arXiv subjects

Gerd Puehlhofer

Publications and source records attributed to Gerd Puehlhofer.

9 recordsLinked to original sources

arXiv2025

eROSITA X-ray Analysis of the PeVatron Candidate Westerlund 1

It is unclear which fraction of cosmic rays above an energy of 1 PeV is accelerated by the observed Galactic PeVatron population. These sources' gamma-ray data is typically degenerate between hadronic and leptonic emission scenarios, which hinders their straightforward association with the cosmic ray population. Here, we aimed to distinguish between leptonic and hadronic particle acceleration scenarios for the PeVatron candidate HESS J1646-458, associated with the star cluster Westerlund 1 (Wd 1). We first studied the diffuse X-ray emission from Wd 1 to better understand if its origin is of thermal or nonthermal nature. In addition, we searched for X-ray synchrotron emission from the associated PeVatron candidate HESS J1646-458 to put new constraints on the magnetic field strength and the leptonic particle population of this source. We used data from eROSITA on board the SRG orbital platform to spectrally analyze the diffuse emission from Wd 1 and HESS J1646-458. For Wd 1, we compared a purely thermal model and a model with a thermal and a nonthermal component. Next, we analyzed the spectra of four annuli around Wd 1 which coincide with HESS J1646-458 to search for synchrotron radiation. We find that eROSITA data cannot distinguish between thermal and nonthermal source scenarios for the diffuse emission from Wd 1 itself. In the case of HESS J1646-458, we find no evidence of synchrotron emission. We estimated an upper confidence bound of the synchrotron flux up to 40' around Wd 1 of 1.9e-3 keV-1 cm-2 s-1, which we used to study the spectral energy distribution of the source. From this, we obtained an upper 1 sigma bound on the magnetic field strength of HESS J1646-458 of 7 uG. This is compatible with a previous estimate in the literature for a fully leptonic source scenario. A purely leptonic emission scenario, a hadronic, and a hybrid one are compatible with our results.

astro-ph.HE↗

arXiv2024

Study of X-ray emission from the S147 nebula by SRG/eROSITA: supernova-in-the-cavity scenario

The Simeis~147 nebula (S147), particularly well known for a spectacular net of ${\rm H}_α$-emitting filaments, is often considered one of the largest and oldest known supernova remnants in the Milky Way. Here, and in a companion paper, we present studies of X-ray emission from the S147 nebula using the data of SRG/eROSITA All-Sky Survey observations. In this paper, we argue that many inferred properties of the X-ray emitting gas are broadly consistent with a scenario of the supernova explosion in a low-density cavity, e.g. a wind-blown-bubble. This scenario assumes that a $\sim 20\,{\rm M_\odot}$ progenitor star has had small velocity with respect to the ambient ISM, so it stayed close to the center of a dense shell created during its Main Sequence evolution till the moment of the core-collapse explosion. The ejecta first propagate through the low-density cavity until they collide with the dense shell, and only then the reverse shock goes deeper into the ejecta and powers the observed X-ray emission of the nebula. The part of the remnant inside the dense shell remains non-radiative till now and, plausibly, in a state with $T_e<T_i$ and Non-Equilibrium Ionization (NEI). On the contrary, the forward shock becomes radiative immediately after entering the dense shell, and, being subject to instabilities, creates a characteristic "foamy" appearance of the nebula in ${\rm H}_α$ and radio emission.

