RX J1713 Research Articles

Search for the Galactic accelerators of cosmic rays up to the knee with the Pevatron test statistic

ABSTRACT The Pevatron test statistic (PTS) is applied to data from γ-ray observatories to test for the origin of cosmic rays (CRs) at energies around the knee of the CR spectrum. Several sources are analysed within hadronic emission models. Previously derived results for RX J1713.7−3946, Vela Jr, and HESS J1745−290 are confirmed to demonstrate the concept, reliability, and advantages of the PTS. It is excluded with a significance more than 5σ that the sources RX J1713.7−3946 and Vela Jr are Pevatrons, while strong indications exceeding 4σ are found for excluding HESS J1745−290 as a Pevatron. The importance to resolve source confusion with high angular resolution observations for Pevatrons searches is demonstrated using PTS for the region containing the SNR G106.3+2.7 and the Boomerang nebula. No statistically significant conclusion with respect to Pevatron associations could be drawn from this region, for the diffuse γ-ray emission around the Galactic Centre, and the unidentified γ-ray sources LHAASO J2108+5157, HESS J1702−420A, and MGRO J1908+06. Assuming the entire γ-ray emission from MGRO J1908+06 and the tail region of SNR G106.3+2.7 are hadronic, a statistical indication exceeding 3σ is found for the underlying proton spectrum to extend beyond 350–400 TeV as a power law. This result can indicate that these sources are proton and helium Pevatrons, in which the accelerated particles contribute to the knee of proton and helium spectra observed at Earth.

Timing the X-ray pulsating companion of the hot subdwarf HD 49798 with NICER

ABSTRACT HD 49798 is a hot subdwarf of O spectral type in a 1.55 d orbit with the X-ray source RX J0648.0−4418, a compact object with a spin period of $13.2\,$s. We use recent data from the Neutron Star Interior Composition Explorer instrument, joined with archival data from XMM–Newton and ROSAT, to obtain a phase-connected timing solution spanning ∼30 yr. Contrary to previous works, which relied on parameters determined through optical observations, the new timing solution could be derived using only X-ray data. We confirm that the compact object is steadily spinning up with $\dot{P} = -2.28(2) \times 10^{-15}\,$s s−1 and obtain a refined measure of the projected semimajor axis of the compact object aXsin i = 9.60(5) light-second. This allows us to determine the inclination and masses of the system as $i=84.5(7)\,$deg, MX = 1.220(8) $\rm {M}_\odot$, and $M_{\rm opt}=1.41(2)\,$$\rm {M}_\odot$. We also study possible long-term (approximately years) and orbital variations of the soft X-ray pulsed flux, without finding evidence for variability. In the light of the new findings, we discuss the nature of the compact object, concluding that the possibility of a neutron star in the subsonic propeller regime is unlikely, while accretion of the subdwarf wind on to a massive white dwarf can explain the observed luminosity and spin-up rate for a wind velocity of ∼800 km s−1.

Forecast of Observing Time Delay of Strongly Lensed Quasars with the Muztagh-Ata 1.93 m Telescope

As a completely independent method, the measurement of time delay of strongly lensed quasars (TDSL) are crucial to resolve the Hubble tension. Extensive monitoring is required but so far limited to a small sample of strongly lensed quasars. Together with several partner institutes, Beijing Normal University is constructing a 1.93 m reflector telescope at the Muztagh-Ata site in west China, which has the world class observing conditions with median seeing of 0.″82 and median sky brightness of 21.74 in V-band during the dark time. The telescope will be equipped with both a three-channel imager/photometer which covers 3500–11,000 Å wavelength band, and a low-medium resolution (λ/δ λ = 500/2000/7500) spectrograph. In this paper, we investigate the capability of the Muztagh-Ata 1.93 m telescope in measuring time delays of strongly lensed quasars. We generate mock strongly lensed quasar systems and light curves with microlensing effects based on five known strongly lensed quasars, i.e., RX J1131-1231, HE 0435-1223, PG 1115+080, WFI 2033-4723 and SDSS 1206+4332. In particular, RX J1131-1231 is generated based on the lens modeling results of Suyu et al. Due to the lack of enough information, the other four systems are calculated by a simple analytical approximation. According to simulations, for RX J1131-like systems (wide variation in time delay between images) the TDSL measurement can be achieved with the precision about Δt = 0.5 day with four seasons campaign length and 1 day cadence. This accuracy is comparable to the up-coming TDCOSMO project. And it would be better when the campaign length keeps longer and with high cadence. As a result, the capability of the Muztagh-Ata 1.93 m telescope allows it to join the network of TDSL observatories. It will enrich the database for strongly lensed quasar observations and make more precise measurements of time delays, especially considering the unique coordinate of the site.

