arXiv subjects

Miguel Araya

Publications and source records attributed to Miguel Araya.

At least 19 recordsLinked to original sources

arXiv2026

GeV emission in the region of Vela: a new view of the supernova remnant

The Vela supernova remnant (SNR), G263.9-3.3, and its pulsar wind nebula (PWN), Vela X, is one of the closest such systems, and it has been studied using observations across the electromagnetic spectrum. SNRs are known sources of gamma rays with energies from GeV to the TeV range. In the GeV band, a cluster of cataloged unidentified Fermi-LAT point sources are found across the large angular extension of the Vela SNR. We aim to search for a high-energy signature associated to the SNR. We applied two independent machine learning algorithms to classify unidentified point sources in the Vela region by comparing their properties to those of known populations of Fermi pulsars and active galactic nuclei. We analyzed LAT data and modeled the spectrum of any emission attributable to Vela using leptonic and hadronic processes typical of SNRs. We find that most of the "point sources" cataloged within the extent of Vela do not share characteristics with those of the two most common Fermi point-like source populations and that even after the emission attributed to these "point sources" is subtracted, considerable residual emission is seen throughout Vela. Morphologically, most of the GeV emission is found within the shell of the SNR. We conclude that the majority of the cataloged point sources are likely spurious, and the GeV gamma rays come from an extended source, which we argue is the counterpart of the Vela SNR. Adopting a simple morphology given by a uniform disk for the emission the resulting extension is 6.5 deg. The northeastern portion of G263.9-3.3, where the ambient density is thought to be higher, is brighter in gamma rays than the south and west. The spectrum of the emission is best fit with a hadronic model. These facts make the hadronic origin for the gamma rays more likely.

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arXiv2025

Teleios (G305.4-2.2) -- the mystery of a perfectly shaped new Galactic supernova remnant

We present the serendipitous radio-continuum discovery of a likely Galactic supernova remnant (SNR) G305.4-2.2. This object displays a remarkable circular symmetry in shape, making it one of the most circular Galactic SNRs known. Nicknamed Teleios due to its symmetry, it was detected in the new Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) radio-continuum images with an angular size of 1320"x1260" and PA = 0 deg. While there is a hint of possible H$\alpha$ and gamma-ray emission, Teleios is exclusively seen at radio-continuum frequencies. Interestingly, Teleios is not only almost perfectly symmetric, but it also has one of the lowest surface brightnesses discovered among Galactic SNRs and a steep spectral index of $\alpha=-0.6\pm 0.3$. Our estimates from HI studies and the Sigma-D relation place Teleios as a type Ia SNR at a distance of either ~2.2 kpc of ~7.7 kpc. This indicates two possible scenarios, either a young (under 1000 yr) or an older SNR (over 10000 yr). With a corresponding diameter of 14/48 pc, our evolutionary studies place Teleios at the either early or late Sedov phase, depending on the distance estimate. However, our modelling also predicts X-ray emission, which we do not see in the present generation of eROSITA images. We also explored a type Iax explosion scenario that points to a much closer distance of <1 kpc and Teleios size of only ~3.3 pc, which would be similar to the only known type Iax remnant SN1181. Unfortunately, all examined scenarios have their challenges, and no definitive supernova (SN) origin type can be established at this stage. Teleios's symmetrical shape suggests expansion into a rarefied and isotropic ambient medium. The low radio surface brightness and the lack of pronounced polarisation can be explained by a high level of ambient rotation measure (RM), with the largest RM being observed at centre.

