Aims.
The supernova remnant (SNR) G150.3+4.5 was recently discovered in the radio band; it exhibits a shell-like morphology with an angular size of ~ 3°, suggesting either an old or a nearby SNR. ...Extended
γ
-ray emission spatially coincident with the SNR was reported in the
Fermi
Galactic Extended Source Catalog, with a power-law spectral index of Γ = 1.91 ± 0.09. Studying particle acceleration in SNRs through their
γ
-ray emission is of primary concern to assess the nature of accelerated particles and the maximum energy they can reach.
Methods.
Using more than ten years of
Fermi
-LAT data, we investigate the morphological and spectral properties of the SNR G150.3+4.5 from 300 MeV to 3 TeV. We use the latest releases of the
Fermi
-LAT catalog, the instrument response functions and the Galactic and isotropic diffuse emissions. We use ROSAT all-sky survey data to assess any thermal and nonthermal X-ray emission, and we derive minimum and maximum distance to G150.3+4.5.
Results.
We describe the
γ
-ray emission of G150.3+4.5 by an extended component which is found to be spatially coincident with the radio SNR. The spectrum is hard and the detection of photons up to hundreds of GeV points towards an emission from a dynamically young SNR. The lack of X-ray emission gives a tight constraint on the ambient density
n
0
≤ 3.6 × 10
−3
cm
−3
. Since G150.3+4.5 is not reported as a historical SNR, we impose a lower limit on its age of
t
= 1 kyr. We estimate its distance to be between 0.7 and 4.5 kpc. We find that G150.3+4.5 is spectrally similar to other dynamically young and shell-type SNRs, such as RX J1713.7−3946 or Vela Junior. The broadband nonthermal emission is explained with a leptonic scenario, implying a downstream magnetic field of
B
= 5
μ
G and acceleration of particles up to few TeV energies.
ABSTRACT
The repeating fast radio burst (FRB) source FRB 20200120E is exceptional because of its proximity and association with a globular cluster. Here we report 60 bursts detected with the ...Effelsberg telescope at 1.4 GHz. We observe large variations in the burst rate, and report the first FRB 20200120E ‘burst storm’, where the source suddenly became active and 53 bursts (fluence ≥0.04 Jy ms) occurred within only 40 min. We find no strict periodicity in the burst arrival times, nor any evidence for periodicity in the source’s activity between observations. The burst storm shows a steep energy distribution (power-law index α = 2.39 ± 0.12) and a bimodal wait-time distribution, with log-normal means of 0.94$^{+0.07}_{-0.06}$ s and 23.61$^{+3.06}_{-2.71}$ s. We attribute these wait-time distribution peaks to a characteristic event time-scale and pseudo-Poisson burst rate, respectively. The secondary wait-time peak at ∼1 s is ∼50 × longer than the ∼24 ms time-scale seen for both FRB 20121102A and FRB 20201124A – potentially indicating a larger emission region, or slower burst propagation. FRB 20200120E shows order-of-magnitude lower burst durations and luminosities compared with FRB 20121102A and FRB 20201124A. Lastly, in contrast to FRB 20121102A, which has observed dispersion measure (DM) variations of ΔDM > 1 pc cm−3 on month-to-year time-scales, we determine that FRB 20200120E’s DM has remained stable (ΔDM < 0.15 pc cm−3) over >10 months. Overall, the observational characteristics of FRB 20200120E deviate quantitatively from other active repeaters, but it is unclear whether it is qualitatively a different type of source.
ABSTRACT We report for the first time a γ-ray and multiwavelength nearly periodic oscillation in an active galactic nucleus. Using the Fermi Large Area Telescope we have discovered an apparent ...quasi-periodicity in the γ-ray flux (E > 100 MeV) from the GeV/TeV BL Lac object PG 1553+113. The marginal significance of the 2.18 0.08 year period γ-ray cycle is strengthened by correlated oscillations observed in radio and optical fluxes, through data collected in the Owens Valley Radio Observatory, Tuorla, Katzman Automatic Imaging Telescope, and Catalina Sky Survey monitoring programs and Swift-UVOT. The optical cycle appearing in ∼10 years of data has a similar period, while the 15 GHz oscillation is less regular than seen in the other bands. Further long-term multiwavelength monitoring of this blazar may discriminate among the possible explanations for this quasi-periodicity.
