arXiv subjects

Alice Borghese

Publications and source records attributed to Alice Borghese.

14 recordsLinked to original sources

arXiv2026

The long quest for vacuum birefringence in magnetars: 1E 1547.0-5408 and the elusive smoking gun

Magnetars are now known to be among the most strongly polarized celestial sources in X-rays. Here we report on the $500\,\mathrm{ks}$ observation of the magnetar 1E 1547.0-5408 performed by the Imaging X-ray Polarimetry Explorer (IXPE) in March 2025. The IXPE spectrum is well reproduced by a single thermal component with blackbody temperature $kT_\mathrm{BB}\sim 0.67\,\mathrm{keV}$ and emission radius $R_\mathrm{BB}\sim 1.2\,\mathrm{km}$. The source exhibits a high linear polarization degree in the $2$--$6\,\mathrm{keV}$ band ($\mathrm{PD}=47.7\pm2.9\%$) with polarization angle $\mathrm{PA}=75^\circ.8 \pm 1.^\circ8$, measured West of celestial North. While $\mathrm{PA}$ does not appear to vary with energy, there is some evidence (at the $1\sigma$ confidence level) of a minimum in $\mathrm{PD}$ between $3$ and $4\,\mathrm{keV}$, compatible with what is expected by partial mode conversion at the vacuum resonance in a magnetized atmosphere. Phase-resolved spectral and polarimetric analyses reveal that X-ray thermal radiation likely originates from a single, fairly small hot spot with a non-uniform temperature distribution. Fitting the phase-dependent $\mathrm{PA}$ measured by IXPE with a rotating vector model (RVM) constrains the source geometry and indicates that both the dipole axis and line-of-sight are misaligned with respect to the spin axis. Under these conditions, the high polarization of the source cannot be regarded as compelling evidence for the presence of vacuum birefringence in the star magnetosphere. Nevertheless, the fact that the RVM successfully reproduces the modulation of the X-ray polarization angle and the behavior of $\mathrm{PD}$ with the energy hint once more to the presence of QED effects in magnetars.

astro-ph.HE↗

arXiv2025

The Advanced X-ray Imaging Satellite (AXIS) Community Science Book

The AXIS Community Science Book represents the collective effort of 592 scientists worldwide to define the transformative science enabled by the Advanced X-ray Imaging Satellite (AXIS), a next-generation X-ray mission selected by NASA's Astrophysics Probe Program for Phase A study. AXIS will advance the legacy of high-angular-resolution X-ray astronomy with ~1.5'' imaging over a wide 24' field of view and an order of magnitude greater collecting area than Chandra in the 0.3-12 keV band. Combining sharp imaging, high throughput, and rapid response capabilities, AXIS will open new windows on virtually every aspect of modern astrophysics, exploring the birth and growth of supermassive black holes, the feedback processes that shape galaxies, the life cycles of stars and exoplanet environments, and the nature of compact stellar remnants, supernova remnants, and explosive transients. This book compiles 138 community-contributed science cases developed by five Science Working Groups focused on AGN and supermassive black holes, galaxy evolution and feedback, compact objects and supernova remnants, stellar physics and exoplanets, and time-domain and multi-messenger astrophysics. Together, these studies establish the scientific foundation for next-generation X-ray exploration in the 2030s and highlight strong synergies with facilities of the 2030s, such as JWST, Roman, Rubin/LSST, SKA, ALMA, ngVLA, and next-generation gravitational-wave and neutrino networks.

astro-ph.HE↗

arXiv2025

The Science of the Einstein Telescope

Einstein Telescope (ET) is the European project for a gravitational-wave (GW) observatory of third-generation. In this paper we present a comprehensive discussion of its science objectives, providing state-of-the-art predictions for the capabilities of ET in both geometries currently under consideration, a single-site triangular configuration or two L-shaped detectors. We discuss the impact that ET will have on domains as broad and diverse as fundamental physics, cosmology, early Universe, astrophysics of compact objects, physics of matter in extreme conditions, and dynamics of stellar collapse. We discuss how the study of extreme astrophysical events will be enhanced by multi-messenger observations. We highlight the ET synergies with ground-based and space-borne GW observatories, including multi-band investigations of the same sources, improved parameter estimation, and complementary information on astrophysical or cosmological mechanisms obtained combining observations from different frequency bands. We present advancements in waveform modeling dedicated to third-generation observatories, along with open tools developed within the ET Collaboration for assessing the scientific potentials of different detector configurations. We finally discuss the data analysis challenges posed by third-generation observatories, which will enable access to large populations of sources and provide unprecedented precision.