Photometric Observations of Nine High Mass X-Ray Binaries and Analysis of Potential Periodicities and Variations

Beginning with American Association of Variable Star Observers Alert Notice 348 (2007 April 6) and being continually extended and updated through 2020 April 17 with Alert Notice 377, Dr. Gordon Sarty requested continuing assistance with his ongoing radial velocity observations of High Mass X-Ray Binaries. As of Alert Notice 377, nine targets were identified. These are: 1H 1936+541, RX J2030.5+4751, V2175 Cyg, V1008 Cep, V831 Cas, RX J0440.9+4431/LS V+44 17, V420 Aur, HD 249179, and SAX J0635+0533. While these Alert Notices prioritized radial velocity observations with the objective of determining orbital periods of these binary systems, optical photometry can also reveal other periods and variations due to mass transfer, pulsations, rotations, spin rates, and other effects. This Research Note will address in more detail the observation and analysis of one of these nine High Mass X-Ray Binaries, specifically 1H 1936+541.

Two decades of optical timing of the shortest-period binary star system HM Cancri

ABSTRACT The shortest-period binary star system known to date, RX J0806.3+1527 (HM Cancri), has now been observed in the optical for more than two decades. Although it is thought to be a double degenerate binary undergoing mass transfer, an early surprise was that its orbital frequency, f0, is currently increasing as the result of gravitational wave radiation. This is unusual since it was expected that the mass donor was degenerate and would expand on mass loss, leading to a decreasing f0. We exploit two decades of high-speed photometry to precisely quantify the trajectory of HM Cancri, allowing us to find that $\ddot{f}_0$ is negative, where $\ddot{f}_0~=~(-5.38\pm 2.10)\times 10^{-27}$ Hz s−2. Coupled with our positive frequency derivative, we show that mass transfer is counteracting gravitational-wave dominated orbital decay and that HM Cancri will turn around within 2100 ± 800 yr from now. We present Hubble Space Telescope ultra-violet spectra which display Lyman-α absorption, indicative of the presence of hydrogen accreted from the donor star. We use these pieces of information to explore a grid of permitted donor and accretor masses with the Modules for Experiments in Stellar Astrophysics suite, finding models in good accordance with many of the observed properties for a cool and initially hydrogen-rich extremely low mass white dwarf (≈0.17 M⊙) coupled with a high-accretor mass white dwarf (≈1.0 M⊙). Our measurements and models affirm that HM Cancri is still one of the brightest verification binaries for the Laser Interferometer Space Antenna spacecraft.

Gravitational lensing effects of supermassive black holes in cluster environments

ABSTRACT This study explores the gravitational lensing effects of supermassive black holes (SMBHs) in galaxy clusters. While the presence of central SMBHs in galaxies is firmly established, recent work from high-resolution simulations predict the existence of an additional population of wandering SMBHs. Though the masses of these SMBHs are a minor perturbation on the larger scale and individual galaxy scale dark matter components in the cluster, they can impact statistical lensing properties and individual lensed image configurations. Probing for these potentially observable signatures, we find that SMBHs imprint detectable signatures in rare, higher order strong lensing image configurations although they do not manifest any statistically significant detectable evidence in either the magnification distribution or the integrated shear profile. Investigating specific lensed image geometries, we report that a massive, near point-like, potential of an SMBH causes the following detectable effects: (i) image splitting leading to the generation of extra images; (ii) positional and magnification asymmetries in multiply imaged systems; and (iii) the apparent disappearance of a lensed counter image. Of these, image splitting inside the cluster tangential critical curve, is the most prevalent notable observational signature. We demonstrate these possibilities in two cases of observed giant arcs in SGAS J003341.5+024217 and RX J1347.5−1145, wherein specific image configurations seen can be reproduced with SMBHs. Future observations with high-resolution instrumentation (e.g. MAVIS-Very Large Telescope, MICADO-Extremely Large Telescope, and the upgraded ngVLA, along with data from the Euclid and Nancy Grace Roman Space Telescopes and the Rubin LSST Observatory are likely to allow us to probe these unique yet rare SMBHs lensing signatures.

