Abstract
PeVatrons are the most powerful naturally occurring particle accelerators in the Universe. The identification of counterparts associated to astrophysical objects such as dying massive stars, ...molecular gas, star-forming regions, and star clusters is essential to clarify the underlying nature of the PeV emission, i.e., hadronic or leptonic. We present 12,13CO (J = 2→1) observations made with the 1.85 m radio-telescope of the Osaka Prefecture University toward the Cygnus OB7 molecular cloud, which contains the PeVatron candidate LHAASO J2108+5157. We investigate the nature of the sub-PeV (gamma-ray) emission by studying the nucleon density determined from the content of H i and H2, derived from the CO observations. In addition to MML20174607, detected via the observations of the optically thick 12CO (J = 1→0) emission, we infer the presence of an optically thin molecular cloud, named FKT-MC2022, whose angular size is 1${_{.}^{\circ}}$1 ± 0${_{.}^{\circ}}$2. We propose this cloud as a new candidate to produce the sub-PeV emission observed in LHAASO J2108+5157. Considering a distance of 1.7 kpc, we estimate a nucleon (H i + H2) density of 37 ± 14 cm−3, and a total nucleon mass(H i + H2) of 1.5 ± 0.6 × 104 M⊙. On the other hand, we confirm that Kronberger 82 is a molecular clump with an angular size of 0${_{.}^{\circ}}$1, a nucleon density ∼103 cm−3, and a mass ∼103 M⊙. Although Kronberger 82 hosts the physical conditions to produce the observed emission of LHAASO J2108+5157, FKT-MC2022 is located closer to it, suggesting that the latter could be the one associated to the sub-PeV emission. Under this scenario, our results favour a hadronic origin for the emission.
The Cygnus region of our Galaxy consists of an active star forming region and a wealth of various astrophysical sources such as pulsar wind nebulae (PWN), supernova remnants (SNRs), and massive star ...clusters. Massive stellar clusters and associations have been postulated as possible sources of cosmic rays (CRs) in our Galaxy. One example of a gamma-ray source associated with a stellar association lies in the Cygnus region known as the "Cygnus Cocoon". It is an extended region of gamma-ray emission in the Cygnus X region and attributed to a possible superbubble with freshly accelerated CRs which are hypothesized to produce gamma rays via interaction with the ambient gas nuclei. The emission region is an environment of lower particle density and is surrounded by ionization fronts like a carved-out cavity or a cocoon. CRs in the Cocoon could have originated in the OB2 association and been accelerated at the interaction sites of stellar winds of massive type O stars. So far, there is no clear association at TeV energies. In the study presented in this thesis, I used data collected by the HAWC Observatory over 1038 days to disentangle the TeV gamma-ray emission from 2HWC J2031+415, a source which was previously reported in the 2nd HAWC catalog and is collocated with the Cygnus Cocoon, into two components: a pulsar wind nebula and the Cygnus superbubble. The contribution from the Cygnus superbubble is detected at a significance level of ~ 12 sigma with maximum photon energies above 100 TeV, the highest measured yet. Based on the spectrum and morphology of gamma-rays across six decades of energy, and the non-detection of radio and X-ray photons from this region, the gamma-rays are plausibly of a hadronic origin. There is a spectral softening above 1 TeV, which can be explained by two hadronic scenarios. Either there is a leakage of CRs from the superbubble resulting in a spectral break from GeV to TeV or the spectral softening is due to cutoff energy, an upper limit to the particle acceleration by the stellar winds.
The High Altitude Water Cherenkov (HAWC) Observatory is a wide-field-of-view gamma-ray observatory that is optimized to detect gamma rays between 300 GeV and several hundred TeV. The HAWC ...Collaboration recently released their third source catalog (3HWC), which contains 65 sources. One of these sources, the ultra-high-energy gamma-ray source 3HWC J1908+063, may exhibit a hardening of the spectral index at the highest energies (above 56 TeV). At least two populations of particles are needed to satisfactorily explain the highest energy emission. This second component could be leptonic or hadronic in origin. If it is hadronic in origin, it would imply the presence of protons with energies up to ~1 PeV near the source. We have searched other 3HWC sources for the presence of this spectral hardening feature. If observed, this would imply that the sources could make good PeVatron candidates.
The Ultra-High-Energy Source MGRO J1908+06 Malone, Kelly; Abeysekara, Anushka Udara; Albert, Andrea ...
Pos : proceedings of science,
07/2021, Letnik:
395
Journal Article
Recenzirano
Odprti dostop
The TeV gamma-ray source MGRO J1908+06 is one of the highest-energy sources known, with observed emission by the High Altitude Water Cherenkov (HAWC) Observatory extending well past 100 TeV. The ...source exhibits both energy-dependent morphology and a spatially-dependent spectral index. The emission is likely to be dominantly leptonic, and associated with the radio-quiet PSR J1907+0602. However, one-population models do not describe the data well; a second particle population is needed to explain the shape of the spectral energy distribution at the highest energies. This component can be well-described by either leptonic or hadronic hypotheses. We discuss this feature and implications for detection by multi-wavelength and multi-messenger experiments.
