XMM-Newton observations of 1A 0535+262 in quiescence

Accretion onto magnetized neutron stars is expected to be centrifugally inhibited at low accretion rates. Several sources, however, are known to pulsate in quiescence at luminosities below the theoretical limit predicted for the onset of the centrifugal barrier. The source 1A 0535+262 is one of them. Here we present the results of an analysis of a ~50 ks long XMM-Newton observation of 1A 0535+262 in quiescence. At the time of the observation, the neutron star was close to apastron, and the source had remained quiet for two orbital cycles. In spite of this, we detected a pulsed X-ray flux of ~3e-11 erg/cm2/s . Several observed properties, including the power spectrum, remained similar to those observed in the outbursts. Particularly, we have found that the frequency of the break detected in the quiescent noise power spectrum follows the same correlation with flux observed when the source is in outburst. This correlation has been associated with the truncation of the accretion disk at the magnetosphere boundary. We argue that our result, along with other arguments previously reported in the literature, suggests that the accretion in quiescence also proceeds from an accretion disk around the neutron star. The proposed scenario consistently explains the energy of the cyclotron line observed in 1A 0535+262, and the timing properties of the source including the spin frequency evolution within and between the outbursts, and the frequency of the break in power spectrum.Comment: 7 pages, 5 figures, accepted for publication in A&

Orbit and intrinsic spin-up of the newly discovered transient X-ray pulsar Swift J0243.6+6124

We present the orbital solution for the newly discovered transient Be X-ray binary Swift J0243.6+6124 based on the data from gamma-ray burst monitor onboard Fermi obtained during the Oct 2017 outburst. We model the Doppler induced and intrinsic spin variations of the neutron star assuming that the later is driven by accretion torque and discuss the implications of the observed spin variations for the parameters of the neutron star and the binary. In particular we conclude that the neutron star must be strongly magnetized, and estimate the distance to the source at $\sim$5 kpc.Comment: accepted in A&

Expansion and ongoing cosmic ray acceleration in HESS J1731-347

Diffusive shock acceleration in supernova remnants (SNRs) is considered one of the prime mechanisms for Galactic Cosmic Ray (GCR) acceleration. It is still unclear, however, whether SNRs can contribute to GCR spectrum up to the ``knee'' (1\,PeV) band as acceleration to such energies requires an efficient magnetic field amplification process around the shocks. The presence of such a process is challenging to test observationally. Here we report on the detection of fast variability of the X-ray synchrotron emission from the forward shock in the supernova remnant HESS J1731-347, which implies the presence of a strong ($\sim$0.2\,mG) field exceeding background values and thus of effective field amplification. We also report a direct measurement of the high forward shock expansion velocity of 4000-5500\,km/s confirming that the SNR is expanding in a tenuous wind bubble blown by the SNR progenitor, is significantly younger (2.4-9\,kyr) than previously assumed by some authors, and only recently started interaction with the dense material outside the bubble. We finally conclude that there is strong evidence for ongoing hadronic CR acceleration in this SNR.Comment: 6 pages 3 figures, accepted in A&

XRBcats: Galactic High Mass X-ray Binary Catalogue

We present a new catalogue of the high-mass X-ray binaries (HMXBs) in the Galaxy improving upon the most recent such catalogue. We include new HMXBs discovered since aforementioned publication and revise the classification for several objects previously considered HMXBs or candidates. The catalogue includes both basic information such as source names, coordinates, types, and more detailed data such as distance and X-ray luminosity estimates, binary system parameters and other characteristic properties of 169 HMXBs, together with appropriate references to the literature. Finding charts in several bands from infra-red to hard X-rays are also included for each object. The aim of this catalogue is to provide the reader a list of all currently known Galactic HMXBs with some basic information on both compact objects and non-degenerate counterpart properties (where available). We also include objects tentatively classified as HXMBs in the literature and give a brief motivation for the classifcation in each relevant case. The catalogue is compiled based on a search of known HMXBs and candidates in all commonly available databases and literature published before 31 October 2022. Relevant properties in the optical and other bands were collected for all objects either from the literature or using the data provided by large-scale surveys. In the later case, the counterparts in each individual survey were found by cross-correlating positions of identified HMXBs with relevant databases. An up-to date catalogue of Galactic HMXBs is presented to facilitate research in this area. An attempt was made to collect a larger set of relevant HMXB properties in a more uniform way compared to previously published works.Comment: 10 pages, 2 figures, submitted to A&A. For auxillary files, see http://astro.uni-tuebingen.de/~xrbcat

Interfacing liquid chromatography with atmospheric pressure MALDI-MS

Two different strategies for coupling liquid chromatography with atmospheric pressure matrix assisted laser desorption/ionization (AP MALDI) are presented. The first method is flow-injection liquid AP UV-MALDI. Compared with previous similar research, the detection limit was improved 10 times to 8.3fmol using a solution of 50nM peptide with 25mM α-cyano-4-hydroxycinnamic acid. The applicability of this method to measure oligosaccharides, actinomycin antibiotics, antibiotics, phosphopeptides, and proteins is demonstrated. The upper mass limit achieved with the current instrumentation is 6,500Da (doubly charged cytochrome c). The feasibility of a second strategy based on single-droplet IR AP MALDI is demonstrated here. Aqueous peptide solutions were successfully measured by this metho

Cyclotron emission, absorption, and the two faces of X-ray pulsar A 0535+262

Deep NuSTAR observation of X-ray pulsar A 0535+262, performed at a very low luminosity of $\sim7\times10^{34}$ erg s$^{-1}$, revealed the presence of two spectral components. We argue that the high-energy component is associated with cyclotron emission from recombination of electrons collisionally excited to the upper Landau levels. The cyclotron line energy of $E_{\rm cyc}=47.7\pm0.8$ keV was measured at the luminosity of almost an order of magnitude lower than what was achieved before. The data firmly exclude a positive correlation of the cyclotron energy with the mass accretion rate in this source.Comment: 5 pages, 3 figures, accepted by MNRAS Letter

Expected polarization properties of nonmagnetized CCOs

Central compact objects (CCOs) are neutron stars found close to the center of some supernova remnants. A certain number of them are presumably covered by carbon envelopes. Their unpulsed thermal X-ray emission can originate either from the entire surface covered by a carbon atmosphere or alternatively from a nonuniformly emitting hydrogen atmosphere. However, the latter scenario appears unlikely given the available upper limits on the amplitude of pulsations. Here we explore a possibility to further discriminate between the two scenarios using X-ray polarimetric observations. We compute the polarization degree (PD) for nonmagnetized pure-carbon and pure-hydrogen atmospheres with effective temperatures of between 1 and 6 MK and find that it can reach up to 25% and 40% for hydrogen and carbon atmospheres, respectively, in the photon energy band 1-10 keV. However, given the available constraints on possible inhomogeneities of the temperature distribution deduced from models of the X-ray spectrum of the CCO in HESS J1731-347, the integrated PD appears to be very low for both carbon (<0.25%) and hydrogen (a few percent) compositions in the energy band of 2-8 keV covered by the recently launched Imaging X-ray Polarimetry Explorer. We therefore conclude that polarization from CCOs is not expected to be detectable by current facilities, but future detection would strongly support nonuniform hydrogen composition models.Comment: 10 pages, 16 figures. accepted to be published by A&A, corrected after the language Editor remarks, misprints in some numbers were corrected, a new version of Fig.1