Two decades of X-ray observations of the isolated neutron star RX J1856.5 − 3754: detection of thermal and non-thermal hard X-rays and refined spin-down measurement

ABSTRACT The soft X-ray pulsar RX J1856.5 − 3754 is the brightest member of a small class of thermally emitting, radio-silent, isolated neutron stars. Its X-ray spectrum is almost indistinguishable from a blackbody with $kT^\infty \approx {60}\, {\rm eV}$, but evidence of harder emission above $\sim {1}\, {\rm keV}$ has been recently found. We report on a spectral and timing analysis of RX J1856.5 − 3754 based on the large amount of data collected by XMM-Newton in 2002–2022, complemented by a dense monitoring campaign carried out by NICER in 2019. Through a phase-coherent timing analysis we obtained an improved value of the spin-down rate $\dot{\nu }=-6.042(4)\times 10^{-16}\, {\rm Hz\, s}^{-1}$, reducing by more than one order magnitude the uncertainty of the previous measurement, and yielding a characteristic spin-down field of $1.47\times 10^{13}\, {\rm G}$. We also detect two spectral components above $\sim 1\, {\rm keV}$: a blackbody-like one with $kT^\infty =138\pm 13\,$eV and emitting radius $31_{-16}^{+8}\,$m, and a power law with photon index $\Gamma =1.4_{-0.4}^{+0.5}$. The power-law 2–8 keV flux, $(2.5_{-0.6}^{+0.7})\times 10^{-15}\, {\rm erg}\, {\rm cm}^{-2}\, {\rm s}^{-1}$, corresponds to an efficiency of 10−3, in line with that seen in other pulsars. We also reveal a small difference between the 0.1–0.3 keV and 0.3–1.2 keV pulse profiles, as well as some evidence for a modulation above 1.2 keV. These results show that, notwithstanding its simple spectrum, RX J1856.5 − 3754 still has a non-trivial thermal surface distribution and features non-thermal emission as seen in other pulsars with higher spin-down power.

Compact and Variable Radio Emission from an Active Galaxy with Supersoft X-Ray Emission

RX J1301.9+2747 is a unique active galaxy with a supersoft X-ray spectrum that lacks significant emission at energies above 2 keV. In addition, it is one of few galaxies displaying quasiperiodic X-ray eruptions that recur on a timescale of 13–20 ks. We present multiepoch radio observations of RX J1301.9+2747 using GMRT, Very Large Array (VLA), and Very Long Baseline Array (VLBA). The VLBA imaging at 1.6 GHz reveals a compact radio emission unresolved at a scale of <0.7 pc, with a brightness temperature of T b > 5 × 107 K. The radio emission is variable by more than a factor of 2.5 over a few days, based on the data taken from VLA monitoring campaigns. The short-term radio variability suggests that the radio emitting region has a size as small as 8 × 10−4 pc, resulting in an even higher brightness temperature of T b ∼ 1012 K. A similar limit on the source size can be obtained if the observed flux variability is not intrinsic and caused by the interstellar scintillation effect. The overall radio spectrum is steep with a time-averaged spectral index α = −0.78 ± 0.03 between 0.89 and 14 GHz. These observational properties rule out a thermal or star formation origin of the radio emission, and appear to be consistent with the scenario of episodic jet ejections driven by a magnetohydrodynamic process. Simultaneous radio and X-ray monitoring observations down to a cadence of hours are required to test whether the compact and variable radio emission is correlated with the quasiperiodic X-ray eruptions.

