93 research outputs found
A hadronic scenario for HESS J1818-154
Aims: G15.4+0.1 is a faint supernova remnant (SNR) that has recently been
associated with the gamma-ray source HESS J1818-154. We investigate a hadronic
scenario for the production of the gamma-ray emission. Methods: Molecular 13CO
(J=1-0) taken from the Galactic Ring Survey (GRS) and neutral hydrogen (HI)
data from the Southern Galactic Plane Survey (SGPS) have been used in
combination with new 1420 MHz radio continuum observations carried out with the
Giant Metrewave Radio Telescope (GMRT). Results: From the new observations and
analysis of archival data we provided for the first time a reliable estimate
for the distance to the SNR G15.4+0.1 and discovered molecular clouds located
at the same distance. On the basis of HI absorption features, we estimate the
distance to G15.4+0.1 in 4.8+/-1.0 kpc. The 13CO observations clearly show a
molecular cloud about 5 arcmin in size with two bright clumps, labeled A and B,
clump A positionally associated with the location of HESS J1818-154 and clump B
in coincidence with the brightest northern border of the radio SNR shell. The
HI absorption and the 13CO emission study indicates a possible interaction
between the molecular material and the remnant. We estimate the masses and
densities of the molecular gas as (1.2+/-0.5)X10^3 M_sun and (1.5+/-0.4)X10^3
cm^-3 for clump A and (3.0+/-0.7)X10^3 M_sun and (1.1+/-0.3)X10^3 cm^-3 for
clump B. Calculations show that the average density of the molecular clump A is
sufficient to produce the detected gamma-ray flux, thus favoring a hadronic
origin for the high-energy emission.Comment: Accepted to be published in Astronomy and Astrophysics Letter
A complete radio study of SNR G15.4+0.1 from new GMRT observations
The supernova remnant G15.4+0.1 is considered to be the possible counterpart
of the gamma-ray source HESSJ1818-154. With the goal of getting a complete view
of this remnant and understanding the nature of the gamma-ray flux, we
conducted a detailed radio study that includes the search for pulsations and a
model of the broadband emission for the G15.4+0.1/HESSJ1818-154 system.
Low-frequency imaging at 624 MHz and pulsar observations at 624 and 1404 MHz
towards G15.4+0.1 were carried out with the Giant Metrewave Radio Telescope
(GMRT). We correlated the new radio data with observations of the source at
X-ray and infrared wavelengths from XMM-Newton and Herschel observatories,
respectively. To characterize the neutral hydrogen medium (HI) towards
G15.4+0.1, we used data from the Southern Galactic Plane Survey. We modelled
the spectral energy distribution using both hadronic and leptonic scenarios.
From the combination of the new GMRT observations with existing data, we
derived a continuum spectral index alpha=-0.62+-0.03 for the whole remnant. The
local synchrotron spectra of G15.4+0.1, calculated from the combination of the
GMRT data with 330 MHz observations from the VLA, tends to be flatter in the
central part of the remnant, accompanying the region where the blast wave is
impinging molecular gas. No spectral index trace was found indicating the radio
counterpart to the pulsar wind nebula proposed from X-ray observations. In
addition, the search for radio pulsations yielded negative results. Emission at
far-infrared wavelengths is observed in the region where the SNR shock is
interacting with dense molecular clumps. We also identified HI features forming
a shell that wraps most of the outer border of G15.4+0.1. Characteristic
parameters were estimated for the shocked HI gas. We found that either a purely
hadronic or leptonic model is compatible with the broadband emission known so
far.Comment: 11 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
A complete radio study of SNR G15.4+0.1 from new GMRT observations
Aims. The supernova remnant (SNR) G15.4+0.1 is considered to be the possible counterpart of the γ-ray source HESS J1818−154. With the goal of getting a complete view of this remnant and understanding the nature of the gamma-ray flux, we conducted a detailed radio study that includes the search for pulsations and a model of the broadband emission for the SNR G15.4+0.1/HESS J1818−154 system. Methods. Low-frequency imaging at 624 MHz and pulsar observations at 624 and 1404 MHz towards G15.4+0.1 were carried out with the Giant Metrewave Radio Telescope (GMRT). We correlated the new radio data with observations of the source at X-ray and infrared wavelengths from XMM-Newton and Herschel observatories, respectively. To characterize the neutral hydrogen (HI) medium towards G15.4+0.1, we used data from the Southern Galactic Plane Survey. We modelled the spectral energy distribution (SED) using both hadronic and leptonic scenarios. Results. From the combination of the new GMRT observations with existing data, we derived a continuum spectral index alpha = -0.62 +- 0.03 for the whole remnant. The local synchrotron spectra of G15.4+0.1, calculated from the combination of the GMRT data with 330 MHz observations from the Very Large Array, tends to be flatter in the central part of the remnant, accompanying the region where the blast wave is impinging molecular gas. No spectral index trace was found indicating the radio counterpart to the pulsar wind nebula proposed from X-ray observations. In addition, the search for radio pulsations yielded negative results. Emission at far-infrared wavelengths is observed in the region where the SNR shock is interacting with dense molecular clumps. We also identified HI features forming a shell that wraps most of the outer border of G15.4+0.1. Characteristic parameters were estimated for the shocked HI gas. We found that either a purely hadronic or leptonic model is compatible with the broadband emission known so far.Fil: Supán, Jorge Leonardo. Consejo Nacional de Investigaciónes CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; ArgentinaFil: Castelletti, Gabriela Marta. Consejo Nacional de Investigaciónes CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; ArgentinaFil: Joshi, B. C.. National Centre for Radio Astrophysics; IndiaFil: Surnis, M. P.. National Centre for Radio Astrophysics; IndiaFil: Supanitsky, Alberto Daniel. Consejo Nacional de Investigaciónes CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; Argentin
Initial results from a realtime FRB search with the GBT
We present the data analysis pipeline, commissioning observations and initial
results from the GREENBURST fast radio burst (FRB) detection system on the
Robert C. Byrd Green Bank Telescope (GBT) previously described by Surnis et al.
which uses the 21~cm receiver observing commensally with other projects. The
pipeline makes use of a state-of-the-art deep learning classifier to winnow
down the very large number of false positive single-pulse candidates that
mostly result from radio frequency interference. In our observations totalling
156.5 days so far, we have detected individual pulses from 20 known radio
pulsars which provide an excellent verification of the system performance. We
also demonstrate, through blind injection analyses, that our pipeline is
complete down to a signal-to-noise threshold of 12. Depending on the observing
mode, this translates to peak flux sensitivities in the range 0.14--0.89~Jy.
Although no FRBs have been detected to date, we have used our results to update
the analysis of Lawrence et al. to constrain the FRB all-sky rate to be
per day above a peak flux density of 1~Jy. We also
constrain the source count index which indicates that the
source count distribution is substantially flatter than expected from a
Euclidean distribution of standard candles (where ). We discuss
this result in the context of the FRB redshift and luminosity distributions.
Finally, we make predictions for detection rates with GREENBURST, as well as
other ongoing and planned FRB experiments.Comment: 9 pages, 7 figures, submitted to MNRA
- …