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Journal articles on the topic 'Unidentified TeV sources'

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Author: Grafiati

Published: 10 December 2022

Last updated: 28 January 2023

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1

Wang, W., Z. J. Jiang, C. S. J. Pun, and K. S. Cheng. "Possible TeV source candidates among the unidentified EGRET sources." Monthly Notices of the Royal Astronomical Society 360, no. 2 (June 21, 2005): 646–54. http://dx.doi.org/10.1111/j.1365-2966.2005.09050.x.

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2

Yamazaki, Ryo, Kazunori Kohri, Aya Bamba, Tatsuo Yoshida, Toru Tsuribe, and Fumio Takahara. "On the Origin of Galactic TeV Unidentified Sources." Progress of Theoretical Physics Supplement 169 (2007): 166–69. http://dx.doi.org/10.1143/ptps.169.166.

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3

Fegan, S. J., and T. C. Weekes. "A Survey of Unidentified Egret Sources at TeV Energies." Astrophysics and Space Science 297, no. 1-4 (June 2005): 431–38. http://dx.doi.org/10.1007/s10509-005-7703-x.

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4

Devin, J., M. Renaud, M. Lemoine-Goumard, and G. Vasileiadis. "Multiwavelength constraints on the unidentified Galactic TeV sources HESS J1427−608, HESS J1458−608, and new VHE γ-ray source candidates." Astronomy & Astrophysics 647 (March 2021): A68. http://dx.doi.org/10.1051/0004-6361/202039563.

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Aims. Among the γ-ray sources discovered at high and very-high energies, a large fraction still lack a clear identification. In particular, the H.E.S.S. Galactic Plane Survey (HGPS) revealed 78 TeV sources among which 47 are not clearly associated with a known object. Multiwavelength data can help identify the origin of the very-high energy γ-ray emission, although some bright TeV sources have been detected without clear counterparts. We present a multiwavelength approach to constrain the origin of the emission from unidentified HGPS sources. Methods. We present a generic pipeline that explores a large database of multiwavelength archival data toward any region in the Galactic plane. Along with a visual inspection of the retrieved multiwavelength observations to search for faint and uncataloged counterparts, we derive a radio spectral index that helps disentangle thermal from nonthermal emission and a mean magnetic field through X-ray and TeV data in case of a leptonic scenario. We also search for a spectral connection between the GeV and the TeV regimes with the Fermi-LAT cataloged sources that may be associated with the unidentified HGPS source. We complete the association procedure with catalogs of known objects (supernova remnants, pulsar wind nebulae, H II regions, etc.) and with the source catalogs from instruments whose data are retrieved. Results. The method is applied on two unidentified sources, namely HESS J1427−608 and HESS J1458−608, for which the multiwavelength constraints favor the pulsar wind nebula (PWN) scenario. We model their broadband nonthermal spectra in a leptonic scenario with a magnetic field B ≲ 10 μG, which is consistent with that obtained from ancient PWNe. We place both sources within the context of the TeV PWN population to estimate the spin-down power and the characteristic age of the putative pulsar. We also shed light on two possibly significant γ-ray excesses in the HGPS: the first is located in the south of the unidentified source HESS J1632−478 and the second is spatially coincident with the synchrotron-emitting supernova remnant G28.6−0.1. The multiwavelength counterparts found toward both γ-ray excesses make these promising candidates for being new very-high energy γ-ray sources.

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5

Spengler, Gerrit. "Search for Galactic Pevatron candidates in a population of unidentified γ-ray sources." Astronomy & Astrophysics 633 (January 2020): A138. http://dx.doi.org/10.1051/0004-6361/201936632.

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Aims. A list of Pevatron candidates is presented to enable deeper observations and dedicated analyses. Methods. Lower limits on the energy cutoff for unidentified γ-ray sources detected in the High Energy Stereoscopic System (HESS) Galactic plane survey were derived. Additional public data from the Very Energetic Radiation Imaging Telescope Array System, HESS, and Milagro experiments were used for MGRO J1908+06 to confirm the limit derived from the HESS Galactic plane survey data and to enable further conclusions on the presence of spectral breaks. Results. Five Pevatron candidates are identified in the HESS Galactic plane survey. The cutoff of the γ-ray spectrum for these sources is larger than 20 TeV at 90% confidence level. The γ-ray sources MGRO J1908+06 and HESS J1641−463, found to be Pevatron candidates in the analysis of the HESS Galactic plane survey catalog, have already been discussed as Pevatron candidates. For MGRO J1908+06, the lower limit on the γ-ray energy cutoff is 30 TeV at 90% confidence level. This is a factor of almost two larger than previous results. Additionally, a break in the γ-ray spectrum at energies between 1 TeV and 10 TeV with an index change ΔΓ > 0.5 can be excluded at 90% confidence level for MGRO J1908+06. The energy cutoff of accelerated particles is larger than 100 TeV at 90% confidence level in a hadronic scenario for all five Pevatron candidates. A hadronic scenario is plausible for at least three of the Pevatron candidates, based on the presence of nearby molecular clouds and supernova remnants.

