arXiv subjects

G. Dubner

Publications and source records attributed to G. Dubner.

49 records · Page 3Linked to original sources

arXiv2006

An Atomic and Molecular Study of the Interstellar Medium Around the SNR RCW 103

We report on the detection of HCO+ and 12CO emission in the rotational transition J=1-0 in the vicinity of the shock front at the southern border of the supernova remnant RCW 103, where previous infrared observations suggest an interaction with a molecular cloud. The observations were carried out with the Australian Millimeter Radiotelescope at Mopra. We observed a depletion of HCO+ behind the supernova shock front. In addition, we studied the interstellar medium over an extended region towards RCW 103 based on archival 21 cm HI line observations from the Australia Telescope Compact Array (ATCA) and the Parkes Telescope. No atomic gas is observed in emission in coincidence with the molecular feature. This absence is interpreted in terms of self absorption processes.

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arXiv2005

The interior of the SNR RX J0852.0-4622 (Vela Jr) at radio wavelengths

Aim: We observed the center of the supernova remnant Vela Jr in radio continuum in order to search for a counterpart to the compact central X-ray source CXOU J085201.4-461753, possibly a neutron star candidate which could be the remnant of the supernova explosion. Method: Observations were made with the Australia Telescope Compact Array at 13 and 20 cm. Spectral indices were obtained using flux density correlations of the data which were spatially filtered to have the same u-v coverage. A multiwavelength search for counterparts to the compact central X-ray source was made. Results: We compiled a new catalogue of 31 small diameter radio sources, including the previously known source PMN J0853-4620, listing the integrated flux densities at 20 cm and, for half of the sources, the flux densities at 13 cm with the corresponding spectral indices. All sources are unresolved at the present angular resolution except for Source 18, which is clearly elongated and lies strikingly close to CXOU J085201.4-461753. Our observations show no evidence for the existence of a pulsar wind driven nebula associated with the point X-ray source. Furthermore, Source 18 has a thermal spectrum with index +0.8 +/- 0.4, and appears to be the counterpart of the optical source Wray 16-30. In spite of the absence of OIII emission lines as reported in the literature, we find that this object could be explained as a low emission planetary nebula belonging to the ``butterfly'' morphological class. Conclusions: We conclude that if the radio source 18 is actually a planetary nebula, then CXOU J085201.4-461753 is more likely to be related to it rather than to Vela Jr.

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arXiv2005

Radio and X-Ray Emission Associated with the Supernova Remnant G352.7-0.1

We report on new VLA radio and XMM-Newton X-ray observations of the SNR G352.7-0.1. These high sensitivity, high resolution data reveal that G352.7-0.1 belongs to the thermal composite morphological class. Small scale structures in radio and X-ray emission are not always correlated and are different for the different X-rays bands examined. The distance to G352.7-0.1 can be constrained between 6.6 and 8.4 kpc. The study of the HI suggests that G352.7-0.1 is located within a cavity probably created by the stellar wind of the precursor star.

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arXiv2005

G0.57-0.018: A young supernova remnant? INTEGRAL and VLA observations

We report INTEGRAL/IBIS gamma-ray and VLA radio observations of G0.570-0.018, a diffuse X-ray source recently discovered by ASCA and Chandra in the Galactic center region. Based on its spectrum and morphology, G0.570-0.018 has been proposed to be a very young supernova remnant. In this scenario, the presence of gamma-ray lines coming from the short-lived radioactive nucleus 44Ti as well as synchrotron radio continuum emission are expected. The first could provide informations on nucleosynthesis environments in the interior of exploding stars, the latter could probe the interaction between the supernova blast wave and the circumstellar/interstellar matter. We have not detected 44Ti lines nor any conspicuous radio feature associated with this source down to the achieved sensitivities. From the derived upper limits we set constraints on the nature of G0.570-0.018.

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arXiv2005

A multi-frequency study of the spectral index distribution in the SNR CTB 80

We have conducted a study at radio wavelengths of the spectral behaviour of the supernova remnant (SNR) CTB 80. Based on an homogenised data set of integrated flux densities, we calculated for the whole SNR a radio index -0.36 +/- 0.02. The shape of the global spectrum suggests absorption by ionized gas in the interstellar medium (ISM) along the line of sight. Spatial spectral variations across the SNR are investigated based on high-angular resolution data at 240, 324, 610, and 1380 MHz using different techniques. The three extended arms associated with this SNR, show a clear indication of spectral steepening when moving outwards from the central nebula, with variations of up to - 0.9. However, while the spectral steepening is smooth along the eastern arm, the northern and soutwestern arms include locally flatter structures, which in all cases coincide with radio, IR, and optical emission enhancements. We interpret this spectral property as the result of the combination of two different particle populations: aging relativistic electrons injected by PSR B1951+32 and particles accelerated at the sites where the SNR shock front encounters interstellar gas inhomogeneities. Concerning the central nebula, the angular resolution of the available database does not permit a detailed spectral study of the core region, i.e. the 45'' region around PSR B1951+32, where we can only confirm an average spectral index alpha=0.0. The surrounding 8' plateau nebula has an ~ -0.25, with a peak of alpha ~ -0.29 coincident with a secondary maximun located at the termination of a twisted filament that trails to the east, behind the pulsar.