We present a search for spatial extension in high-latitude ( ) sources in recent Fermi point source catalogs. The result is the Fermi High-Latitude Extended Sources Catalog, which provides source ...extensions (or upper limits thereof) and likelihood profiles for a suite of tested source morphologies. We find 24 extended sources, 19 of which were not previously characterized as extended. These include sources that are potentially associated with supernova remnants and star-forming regions. We also found extended γ-ray emission in the vicinity of the Cen A radio lobes and-at GeV energies for the first time-spatially coincident with the radio emission of the SNR CTA 1, as well as from the Crab Nebula. We also searched for halos around active galactic nuclei, which are predicted from electromagnetic cascades induced by the e+e− pairs that are deflected in intergalactic magnetic fields. These pairs are produced when γ-rays interact with background radiation fields. We do not find evidence for extension in individual sources or in stacked source samples. This enables us to place limits on the flux of the extended source components, which are then used to constrain the intergalactic magnetic field to be stronger than 3 × 10−16 G for a coherence length λ 10 kpc, even when conservative assumptions on the source duty cycle are made. This improves previous limits by several orders of magnitude.
Context. The breakthrough developments of Cherenkov telescopes in the past decade have led to angular resolution of 0.1° and an unprecedented sensitivity. This has allowed the current generation of ...Cherenkov telescopes (H.E.S.S., MAGIC, and VERITAS) to discover a population of supernova remnants (SNRs) radiating in very-high-energy (VHE; E > 100 GeV) γ-rays. A number of those VHE SNRs exhibit a shell-type morphology that is spatially coincident with the shock front of the SNR. Aims. The members of this VHE shell SNR club are RX J1713.7−3946, RX J0852.0−4622, RCW 86, SN 1006, and HESS J1731−347. The last two objects have been poorly studied in high-energy (HE; 0.1 < E < 100 GeV) γ-rays and need to be investigated in order to draw the overall picture of this class of SNRs and to constrain the characteristics of the underlying population of accelerated particles. Methods. Using 6 years of Fermi-LAT P7 reprocessed data, we studied the GeV counterpart of the SNRs HESS J1731−347 and SN 1006. The two SNRs are not detected in the data set, and given that there is no hint of detection, we do not expect any detection in coming years from the SNRs. However in both cases, we derived upper limits that significantly constrain the γ-ray emission mechanism and can rule out a standard hadronic scenario with a confidence level >5σ. Results. With this Fermi analysis, we now have a complete view of the HE to VHE γ-ray emission of TeV shell SNRs. All five sources have a hard HE photon index (Γ < 1.8), which suggests a common scenario where the bulk of the emission is produced by accelerated electrons radiating from radio to VHE γ-rays through synchrotron and inverse Compton processes. In addition when correcting for the distance, all SNRs show a surprisingly similar γ-ray luminosity supporting the idea of a common emission mechanism. While the γ-ray emission is likely to be leptonic-dominated at the scale of the whole SNR, this does not rule out efficient hadron acceleration in those objects.
Fast radio bursts (FRBs) are flashes of unknown physical origin
. The majority of FRBs have been seen only once, although some are known to generate multiple flashes
. Many models invoke magnetically ...powered neutron stars (magnetars) as the source of the emission
. Recently, the discovery
of another repeater (FRB 20200120E) was announced, in the direction of the nearby galaxy M81, with four potential counterparts at other wavelengths
. Here we report observations that localized the FRB to a globular cluster associated with M81, where it is 2 parsecs away from the optical centre of the cluster. Globular clusters host old stellar populations, challenging FRB models that invoke young magnetars formed in a core-collapse supernova. We propose instead that FRB 20200120E originates from a highly magnetized neutron star formed either through the accretion-induced collapse of a white dwarf, or the merger of compact stars in a binary system
. Compact binaries are efficiently formed inside globular clusters, so a model invoking them could also be responsible for the observed bursts.