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6

Fox, D. B., K. Kashiyama, and P. Mészarós. "SUB-PeV NEUTRINOS FROM TeV UNIDENTIFIED SOURCES IN THE GALAXY." Astrophysical Journal 774, no. 1 (August 19, 2013): 74. http://dx.doi.org/10.1088/0004-637x/774/1/74.

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7

Ioka, Kunihito, and Peter Mészáros. "HYPERNOVA AND GAMMA-RAY BURST REMNANTS AS TeV UNIDENTIFIED SOURCES." Astrophysical Journal 709, no. 2 (January 13, 2010): 1337–42. http://dx.doi.org/10.1088/0004-637x/709/2/1337.

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8

Rowell, G. P. "Ground-Based Gamma-Ray Detection of High Energy Galactic Sources: An Update." Symposium - International Astronomical Union 218 (2004): 407–14. http://dx.doi.org/10.1017/s0074180900181495.

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I review the present status of ground-based γ-ray astronomy, concentrating on the population of Galactic TeV sources. A number of new telescope systems are now being completed, and promise to yield exciting new discoveries, expanding rapidly the number of sources. The TeV Galactic sources today include a number of plerions, shell-type supernova remnants, an X-ray binary, and also one unidentified candidate. Their present status, and our understanding of their TeV γ-ray emission processes are summarized and some motivation driving development of the field is outlined.

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9

Wang, W., Y. Zhao, and Y. Lu. "Gamma-ray Mature Pulsars: Unidentified EGRET Sources, Possible TeV Sources and Radio Detectivity." Chinese Journal of Astronomy and Astrophysics 6, S2 (October 2006): 259–62. http://dx.doi.org/10.1088/1009-9271/6/s2/48.

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10

Chang, Chulhoon, Alexander Konopelko, and Wei Cui. "Search for Pulsar Wind Nebula Associations with Unidentified TeV γ‐Ray Sources." Astrophysical Journal 682, no. 2 (August 2008): 1177–84. http://dx.doi.org/10.1086/589225.

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11

Acciari, V. A., S. Ansoldi, L. A. Antonelli, A. Arbet Engels, K. Asano, D. Baack, A. Babić, et al. "Studying the nature of the unidentified gamma-ray source HESS J1841−055 with the MAGIC telescopes." Monthly Notices of the Royal Astronomical Society 497, no. 3 (July 24, 2020): 3734–45. http://dx.doi.org/10.1093/mnras/staa2135.

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ABSTRACT We investigate the physical nature and origin of the gamma-ray emission from the extended source HESS J1841−055 observed at TeV and GeV energies. We observed HESS J1841−055 at TeV energies for a total effective time of 43 h with the MAGIC telescopes, in 2012 and 2013. Additionally, we analysed the GeV counterpart making use of about 10 yr of Fermi-LAT data. Using both Fermi-LAT and MAGIC, we study both the spectral and energy-dependent morphology of the source for almost four decades of energy. The origin of the gamma-ray emission from this region is investigated using multiwaveband information on sources present in this region, suggested to be associated with this unidentified gamma-ray source. We find that the extended emission at GeV–TeV energies is best described by more than one source model. We also perform the first energy-dependent analysis of the HESS J1841−055 region at GeV–TeV. We find that the emission at lower energies comes from a diffuse or extended component, while the major contribution of gamma rays above 1 TeV arises from the southern part of the source. Moreover, we find that a significant curvature is present in the combined observed spectrum of MAGIC and Fermi-LAT. The first multiwavelength spectral energy distribution of this unidentified source shows that the emission at GeV–TeV energies can be well explained with both leptonic and hadronic models. For the leptonic scenario, bremsstrahlung is the dominant emission compared to inverse Compton. On the other hand, for the hadronic model, gamma-ray resulting from the decay of neutral pions (π0) can explain the observed spectrum. The presence of dense molecular clouds overlapping with HESS J1841−055 makes both bremsstrahlung and π0-decay processes the dominant emission mechanisms for the source.

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12

Paredes, Josep M., Josep Martí, C. H. Ishwara Chandra, and Valentí Bosch-Ramon. "The Population of Radio Sources in the Field of the Unidentified Gamma-Ray Source TeV J2032+4130." Astrophysical Journal 654, no. 2 (December 28, 2006): L135—L138. http://dx.doi.org/10.1086/511178.