astro-ph.HE↗

arXiv2016

Evidence for a binary origin of a central compact object

Central compact objects (CCOs) are thought to be young thermally emitting isolated neutron stars that were born during the preceding core-collapse supernova explosion. Here we present evidence that at least in one case the CCO could have been formed within a binary system. We show that the highly reddened optical source IRAS~17287$-$3443, located $25^{\prime \prime}$ away from the CCO candidate XMMUJ173203.3$-$344518 and classified previously as a post asymptotic giant branch star, is indeed surrounded by a dust shell. This shell is heated by the central star to temperatures of $\sim90$\,K and observed as extended infrared emission in 8-160\,$μ$m band. The dust temperature also increases in the vicinity of the CCO which implies that it likely resides within the shell. We estimate the total dust mass to be $\sim0.4-1.5\,M_\odot$ which significantly exceeds expected dust yields by normal stars and thus likely condensed from supernova ejecta. Taking into account that both the age of the supernova remnant and the duration of active mass loss phase by the optical star are much shorter than the total lifetime of either object, the supernova and the onset of the active mass loss phase of the companion have likely occurred approximately simultaneously. This is most easily explained if the evolution of both objects is interconnected. We conclude, therefore, that both stars were likely members of the same binary system disrupted by a supernova.

astro-ph.HE↗

arXiv2014

XMM-Newton observation of the Galactic supernova remnant W51C (G49.1-0.1)

The supernova remnant (SNR) W51C is a Galactic object located in a strongly inhomogeneous interstellar medium with signs of an interaction of the SNR blast wave with dense molecular gas. Diffuse X-ray emission from the interior of the SNR can reveal element abundances in the different emission regions and shed light on the type of supernova (SN) explosion and its progenitor. The hard X-ray emission helps to identify possible candidates for a pulsar formed in the SN explosion and for its pulsar wind nebula (PWN). We have analysed X-ray data obtained with XMM-Newton. Spectral analyses in selected regions were performed. Ejecta emission in the bright western part of the SNR, located next to a complex of dense molecular gas, was confirmed. The Ne and Mg abundances suggest a massive progenitor with a mass of > 20 M_sun. Two extended regions emitting hard X-rays were identified (corresponding to the known sources [KLS2002] HX3 west and CXO J192318.5+140305 discovered with ASCA and Chandra, respectively), each of which has an additional point source inside and shows a power-law spectrum with Gamma ~ 1.8. Based on their X-ray emission, both sources can be classified as PWN candidates.

astro-ph.HE↗

arXiv2013

An X-ray counterpart of HESS J1427-608 discovered with Suzaku

We report the discovery of an X-ray counterpart of the unidentified very high energy gamma-ray source HESS J1427-608. In the sky field coincident with HESS J1427-608, an extended source was found in the 2-8 keV band, and was designated as Suzaku J1427-6051. Its X-ray radial profile has an extension of sigma=0.9' +/- 0.1' if approximated by a Gaussian. The spectrum was well fitted by an absorbed power-law with N_H=(1.1 +/- 0.3) times 10^23 cm^-2, Gamma=3.1 +0.6/-0.5, and the unabsorbed flux F_X=(9 +4/-2) times 10^-13 erg s^-1 cm^-2 in the 2-10 keV band. Using XMM-Newton archive data, we found seven point sources in the Suzaku source region. However, because their total flux and absorbing column densities are more than an order of magnitude lower than those of Suzaku J1427-6051, we consider that they are unrelated to the Suzaku source. Thus, Suzaku J1427-6051 is considered to be a truly diffuse source and an X-ray counterpart of HESS J1427-608. The possible nature of HESS J1427-608 is discussed based on the observational properties.

astro-ph.HE↗

arXiv2012

Suzaku Observations of the Non-thermal Supernova Remnant HESS J1731-347

A detailed analysis of the nonthermal X-ray emission from the North-Western and Southern parts of the supernova remnant (SNR) HESS J1731$ - $347 with {\it Suzaku} is presented. The shell portions covered by the observations emit hard and line-less X-rays. The spectrum can be reproduced by a simple absorbed power-law model with a photon index $Γ$ of 1.8-2.7 and an absorption column density $N_{\rm H}$ of (1.0-2.1)$\times 10^{22}$ cm$^{-2}$. These quantities change significantly from region to region; the North-Western part of the SNR has the hardest and most absorbed spectrum. The Western part of the X-ray shell has a smaller curvature than North-Western and Southern shell segments. A comparison of the X-ray morphology to the Very High Energy (VHE) gamma-ray and radio images was performed. The efficiency of electron acceleration and emission mechanism in each portion of the shell are discussed. Thermal X-ray emission from the SNR was searched for but could not be detected at a significant level.

