbattista
(1)
,
F. Piron
(4)
,
G. Pivato
,
T.A. Porter
,
S. Rain'O
,
M. Razzano
,
A. Reimer
,
O. Reimer
,
M. Roth
,
H. F.-W. Sadrozinski
,
C. Sgr'O
,
E. J. Siskind
,
G. Spandre
,
P. Spinelli
,
A. W. Strong
,
H. Takahashi
,
T. Takahashi
,
T. Tanaka
,
J. G. Thayer
,
J. B. Thayer
,
O. Tibolla
,
M. Tinivella
,
D. F. Torres
,
A. Tramacere
,
E. Troja
,
Y. Uchiyama
,
T. L. Usher
,
J. Vandenbroucke
,
V. Vasileiou
(4)
,
G. Vianello
,
V. Vitale
,
A. P. Waite
,
P. Wang
,
B. L. Winer
,
K. S. Wood
,
Z. Yang
,
S. Zimmer
Markus Ackermann
- Function : Author
Marco Ajello
- Function : Author
A. Allafort
- Function : Author
E. Antolini
- Function : Author
Luca Baldini
- Function : Author
Guido Barbiellini
- Function : Author
D. Bastieri
- Function : Author
K. Bechtol
- Function : Author
R. Bellazzini
- Function : Author
B. Berenji
- Function : Author
R. D. Blandford
- Function : Author
E. D. Bloom
- Function : Author
E. Bonamente
- Function : Author
A. W. Borgland
- Function : Author
E. Bottacini
- Function : Author
J. Bregeon
- Function : Author
- PersonId : 741214
- IdHAL : johan-bregeon
- ORCID : 0000-0002-6790-5328
- IdRef : 095856943
M. Brigida
- Function : Author
R. Buehler
- Function : Author
S. Buson
- Function : Author
G. A. Caliandro
- Function : Author
R. A. Cameron
- Function : Author
P. A. Caraveo
- Function : Author
C. Cecchi
- Function : Author
A. Chekhtman
- Function : Author
J. Chiang
- Function : Author
S. Ciprini
- Function : Author
R. Claus
- Function : Author
J. Cohen-Tanugi
- Function : Author
- PersonId : 3626
- IdHAL : johann-cohen-tanugi
- ORCID : 0000-0001-9022-4232
- IdRef : 172626544
J. Conrad
- Function : Author
F. d'Ammando
- Function : Author
A. de Angelis
- Function : Author
F. de Palma
- Function : Author
C. D. Dermer
- Function : Author
E. Do Couto E Silva
- Function : Author
P. S. Drell
- Function : Author
A. Drlica-Wagner
- Function : Author
T. Enoto
- Function : Author
- PersonId : 764101
- ORCID : 0000-0003-1244-3100
L. Falletti
- Function : Author
C. Favuzzi
- Function : Author
S. J. Fegan
- Function : Author
- PersonId : 740343
- IdHAL : stephen-fegan
- ORCID : 0000-0002-9978-2510
- IdRef : 253133149
E. C. Ferrara
- Function : Author
W. B. Focke
- Function : Author
Y. Fukazawa
- Function : Author
- PersonId : 760581
- ORCID : 0000-0002-0921-8837
Y. Fukui
- Function : Author
P. Fusco
- Function : Author
F. Gargano
- Function : Author
D. Gasparrini
- Function : Author
S. Germani
- Function : Author
N. Giglietto
- Function : Author
- PersonId : 755413
- ORCID : 0000-0002-9021-2888
F. Giordano
- Function : Author
M. Giroletti
- Function : Author
T. Glanzman
- Function : Author
G. Godfrey
- Function : Author
S. Guiriec
- Function : Author
D. Hadasch
- Function : Author
- PersonId : 761675
- ORCID : 0000-0001-8663-6461
Y. Hanabata
- Function : Author
A. K. Harding
- Function : Author
M. Hayashida
- Function : Author
K. Hayashi
- Function : Author
R. E. Hughes
- Function : Author
M. S. Jackson
- Function : Author
G. J 'Ohannesson
- Function : Author
A. S. Johnson
- Function : Author
T. Kamae
- Function : Author
H. Katagiri
- Function : Author
J. Kataoka
- Function : Author
M. Kerr
- Function : Author
Jürgen Knödlseder
- Function : Author
- PersonId : 178646
- IdHAL : jurgen-knodlseder
- ORCID : 0000-0002-0014-7809
- IdRef : 069521360
M. Kuss
- Function : Author
S. Larsson
- Function : Author
S.-H. Lee
- Function : Author
F. Longo
- Function : Author
- PersonId : 755442
- ORCID : 0000-0003-2501-2270
F. Loparco
- Function : Author
M. N. Lovellette
- Function : Author
P. Lubrano
- Function : Author
K. Makishima
- Function : Author
M. N. Mazziotta
- Function : Author