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13

Yang, Hui, Jeremy Hare, Oleg Kargaltsev, Igor Volkov, Steven Chen, and Blagoy Rangelov. "Classifying Unidentified X-Ray Sources in the Chandra Source Catalog Using a Multiwavelength Machine-learning Approach." Astrophysical Journal 941, no. 2 (December 1, 2022): 104. http://dx.doi.org/10.3847/1538-4357/ac952b.

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Abstract The rapid increase in serendipitous X-ray source detections requires the development of novel approaches to efficiently explore the nature of X-ray sources. If even a fraction of these sources could be reliably classified, it would enable population studies for various astrophysical source types on a much larger scale than currently possible. Classification of large numbers of sources from multiple classes characterized by multiple properties (features) must be done automatically and supervised machine learning (ML) seems to provide the only feasible approach. We perform classification of Chandra Source Catalog version 2.0 (CSCv2) sources to explore the potential of the ML approach and identify various biases, limitations, and bottlenecks that present themselves in these kinds of studies. We establish the framework and present a flexible and expandable Python pipeline, which can be used and improved by others. We also release the training data set of 2941 X-ray sources with confidently established classes. In addition to providing probabilistic classifications of 66,369 CSCv2 sources (21% of the entire CSCv2 catalog), we perform several narrower-focused case studies (high-mass X-ray binary candidates and X-ray sources within the extent of the H.E.S.S. TeV sources) to demonstrate some possible applications of our ML approach. We also discuss future possible modifications of the presented pipeline, which are expected to lead to substantial improvements in classification confidences.

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14

Abdalla, H., A. Abramowski, F. Aharonian, F. Ait Benkhali, E. O. Angüner, M. Arakawa, C. Armand, et al. "HESS J1741−302: a hidden accelerator in the Galactic plane." Astronomy & Astrophysics 612 (April 2018): A13. http://dx.doi.org/10.1051/0004-6361/201730581.

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The H.E.S.S. Collaboration has discovered a new very high energy (VHE, E > 0.1 TeV) γ-ray source, HESS J1741−302, located in the Galactic plane. Despite several attempts to constrain its nature, no plausible counterpart has been found so far at X-ray and MeV/GeV γ-ray energies, and the source remains unidentified. An analysis of 145-h of observations of HESS J1741−302 at VHEs has revealed a steady and relatively weak TeV source (~1% of the Crab Nebula flux), with a spectral index of Γ = 2.3 ± 0.2stat ± 0.2sys, extending to energies up to 10 TeV without any clear signature of a cut-off. In a hadronic scenario, such a spectrum implies an object with particle acceleration up to energies of several hundred TeV. Contrary to most H.E.S.S. unidentified sources, the angular size of HESS J1741−302 is compatible with the H.E.S.S. point spread function at VHEs, with an extension constrained to be below 0.068° at a 99% confidence level. The γ-ray emission detected by H.E.S.S. can be explained both within a hadronic scenario, due to collisions of protons with energies of hundreds of TeV with dense molecular clouds, and in a leptonic scenario, as a relic pulsar wind nebula, possibly powered by the middle-aged (20 kyr) pulsar PSR B1737−30. A binary scenario, related to the compact radio source 1LC 358.266+0.038 found to be spatially coincident with the best fit position of HESS J1741−302, is also envisaged.

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15

Tibolla, Omar, Sarah Kaufmann, and Paula Chadwick. "Pulsar Wind Nebulae and Unidentified Galactic Very High Energy Sources." J 5, no. 3 (July 19, 2022): 318–33. http://dx.doi.org/10.3390/j5030022.

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The riddle of the origin of Cosmic Rays (CR) has been an open question for over a century. Gamma ray observations above 100 MeV reveal the sites of cosmic ray acceleration to energies where they are unaffected by solar modulation; recent evidence supports the existence of hadronic acceleration in Supernova Remnants (SNR), as expected in the standard model of cosmic ray acceleration. Nevertheless, the results raise new questions, and no final answer has been provided thus far. Among the suggested possible alternative accelerators in the Very High Energy (VHE) gamma ray sky, pulsar wind nebulae (PWNe, which together with dark matter are the main candidates to explain the local positron excess as well) are the dominant population among known Galactic sources. However, the most numerous population in absolute terms is represented by unidentified sources (~50% of VHE gamma ray sources). The relationship between PWNe and unidentified sources seems very close; in fact, in a PWN, the lifetime of inverse Compton (IC) emitting electrons not only exceeds the lifetime of its progenitor pulsar, but also exceeds the age of the electrons that emit via synchrotron radiation. Therefore, during its evolution, a PWN can remain bright in IC such that its GeV-TeV gamma ray flux remains high for timescales much larger than the lifetimes of the pulsar and the X-ray PWN. In addition, the shell-type remnant of the supernova explosion in which the pulsar was formed has a much shorter lifetime than the electrons responsible for IC emission. Hence, understanding PWNe and VHE unidentified sources is a crucial piece of the solution to the riddle of the origin of cosmic rays. Both theoretical aspects (with particular emphasis on the ancient pulsar wind nebulae scenario) and their observational proofs are discussed in this paper. Specifically, the scientific cases of HESS J1616-508 and HESS J1813-126 are examined in detail.

