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Title: Extended gamma-ray emission from the G25.0+0.0 region: A star-forming region powered by the newly found OB association?

Abstract

We report a study of extended γ-ray emission with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope, which is likely to be the second case of a γ-ray detection from a star-forming region (SFR) in our Galaxy. The LAT source is located in the G25 region, 1°7 × 2°1 around (l, b) = (25°0, 0°0). The γ-ray emission is found to be composed of two extended sources and one pointlike source. The extended sources have similar sizes of about 1°4 × 0fdg6. An ~0°4 diameter subregion of one has a photon index of Γ = 1.53 ± 0.15, and is spatially coincident with HESS J1837–069, likely a pulsar wind nebula. The other parts of the extended sources have a photon index of Γ = 2.1 ± 0.2 without significant spectral curvature. Given their spatial and spectral properties, they have no clear associations with sources at other wavelengths. Their γ-ray properties are similar to those of the Cygnus cocoon SFR, the only firmly established γ-ray detection of an SFR in the Galaxy. Indeed, we find bubble-like structures of atomic and molecular gas in G25, which may be created by a putative OB association/cluster. The γ-ray emitting regionsmore » appear confined in the bubble-like structure; similar properties are also found in the Cygnus cocoon. In addition, using observations with the XMM-Newton, we find a candidate young massive OB association/cluster G25.18+0.26 in the G25 region. Here, we propose that the extended γ-ray emission in G25 is associated with an SFR driven by G25.18+0.26. Based on this scenario, we discuss possible acceleration processes in the SFR and compare them with the Cygnus cocoon.« less

Authors:
ORCiD logo [1];  [2]; ORCiD logo [3]
  1. Hiroshima Univ., Hiroshima (Japan)
  2. Rikkyo Univ., Tokyo (Japan)
  3. Erlangen Centre for Astroparticle Physics, Erlangen (Germany)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1355728
Grant/Contract Number:
AC02-76SF00515
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 839; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; acceleration of particles; cosmic rays; gamma rays: ISM; ISM: bubbles; open clusters and associations: general; X-rays: stars

Citation Formats

Katsuta, J., Uchiyama, Y., and Funk, S. Extended gamma-ray emission from the G25.0+0.0 region: A star-forming region powered by the newly found OB association?. United States: N. p., 2017. Web. doi:10.3847/1538-4357/aa6aa3.
Katsuta, J., Uchiyama, Y., & Funk, S. Extended gamma-ray emission from the G25.0+0.0 region: A star-forming region powered by the newly found OB association?. United States. doi:10.3847/1538-4357/aa6aa3.
Katsuta, J., Uchiyama, Y., and Funk, S. Thu . "Extended gamma-ray emission from the G25.0+0.0 region: A star-forming region powered by the newly found OB association?". United States. doi:10.3847/1538-4357/aa6aa3. https://www.osti.gov/servlets/purl/1355728.
@article{osti_1355728,
title = {Extended gamma-ray emission from the G25.0+0.0 region: A star-forming region powered by the newly found OB association?},
author = {Katsuta, J. and Uchiyama, Y. and Funk, S.},
abstractNote = {We report a study of extended γ-ray emission with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope, which is likely to be the second case of a γ-ray detection from a star-forming region (SFR) in our Galaxy. The LAT source is located in the G25 region, 1°7 × 2°1 around (l, b) = (25°0, 0°0). The γ-ray emission is found to be composed of two extended sources and one pointlike source. The extended sources have similar sizes of about 1°4 × 0fdg6. An ~0°4 diameter subregion of one has a photon index of Γ = 1.53 ± 0.15, and is spatially coincident with HESS J1837–069, likely a pulsar wind nebula. The other parts of the extended sources have a photon index of Γ = 2.1 ± 0.2 without significant spectral curvature. Given their spatial and spectral properties, they have no clear associations with sources at other wavelengths. Their γ-ray properties are similar to those of the Cygnus cocoon SFR, the only firmly established γ-ray detection of an SFR in the Galaxy. Indeed, we find bubble-like structures of atomic and molecular gas in G25, which may be created by a putative OB association/cluster. The γ-ray emitting regions appear confined in the bubble-like structure; similar properties are also found in the Cygnus cocoon. In addition, using observations with the XMM-Newton, we find a candidate young massive OB association/cluster G25.18+0.26 in the G25 region. Here, we propose that the extended γ-ray emission in G25 is associated with an SFR driven by G25.18+0.26. Based on this scenario, we discuss possible acceleration processes in the SFR and compare them with the Cygnus cocoon.},
doi = {10.3847/1538-4357/aa6aa3},
journal = {The Astrophysical Journal (Online)},
number = 2,
volume = 839,
place = {United States},
year = {Thu Apr 20 00:00:00 EDT 2017},
month = {Thu Apr 20 00:00:00 EDT 2017}
}