SHARP – VIII. J0924+0219 lens mass distribution and time-delay prediction through adaptive-optics imaging

ABSTRACT Strongly lensed quasars can provide measurements of the Hubble constant (H0) independent of any other methods. One of the key ingredients is exquisite high-resolution imaging data, such as Hubble Space Telescope (HST) imaging and adaptive-optics (AO) imaging from ground-based telescopes, which provide strong constraints on the mass distribution of the lensing galaxy. In this work, we expand on the previous analysis of three time-delay lenses with AO imaging (RX J1131−1231, HE 0435−1223, and PG 1115+080), and perform a joint analysis of J0924+0219 by using AO imaging from the Keck telescope, obtained as part of the Strong lensing at High Angular Resolution Program (SHARP) AO effort, with HST imaging to constrain the mass distribution of the lensing galaxy. Under the assumption of a flat Λ cold dark matter (ΛCDM) model with fixed Ωm = 0.3, we show that by marginalizing over two different kinds of mass models (power-law and composite models) and their transformed mass profiles via a mass-sheet transformation, we obtain $\Delta t_{\rm BA}=6.89\substack{+0.8\\-0.7}\, h^{-1}\hat{\sigma }_{v}^{2}$ d, $\Delta t_{\rm CA}=10.7\substack{+1.6\\-1.2}\, h^{-1}\hat{\sigma }_{v}^{2}$ d, and $\Delta t_{\rm DA}=7.70\substack{+1.0\\-0.9}\, h^{-1}\hat{\sigma }_{v}^{2}$ d, where $h=H_{0}/100\,\rm km\, s^{-1}\, Mpc^{-1}$ is the dimensionless Hubble constant and $\hat{\sigma }_{v}=\sigma ^{\rm ob}_{v}/(280\,\rm km\, s^{-1})$ is the scaled dimensionless velocity dispersion. Future measurements of time delays with 10 per cent uncertainty and velocity dispersion with 5 per cent uncertainty would yield a H0 constraint of ∼15 per cent precision.

Investigating the Low-flux States in Six Intermediate Polars

Abstract We present optical photometry of six intermediate polars that exhibit transitions to a low-flux state. For four of these systems, DW Cnc, V515 And, V1223 Sgr, and RX J2133.7+5107, we are able to perform timing analysis in and out of the low states. We find that, for DW Cnc and V515 And, the dominant periodicities in the light curves change as the flux decreases, indicating a change in the sources’ accretion properties as they transition to the low state. For V1223 Sgr, we find that the variability is almost completely quenched at the lowest flux, but we do not find evidence for a changing accretion geometry. For RX J2133.7+5107, the temporal properties do not change in the low state, but we do see a period of enhanced accretion that is coincident with increased variability on the beat frequency, which we do not associate with a change in the accretion mechanisms in the system.

Measuring the Nonaxially Symmetric Surface Temperature Distribution of the Central Compact Object in Puppis A

Abstract The surface temperature distributions of central compact objects (CCOs) are powerful probes of their crustal magnetic field strengths and geometries. Here we model the surface temperature distribution of RX J0822−4300, the CCO in the Puppis A supernova remnant, using 471 ks of XMM-Newton data. We compute the energy-dependent pulse profiles in 16 energy bands, fully including the general relativistic effects of gravitational redshift and light bending, to accurately model the two heated surface regions of different temperatures and areas, in addition to constraining the viewing geometry. This results in precise measurements of the two temperatures: kT warm = ( 1 + z ) × 0.222 − 0.019 + 0.018 keV and kT hot = (1 + z) × 0.411 ± 0.011 keV. The two heated surface regions are likely located very close to the rotational poles, with the most probable position of the hotter component ≈ 6° from the rotational pole. For the first time, we are able to measure a deviation from a pure antipodal hot-spot geometry, with a longitudinal offset δ γ = 11 .° 7 − 2 .° 5 + 2 .° 6 . The discovery of this asymmetry, along with the factor of ≈2 temperature difference between the two emitting regions, may indicate that RX J0822−4300 was born with a strong, tangled crustal magnetic field.

The Missing Metal Problem in Galaxy Clusters: Characterizing the Early Enrichment Population