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Mukherjee, R., E. V. Gotthelf, and J. P. Halpern. "Transient X-ray sources in the field of the unidentified gamma-ray source TeV J2032+4130 in Cygnus." Astrophysics and Space Science 309, no. 1-4 (April 12, 2007): 29–33. http://dx.doi.org/10.1007/s10509-007-9452-5.

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17

De Sarkar, Agnibha, Nirupam Roy, Pratik Majumdar, Nayantara Gupta, Andreas Brunthaler, Karl M. Menten, Sergio A. Dzib, Sac Nicté X. Medina, and Friedrich Wyrowski. "Possible TeV Gamma-Ray Binary Origin of HESS J1828–099." Astrophysical Journal Letters 927, no. 2 (March 1, 2022): L35. http://dx.doi.org/10.3847/2041-8213/ac5aba.

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Abstract The High Energy Stereoscopic System (H.E.S.S.) observatory has carried out a deep survey of the Galactic plane, in the course of which the existence of a significant number of (∼78) TeV γ-ray sources was confirmed, many of which remain unidentified. HESS J1828–099 is a point-like (Gaussian standard deviation < 0.°07) unidentified source among the 17 confirmed point-like sources in the H.E.S.S. Galactic Plane Survey (HGPS) catalog. This source is also unique because it does not seem to have any apparent association with any object detected at other wavelengths. We investigate the nature and association of HESS J1828–099 with multiwavelength observational data. A high-mass X-ray binary (HMXB)—composed of the pulsar XTE J1829–098 and a companion Be star—has been observed earlier in the X-ray and infrared bands, 14′ away from HESS J1828–099. With 12 yr of Fermi-LAT γ-ray data, we explore the possibility of 4FGL J1830.2–1005 being the GeV counterpart of HESS J1828–099. Within the RXTE confidence region, a steep-spectrum (α radio = −0.746 ± 0.284) plausible counterpart is detected in data from existing radio frequency surveys. In this Letter, we probe for the first time, using multiwavelength data, whether HESS J1828–099, 4FGL J1830.2–1005, and the HMXB system have a common origin. Our study indicates that HESS J1828–099 might be a TeV high-mass γ-ray binary source.

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18

Walker, G., R. Atkins, and D. Kieda. "Evidence for New Unidentified TeV γ-ray Sources from Angularly Correlated Hot Spots Observed by Independent TeV γ-ray Sky Surveys." Astrophysical Journal 614, no. 2 (September 28, 2004): L93—L96. http://dx.doi.org/10.1086/425863.

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19

Montanari, A., E. Moulin, D. Malyshev, and D. Glawion. "Searching signals of dark matter from unidentified Fermi-LAT objects with H.E.S.S." Journal of Physics: Conference Series 2156, no. 1 (December 1, 2021): 012075. http://dx.doi.org/10.1088/1742-6596/2156/1/012075.

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Abstract Milky Way-sized galaxies harbor a population of unmerged dark matter subhalos, as shown from cosmological N-body simulations. These subhalos could shine in gamma-rays and be eventually detected as unidentified sources in gamma-ray surveys. From a thorough selection of unidentified Fermi-LAT Objects (UFOs), we observe four UFOs with H.E.S.S. and we search for very high-energy (VHE, E ≥ 100 GeV) gamma-ray emission. Considering dark matter masses above a few hundred GeV, the observed UFOs could be identified as dark matter subhalos, given their hard gamma-ray spectra in the few-ten-to-hundred GeV energy range. Since no significant very-high-energy gamma-ray emission is detected in any of the four UFOs dataset nor in the combined one, we derive constraints on the product of the velocity-weighted annihilation cross-section 〈συ〉 by the J-factor for the dark matter models. We derive 95% CL upper limits on 〈συ〉 J in W + W − and τ+τ− annihilation channels for the TeV dark matter particles. Considering thermal WIMPs, we derive constraints on the J-factors from the H.E.S.S. observations. Assuming model-dependent predictions from cosmological N-body simulations on the J-factor distribution for Milky Way-sized galaxies, the dark matter models with masses greater than 0.3 TeV for the UFO emissions can be ruled out at high confidence level.