W. Mitthumsiri
- Function : Author
A. A. Moiseev
- Function : Author
C. Monte
- Function : Author
M. E. Monzani
- Function : Author
A. Morselli
- Function : Author
I. V. Moskalenko
- Function : Author
S. Murgia
- Function : Author
T. Nakamori
- Function : Author
- PersonId : 760584
- ORCID : 0000-0002-7308-2356
M. Naumann-Godo
- Function : Author
S. Nishino
- Function : Author
J. P. Norris
- Function : Author
M. Ohno
- Function : Author
T. Ohsugi
- Function : Author
A. Okumura
- Function : Author
M. Orienti
- Function : Author
E. Orlando
- Function : Author
J. F. Ormes
- Function : Author
M. Ozaki
- Function : Author
- PersonId : 759061
- ORCID : 0000-0002-1320-9781
D. Paneque
- Function : Author
- PersonId : 755279
- ORCID : 0000-0002-2830-0502
J. H. Panetta
- Function : Author
D. Parent
- Function : Author
M. Pesce-Rollins
- Function : Author
- PersonId : 760585
- ORCID : 0000-0003-1790-8018
F. Piron
- Function : Author
- PersonId : 172749
- IdHAL : frederic-piron
- ORCID : 0000-0001-6885-7156
G. Pivato
- Function : Author
T.A. Porter
- Function : Author
S. Rain'O
- Function : Author
M. Razzano
- Function : Author
A. Reimer
- Function : Author
- PersonId : 755465
- ORCID : 0000-0001-8604-7077
O. Reimer
- Function : Author
M. Roth
- Function : Author
H. F.-W. Sadrozinski
- Function : Author
C. Sgr'O
- Function : Author
E. J. Siskind
- Function : Author
G. Spandre
- Function : Author
P. Spinelli
- Function : Author
A. W. Strong
- Function : Author
H. Takahashi
- Function : Author
T. Takahashi
- Function : Author
T. Tanaka
- Function : Author
- PersonId : 756461
- ORCID : 0000-0002-4383-0368
J. G. Thayer
- Function : Author
J. B. Thayer
- Function : Author
O. Tibolla
- Function : Author
M. Tinivella
- Function : Author
D. F. Torres
- Function : Author
A. Tramacere
- Function : Author
E. Troja
- Function : Author
Y. Uchiyama
- Function : Author
T. L. Usher
- Function : Author
J. Vandenbroucke
- Function : Author
G. Vianello
- Function : Author
V. Vitale
- Function : Author
- PersonId : 760184
- ORCID : 0000-0001-8040-7852
A. P. Waite
- Function : Author
P. Wang
- Function : Author
B. L. Winer
- Function : Author
K. S. Wood
- Function : Author
Z. Yang
- Function : Author
S. Zimmer
- Function : Author
Abstract
We report on the gamma-ray observations of giant molecular clouds Orion A and B with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. The gamma-ray emission in the energy band between ∼100 MeV and ∼100 GeV is predicted to trace the gas mass distribution in the clouds through nuclear interactions between the Galactic cosmic rays (CRs) and interstellar gas. The gamma-ray production cross-section for the nuclear interaction is known to ∼10% precision which makes the LAT a powerful tool to measure the gas mass column density distribution of molecular clouds for a known CR intensity. We present here such distributions for Orion A and B, and correlate them with those of the velocity-integrated CO intensity (WCO) at a 1◦ × 1◦ pixel level. The correlation is found to be linear over a WCO range of ∼10-fold when divided in three regions, suggesting penetration of nuclear CRs to most of the cloud volumes. The WCO-to-mass conversion factor, XCO, is found to be ∼2.3 × 1020 cm−2 (K km s−1)−1 for the high-longitude part of Orion A (l > 212◦), ∼1.7 times higher than ∼1.3 × 1020 found for the rest of Orion A and B. We interpret the apparent high XCO in the high-longitude region of Orion A in the light of recent works proposing a nonlinear relation between H2 and CO densities in the diffuse molecular gas. WCO decreases faster than the H2 column density in the region making the gas "darker" to WCO.