arXiv subjects

G. Dubner

Publications and source records attributed to G. Dubner.

At least 37 records · Page 2Linked to original sources

arXiv2011

Radio observations of Supernova Remnants and the surrounding molecular gas

Supernova Remnants (SNRs) are believed to be the main source of Galactic cosmic rays (CR). The strong SNR shocks provide ideal acceleration sites for particles of at least 10^14 eV/nucleon. Radio continuum studies of SNRs carried out with good sensitivity and high angular resolution convey information about three main aspects of the SNRs: morphology, polarization and spectrum. Based on this information it is possible to localize sites of higher compression and particle acceleration as well as the orientation and degree of order of the magnetic fields, and in some cases even its intensity. All this information, when complemented with the study of the distribution and kinematics of the surrounding interstellar gas, results in a very useful dataset to investigate the role of SNRs as cosmic ray accelerators. In this presentation, I analyze the radio observations of SNRs and surrounding molecular clouds, showing the contribution of these studies to the understanding of the role of SNRs as factories of CRs.

astro-ph.HE↗

arXiv2011

First high-resolution radio study of the Supernova Remnant G338.3-0.0 associated with the gamma-ray source HESS J1640-465

We report on a multifrequency radio study of the supernova remnant (SNR) G338.3-0.0, in positional coincidence with the TeV source HESS J1640-465. To carry out this research we observed the SNR G338.3-0.0 using the Giant Metrewave Radio Telescope (GMRT) at 235, 610, and 1280 MHz. We also reprocessed archival data from the Australia Telescope Compact Array (ATCA) at 1290 and 2300 MHz. Also we conducted a search for radio pulsations towards a central point-like source, using the GMRT antennas at 610 and 1280 MHz. The molecular material in the region of the SNR was investigated based on observations made with the NANTEN telescope in the 12^CO (J=1-0) emission line. The new radio observations revealed a remnant with a bilateral morphology, which at 235 MHz has the western wing completely attenuated because of absorption due to foreground ionized gas. The quality of the new images allows us to provide accurate estimates for the total radio flux density of the whole SNR at different radio frequencies. From the new and existing flux density estimates between 235 and 5000 MHz we derived for the whole remnant a spectral index alpha=-0.51 +/-0.06 with a local free-free continuum optical depth at 235 MHz tau_{235}=0.9+/-0.3. No radio pulsations were detected towards the only radio point-like source within the HESS error circle. We derived upper limits of 2.0 and 1.0 mJy at 610 and 1280 MHz, respectively, for the pulsed flux towards this source. No radio counterpart was found for the pulsar wind nebula discovered in X-rays. The inspection of the interstellar molecular gas towards G338.3-0.0 and surroundings revealed that there is not any associated dense cloud that might explain a hadronic origin for the TeV detection.

astro-ph.GA↗

arXiv2011

Study of the dense molecular gas surrounding the "Extended Green Object" G35.03+0.35

We present the results of a new study of the molecular gas associated with the "extended green object" (EGO) G35.03+0.35. This object, very likely a massive young stellar object, is embedded in a molecular cloud at the border of an HII region. The observations were performed with the Atacama Submillimeter Telescope Experiment (ASTE) in the 12CO and 13CO J=3-2, HCO+ J=4-3, and CS J=7-6 lines with an angular resolution about 22". From the 12CO J=3-2 line we discovered outflowing activity of the massive young stellar object. We obtained a total mass and kinetic energy for the outflows of 30 M_sun and 3000 M_sun (km/s)^2 (6 x 10^{46} ergs), respectively. We discovered a HCO+ and CS clump towards the EGO G35.03+0.35. The detection of these molecular species supports the presence of molecular outflows and a dense molecular envelope with temperatures and densities above 40 K and 6 x 10^{6} cm^{-3}, respectively. Using public near- and mid-IR, and sub-mm data we investigated the spectral energy distribution confirming that EGO G35.03+0.35 is a massive young stellar object at the earliest evolutionary stage (i.e. a class I young stellar object). By anlysing radio continuum archival data we found three radio sources towards the object, suggesting the presence of several young stellar objects in the region. Our radio continuum analysis is consistent with the presence of at least one ultracompact HII region and an hypercompact HII region or a constant-velocity ionized wind source.