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20

Pedaletti, Giovanna, Emma de Oña Wilhelmi, Diego F. Torres, and Giovanni Natale. "Estimating Galactic gas content using different tracers: Compatibility of results, dark gas, and unidentified TeV sources." Journal of High Energy Astrophysics 5-6 (March 2015): 15–21. http://dx.doi.org/10.1016/j.jheap.2014.12.001.

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21

Coronado-Blázquez, Javier, and Miguel A. Sánchez-Conde. "Constraints to Dark Matter Annihilation from High-Latitude HAWC Unidentified Sources." Galaxies 8, no. 1 (December 30, 2019): 5. http://dx.doi.org/10.3390/galaxies8010005.

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The Λ CDM cosmological framework predicts the existence of thousands of subhalos in our own Galaxy not massive enough to retain baryons and become visible. Yet, some of them may outshine in gamma rays provided that the dark matter is made of weakly interacting massive particles (WIMPs), which would self-annihilate and would appear as unidentified gamma-ray sources (unIDs) in gamma-ray catalogs. Indeed, unIDs have proven to be competitive targets for dark matter searches with gamma rays. In this work, we focus on the three high-latitude ( | b | ≥ 10 ) sources present in the 2HWC catalog of the High Altitude Water Cherenkov (HAWC) observatory with no clear associations at other wavelengths. Indeed, only one of these sources, 2HWC J1040+308, is found to be above the HAWC detection threshold when considering 760 days of data, i.e., a factor 1.5 more exposure time than in the original 2HWC catalog. Other gamma-ray instruments, such as Fermi-LAT or VERITAS at lower energies, do not detect the source. Also, this unID is reported as spatially extended, making it even more interesting in a dark matter search context. While waiting for more data that may shed further light on the nature of this source, we set competitive upper limits on the annihilation cross section by comparing this HAWC unID to expectations based on state-of-the-art N-body cosmological simulations of the Galactic subhalo population. We find these constraints to be particularly competitive for heavy WIMPs, i.e., masses above ∼25 (40) TeV in the case of the b b ¯ ( τ + τ − ) annihilation channel, reaching velocity-averaged cross section values of 2 × 10 − 25 ( 5 × 10 − 25 ) cm 3 ·s − 1 . Although far from testing the thermal relic cross section value, the obtained limits are independent and nicely complementary to those from radically different DM analyses and targets, demonstrating once again the high potential of this DM search approach.

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22

Skrzypek, B., M. Chianese, and C. A. Argüelles. "Multi-messenger high-energy signatures of decaying dark matter and the effect of background light." Journal of Cosmology and Astroparticle Physics 2023, no. 01 (January 1, 2023): 037. http://dx.doi.org/10.1088/1475-7516/2023/01/037.

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Abstract The IceCube Neutrino Observatory at the South Pole has measured astrophysical neutrinos using through-going and starting events in the TeV to PeV energy range. The origin of these astrophysical neutrinos is still largely unresolved, and among their potential sources could be dark matter decay. Measurements of the astrophysical flux using muon neutrinos are in slight tension with starting event measurements. This tension is driven by an excess observed in the energy range of 40–200 TeV with respect to the through-going expectation. Previous works have considered the possibility that this excess may be due to heavy dark matter decay and have placed constraints using gamma-ray and neutrino data. However, these constraints are not without caveats, since they rely on the modeling of the astrophysical neutrino flux and the sources of gamma-ray emission. In this work, we derive background-agnostic galactic and extragalactic constraints on decaying dark matter by considering Tibet-ASγ data, Fermi-LAT diffuse data, and the IceCube high-energy starting event sample. For the gamma-ray limits, we investigate the uncertainties on secondary emission from electromagnetic cascades during propagation arising from the unknown intensity of the extragalactic background light. We find that such uncertainties amount to a variation of up to ∼ 55% in the gamma-ray limits derived with extragalactic data. Our results imply that a significant fraction of the astrophysical neutrino flux could be due to dark matter and that ruling it out depends on the assumptions on the gamma-ray and neutrino background. The latter depends on the yet unidentified sources.

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23

HEINZELMANN, GÖTZ. "RESULTS FROM H.E.S.S." International Journal of Modern Physics A 20, no. 29 (November 20, 2005): 7001–5. http://dx.doi.org/10.1142/s0217751x05030685.