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arXiv2024

Non-thermal GeV emission from the Nereides nebula: confirming the nature of the supernova remnant G107.7-5.1

Recently the Nereides nebula was discovered through deep optical emission line observations and was classified as a supernova remnant (SNR) candidate, G107.7-5.1. Since very little is known about this SNR we look at several archival data sets to better understand the environment and properties of the object. We present a detailed analysis of the gamma-ray emission detected by the \textit{Fermi} Large Area Telescope in the region of the nebula. A model of the non-thermal emission is presented which allows us to derive the particle distribution responsible for the gamma rays. We also use molecular gas and atomic hydrogen observations to try to constrain the source age and distance. An extended (~2deg) GeV source coincident with the location of the nebula is found. The non-thermal emission has a hard spectrum and is detected up to about 100 GeV, confirming the SNR nature of this object. The GeV properties of G107.7-5.1 are similar to those of other SNRs such as G150.3+4.5, and likely expands in a relatively low-density medium. The Nereides nebula is one more example of a growing population of dim SNRs detected at high energies. A simple leptonic model is able to account for the gamma-ray emission. Standard SNR evolutionary models constrain the age to be in the 10-50 kyr range, which is consistent with estimates of the maximum particle energy obtained from GeV observations. However, more detailed observations of the source should be carried out to better understand its properties.

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arXiv2023

Discovery of an extended GeV counterpart to the TeV source 1LHAASO J1945+2424 in Fermi-LAT data

With almost 15 years of data taken by the Large Area Telescope (LAT) onboard the Fermi satellite we discovered an extended source of GeV emission in the region of the very-high-energy (TeV) source 1LHAASO J1945+2424. This TeV source is more extended than the LAT source. The spectrum of the GeV emission is hard (with a photon spectral index ~1.5) and connects smoothly with that of the TeV source, indicating a likely common origin. In order to explain the origin of the gamma rays we explore scenarios which are typically used for supernova remnants (SNRs) and pulsar wind nebulae (PWN). For an SNR with a single particle population, a leptonic particle distribution in the form of a broken power-law with a break energy of ~3.7 TeV explains the spectrum well, while in the hadronic scenario a simple power-law with a hard spectral index of ~1.64 is necessary. In the PWN scenario, reasonable parameters are obtained for a source age of 10 kyr and current pulsar spin-down luminosity of 1e34 erg/s.

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arXiv2022

Fermi-LAT detection of G118.4+37.0: a supernova remnant in the Galactic halo seen around the Calvera pulsar

The discovery of a non-thermal radio ring of low surface brightness about one degree in diameter has been recently reported around the location in the sky of the Calvera pulsar, at a high Galactic latitude. The radio properties point to it likely being a new supernova remnant (SNR), G118.4+37.0. We report an analysis of almost 14 years of observations of this region by the gamma-ray Large Area Telescope onboard the Fermi satellite. We detect extended GeV emission consistent with the size and location of the radio source, which confirms the presence of relativistic particles. The spectrum of the high-energy emission is fully compatible with an origin in the same relativistic particles producing the radio emission. These features and its similarities to other isolated SNRs establish this source as the remnant of a supernova. A simple model of the non-thermal emission from radio to GeV energies resulting from leptonic emission from electrons produced by the SNR is presented. G118.4+37.0 and other similar isolated remnants could be part of a radio-dim SNR population evolving in low density environments showing hard GeV emission of leptonic origin. Future deeper surveys in radio and gamma-rays could discover new members of the group.

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arXiv2021

G17.8+16.7: A New Supernova Remnant

Non-thermal radio emission is detected in the region of the gamma-ray source FHES J1723.5-0501. The emission has an approximately circular shape 0.8 degrees in diameter. The observations confirm its nature as a new supernova remnant, G17.8+16.7. We derive constraints on the source parameters using the radio data and gamma-ray observations of the region. The distance to the object is possibly in the range 1.4-3.5 kpc. An SNR age of the order of 10 kyr is compatible with the radio and GeV features, but an older or younger SNR cannot be ruled out. A simple one-zone leptonic model naturally explains the multi-wavelength non-thermal fluxes of the source at its location outside the Galactic plane.