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arXiv2005

The neutral gas in the environs of the Geminga gamma-ray pulsar

We present a high-resolution (24 arcsec) study of the HI interstellar gas distribution around the radio-quiet neutron star Geminga. Based on Very Large Array (VLA) and MPIfR Effelsberg telescope data, we analyzed a 40' x 40' field around Geminga. These observations have revealed the presence of a neutral gas shell, 0.4 pc in radius, with an associated HI mass of 0.8 Msun, which surrounds Geminga at a radial velocity compatible with the kinematical distance of the neutron star. In addition, morphological agreement is observed between the internal face of the HI shell and the brightest structure of Geminga's tail observed in X-rays.We explore the possibility that this morphological agreement is the result of a physical association.

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arXiv2005

A Multi-Wavelength Study of the Western Lobe of W50 Powered by the Galactic Microquasar SS 433

W50 remains the only supernova remnant (SNR) confirmed to harbor a microquasar: the powerful enigmatic source SS 433. Our past study of this fascinating SNR revealed two X-ray lobes distorting the radio shell as well as non-thermal X-rays at the site of interaction between the SS 433 eastern jet and the eastern lobe of W50. In this paper we present the results of a 75 ksec CHANDRA ACIS-I observation of the peak of W50-west targeted to 1) determine the nature of the X-ray emission and 2) correlate the X-ray emission with that in the radio and infrared domains. We have confirmed that at the site of interaction between the western jet of SS 433 and dense interstellar gas the X-ray emission is non-thermal in nature. The helical pattern observed in radio is also seen with CHANDRA. No correlation was found between the infrared and X-ray emission.

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arXiv2004

Chandra Spatially Resolved Spectroscopic Study and Multi-Wavelength Imaging of the Supernova Remnant 3C 397 (G41.1-0.3)

(Abridged) We present a Chandra observation of the supernova remnant (SNR) 3C 397 (G41.1-0.3) obtained with ACIS-S. Previous studies of this SNR have shown that it harbors a central X-ray `hot spot' suggestive of a compact object associated with 3C 397. With the Chandra data, we can rule out the nature of the hot spot as a pulsar or a pulsar wind nebula, and put an upper limit on the flux of a hidden compact object of F (0.5--10 keV)~6E-13 erg/cm2/s. We found two point sources in the Chandra field. We argue that none of them is associated with 3C 397; and that the hard source, CXO J190741.2+070650, is a newly discovered AGN. The Chandra image reveals arcseconds-scale clumps and knots which are strongly correlated with the radio VLA image, except for the X-ray hot spot. Our Chandra spatially resolved spectroscopic study shows that one-component models are inadequate, and that at least two non-equilibrium ionization thermal components are needed to fit the spectra of each selected region. The derived average spectral parameters are consistent with the previous global ASCA fits performed by Safi-Harb et al. (2000). However, the hard component requires a high abundance of Fe indicating the presence of hot Fe ejecta. When comparing the eastern with the western lobe, we find that the column density, the brightness, and the ionization timescales are generally higher for the western side. This result, combined with our study of the 3C397 environs at millimeter wavelengths, indicate a denser medium to the west of the SNR. Our multi-wavelength imaging and spectral study favors the scenario where 3C 397 is a ~5,300-year old SNR expanding in a medium with a marked density gradient, and which is likely to be encountering a molecular cloud on the western side. We propose that 3C 397 will evolve into a mixed-morphology SNR.