astro-ph.GA↗

arXiv2011

High-resolution radio study of SNR IC443 at low radio frequencies

We investigated in detail the morphology at low radio frequencies of the supernova remnant IC443 and accurately established its radio continuum spectral properties. We used the VLA in multiple configurations to produce high resolution radio images of IC443 at 74 and 330 MHz. The changes with position in the radio spectral index were correlated with data in near infrared from 2MASS, in gamma-rays from VERITAS, and with the molecular 12^CO line emission. The new image at 74 MHz has HPBW=35", rms=30 mJy/beam and at 330 MHz HPBW= 17" and rms=1.7 mJy/beam. The integrated flux densities for the whole SNR are S_74MHz=470+/-51 Jy and S_330MHz=248+/-15 Jy. For the pulsar wind nebula associated with the compact source CXOUJ061705.3+222127, we calculated S_330MHz=0.23+/-0.05 Jy, S_1420MHz=0.20+/-0.04 Jy, and alpha~0.0. Substantial variations are observed in spectral index between 74 and 330 MHz across IC443. The flattest spectral components (-0.25< alpha<-0.05) coincide with the brightest parts of the SNR along the eastern border, with an impressive agreement with ionic lines as observed in the 2MASS J and H bands. This result strongly suggests that the passage of a fast dissociating J-type shock across the interacting molecular cloud dissociated the molecules and ionized the gas. We therefore conclude that thermal absorption at 74 MHz is responsible for the localized spectral index flattening observed along the eastern border of IC443. The diffuse interior of IC443 has a spectrum steeper than found anywhere in the SNR (-0.85<alpha<-0.6), while the southern ridge again has a flatter spectrum (alpha -0.4), consequence in this case of the strong shock/molecular cloud interaction. At the available statistics the VERITAS gamma-ray emission strikingly matches the CO distribution, but no clear evidence is found for a morphological correlation between the TeV distribution and radio emission.

astro-ph.GA↗

arXiv2011

Study of the molecular clump associated with the high-energy source HESS J1858+020

HESS J1858+020 is a weak gamma-ray source lying near the southern border of the SNR G35.6-0.4. A molecular cloud, composed by two clumps, shows signs of interaction with the SNR and with a nearby extended HII region. In particular, the southernmost clump coincides with the center of the HESS source. In this work we study this clump in detail with the aim of adding information that helps in the identification of the nature of the very-high energy emission. We observed the mentioned molecular clump using the Atacama Submillimeter Telescope Experiment (ASTE) in the 12CO J=3-2, 13CO J=3-2, HCO+ J=4-3 and CS J=7-6 lines with an angular resolution of 22". To complement this observations we analyzed IR and submillimeter continuum archival data. From the 12CO and 13CO J=3-2 lines and the 1.1 mm continuum emission we derived a density of between 10^{3} and 10^{4} cm^-3 for the clump. We discovered a young stellar object (YSO), probably a high mass protostar, embedded in the molecular clump. However, we did not observe any evidence of molecular outflows from this YSO which would reveal the presence of a thermal jet capable of generating the observed gamma-rays. We conclude that the most probable origin for the TeV gamma-ray emission are the hadronic interactions between the molecular gas and the cosmic rays accelerated by the shock front of the SNR G35.6-0.4.

astro-ph.GA↗

arXiv2010

Study of the gamma-ray source 1AGL J2022+4032 in the Cygnus Region

Identification of gamma-ray-emitting Galactic sources is a long-standing problem in astrophysics. One such source, 1AGL J2022+4032, coincident with the interior of the radio shell of the supernova remnant Gamma Cygni (SNR G78.2+2.1) in the Cygnus Region, has recently been identified by Fermi as a gamma-ray pulsar, LAT PSR J2021+4026. We present long-term observations of 1AGL J2022+4032 with the AGILE gamma-ray telescope, measuring its flux and light curve. We compare the light curve of 1AGL J2022+4032 with that of 1AGL J2021+3652 (PSR J2021+3651), showing that the flux variability of 1AGL J2022+4032 appears to be greater than the level predicted from statistical and systematic effects and producing detailed simulations to estimate the probability of the apparent observed variability. We evaluate the possibility that the gamma-ray emission may be due to the superposition of two or more point sources, some of which may be variable, considering a number of possible counterparts. We consider the possibility of a nearby X-ray quiet microquasar contributing to the flux of 1AGL J2022+4032 to be more likely than the hypotheses of a background blazar or intrinsic gamma-ray variabilty of LAT PSR J2021+4026.