ABSTRACT
FRB 20121102A is the first known fast radio burst (FRB) from which repeat bursts were detected, and one of the best-studied FRB sources in the literature. Here we report on the analysis of ...478 bursts (333 previously unreported) from FRB 20121102A using the 305-m Arecibo telescope – detected during approximately 59 hours of observations between December 2015 and October 2016. The majority of bursts are from a burst storm around September 2016. This is the earliest available sample of a large number of FRB 20121102A bursts, and it thus provides an anchor point for long-term studies of the source’s evolving properties. We observe that the bursts separate into two groups in the width-bandwidth-energy parameter space, which we refer to as the low-energy bursts (LEBs) and high-energy bursts (HEBs). The LEBs are typically longer duration and narrower bandwidth than the HEBs, reminiscent of the spectro-temporal differences observed between the bursts of repeating and non-repeating FRBs. We fit the cumulative burst rate-energy distribution with a broken power law and find that it flattens out toward higher energies. The sample shows a diverse zoo of burst morphologies. Notably, burst emission seems to be more common at the top than the bottom of our 1150–1730 MHz observing band. We also observe that bursts from the same day appear to be more similar to each other than to those of other days, but this observation requires confirmation. The wait times and burst rates that we measure are consistent with previous studies. We discuss these results, primarily in the context of magnetar models.
The Indian megacity of Delhi suffers from some of the
poorest air quality in the world. While ambient NO2 and particulate
matter (PM) concentrations have received considerable attention in the city,
...high ground-level ozone (O3) concentrations are an often overlooked
component of pollution. O3 can lead to significant ecosystem damage and
agricultural crop losses, and adversely affect human health. During October 2018,
concentrations of speciated non-methane hydrocarbon volatile organic
compounds (C2–C13), oxygenated volatile organic compounds
(o-VOCs), NO, NO2, HONO, CO, SO2, O3, and photolysis rates,
were continuously measured at an urban site in Old Delhi. These observations
were used to constrain a detailed chemical box model utilising the Master
Chemical Mechanism v3.3.1. VOCs and NOx (NO + NO2) were varied
in the model to test their impact on local O3 production rates,
P(O3), which revealed a VOC-limited chemical regime. When only NOx
concentrations were reduced, a significant increase in P(O3) was
observed; thus, VOC co-reduction approaches must also be considered in
pollution abatement strategies. Of the VOCs examined in this work, mean
morning P(O3) rates were most sensitive to monoaromatic compounds,
followed by monoterpenes and alkenes, where halving their concentrations in
the model led to a 15.6 %, 13.1 %, and 12.9 % reduction in
P(O3), respectively. P(O3) was not sensitive to direct changes in
aerosol surface area but was very sensitive to changes in photolysis rates,
which may be influenced by future changes in PM concentrations. VOC and
NOx concentrations were divided into emission source sectors, as
described by the Emissions Database for Global Atmospheric Research (EDGAR) v5.0 Global Air Pollutant Emissions and EDGAR
v4.3.2_VOC_spec inventories, allowing for the
impact of individual emission sources on P(O3) to be investigated.
Reducing road transport emissions only, a common strategy in air pollution
abatement strategies worldwide, was found to increase P(O3), even when
the source was removed in its entirety. Effective reduction in P(O3)
was achieved by reducing road transport along with emissions from combustion
for manufacturing and process emissions. Modelled P(O3) reduced by
∼ 20 ppb h−1 when these combined sources were halved. This study
highlights the importance of reducing VOCs in parallel with NOx and PM
in future pollution abatement strategies in Delhi.
We describe the HadGEM2 family of climate configurations of the Met Office Unified Model, MetUM. The concept of a model "family" comprises a range of specific model configurations incorporating ...different levels of complexity but with a common physical framework. The HadGEM2 family of configurations includes atmosphere and ocean components, with and without a vertical extension to include a well-resolved stratosphere, and an Earth-System (ES) component which includes dynamic vegetation, ocean biology and atmospheric chemistry. The HadGEM2 physical model includes improvements designed to address specific systematic errors encountered in the previous climate configuration, HadGEM1, namely Northern Hemisphere continental temperature biases and tropical sea surface temperature biases and poor variability. Targeting these biases was crucial in order that the ES configuration could represent important biogeochemical climate feedbacks. Detailed descriptions and evaluations of particular HadGEM2 family members are included in a number of other publications, and the discussion here is limited to a summary of the overall performance using a set of model metrics which compare the way in which the various configurations simulate present-day climate and its variability.
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