gr-qc↗

arXiv2025

The zoo of isolated neutron stars

Discovered over fifty years ago, neutron stars exhibit a remarkable variety of behaviors depending on their age, magnetic field strength, rotational dynamics, emission mechanisms, and surrounding environments. This diversity in their observational manifestations has led astronomers to classify neutron stars into numerous categories, much like wandering through a zoo and admiring various species. This chapter focuses on isolated (i.e., non-accreting) neutron stars. We review extensive observational results of rotation-powered pulsars, magnetars, X-ray dim isolated neutron stars and central compact objects, highlighting the unique properties and recent discoveries of these neutron star classes. We briefly touch on theoretical models that have significantly advanced our understanding of these classes, emphasizing the valuable insights they provide into the underlying physics of neutron stars.

astro-ph.HE↗

arXiv2024

IXPE detection of highly polarized X-rays from the magnetar 1E 1841-045

The Imaging X-ray Polarimetry Explorer (IXPE) observed for the first time highly polarized X-ray emission from the magnetar 1E 1841-045, targeted after a burst-active phase in August 2024. To date, IXPE has observed four other magnetars during quiescent periods, highlighting substantially different polarization properties. 1E 1841-045 exhibits a high, energy-dependent polarization degree, which increases monotonically from ~15% at 2-3 keV up to ~55% at 5.5-8 keV, while the polarization angle, aligned with the celestial North, remains fairly constant. The broadband spectrum (2-79 keV) obtained by combining simultaneous IXPE and NuSTAR data is well modeled by a blackbody and two power-law components. The unabsorbed 2-8 keV flux (~2E-11 erg/cm2/s) is about 10% higher than that obtained from archival XMM-Newton and NuSTAR observations. The polarization of the soft, thermal component does not exceed ~25%, and may be produced by a condensed surface or a bombarded atmosphere. The intermediate power law is polarized at around 30%, consistent with predictions for resonant Compton scattering in the star magnetosphere; while, the hard power law exhibits a polarization degree exceeding 65%, pointing to a synchrotron/curvature origin.

astro-ph.HE↗

arXiv2024

Ultra-long period compact sources: a glimpse into observational breakthroughs and theoretical challenges

At the Seventeenth Marcel Grossman meeting, researchers gathered to discuss significant advances in the study of ultra-long period sources. Presentations covered key aspects, including emission properties, evolutionary scenarios, and models for their emission. In this proceeding, we summarize key observational breakthroughs and touch upon the proposed evolutionary pathways and state-of-the-art models that seek to explain these sources. Finally, we outline future directions, including the potential of ongoing and upcoming surveys, improved detection algorithms, and multiwavelength observations to significantly expand the known population of these mysterious sources.

astro-ph.HE↗

arXiv2024

Exploring the neutron star zoo: An observational review

Neutron stars have shown diverse characteristics, leading us to classify them into different classes. In this proceeding, I review the observational properties of isolated neutron stars: from magnetars, the strongest magnets we know of, to central compact objects, the so-called anti-magnetars, stopping by the rotation-powered pulsars and X-ray dim isolated neutron stars. Finally, I highlight a few sources that have exhibited features straddling those of different groups, blurring the apparent diversity of the neutron star zoo.

astro-ph.HE↗

arXiv2024

Long-term study of the 2020 magnetar-like outburst of the young pulsar PSRJ1846-0258 in Kes 75