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H.E.S.S. is an experiment for ground based GeV/TeV gamma ray astronomy of the new generation. It consists of four large Cherenkov telescopes operating in stereoscopic observation mode. Its construction in Namibia was completed at the end of 2003. Already during the installation phase, exciting results have been achieved, and after completion several discoveries have been made. Some of the results and discoveries are reported, such as the first image of a shell-type supernova remnant resolved at arc minute scale (RXJ 1713 – 3946), the discovery of the unique binary pulsar system PSR B1259 – 63 and of a yet-unidentified source in the same field of view (HESS J1303 – 631), and the observation of the galactic centre region. Amongst the extragalactic sources, the blazers Mkn 421 and PKS 2155 – 304 have also been detected.

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Zhang, Xiao, Yang Chen, Fa-xiang Zheng, Qian-Cheng Liu, Ping Zhou, and Bing Liu. "GeV Gamma-Ray Emission and Molecular Clouds toward Supernova Remnant G35.6–0.4 and the TeV Source HESS J1858+020." Astrophysical Journal 931, no. 2 (June 1, 2022): 128. http://dx.doi.org/10.3847/1538-4357/ac6957.

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Abstract It is difficult to distinguish the hadronic process from the leptonic one in γ-ray observation, which is however crucial in revealing the origin of cosmic rays. As an endeavor in this regard, we focus in this work on the complex γ-ray emitting region, which partially overlaps with the unidentified TeV source HESS J1858+020 and includes supernova remnant (SNR) G35.6−0.4 and H ii region G35.6−0.5. We reanalyze CO line, H i, and Fermi-LAT GeV γ-ray emission data of this region. The analysis of the molecular and H i data suggests that SNR G35.6−0.4 and H ii region G35.6−0.5 are located at different distances. The analysis of the GeV γ-rays shows that GeV emission arises from two point sources: one (SrcA) coincident with the SNR, and the other (SrcB) coincident with both HESS J1858+020 and H ii region G35.6−0.5. The GeV emission of SrcA can be explained by the hadronic process in the SNR–molecular cloud association scenario. The GeV-band spectrum of SrcB and the TeV-band spectrum of HESS J1858+020 can be smoothly connected by a power-law function, with an index of ∼2.2. The connected spectrum is well explained with a hadronic emission, with the cutoff energy of protons above 1 PeV. It thus indicates that there is a potential PeVatron in the H ii region and should be further verified with ultrahigh-energy observations with, e.g., LHAASO.

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Ciprini, Stefano, Dario Gasparrini, and Denis Bastieri. "Fermi LAT Flare Advocate Activity." Proceedings of the International Astronomical Union 7, S285 (September 2011): 294–95. http://dx.doi.org/10.1017/s174392131200083x.

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AbstractThe Fermi Flare Advocate (also known as Gamma-ray Sky Watcher, FA-GSW) service provides a daily quick-look analysis and review of the high-energy gamma-ray sky seen by the Fermi Gamma-ray Space Telescope. The duty offers alerts for potentially new gamma-ray sources, interesting transients and flares. A weekly digest containing the highlights about the GeV gamma-ray sky is published in the web-based Fermi Sky Blog. During the first 3 years of all-sky survey, more than 150 Astronomical Telegrams, several alerts to the TeV Cherenkov telescopes, and targets of opportunity to Swift and other observatories, were realized. That increased the rate of simultaneous multi-frequency observing campaigns and the level of international cooperation. Many gamma-ray flares from blazars (such as extraordinary outbursts of 3C 454.3, intense flares of PKS 1510-089, 4C 21.35, PKS 1830-211, AO 0235+164, PKS 1502+106, 3C 279, 3C 273, PKS 1622-253), short/long flux duty cycles, unidentified transients near the Galactic plane (like J0910-5041, J0109+6134, the Galactic center region), flares associated with Galactic sources (like the Crab nebula, the nova V407 Cyg, the microquasar Cyg X-3), emission of the quiet and active sun, were observed by Fermi and communicated by FA-GSWs.

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26

Aharonian, F. A., A. G. Akhperjanian, M. Beilicke, K. Bernlöhr, H. Bojahr, O. Bolz, H. Börst, et al. "A search for TeV gamma-ray emission from SNRs, pulsars and unidentified GeV sources in the Galactic plane in the longitude range between $-2^\circ$ and $85^\circ$." Astronomy & Astrophysics 395, no. 3 (November 18, 2002): 803–11. http://dx.doi.org/10.1051/0004-6361:20021347.

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27

Horns, Dieter, and Gavin Rowell. "HEGRA discovery of the first unidentified TeV source." New Astronomy Reviews 48, no. 5-6 (April 2004): 489–92. http://dx.doi.org/10.1016/j.newar.2003.12.028.