astro-ph.HE↗

arXiv2009

A multiwavelength study of the star forming region IRAS 18544+0112

This work aims at investigating the molecular and infrared components in the massive young stellar object (MYSO) candidate IRAS 18544+0112. The purpose is to determine the nature and the origin of this infrared source. To analyze the molecular gas towards IRAS 18544+0112, we have carried out observations in a 90" x 90" region around l = 34.69, b = -0.65, using the Atacama Submillimeter Telescope Experiment (ASTE) in the 12CO J=3-2, 13CO J=3-2, HCO+ J=4-3 and CS J=7-6 lines with an angular resolution of 22". The infrared emission in the area has been analyzed using 2MASS and Spitzer public data. From the molecular analysis, we find self-absorbed 12CO J=3-2 profiles, which are typical in star forming regions, but we do not find any evidence of outflow activity. Moreover, we do not detect either HCO+ J=4-3 or CS J=7-6 in the region, which are species normally enhanced in molecular outflows and high density envelopes. The 12CO J=3-2 emission profile suggests the presence of expanding gas in the region. The Spitzer images reveal that the infrared source has a conspicuous extended emission bright at 8 um with an evident shell-like morphology of ~ 1.5 arcmin in size (~ 1.4 pc at the proposed distance of 3 kpc) that encircles the 24 um emission. The non-detection of ionized gas related to IRAS 18544+0112, together with the fact that it is still embedded in a molecular clump suggest that IRAS 18544+0112, has not reached the UCHII region stage yet. Based on near infrared photometry we search for YSO candidates in the region and propos that 2MASS 18565878+0116233 is the infrared point source associated with IRAS 18544+0112. Finally, we suggest that the expansion of a larger nearby HII region, G034.8-0.7, might be related to the formation of IRAS 18544+0112.

astro-ph.GA↗

arXiv2009

Radio and X-ray study of two multi-shell Supernova Remnants: Kes79 and G352.7-0.1

We investigate two multi-shell galactic supernova remnants (SNRs), Kes79 and G352.7-0.1, to understand the causes of such morphology. The research was carried out based on new and reprocessed archival VLA observations and XMM-Newton archival data. The surrounding was investigated based on data extracted from the HI Canadian Galactic Plane Survey, the 13^CO Galactic Ring Survey and the HI Southern Galactic Plane Survey. The present study revealed that the overall morphology of both SNRs is the result of the mass-loss history of their respective progenitor stars. Kes79 would be the product of the gravitational collapse of a massive O9 star evolving near a molecular cloud and within the precursor's wind-driven bubble, while G352.7-0.1 would be the result of interactions of the SNR with an asymmetric wind from the progenitor together with projection effects. No radio point source or pulsar wind nebula was found associated with the X-ray pulsar CXOU J185238.6+004020 in Kes79. The X-ray study of G352.7-0.1, on its hand, revealed that most of the thermal X-ray radiation completely fills in the interior of the remnant and originates in heated ejecta. Characteristic parameters, like radio flux, radio spectral index, age, distance, shock velocity, initial energy and luminosity, were estimated for both SNRs.

astro-ph.GA↗

arXiv2009

Predicted gamma-ray image of SN 1006 due to inverse Compton emission

We propose a method to synthesize the inverse Compton (IC) gamma-ray image of a supernova remnant starting from the radio (or hard X-ray) map and using results of the spatially resolved X-ray spectral analysis. The method is successfully applied to SN 1006. We found that synthesized IC gamma-ray images of SN 1006 show morphology in nice agreement with that reported by the H.E.S.S. collaboration. The good correlation found between the observed very-high energy gamma-ray and X-ray/radio appearance can be considered as an evidence that the gamma-ray emission of SN 1006 observed by H.E.S.S. is leptonic in origin, though the hadronic origin may not be excluded.