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arXiv2021

Probing the origin of 4FGL J0822.8-4207: cosmic ray illumination from the SNR Puppis A and the Herbig-Haro object HH219

4FGL J0822.8-4207 is a point source found in the 4FGL-DR2 catalog by the gamma-ray observatory Fermi-LAT and has no known association. We carry out X-ray observations of 4FGL J0822.8-4207 to help understand its nature. We explore two scenarios for the origin of 4FGL J0822.8-4207. In the first case we study the possibility that cosmic rays from the supernova remnant (SNR) Puppis A, seen nearby in the sky, reach the dense gas at the location of the source and produce the gamma-rays through inelastic proton-proton collisions. We apply a standard model for particle diffusion in the interstellar medium and derive the required physical parameters. We find that this scenario for the gamma rays is possible if the gas is located at a distance that is not higher than ~40 pc from Puppis A, unless the SNR is older than 7 kyr or the diffusion coefficient is higher than typical Galactic values, and relatively low-energy cosmic rays are currently escaping from the SNR. In the second scenario, we consider the protostellar jet HH219 as the origin of the GeV source and find the very interesting possibility that particles could be accelerated up to energies of at least several TeV in HH219. This would make this system the first known of its kind to produce gamma-ray emission extending up to hundreds of GeV without any apparent cutoff and an excellent laboratory to study the process of particle acceleration.

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arXiv2021

GeV emission in the region of the supernova remnant G51.26+0.11

The supernova remnant (SNR) G51.26+0.11 was recently discovered and little is known about its properties and environment. Using data from the \emph{Fermi} Large Area Telescope we study the GeV emission seen in the direction of G51.26+0.11 to constrain the origin of the gamma rays and their possible relation to this SNR or to a star-forming region. We also search for emission from molecular gas in the region that could provide dense material for the production of gamma rays. By modeling the multi-wavelength spectrum of G51.26+0.11 from radio to gamma rays we derive the properties of the particle populations that could produce the emission in several possible scenarios. We rule out the star-forming regions (such as G051.010+00.060) seen nearby as the origin of the GeV emission. The correspondence seen between the gamma-ray and radio morphologies support a scenario where G51.26+0.11 is the cause of the gamma rays. The flat spectral energy distribution observed at GeV energies is best fit by hadronic or inverse Compton emission, while a bremsstrahlung model cannot properly account for the radio fluxes under a simple one-zone scenario. A pulsar wind nebula origin of the high-energy photons cannot be ruled out or confirmed.

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arXiv2020

G279.0+1.1: a new extended source of high-energy gamma rays

G279.0+1.1 is a supernova remnant (SNR) with poorly known parameters, first detected as a dim radio source and classified as an evolved system. An analysis of data from the Fermi-LAT revealing for the first time an extended source of gamma rays in the region is presented. The diameter of the GeV region found is ~2.8$^{\circ}$, larger than the latest estimate of the SNR size from radio data. The gamma-ray emission covers most of the known shell and extends further to the north and east of the bulk of the radio emission. The photon spectrum in the 0.5--500 GeV range can be described by a simple power law, $\frac{dN}{dE} \propto E^{-Γ}$, with a spectral index of $Γ= 1.86\pm 0.03_{stat} \pm 0.06_{sys}$. In the leptonic scenario, a steep particle spectrum is required and a distance lower than the previously estimated value of 3 kpc is favored. The possibility that the high-energy emission results from electrons that already escaped the SNR is also investigated. A hadronic scenario for the gamma rays yields a particle spectral index of $\sim2.0$ and no significant constraints on the distance. The production of gamma rays in old SNRs is discussed. More observations of this source are encouraged to probe the true extent of the shell and its age.

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arXiv2019

Exploring the nature of 2HWC J2006+341 with HAWC and Fermi-LAT

The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is carrying out a detailed survey of the northern sky at TeV energies. 2HWC J2006+341 is a newly discovered source reported by the point source search in the 2HWC HAWC Observatory Gamma Ray Catalog. Using $\sim$1038 days of HAWC data we carried out a detailed analysis of the region revealing extended emission. No emission has been detected by other TeV instruments at the location of 2HWC J2006+341. We also analyzed publicly available data from the \textit{Fermi}-LAT that show for the first time the existence of an extended GeV source with a hard spectrum in the region of 2HWC J2006+341. Combined modeling of the data from HAWC and the \textit{Fermi}-LAT allowed us to explore different scenarios for the origin of 2HWC J2006+341.