Abstract Rich and poor galaxy clusters have the same measured halo metallicity, 0.35–0.4 Z ⊙, even though they are an order of magnitude apart in stellar fraction, M */M gas. The measured intracluster medium (ICM) metallicity in high-mass clusters cannot be explained by the visible stellar population as stars typically make up 3%–20% of the total baryon mass. The independence of metallicity of M */M gas suggests an external and universal source of metals such as an early enrichment population (EEP). Galaxy cluster RX J1416.4+2315, classified as a fossil system, has a stellar fraction of M */M gas = 0.054 ± 0.018, and here we improve the halo metallicity determination using archival Chandra and XMM-Newton observations. We determine the ICM metallicity of RXJ1416 to be 0.303 ± 0.053 Z ⊙ within 0.3 &lt; R/R 500 &lt; 1, excluding the central galaxy. We combine this measurement with other clusters with a wider range of M */M gas, resulting in the fit of Z tot = (0.36 ± 0.01) + (0.10 ± 0.17)(M */M gas). This fit is largely independent of M */M gas and shows that for a low M */M gas system, the observed stellar population can make only 10%–20% of the total metals. We quantify the Fe contribution of the EEP further by adopting a standard Fe yield for visible stellar populations, and find that Z EEP = (0.36 ± 0.01) − − (0.96 ± 0.17)(M */M gas). To account for the observed Fe mass, a supernova (SN) rate of 10 ± 5 SNe yr−1 (Type Ia) and 40 ± 19 SNe yr−1 (core collapse) is required over the redshift range 3 &lt; z &lt; 10 for a single galaxy cluster with mass ∼3 × 1014 M ⊙ at z = 0. These SNe might be visible in observations of high-redshift clusters and protoclusters with the James Webb Space Telescope.

Toward Constraining Axions with Polarimetric Observations of the Isolated Neutron Star RX J1856.5–3754

Abstract Photon–axion mixing can create observable signatures in the thermal spectra of isolated, cooling neutron stars. Their shape depends on the polarization properties of the radiation, which, in turn, are determined by the structure of the stellar outermost layers. Here we investigate the effect of mixing on the spectrum and polarimetric observables, polarization fraction and polarization angle, using realistic models of surface emission. We focus on RX J1856.5–3754, the only source among the X-ray-dim isolated neutron stars for which polarimetric measurements in the optical band were performed. Our results show that in the case of a condensed surface in both fixed and free-ion limits, the mixing can significantly limit the geometric configurations that reproduce the observed linear polarization fraction of 16.43%. In the case of an atmosphere, the mixing does not create any noticeable signatures. Complementing our approach with the data from upcoming soft X-ray polarimetry missions will allow one to obtain constraints on g γ a ∼ 10−11 GeV−1 and m a ≲ 10−6 eV, improving the present experimental and astrophysical limits.

Nonperiodic Type I Be/X-Ray Binary Outbursts

Abstract Type I Be/X-ray binary outbursts are driven by mass transfer from a Be star decretion disk to a neutron star companion during each orbital period. Treiber et al. recently observed nonperiodic type I outbursts in RX J0529.8–6556 that has unknown binary orbital properties. We show that nonperiodic type I outbursts may be temporarily driven in a low eccentricity binary with a disk that is inclined sufficiently to be mildly unstable to Kozai–Lidov oscillations. The inclined disk becomes eccentric and material is transferred to the neutron star at up to three locations in each orbit: when the neutron star passes the disk apastron or one of the two nodes of the disk. The timing and magnitude of each vary with the disk argument of periapsis and longitude of the ascending node that precess in opposite directions. Calculating the orbital period of the RX J0529.8–6556 system is nontrivial but we suggest it may be &gt;300 days, longer than previous estimates.

Possible Detection of X-Ray Emitting Circumstellar Material in the Synchrotron-dominated Supernova Remnant RX J1713.7−3946

Abstract We report on a discovery of an X-ray emitting circumstellar material (CSM) knot inside the synchrotron dominant supernova remnant RX J1713.7−3946. This knot was previously thought to be a Wolf–Rayet star (WR 85), but we realized that it is in fact ∼40″ away from WR 85, indicating no relation to WR 85. We performed high-resolution X-ray spectroscopy with the Reflection Grating Spectrometer (RGS) on board XMM-Newton. The RGS spectrum clearly resolves a number of emission lines, such as N Lyα, O Lyα, Fe xviii, Ne x, Mg xi, and Si xiii. The spectrum can be well represented by an absorbed thermal-emission model with a temperature of k B T e = 0.65 ± 0.02 keV. The elemental abundances are obtained to be N / H = 3.5 ± 0.8 N / H ⊙ , O / H = 0.5 ± 0.1 O / H ⊙ , Ne / H = 0.9 ± 0.1 Ne / H ⊙ , Mg / H = 1.0 ± 0.1 Mg / H ⊙ , Si / H = 1.0 ± 0.2 Si / H ⊙ , and Fe / H = 1.3 ± 0.1 Fe / H ⊙ . The enhanced N abundance with others being about the solar values allows us to infer that this knot is CSM ejected when the progenitor star evolved into a red supergiant. The abundance ratio of N to O is obtained to be N / O = 6.8 − 2.1 + 2.5 N / O ⊙ . By comparing this to those in outer layers of red supergiant stars expected from stellar evolution simulations, we estimate the initial mass of the progenitor star to be 15 M ⊙ ≲ M ≲ 20 M ⊙.