astro-ph.HE↗

arXiv2009

Discovery of a dense molecular cloud towards a young massive embedded star in 30 Doradus

The 30 Doradus region in the Large Magellanic Cloud is one of the most outstanding star forming regions of the Local Group and a primary target to study star formation in an environment of low metallicity. In order to obtain a more complete picture of the not yet consumed or dispersed cool gas, we searched for line emission from molecular clouds that could be associated with molecular hydrogen emission detected in the region. We obtained a high sensitivity 12CO J=2-1 map with the 15-m SEST telescope, complemented by pointed observations of 13CO J=2-1 and CS J=2-1. We report the discovery of a dense molecular cloud towards an embedded young massive star at ~ 20" (~5 pc, at the distance of 50 kpc) northwest of R136, the compact massive central stellar cluster powering 30 Doradus in the LMC, that could be triggering star formation in the surrounding molecular clouds. We derived a molecular mass of $\lesssim 10^4$ \msol, a linear radius of 3 pc, as an upper limit, and a mean density of $\gtrsim 10^{3}$ cm$^{-3}$ for the cloud. The detection of CS J=2-1 emission line indicates larger densities, $\sim 10^{6}$ cm$^{-3}$. The dense molecular cloud is associated with molecular 2.12 um H2 emission. We suggest that the observed molecular gas could be the remains of dense molecular material surviving the action of strong UV fields and winds in which the young massive star has formed.

astro-ph.CO↗

arXiv2009

A joint spectro-imaging analysis of the XMM-Newton and HESS observations of the supernova remnant RX J1713.7-3946

The supernova remnant (SNR) RX J1713.7-3946 (also known as G347.3-0.5) is part of the class of remnants dominated by synchrotron emission in X-rays. It is also one of the few shell-type SNRs observed at TeV energies allowing to investigate particle acceleration at SNRs shock. Our goal is to compare spatial and spectral properties of the remnant in X- and gamma-rays to understand the nature of the TeV emission. This requires to study the remnant at the same spatial scale at both energies. To complement the non-thermal spectrum of the remnant, we attempt to provide a reliable estimate for the radio flux density. In radio, we revisited ATCA data and used HI and mid-infrared observations to disentangle the thermal from the non-thermal emission. In X-rays, we produced a new mosaic of the remnant and degraded the spatial resolution of the X-ray data to the resolution of the HESS instrument to perform spatially resolved spectroscopy at the same spatial scale in X- and gamma-rays. Radial profiles were obtained to investigate the extension of the emission at both energies. We found that part of the radio emission within the SNR contours is thermal in nature. Taking this into account, we provide new lower and upper limits for the integrated synchrotron flux of the remnant at 1.4 GHz of 22 Jy and 26 Jy respectively. In X-rays, we obtained the first full coverage of RX J1713.7-3946 with XMM-Newton. The spatial variation of the photon index seen at small scale in X-rays is smeared out at HESS resolution. A non-linear correlation between the X- and gamma-ray fluxes of the type Fx \propto Fg^2.41 is found.

astro-ph.HE↗

arXiv2009

Thermal emission, shock modification, and X-ray emitting ejecta in SN 1006

Efficient particle acceleration can modify the structure of supernova remnants. In this context we present the results of the combined analysis of the XMM-Newton EPIC archive observations of SN 1006. We aim at describing the spatial distribution of the physical and chemical properties of the X-ray emitting plasma at the shock front. We investigate the contribution of thermal and non-thermal emission to the X-ray spectrum at the rim of the remnant to study how the acceleration processes affect the X-ray emitting plasma. We perform a spatially resolved spectral analysis on a set of regions covering the whole rim of the shell and we exploit the results of the spectral analysis to produce a count-rate image of the "pure" thermal emission of SN 1006 in the 0.5-0.8 keV energy band (subtracting the non-thermal contribution). This image significantly differs from the total image in the same band, specially near the bright limbs. We find that thermal X-ray emission can be associated with the ejecta and we study the azimuthal variation of their physical and chemical properties finding anisotropies in temperature and chemical composition. Thanks to our thermal image we trace the position of the contact discontinuity over the whole shell and we compare it with that expected from 3-D MHD models of SNRs with unmodified shock. We conclude that the shock is modified everywhere in the rim and that the aspect angle between the interstellar magnetic field and the line of sight is significantly lower than 90 degrees