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arXiv2018

GeV emission in the region of HESS J1809-193 and HESS J1813-178: is HESS J1809-193 a proton pevatron?

HESS J1809-193 is an unidentified TeV source discovered by the High Energy Stereoscopic System and originally classified as a pulsar wind nebula (PWN) candidate associated with the pulsar PSR J1809-1917. However, a recent study of deep radio observations and the interstellar medium near the source has found evidence for a hadronic scenario for the gamma-rays. Here, a detailed study of the GeV emission in the region using data from the \emph{Fermi} LAT is presented. The GeV emission has an extended morphology in the region of the TeV emission and the overall spectrum can be accounted for by a cosmic ray population having a simple power-law spectrum with energies extending up to 1 PeV. However, the spectrum at tens of TeV should be observed more deeply in the future to confirm its hadronic nature, and other scenarios involving combinations of leptonic and hadronic emission from several of the known supernova remnants in the region cannot be ruled out. The nearby TeV source HESS J1813-178, thought to be a PWN, is also studied in detail at GeV energies and we find a region of significant emission which is much more extended than the TeV emission and whose spectrum is softer than expected from a PWN but similar to those seen in several star forming regions that are believed to accelerate protons. There is marginal evidence for a GeV point source at the location of the X-ray PWN, beside the extended emission.

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arXiv2018

Discovery of an extended source of gamma-ray emission in the Southern Hemisphere

We report the discovery of a $\sim$ $3.4\degr$-wide region of high-energy emission in data from the \emph{Fermi} LAT satellite. The centroid of the emission is located in the Southern Hemisphere sky, a few degrees away from the plane of the Galaxy at the Galactic coordinates l=350.6$\degr$, b=-4.7$\degr$. It shows a hard spectrum that is compatible with a simple power-law, $\frac{dN}{dE}\propto E^{-Γ}$, in the energy range 0.7--500 GeV, with a spectral index $Γ= 1.68 \pm 0.04_{\mbox{stat}} \pm 0.1_{\mbox{sys}}$. The integrated source photon flux above 0.7 GeV is $(4.71 \pm 0.49_{\mbox{stat}}\pm 2.13_{\mbox{sys}}) \times 10^{-9}$ cm$^{-2}$ s$^{-1}$. We discuss several hypotheses for the nature of the source, particularly that the emission comes from the shell of an unknown supernova remnant.

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arXiv2017

Detection of GeV Gamma-rays from HESS J1534-571 and Multiwavelength Implications for the Origin of the Non-thermal Emission

HESS J1534-571 is a very high energy gamma-ray source that was discovered by the H.E.S.S. observatory and reported as one of several new sources with a shell-like morphology at TeV energies, matching in size and location with the supernova remnant G323.7-1.0 discovered in radio observations by the Molonglo Galactic Plane Survey. Many known TeV shells also show X-ray emission, however, no X-ray counterpart has been seen for HESS J1534-571. The detection of a new GeV source using data from the \emph{Fermi} satellite that is compatible in extension with the radio supernova remnant and shows a very hard power-law spectrum ($\frac{dN}{dE} \propto E^{-1.35}$) is presented here, together with the first broadband modeling of the nonthermal emission from this source. It is shown that leptonic emission is compatible with the known multiwavelength data and a corresponding set of physical source parameters is given. The required total energy budget in leptons is reasonable, $\sim 1.5\times10^{48}$ erg for a distance to the object of $5$ kpc. The new GeV observations imply that a hadronic scenario, on the other hand, requires a cosmic ray spectrum that deviates considerably from theoretical expectations of particle acceleration.

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arXiv2017

Fermi LAT observation of VER J2019+407

Analysis of data from the Fermi Large Area Telescope (LAT) in the region of the supernova remnant G78.2+2.1 reveals an excess at the position of the TeV source VER J2019+407. The GeV source is extended with a hard spectrum and it is likely the counterpart of the TeV source. The spectrum of the LAT emission connects smoothly with that of VER J2019+407, and the overall GeV--TeV spectrum is best described by a broken power-law with indices 1.8 and 2.5 below and above a break energy of 71 GeV. Several scenarios are considered to explain the nature of this unidentified gamma ray source.