Magnetar-like activity has been observed in a large variety of neutron stars. PSR J1846-0258 is a young 327 ms radio-quiet pulsar with a large rotational power ($\sim 8 \times 10^{36}$ erg s$^{-1}$), and resides at the center of the supernova remnant Kes 75. It is one of the rare examples of a high magnetic field pulsar showing characteristics both of magnetars and radio pulsars, and can thus provide important clues on the differences in the emission mechanisms between these two classes. In 2006, PSR J1846-0258 was detected to undergo an outburst for the first time, accompanied by a large flux increase, millisecond X-ray bursts, significant spectral changes and a large timing glitch. In the period between May-June 2020, after fourteen years of quiescent stable emission, the source underwent a second magnetar-like outburst, which was followed up with several observations by NICER, XMM-Newton, NuSTAR and Swift. In this work, we report on the long-term timing and X-ray spectral properties of the source following the 2020 outburst, and place upper limits on any source activity at radio wavelengths. We demonstrate that the pulsed flux increased by a factor $> 6$ during the outburst, followed by non-trivial variability in the spin-down rate. Our timing analysis shows that the spin frequency and its derivative are clearly affected by magnetospheric activity due to the outburst. We find hints for an oscillation in the frequency derivative with a timescale of 50-60 days, recovering later on to stable quiescence.

astro-ph.HE↗

arXiv2023

Isolated Neutron Stars

Non-accreting neutron stars display diverse characteristics, leading us to classify them into several groups. This chapter is an observational driven review in which we survey the properties of the different classes of isolated neutron stars: from the 'normal' rotation-powered pulsars, to magnetars, the most magnetic neutron stars in the Universe we know of; from central compact objects (sometimes called also anti-magnetars) in supernova remnants, to the X-ray dim isolated neutron stars. We also highlight a few sources that have exhibited features straddling those of different sub-groups, blurring the apparent diversity of the neutron star zoo and pointing to a gran unification.

astro-ph.HE↗

arXiv2022

The first 7 months of the 2020 X-ray outburst of the magnetar SGR J1935+2154

The magnetar SGR J1935+2154 underwent a new active episode on 2020 April 27-28, when a forest of hundreds of X-ray bursts and a large enhancement of the persistent flux were detected. For the first time, a radio burst with properties similar to those of fast radio bursts and with a X-ray counterpart was observed from this source, showing that magnetars can power at least a group of fast radio bursts. In this paper, we report on the X-ray spectral and timing properties of SGR J1935+2154 based on a long-term monitoring campaign with Chandra, XMM-Newton, NuSTAR, Swift and NICER covering a time span of ~7 months since the outburst onset. The broadband spectrum exhibited a non-thermal power-law component (photon index~1.2) extending up to ~20-25 keV throughout the campaign and a blackbody component with temperature decreasing from ~1.5 keV at the outburst peak to ~0.45 keV in the following months. We found that the luminosity decay is well described by the sum of two exponential functions, reflecting the fast decay (~1 d) at the early stage of the outburst followed by a slower decrease (~30 d). The source reached quiescence about ~80 days after the outburst onset, releasing an energy of ~6e40 erg during the outburst. We detected X-ray pulsations in the XMM-Newton data sets and derived an average spin-down rate of ~3.5e-11 s/s using the spin period measurements derived in this work and three values reported previously during the same active period. Moreover, we report on simultaneous radio observations performed with the Sardinia Radio Telescope. No evidence for periodic or single-pulse radio emission was found.

astro-ph.HE↗

arXiv2021

Back to quiescence: post-outburst evolution of the pulsar J1119-6127 and its wind nebula

We report on the analysis of a deep Chandra observation of the high-magnetic field pulsar (PSR) J1119-6127 and its compact pulsar wind nebula (PWN) taken in October 2019, three years after the source went into outburst. The 0.5-7 keV post-outburst (2019) spectrum of the pulsar is best described by a two-component blackbody plus powerlaw model with a temperature of 0.2\pm0.1 keV, photon index of 1.8\pm0.4 and X-ray luminosity of ~1.9e33 erg s^{-1}, consistent with its pre-burst quiescent phase. We find that the pulsar has gone back to quiescence. The compact nebula shows a jet-like morphology elongated in the north-south direction, similar to the pre-burst phase. The post-outburst PWN spectrum is best fit by an absorbed powerlaw with a photon index of 2.3\pm0.5 and flux of ~3.2e-14 erg cm^{-2} s^{-1} (0.5-7 keV). The PWN spectrum shows evidence of spectral softening in the post-outburst phase, with the pre-burst photon index of 1.2\pm0.4 changing to 2.3\pm0.5, and pre-burst luminosity of ~1.5e32 erg s^{-1} changing to 2.7e32 erg s^{-1} in the 0.5-7 keV band, suggesting magnetar outbursts can impact PWNe. The observed timescale for returning to quiescence, of just a few years, implies a rather fast cooling process and favors a scenario where J1119 is temporarily powered by magnetic energy following the magnetar outburst, in addition to its spin-down energy.