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Aharonian, F., A. Akhperjanian, M. Beilicke, K. Bernlöhr, H. Börst, H. Bojahr, O. Bolz, et al. "An unidentified TeV source in the vicinity of Cygnus OB2." Astronomy & Astrophysics 393, no. 2 (September 23, 2002): L37—L40. http://dx.doi.org/10.1051/0004-6361:20021171.

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Horns, D., A. I. D. Hoffmann, A. Santangelo, F. A. Aharonian, and G. P. Rowell. "XMM-Newton observations of the first unidentified TeV gamma-ray source TeV J2032+4130." Astronomy & Astrophysics 469, no. 1 (May 2, 2007): L17—L21. http://dx.doi.org/10.1051/0004-6361:20066836.

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Albert, J., E. Aliu, H. Anderhub, P. Antoranz, C. Baixeras, J. A. Barrio, H. Bartko, et al. "MAGIC Observations of the Unidentified γ-Ray Source TeV J2032+4130." Astrophysical Journal 675, no. 1 (February 5, 2008): L25—L28. http://dx.doi.org/10.1086/529520.

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Aharonian, F., A. Akhperjanian, M. Beilicke, K. Bernlöhr, H. G. Börst, H. Bojahr, O. Bolz, et al. "The unidentified TeV source (TeV J2032+4130) and surrounding field: Final HEGRA IACT-System results." Astronomy & Astrophysics 431, no. 1 (February 2005): 197–202. http://dx.doi.org/10.1051/0004-6361:20041552.

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Murakami, Hiroshi, Shunji Kitamoto, Akiko Kawachi, and Takeshi Nakamori. "Detection of X-Ray Emission from the Unidentified TeV Gamma-Ray Source TeV J2032+4130." Publications of the Astronomical Society of Japan 63, sp3 (November 25, 2011): S873—S878. http://dx.doi.org/10.1093/pasj/63.sp3.s873.

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Cui, Wei, and Alexander Konopelko. "Chandra View of the Unidentified TeV Gamma-Ray Source HESS J1804-216." Astrophysical Journal 652, no. 2 (November 9, 2006): L109—L112. http://dx.doi.org/10.1086/510364.

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Aliu, E., T. Aune, B. Behera, M. Beilicke, W. Benbow, K. Berger, R. Bird, et al. "OBSERVATIONS OF THE UNIDENTIFIED GAMMA-RAY SOURCE TeV J2032+4130 BY VERITAS." Astrophysical Journal 783, no. 1 (February 7, 2014): 16. http://dx.doi.org/10.1088/0004-637x/783/1/16.

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Butt, Yousaf M., Paula Benaglia, Jorge A. Combi, Michael Corcoran, Thomas M. Dame, Jeremy Drake, Marina Kaufman Bernado, et al. "Chandra/Very Large Array Follow‐Up of TeV J2032+4131, the Only Unidentified TeV Gamma‐Ray Source." Astrophysical Journal 597, no. 1 (November 2003): 494–512. http://dx.doi.org/10.1086/378121.

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Aharonian, F., A. G. Akhperjanian, K. M. Aye, A. R. Bazer-Bachi, M. Beilicke, W. Benbow, D. Berge, et al. "Serendipitous discovery of the unidentified extended TeV γ-ray source HESS J1303-631." Astronomy & Astrophysics 439, no. 3 (August 12, 2005): 1013–21. http://dx.doi.org/10.1051/0004-6361:20053195.

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Konopelko, A., R. W. Atkins, G. Blaylock, J. H. Buckley, Y. Butt, D. A. Carter‐Lewis, O. Celik, et al. "Observations of the Unidentified TeV γ‐Ray Source TeV J2032+4130 with the Whipple Observatory 10 m Telescope." Astrophysical Journal 658, no. 2 (April 2007): 1062–68. http://dx.doi.org/10.1086/511262.

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Eger, P., G. Rowell, A. Kawamura, Y. Fukui, L. Rolland, and C. Stegmann. "A multi-wavelength study of the unidentified TeV gamma-ray source HESS J1626−490." Astronomy & Astrophysics 526 (December 24, 2010): A82. http://dx.doi.org/10.1051/0004-6361/201015727.

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Falcone, A. D., J. Grube, J. Hinton, J. Holder, G. Maier, R. Mukherjee, J. Skilton, and M. Stroh. "PROBING THE NATURE OF THE UNIDENTIFIED TeV GAMMA-RAY SOURCE HESS J0632+057 WITHSWIFT." Astrophysical Journal 708, no. 1 (December 16, 2009): L52—L56. http://dx.doi.org/10.1088/2041-8205/708/1/l52.