Gamma-rays and neutrinos from RX J1713–3946 in a lepto–hadronic scenario

ABSTRACT The gamma-ray emission of RX J1713–3946, despite being extensively studied in the GeV and TeV domains, remains poorly understood. This is mostly because, in this range, two competing mechanisms can efficiently produce gamma-rays: the inverse Compton scattering of accelerated electrons, and interactions of accelerated protons with the nuclei of the interstellar medium (ISM). In addition to the acceleration of particles from the thermal pool, the re-acceleration of pre-existing cosmic rays is often overlooked, and has in fact also been taken into account. Especially, because of the distance to the SNR (∼1 kpc), and the low density in which the shock is currently expanding (∼10−2 cm−3), the re-acceleration of cosmic-ray electrons pre-existing in the ISM can account for a significant fraction of the observed gamma-ray emission, and contribute to the shaping of the spectrum in the GeV–TeV range. Remarkably, this emission of leptonic origin is found to be close to the level of the gamma-ray signal in the TeV range, provided that the spectrum of pre-exisiting cosmic-ray electrons is similar to that observed in the local ISM. The overall gamma-ray spectrum of RX J1713–3946 is naturally produced as the sum of leptonic emission from re-accelerated cosmic-ray electrons, and a subdominant hadronic emission from accelerated protons. We also argue that neutrino observations with next-generation detectors might lead to a detection even in the case of a lepto–hadronic origin of the gamma-ray emission.

The ultra-steep diffuse radio emission observed in the cool-core cluster RX J1720.1+2638 with LOFAR at 54 MHz

ABSTRACT Diffuse radio emission at the centre of galaxy clusters has been observed both in merging clusters on scales of Mpc, called giant radio haloes, and in relaxed systems with a cool-core on smaller scales, named mini haloes. Giant radio haloes and mini haloes are thought to be distinct classes of sources. However, recent observations have revealed the presence of diffuse radio emission on Mpc scales in clusters that do not show strong dynamical activity. RX J1720.1+2638 is a cool-core cluster, presenting both a bright central mini halo and a fainter diffuse, steep-spectrum emission extending beyond the cluster core that resembles giant radio halo emission. In this paper, we present new observations performed with the LOw Frequency ARray Low Band Antennas (LBA) at 54 MHz. These observations, combined with data at higher frequencies, allow us to constrain the spectral properties of the radio emission. The large-scale emission presents an ultrasteep spectrum with $\alpha _{54}^{144}\sim 3.2$. The radio emission inside and outside the cluster core have strictly different properties, as there is a net change in spectral index and they follow different radio-X-ray surface brightness correlations. We argue that the large-scale diffuse emission is generated by particles re-acceleration after a minor merger. While for the central mini halo, we suggest that it could be generated by secondary electrons and positrons from hadronic interactions of relativistic nuclei with the dense cool-core gas, as an alternative to re-acceleration models.

Stellar Transits across a Magnetized Accretion Torus as a Mechanism for Plasmoid Ejection

Abstract The close neighborhood of a supermassive black hole contains not only the accreting gas and dust but also stellar-sized objects, such as late-type and early-type stars and compact remnants that belong to the nuclear star cluster. When passing through the accretion flow, these objects perturb it by the direct action of stellar winds, as well as their magnetic and gravitational effects. By performing general-relativistic magnetohydrodynamic simulations, we investigate how the passages of a star can influence the supermassive black hole gaseous environment. We focus on the changes in the accretion rate and the emergence of blobs of plasma in the funnel of an accretion torus. We compare results from 2D and 3D numerical computations that have been started with comparable initial conditions. We find that a quasi-stationary inflow can be temporarily inhibited by a transiting star, and the plasmoids can be ejected along the magnetic field lines near the rotation axis. We observe the characteristic signatures of the perturbing motion in the power spectrum of the accretion variability, which provides an avenue for a multi-messenger detection of these transient events. Finally, we discuss the connection of our results to multiwavelength observations of galactic nuclei, with the emphasis on ten promising sources (Sgr A*, OJ 287, J0849+5108, RE J1034+396, 1ES 1927+65, ESO 253–G003, GSN 069, RX J1301.9+2747, eRO-QPE1, and eRO-QPE2).