astro-ph.HE↗

arXiv2011

Suzaku observation of the unidentified VHE gamma-ray source HESS J1702-420

A deep X-ray observation of the unidentified very high energy (VHE) gamma-ray source HESS J1702-420, for the first time, was carried out by Suzaku. No bright sources were detected in the XIS field of view (FOV) except for two faint point-like sources. The two sources, however, are considered not to be related to HESS J1702-420, because their fluxes in the 2-10 keV band (~ 10^-14 erg s^-1 cm^-2) are ~ 3 orders of magnitude smaller than the VHE gamma-ray flux in the 1-10 TeV band (F_{TeV} = 3.1 x 10^-11 erg s^-1 cm^-2). We compared the energy spectrum of diffuse emission, extracted from the entire XIS FOV with those from nearby observations. If we consider the systematic error of background subtraction, no significant diffuse emission was detected with an upper limit of F_X <2.7 x 10^-12 erg s^-1 cm^-2 in the 2-10 keV band for an assumed power-law spectrum of Γ=2.1 and a source size same as that in the VHE band. The upper limit of the X-ray flux is twelve times as small as the VHE gamma-ray flux. The large flux ratio (F_{TeV}/F_X) indicates that HESS J1702-420 is another example of a "dark" particle accelerator. If we use a simple one-zone leptonic model, in which VHE gamma-rays are produced through inverse Compton scattering of the cosmic microwave background and interstellar far-infrared emission, and the X-rays via the synchrotron mechanism, an upper limit of the magnetic field (1.7 μG) is obtained from the flux ratio. Because the magnetic field is weaker than the typical value in the Galactic plane (3-10 μG), the simple one-zone model may not work for HESS J1702-420 and a significant fraction of the VHE gamma-rays may originate from protons.

astro-ph.HE↗

arXiv2010

Detailed Studies of Atmospheric Calibration in Imaging Cherenkov Astronomy

The current generation of Imaging Atmospheric Cherenkov telescopes are allowing the sky to be probed with greater sensitivity than ever before in the energy range around and above 100 GeV. To minimise the systematic errors on derived fluxes a full calibration of the atmospheric properties is important given the calorimetric nature of the technique. In this paper we discuss an approach to address this problem by using a ceilometer co-pointed with the H.E.S.S. telescopes and present the results of the application of this method to a set of observational data taken on the active galactic nucleus (AGN) PKS 2155-304 in 2004.

astro-ph.IM↗

arXiv2008

X-Ray Observation of Very High Energy Gamma-Ray Source, HESS J1745-303, with Suzaku

Suzaku observations of a TeV unidentified (unID) source, HESS J1745-303, are presented. A possible excess of neutral iron line emission is discovered, and is likely associated with the main part of HESS J1745-303, named "region A". It may be an X-ray reflection nebula where the X-rays from previous Galactic Center (GC) activity are reflected by a molecular cloud. This result further strengthens the assumption that the molecular cloud which is spatially coincident with region A of HESS J1745-303 is located in the GC region. The TeV emission from molecular clouds is reminiscent of the diffuse TeV gamma-rays from the GC giant molecular clouds, and it could have the same emission mechanism. With deep exposure mapping observations by Suzaku, a tight upper-limit on the 2-10 keV continuum diffuse emission from region A is obtained, as 2.1x10^-13ergs s^-1cm^-2. The flux ratio between 1-10 TeV and 2-10 keV is larger than 4. Possible scenarios to reproduce wide-band spectra from keV to TeV are examined. Thermal X-rays from nearby two old supernova remnants, G359.0-0.9 and G359.1-0.5, are detected, and their emission properties are well determined in the present study with deep exposure.

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