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arXiv2016

Search for gamma-ray emission from star-forming galaxies with Fermi LAT

Recent studies have found a positive correlation between the star-formation rate of galaxies and their gamma-ray luminosity. Galaxies with a high star-formation rate are expected to produce a large amount of high-energy cosmic rays, which emit gamma-rays when interacting with the interstellar medium and radiation fields. We search for gamma-ray emission from a sample of galaxies within and beyond the Local Group with data from the LAT instrument onboard the Fermi satellite. We exclude recently detected galaxies (NGC 253, M82, NGC 4945, NGC 1068, NGC 2146, Arp 220) and use seven years of cumulative Pass 8 data from the LAT in the 100 MeV to 100 GeV range. No new detections are seen in the data and upper limits for the gamma- ray fluxes are calculated. The correlation between gamma-ray luminosity and infrared luminosity for galaxies obtained using our new upper limits is in agreement with a previously published correlation, but the new upper limits imply that some galaxies are not as efficient gamma-ray emitters as previously thought.

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arXiv2016

The GeV counterpart of VER J2019+407 in the northern shell of the supernova remnant G78.2+2.1 ($γ$ Cygni)

Analysis of gamma-ray emission from the supernova remnant G78.2+2.1 ($γ$ Cygni) with 7.2 years of cumulative data from the Fermi-LAT telescope shows a distinct hard, bright and extended component to the north of the shell coincident with the known TeV source VER J2019+407. In the GeV-TeV energy range its spectrum is best described by a broken power-law with indices 1.8 below a break energy of 71 GeV and 2.5 above the break. A broadband spectral energy distribution is assembled and different scenarios for the origin of the gamma-rays are explored. Both hadronic and leptonic mechanisms are able to account for the GeV-TeV observations. In the leptonic framework, a superposition of inverse Compton and nonthermal bremsstrahlung emissions is needed whereas the hadronic scenario requires a cosmic ray population described by a broken power-law distribution with a relatively hard spectral index of $\sim1.8$ below a break particle energy of 0.45 TeV. In addition, the neutrino flux expected from cosmic ray interactions is calculated.

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arXiv2015

Modeling the multiwavelength emission from G73.9+0.9: Gamma-rays from a SNR-MC interaction

G73.9+0.9 has been classified as a probable shell-type supernova remnant (SNR), although it has also been suggested that this object could be a pulsar wind nebula (PWN). Here, a broadband model of the non-thermal emission of G73.9+0.9 from radio to gamma-rays is presented. The model includes a new gamma-ray observation obtained with analysis of 7 years of data from the Fermi-LAT telescope. Above 200 MeV the source is detected with a significance of 13-sigma and the spectrum of the radiation is best described by a power law with an index of -2.5. The leptonic mechanisms are hard to reconcile with the measured radio and gamma-ray SED. A PWN origin for the high-energy emission is also not very likely, due to the lack of detection of pulsars and of X-ray emission in the region, as well as from the shape of the gamma-ray spectrum. Given the possibility that the object is interacting with molecular clouds, a hadronic origin of the high-energy emission is more likely, and the spectral properties of the cosmic rays responsible for this radiation are derived.

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arXiv2014

Fermi LAT Observation of Supernova Remnant HB9

A 5.5-year Fermi LAT gamma-ray observation shows significant extended emission at the position of the supernova remnant HB9 (G160.9+2.6). The significance of the detection above the background for photon energies above 0.2 GeV is 16$σ$. The gamma-ray flux above 0.2 GeV is (2.23E-8) photons/cm$^2$ s, and the corresponding luminosity above 1 GeV is 1.4E33 erg/s (for a source distance of 1 kpc). The spectrum of the source is best described by a curved power-law (log-parabola). The gamma-ray spectrum of the source is consistent with both leptonic and hadronic models, and the relevant physical parameters in each case are derived. More studies on the ambient density in the region of HB9 should be carried out to rule out or confirm hadronic and non-thermal bremsstrahlung scenarios for the gamma-ray emission.

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