A kinematic study of central compact objects and their host supernova remnants

Context. Central compact objects (CCOs) are a peculiar class of neutron stars, primarily encountered close to the center of young supernova remnants (SNRs) and characterized by thermal X-ray emission. Measurements of their proper motion and the expansion of the parent SNR are powerful tools for constraining explosion kinematics and the age of the system. Aims. Our goal is to perform a systematic study of the proper motion of all known CCOs with appropriate data available. From this, we hope to obtain constraints on the violent kick acting on the neutron star during the supernova explosion and infer the exact site of the explosion within the SNR. In addition, we aim to measure the expansion of three SNRs within our sample to obtain a direct handle on their kinematics and age. Methods. We analyze multiple archival Chandra data sets that consist of HRC and ACIS observations separated by temporal baselines of between 8 and 15 years. We achieve accurate source positions by fitting the imaging data with ray-tracing models of the Chandra point spread function. In order to correct for Chandra’s systematic astrometric uncertainties, we establish a reference frame using X-ray-detected sources in Gaia DR2 to provide accurate proper motion estimates for our target CCOs. Complementarily, we use our coaligned data sets to trace the expansion of three SNRs by directly measuring the spatial offset of various filaments and ejecta clumps between different epochs. Results. In total, we present new proper motion measurements for six CCOs. Within our sample, we do not find any indication of a hypervelocity object, and we determine comparatively tight upper limits (&lt; 230 km s−1) on the transverse velocities of the CCOs in G330.2+1.0 and RX J1713.7−3946. We tentatively identify direct signatures of expansion for the SNRs G15.9+0.2 and Kes 79, at an estimated significance of 2.5σ and 2σ, respectively. Moreover, we confirm recently reported results, measuring the rapid expansion of G350.1−0.3 at almost 6000 km s−1, which places its maximal age at 600 − 700 years, making this object one of the youngest Galactic core-collapse SNRs. The observed expansion, combined with the proper motion of its CCO, which is much slower than previously predicted, implies the need for a very inhomogeneous circumstellar medium to explain the highly asymmetric appearance of the SNR. Finally, for the SNR RX J1713.7−3946, we combine previously published expansion measurements with our measurement of the CCO’s proper motion to obtain a constraining upper limit of 1700 years on the system’s age.

Pursuing the Origin of the Gamma Rays in RX J1713.7-3946 Quantifying the Hadronic and Leptonic Components

Abstract We analyzed the TeV gamma-ray image of a supernova remnant RX J1713.7−3946 (RX J1713) through a comparison with the interstellar medium (ISM) and nonthermal X-rays. The gamma-ray data sets at two energy bands of &gt;2 TeV and &gt;250–300 GeV were obtained with H.E.S.S. and utilized in the analysis. We employed a new methodology, which assumes that the gamma-ray counts can be expressed as a linear combination of two terms: one is proportional to the ISM column density and the other proportional to the X-ray count. We then assume that these represent the hadronic and leptonic components, respectively. By fitting the expression to the data pixels, we find that the gamma-ray counts are well represented by a flat plane in the 3D space formed by the gamma-ray counts, the ISM column density, and the X-ray counts. The results using the latest H.E.S.S. data at 4.′8 resolution show that the hadronic and leptonic components constitute (67 ± 8)% and (33 ± 8)% of the total gamma rays, respectively, where the two components have been quantified for the first time. The hadronic component is greater than the leptonic component, which reflects the massive ISM of ∼104 M ⊙ associated with the remnant, lending support for the acceleration of cosmic-ray protons. There is a marginal hint that the gamma rays are suppressed at high gamma-ray counts, which may be ascribed to second-order effects including the shock–cloud interaction and the effect of penetration depth.