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arXiv2004

XMM-Newton observations of the supernova remnant RX J1713.7-3946 and its central source

We present new results coming from the observations of the supernova remnant (SNR) RX J1713.7--3946 (also G347.3--0.5) performed in five distinct pointings with the EPIC instrument on board the satellite XMM-Newton. RX J1713.7--3946 is a shell-type SNR dominated by synchrotron radiation in the X-rays. Its emission (emission measure and photon index) as well as the absorption along the line-of-sight has been characterized over the entire SNR. The X-ray mapping of the absorbing column density has revealed strong well constrained variations (0.4 10^22 cm^-2 < NH < 1.1 10^22 cm^-2) and, particularly, a strong absorption in the southwest. Moreover, there are several clues indicating that the shock front of RX J1713.7--3946 is impacting the clouds responsible for the absorption as revealed for instance by the positive correlation between X-ray absorption and X-ray brightness along the western rims. The CO and HI observations show that the inferred cumulative absorbing column densities are in excellent agreement with the X-ray findings in different places of the remnant on condition that the SNR lies at a distance of 1.3 +/- 0.4 kpc, probably in the Sagittarius galactic arm, instead of the commonly accepted value of 6 kpc. An excess in the CO emission is found in the southwest suggesting that the absorption is due to molecular clouds. A search for OH masers in the southwestern region has been unsuccessful, possibly due to the low density of the clouds. The X-ray mapping of the photon index has also revealed strong variations (1.8 < Gamma < 2.6). [See the article for the entire abstract]

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arXiv2003

XMM-Newton observation of SNR RX J1713.7-3946

We present the first results of the observations of the supernova remnant RX J1713.7-3946 (also G347.3-0.5) obtained with the EPIC instrument on board the XMM-Newton satellite. We show a 5 pointings mosaiced image of the X-ray synchrotron emission. We characterize this emission by mapping its spectral parameters (absorbing column density NH and photon index). The synchrotron spectrum is flat at the shock and steep in the interior of the remnant. NH is well correlated with the X-ray brightness. A strong NH is found in the southwest rim of RX J1713.7-3946. We suggest that the SNR is interacting with a HI region there.

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arXiv2003

New high-resolution radio observations of the SNR CTB 80

We report new high resolution and high sensitivity radio observations of the extended supernova remnant (SNR) CTB 80 (G69.0+2.7) at 240 MHz, 324 MHz, 618 MHz, and 1380 MHz. The imaging of CTB 80 at 240 MHz and 618 MHz was performed using the Giant Metrewave Radio Telescope (GMRT) in India. The observations at 324 MHz and 1380 MHz were obtained using the Very Large Array (VLA, NRAO) in its C and D configurations. The new radio images reveal faint extensions for the asymmetric arms of CTB 80. The arms are irregular with filaments and clumps of size 1' (or 0.6 pc at a distance of 2 kpc). The radio image at 1380 MHz is compared with IR and optical emission. The correspondence IR/radio is excellent along the N arm of CTB 80. Ionized gas observed in the [SII] line perfectly matches the W and N edges of CTB 80. The central nebula associated with the pulsar PSR B1951+32 was investigated with an angular resolution of 10" x 6". The new radio image obtained at 618 MHz shows with superb detail structures in the 8' x 4' E-W ``plateau'' nebula that hosts the pulsar on its western extreme. A twisted filament, about 6' in extent (~3.5 pc), trails behind the pulsar in an approximate W-E direction. In the bright ``core'' nebula (size \~45"), located to the W of the plateau, the images show a distortion in the morphology towards the W; this feature corresponds to the direction in which the pulsar escapes from the SNR with a velocity of ~240 km/s. Based on the new observations, the energetics of the SNR and of the PWN are investigated.

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arXiv2001

Environs of Bilateral Supernova Remnants with Neutron Stars

We report on Australia Telescope Compact Array (ATCA) HI observations carried out in the direction of bilateral supernova remnants (SNRs) with associated neutron stars: G296.5+10.0 and G320.4--1.2, in a search for the origin of such morphology. From these studies we conclude that in the case of G296.5+10.0, located far from the Galactic plane, the HI distribution has not influenced the present morphology of the SNR. In the case of G320.4--1.2, evolving in a denser medium, the combined action of the central pulsar, PSR B1509-58, with the peculiar distribution of the surrounding medium, has determined the observed characteristics of the SNR.

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arXiv1996

The Pulsar Wind Nebula Around PSR B1853+01 in the Supernova Remnant W44

We present radio observations of a region in the vicinity of the young pulsar PSR B1853+01 in the supernova remnant W44. The pulsar is located at the apex of an extended feature with cometary morphology. We argue on the basis of its morphology and its spectral index and polarization properties that this is a synchrotron nebula produced by the spin down energy of the pulsar. The geometry and physical parameters of this pulsar-powered nebula and W44 are used to derive three different measures of the pulsar's transverse velocity. A range of estimates between 315 and 470 km/s are derived, resulting in a typical value of 375 km/s. The observed synchrotron spectrum from radio to X-ray wavelengths is used to put constraints on the energetics of the nebula and to derive the parameters of the pulsar wind.

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