astro-ph.HE↗

arXiv2009

A molecular outflow evidencing star formation activity in the vicinity of the HII region G034.8-0.7 and the SNR W44

This work aims at investigating the molecular gas component in the vicinity of two young stellar object (YSO) candidates identified at the border of the HII region G034.8-0.7 that is evolving within a molecular cloud shocked by the SNR W44. The purpose is to explore signatures of star forming activity in this complex region. We performed a near and mid infrared study towards the border of the HII region G034.8-0.7 and observed a 90" X 90" region near 18h 56m 48s, +01d 18' 45" (J2000) using the Atacama Submillimeter Telescope Experiment (ASTE) in the 12CO J=3--2, 13CO J=3--2, HCO+ J=4--3 and CS J=7--6 lines with an angular resolution of 22". Based on the infrared study we propose that the source 2MASS 18564827+0118471 (IR1 in this work) is a YSO candidate. We discovered a bipolar 12CO outflow in the direction of the line of sight and a HCO+ clump towards IR1, confirming that it is a YSO. From the detection of the CS J=7--6 line we infer the presence of high density (>10^7 cm^-3) and warm (>60 K) gas towards IR1, probably belonging to the protostellar envelope where the YSO is forming. We investigated the possible genetic connection of IR1 with the SNR and the HII region. By comparing the dynamical time of the outflows and the age of the SNR W44, we conclude that the possibility of the SNR has triggered the formation of IR1 is unlikely. On the other hand, we suggest that the expansion of the HII region G034.8-0.7 is responsible for the formation of IR1 through the "collect and collapse" process.

astro-ph.GA↗

arXiv2008

Aspect angle for interstellar magnetic field in SN 1006

A number of important processes taking place around strong shocks in supernova remnants (SNRs) depend on the shock obliquity. The measured synchrotron flux is a function of the aspect angle between interstellar magnetic field (ISMF) and the line of sight. Thus a model of non-thermal emission from SNRs should account for the orientation of the ambient magnetic field. We develop a new method for the estimation of the aspect angle, based on the comparison between observed and synthesized radio maps of SNRs, making different assumptions about the dependence of electron injection efficiency on the shock obliquity. The method uses the azimuthal profile of radio surface brightness as a probe for orientation of ambient magnetic field because it is almost insensitive to the downstream distribution of magnetic field and emitting electrons. We apply our method to a new radio image of SN 1006 produced on the basis of archival VLA and Parkes data. The image recovers emission from all spatial structures with angular scales from few arcseconds to 15 arcmin. We explore different models of injection efficiency and find the following best-fitting values for the aspect angle of SN 1006: phi=70 +/- 4.2 deg if the injection is isotropic, phi=64 +/- 2.8 deg for quasi-perpendicular injection (SNR has an equatorial belt in both cases) and phi=11 +/- 0.8 deg for quasi-parallel injection (polar-cap model of SNR). In the last case, SN 1006 is expected to have a centrally-peaked morphology contrary to what is observed. Therefore, our analysis provides some indication against the quasi-parallel injection model.

astro-ph↗

arXiv2008

High resolution CO observations towards the Bright Eastern Knot of the SNR Puppis A