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Mukherjee, R., J. P. Halpern, E. V. Gotthelf, M. Eracleous, and N. Mirabal. "Search for a Point‐Source Counterpart of the Unidentified Gamma‐Ray Source TeV J2032+4130 in Cygnus." Astrophysical Journal 589, no. 1 (May 20, 2003): 487–94. http://dx.doi.org/10.1086/374641.

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Mukherjee, R., and J. P. Halpern. "ChandraObservation of the Unidentified TeV Gamma‐Ray Source HESS J1303−631 in the Galactic Plane." Astrophysical Journal 629, no. 2 (August 20, 2005): 1017–20. http://dx.doi.org/10.1086/431581.

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Mizukami, T., H. Kubo, T. Yoshida, T. Nakamori, R. Enomoto, T. Tanimori, M. Akimoto, et al. "CANGAROO-III OBSERVATION OF TeV GAMMA RAYS FROM THE UNIDENTIFIED GAMMA-RAY SOURCE HESS J1614–518." Astrophysical Journal 740, no. 2 (October 3, 2011): 78. http://dx.doi.org/10.1088/0004-637x/740/2/78.

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Sakai, Michito, Yukie Yajima, and Hironori Matsumoto. "Nature of the Unidentified TeV Source HESS J1614−518, Revealed by Suzaku and XMM-Newton Observations." Publications of the Astronomical Society of Japan 63, sp3 (November 25, 2011): S879—S887. http://dx.doi.org/10.1093/pasj/63.sp3.s879.

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Bartoli, B., P. Bernardini, X. J. Bi, I. Bolognino, P. Branchini, A. Budano, A. K. Calabrese Melcarne, et al. "OBSERVATION OF TeV GAMMA RAYS FROM THE UNIDENTIFIED SOURCE HESS J1841–055 WITH THE ARGO-YBJ EXPERIMENT." Astrophysical Journal 767, no. 2 (April 1, 2013): 99. http://dx.doi.org/10.1088/0004-637x/767/2/99.

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Acciari, V. A., E. Aliu, T. Arlen, M. Beilicke, W. Benbow, D. Boltuch, S. M. Bradbury, et al. "EVIDENCE FOR LONG-TERM GAMMA-RAY AND X-RAY VARIABILITY FROM THE UNIDENTIFIED TeV SOURCE HESS J0632+057." Astrophysical Journal 698, no. 2 (May 28, 2009): L94—L97. http://dx.doi.org/10.1088/0004-637x/698/2/l94.

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Lau, J. C., G. Rowell, F. Voisin, R. Blackwell, M. G. Burton, C. Braiding, G. F. Wong, Y. Fukui, and S. Casanova. "Probing the origin of the unidentified TeV γ-ray source HESS J1702–420 via the surrounding interstellar medium." Monthly Notices of the Royal Astronomical Society 483, no. 3 (December 7, 2018): 3659–72. http://dx.doi.org/10.1093/mnras/sty3326.

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Matsumoto, Hironori, Hideki Uchiyama, Makoto Sawada, Takeshi G. Tsuru, Katsuji Koyama, Hideaki Katagiri, Ryo Yamazaki, et al. "Discovery of Extended X-Ray Emission from an Unidentified TeV Source, HESS J1614$-$518, Using the Suzaku Satellite." Publications of the Astronomical Society of Japan 60, sp1 (February 20, 2008): S163—S172. http://dx.doi.org/10.1093/pasj/60.sp1.s163.

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Giacani, E., M. J. S. Smith, G. Dubner, and N. Loiseau. "A new study of the supernova remnant G344.7-0.1 located in the vicinity of the unidentified TeV source HESS J1702-420." Astronomy & Astrophysics 531 (July 2011): A138. http://dx.doi.org/10.1051/0004-6361/201116768.

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Cui, Wei, and Alexander Konopelko. "Erratum: " Chandra View of the Unidentified TeV Gamma-Ray Source HESS J1804-216" ([URL ADDRESS="/cgi-bin/resolve?2006ApJ...652L.109C" STATUS="OKAY"]ApJ, 652, L109 [2006][/URL])." Astrophysical Journal 665, no. 1 (August 10, 2007): L83. http://dx.doi.org/10.1086/521050.

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Hirotani, Kouichi, Hung-Yi Pu, and Satoki Matsushita. "Lightning black holes as unidentified TeV sources." Journal of Astrophysics and Astronomy 39, no. 4 (August 2018). http://dx.doi.org/10.1007/s12036-018-9545-2.

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