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  • We report a study of extended γ -ray emission with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope , which is likely to be the second case of a γ -ray detection from a star-forming region (SFR) in our Galaxy. The LAT source is located in the G25 region, 1.°7 × 2.°1 around ( l , b ) = (25.°0, 0.°0). The γ -ray emission is found to be composed of two extended sources and one pointlike source. The extended sources have similar sizes of about 1.°4 × 0.°6. An ∼0.°4 diameter subregion of one hasmore » a photon index of Γ = 1.53 ± 0.15, and is spatially coincident with HESS J1837−069, likely a pulsar wind nebula. The other parts of the extended sources have a photon index of Γ = 2.1 ± 0.2 without significant spectral curvature. Given their spatial and spectral properties, they have no clear associations with sources at other wavelengths. Their γ -ray properties are similar to those of the Cygnus cocoon SFR, the only firmly established γ -ray detection of an SFR in the Galaxy. Indeed, we find bubble-like structures of atomic and molecular gas in G25, which may be created by a putative OB association/cluster. The γ -ray emitting regions appear confined in the bubble-like structure; similar properties are also found in the Cygnus cocoon. In addition, using observations with the XMM-Newton , we find a candidate young massive OB association/cluster G25.18+0.26 in the G25 region. We propose that the extended γ -ray emission in G25 is associated with an SFR driven by G25.18+0.26. Based on this scenario, we discuss possible acceleration processes in the SFR and compare them with the Cygnus cocoon.« less
  • We present a 40 ks Chandra observation of the IRAS 20126+4104 core region. In the inner 6'' two X-ray sources were detected, which are coincident with the radio jet source I20S and the variable radio source I20Var. No X-ray emission was detected from the nearby massive protostar I20N. The spectra of both detected sources are hard and highly absorbed, with no emission below 3 keV. For I20S, the measured 0.5-8 keV count rate was 4.3 counts ks{sup -1}. The X-ray spectrum was fitted with an absorbed 1T APEC model with an energy of kT =10 keV and an absorbing columnmore » of N{sub H} = 1.2 x 10{sup 23} cm{sup -2}. An unabsorbed X-ray luminosity of about 1.4 x 10{sup 32} erg s{sup -1} was estimated. The spectrum shows broad line emission between 6.4 and 6.7 keV, indicative of emission from both neutral and highly ionized iron. The X-ray light curve indicates that I20S is marginally variable; however, no flare emission was observed. The variable radio source I20Var was detected with a count rate of 0.9 counts ks{sup -1} but there was no evidence of X-ray variability. The best-fit spectral model is a 1T APEC model with an absorbing hydrogen column of N{sub H} = 1.1 x 10{sup 23} cm{sup -2} and a plasma energy of kT = 6.0 keV. The unabsorbed X-ray luminosity is about 3 x 10{sup 31} erg s{sup -1}.« less
  • X-ray observations of the double-binary OB-star system QZ Car (HD 93206) obtained with the Chandra X-ray Observatory over a period of roughly 2 years are presented. The respective orbits of systems A (O9.7 I+b2 v, P{sub A} = 21 days) and B (O8 III+o9 v, P{sub B} = 6 days) are reasonably well sampled by the observations, allowing the origin of the X-ray emission to be examined in detail. The X-ray spectra can be well fitted by an attenuated three-temperature thermal plasma model, characterized by cool, moderate, and hot plasma components at kT {approx_equal} 0.2, 0.7, and 2 keV, respectively,more » and a circumstellar absorption of {approx_equal}0.2 x 10{sup 22} cm{sup -2}. Although the hot plasma component could be indicating the presence of wind-wind collision shocks in the system, the model fluxes calculated from spectral fits, with an average value of {approx_equal}7 x 10{sup -13} erg s{sup -1} cm{sup -2}, do not show a clear correlation with the orbits of the two constituent binaries. A semi-analytical model of QZ Car reveals that a stable momentum balance may not be established in either system A or B. Yet, despite this, system B is expected to produce an observed X-ray flux well in excess of the observations. If one considers the wind of the O8 III star to be disrupted by mass transfer, the model and observations are in far better agreement, which lends support to the previous suggestion of mass transfer in the O8 III + o9 v binary. We conclude that the X-ray emission from QZ Car can be reasonably well accounted for by a combination of contributions mainly from the single stars and the mutual wind-wind collision between systems A and B.« less