Star forming regions (SFRs) have been postulated as possible sources of cosmic rays (CRs) in our galaxy. One example of a gamma-ray source associated with an SFR is the Fermi-LAT cocoon, an extended ...region of gamma-ray emission in the Cygnus X region and attributed to a possible superbubble with freshly accelerated CRs. Because the emission region is surrounded by ionization fronts, it has been named the "Cygnus cocoon". CRs in the cocoon could have originated in the OB2 association and been accelerated at the interaction sites of stellar winds of massive O type stars. So far, there is no clear association at TeV energies. Spectral and morphological studies of TeV gamma-ray emission detected by the High Altitude Water Cherenkov (HAWC) observatory at the 2HWC J2031+415 region reveal that the spectral energy distribution of the cocoon extends from GeV to at least tens of TeV. Using HAWC data, we are able to study the acceleration of particles to highest energies in the Cygnus OB2 SFR.
PeVatrons are the most powerful naturally occurring particle accelerators in the Universe. The identification of counterparts associated to astrophysical objects such as dying massive stars, ...molecular gas, star-forming regions, and star clusters is essential to clarify the underlying nature of the PeV emission, i.e., hadronic or leptonic. We present \(^{12,13}\)CO(J=2\(\rightarrow\)1) observations made with the 1.85~m radio-telescope of the Osaka Prefecture University toward the Cygnus OB7 molecular cloud, which contains the PeVatron candidate LHAASO J2108+5157. We investigate the nature of the sub-PeV (gamma-ray) emission by studying the nucleon density determined from the content of HI and H\(_2\), derived from the CO observations. In addition to MML20174607, detected via the observations of the optically thick \(^{12}\)CO(J=1\(\rightarrow\)0) emission, we infer the presence of an optically thin molecular cloud, named FKT-MC2022, whose angular size is 1.1\(\pm\)0.2\(^{\circ}\). We propose this cloud as a new candidate to produce the sub-PeV emission observed in LHAASO J2108+5157. Considering a distance of 1.7 kpc, we estimate a nucleon (HI+H\(_2\)) density of 37\(\pm\)14 cm\(^{-3}\), and a total nucleon mass(HI+H\(_2\)) of 1.5\(\pm\)0.6\(\times\)10\(^4\) M\(_{\odot}\). On the other hand, we confirm that Kronberger 82 is a molecular clump with an angular size of 0.1\(^{\circ}\), a nucleon density \(\sim\) 10\(^3\) cm\(^{-3}\), and a mass \(\sim\) 10\(^3\) M\(_{\odot}\). Although Kronberger 82 hosts the physical conditions to produce the observed emission of LHAASO J2108+5157, FKT-MC2022 is located closer to it, suggesting that the latter could be the one associated to the sub-PeV emission. Under this scenario, our results favour a hadronic origin for the emission.
Only five binary systems have been found to emit at TeV energies. Each of these systems is composed of a massive O or B type star and a compact object (black hole or a pulsar). The type of compact ...object and the origin of the gamma-ray emission is unknown for most of these systems. Extending spectral observations to higher energies can help disentangle the nature of the compact object as well as the particle acceleration mechanisms present. Interestingly, the TeV emission from these systems does not always coincide with their emission in GeV or X-ray, which is how many such systems have been originally discovered. Increased coverage of these systems may allow HAWC to see precisely when in the orbit the TeV emission begins and ends. The HAWC Observatory detects TeV gamma-rays with high sensitivity, covering over two-thirds of the overhead sky every day. Applying a stacking method to known TeV binary systems can help HAWC enhance the signal from TeV binaries above the steady background from other sources in the galaxy. We will present results from this stacking analysis using 760 days of HAWC data.
The Cygnus arm of our galaxy is a source-rich and complex region hosting multiple gamma-ray source types such as pulsar wind nebulae (PWN), supernova remnants, binary systems, and star clusters. The ...High Altitude Water Cherenkov (HAWC) observatory has been collecting data continuously since 2015 and has reported five sources within the Cygnus region. Several other instruments have also observed gamma-ray sources in this region. For instance, Fermi-LAT found gamma-ray emission at GeV energies due to a Cocoon of freshly accelerated cosmic rays, which is co-located with a known PWN TeV 2032+4130 seen by several TeV gamma-ray observatories. TeV J2032+4130 is likely powered by the pulsar PSR J2032+4127 based on the multi-wavelength observation and asymmetric morphology reported by VERITAS. The study of HAWC data will provide more information regarding the morphology, emission origin, and the correlation with the GeV emission. This presentation will discuss the analysis of data collected with the HAWC instrument and the Fermi-LAT and the results obtained to provide a deeper understanding of the Cygnus Cocoon across five decades of energy range.