This paper reports molecular observations towards the Bright Eastern Knot (BEK) in the SNR Puppis A, a feature where radio and X-ray studies suggest that the shock front is interacting with a dense molecular clump. We performed high-resolution millimetric observations towards the BEK of Puppis A using the SEST telescope in the 12CO J=1-0 and 2-1 lines (beams of 45" and 23" respectively). More extended, lower angular resolution 12CO J=1-0 observations taken from NANTEN archival data were also analyzed to obtain a complete picture. In the velocity range near 16 km/s, the Puppis A systemic velocity, our study revealed two important properties: (i) no dense molecular gas is detected immediately adjacent to the eastern border of the BEK and (ii) the molecular clump detected very close to the radiocontinuum maximum is probably located in the foreground along the line of sight and has not yet been reached by the SNR shock front. We propose two possible scenarios to explain the absence of molecular emission eastwards of the BEK border of Puppis A. Either the shock front has completely engulfed and destroyed a molecular clump or the shock front is interacting with part of a larger cloud and we do not detect CO emission immediately beyond it because the molecules have been dissociated by photodissociation and by reactions with photoionized material due to the radiative precursor.

astro-ph↗

arXiv2007

The low frequency radio emission and spectrum of the extended SNR W44: new VLA observations at 74 and 324 MHz

We present new Very Large Array (VLA) radio images at 74 and 324 MHz of the SNR W44. The VLA images, obtained with unprecedented angular resolution and sensitivity for such low frequencies have been used in combination with existing 1442 MHz radio data, Spitzer IR data, and ROSAT and Chandra X-ray data to investigate morphological and spectral properties of this SNR. The spatially resolved spectral index study revealed that the bright filaments, both around and across the SNR, have a straight spectrum between 74 and 1442 MHz, with alpha ~ -0.5, with two clear exceptions: a short portion of the SNR limb to the southeast, with alpha varying between 0 and +0.4 and a bright arc to the west where the spectrum breaks around 300 MHz and looks concave down. We conclude that at the shell and along the internal filaments, the electrons responsible for the synchrotron emission were accelerated at the shock according to a simple diffusive shock model; the positive spectrum corresponds to a location where the SN shock is running into a molecular cloud and where the line of sight intersects the photo dissociation region of an HII region and a young stellar object is present. The curved spectrum on the westernmost bright arc is explained as the consequence of strong post-shock densities and enhanced magnetic fields after the interaction of the SN shock with a collindant molecular cloud.

astro-ph↗

arXiv2006

A New Young Galactic Supernova Remnant Containing a Compact Object: G15.9+0.2

We identify the radio-emitting shell-type supernova remnant G15.9+0.2 as a relatively young remnant containing an X-ray point source that may be its associated neutron star. The integrated spectrum of the remnant shell obtained from our 30 ks exploratory Chandra observation shows very strong lines that require elevated element abundances from ejecta, in particular of sulfur. A plane-shock model fit gives a temperature $kT = 0.9 (0.8, 1.0)$ keV, an ionization timescale $n_et = 6 (4, 9) \times 10^{10}$ cm$^{-3}$ s, and a sulfur abundance of 2.1 (1.7, 2.7) times solar (90% confidence limits). Two-component models with one solar and one enriched component are also plausible, but are not well constrained by the data. Various estimates give a remnant age of order $10^3$ yr, which would make G15.9+0.2 among the dozen or so youngest remnants in the Galaxy. The sparse point source spectrum is consistent with either a steep $Γ\sim$ 4 power law or a $kT \sim$ 0.4 keV blackbody. The spectrum is absorbed by a H column density $N_H \sim 4 \times 10^{22}$ cm$^{-2}$ similar to that required for the remnant shell. The implied 2--9.5 keV source luminosity is about $10^{33}$ ergs s$^{-1}$ for an assumed distance of 8.5 kpc consistent with the high absorption column. We suggest that the point source is either a rotation-powered pulsar or a compact central object (CCO).

astro-ph↗

arXiv2006

New VLA observations of the SNR Puppis A: the radio properties and the correlatoin withe the X-ray emission

In this paper we report on a new study of the SNR Puppis A based on VLA observations at 1425 MHz; the improvement represents a factor of two in angular resolution and almost ten times in sensitivity compared to the best previous image of Puppis A. This new image is used to compare with re-processed 327 MHz data and ROSAT and Chandra images to investigate morphological and spectral characteristics.

astro-ph↗