  • We obtained X-ray XMM-Newton observations of the open cluster Berkeley 87 and the massive star-forming region (SFR) ON 2. In addition, archival infrared Spitzer Space Telescope observations were used to study the morphology of ON 2, to uncover young stellar objects, and to investigate their relationship with the X-ray sources. It is likely that the SFR ON 2 and Berkeley 87 are at the same distance, 1.23 kpc, and hence are associated. The XMM-Newton observations detected X-rays from massive stars in Berkeley 87 as well as diffuse emission from the SFR ON 2. The two patches of diffuse X-ray emissionmore » are encompassed in the shell-like H II region GAL 75.84+0.40 in the northern part of ON 2 and in the ON 2S region in the southern part of ON 2. The diffuse emission from GAL 75.84+0.40 suffers an absorption column equivalent to A{sub V} {approx} 28 mag. Its spectrum can be fitted either with a thermal plasma model at T {approx}> 30 MK or by an absorbed power-law model with gamma {approx} -2.6. The X-ray luminosity of GAL 75.84+0.40 is L{sub X} {approx} 6 x 10{sup 31} erg s{sup -1}. The diffuse emission from ON 2S is adjacent to the ultra-compact H II (UCH II) region Cygnus 2N, but does not coincide with it or with any other known UCH II region. It has a luminosity of L{sub X} {approx} 4 x 10{sup 31} erg s{sup -1}. The spectrum can be fitted with an absorbed power-law model with gamma {approx} -1.4. We adopt the view of Turner and Forbes that the SFR ON 2 is physically associated with the massive star cluster Berkeley 87 hosting the WO-type star WR 142. We discuss different explanations for the apparently diffuse X-ray emission in these SFRs. These include synchrotron radiation, invoked by the co-existence of strongly shocked stellar winds and turbulent magnetic fields in the star-forming complex, cluster wind emission, or an unresolved population of discrete sources.« less
  • Star-forming galaxies emit GeV and TeV gamma-rays that are thought to originate from hadronic interactions of cosmic-ray (CR) nuclei with the interstellar medium. To understand the emission, we have used the moving-mesh code Arepo to perform magnetohydrodynamical galaxy formation simulations with self-consistent CR physics. Our galaxy models exhibit a first burst of star formation that injects CRs at supernovae. Once CRs have sufficiently accumulated in our Milky Way–like galaxy, their buoyancy force overcomes the magnetic tension of the toroidal disk field. As field lines open up, they enable anisotropically diffusing CRs to escape into the halo and to accelerate amore » bubble-like, CR-dominated outflow. However, these bubbles are invisible in our simulated gamma-ray maps of hadronic pion-decay and secondary inverse-Compton emission because of low gas density in the outflows. By adopting a phenomenological relation between star formation rate (SFR) and far-infrared emission and assuming that gamma-rays mainly originate from decaying pions, our simulated galaxies can reproduce the observed tight relation between far-infrared and gamma-ray emission, independent of whether we account for anisotropic CR diffusion. This demonstrates that uncertainties in modeling active CR transport processes only play a minor role in predicting gamma-ray emission from galaxies. We find that in starbursts, most of the CR energy is “calorimetrically” lost to hadronic interactions. In contrast, the gamma-ray emission deviates from this calorimetric property at low SFRs due to adiabatic losses, which cannot be identified in traditional one-zone models.« less