astro-ph.HE↗

arXiv2019

The long-term enhanced brightness of the magnetar 1E 1547.0-5408

We present the evolution of the X-ray emission properties of the magnetar 1E 1547.0-5408 since February 2004 over a time period covering three outbursts. We analyzed new and archival observations taken with the Swift, NuSTAR, Chandra and XMM-Newton X-ray satellites. The source has been observed at a relatively steady soft X-ray flux of $\approx$ 10$^{-11}$ erg cm$^{-2}$ s$^{-1}$ (0.3-10 keV) over the last 9 years, which is about an order of magnitude fainter than the flux at the peak of the last outburst in 2009, but a factor of $\sim$ 30 larger than the level in 2006. The broad-band spectrum extracted from two recent NuSTAR observations in April 2016 and February 2019 showed a faint hard X-ray emission up to $\sim$ 70 keV. Its spectrum is adequately described by a flat power law component, and its flux is $\sim$ $7 \times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$ (10-70 keV), that is a factor of $\sim$ 20 smaller than at the peak of the 2009 outburst. The hard X-ray spectral shape has flattened significantly in time, which is at variance with the overall cooling trend of the soft X-ray component. The pulse profile extracted from these NuSTAR pointings displays variability in shape and amplitude with energy (up to $\approx$ 25 keV). Our analysis shows that the flux of 1E 1547.0-5408 is not yet decaying to the 2006 level and that the source has been lingering in a stable, high-intensity state for several years. This might suggest that magnetars can hop among distinct persistent states that are probably connected to outburst episodes and that their persistent thermal emission can be almost entirely powered by the dissipation of currents in the corona.

astro-ph.HE↗

arXiv2016

Magnetar-like activity from the central compact object in the SNR RCW103

The 6.67 hr periodicity and the variable X-ray flux of the central compact object (CCO) at the center of the SNR RCW 103, named 1E 161348-5055, have been always difficult to interpret within the standard scenarios of an isolated neutron star or a binary system. On 2016 June 22, the Burst Alert Telescope (BAT) onboard Swift detected a magnetar-like short X-ray burst from the direction of 1E 161348-5055, also coincident with a large long-term X-ray outburst. Here we report on Chandra, NuSTAR, and Swift (BAT and XRT) observations of this peculiar source during its 2016 outburst peak. In particular, we study the properties of this magnetar-like burst, we discover a hard X-ray tail in the CCO spectrum during outburst, and we study its long-term outburst history (from 1999 to July 2016). We find the emission properties of 1E 161348-5055 consistent with it being a magnetar. However in this scenario, the 6.67 hr periodicity can only be interpreted as the rotation period of this strongly magnetized neutron star, which therefore represents the slowest pulsar ever detected, by orders of magnitude. We briefly discuss the viable slow-down scenarios, favoring a picture involving a period of fall-back accretion after the supernova explosion, similarly to what is invoked (although in a different regime) to explain the "anti-magnetar" scenario for other CCOs.

astro-ph.HE↗

arXiv2015

Discovery of a strongly phase-variable spectral feature in the isolated neutron star RX J0720.4-3125

We present the discovery of a strongly phase-variable absorption feature in the X-ray spectrum of the nearby, thermally-emitting, isolated neutron star RX J0720.4-3125. The absorption line was detected performing detailed phase-resolved spectroscopy in 20 XMM-Newton observations, covering the period May 2000 - September 2012. The feature has an energy of ~750eV, an equivalent width of ~30eV, and it is significantly detected for only ~20% of the pulsar rotation. The absorption feature appears to be stable over the timespan covered by the observations. Given its strong dependence on the pulsar rotational phase and its narrow width, a plausible interpretation is in terms of resonant proton cyclotron absorption/scattering in a confined magnetic structure very close to the neutron star surface. The inferred field in such a magnetic loop is B_loop ~ 2 x 10^{14} G, a factor of ~7 higher than the surface dipolar magnetic field.

astro-ph.HE↗