We report on the discovery of a new member of the magnetar class, SGR J1935+2154, and on its timing and spectral properties measured by an extensive observational campaign carried out between 2014 ...July and 2015 March with Chandra and XMM–Newton (11 pointings). We discovered the spin period of SGR J1935+2154 through the detection of coherent pulsations at a period of about 3.24 s. The magnetar is slowing down at a rate of
$\dot{P} = 1.43(1)\times 10^{-11}$
s s−1 and with a decreasing trend due to a negative
$\ddot{P}$
of −3.5(7) × 10−19 s s−2. This implies a surface dipolar magnetic field strength of ∼2.2 × 1014 G, a characteristic age of about 3.6 kyr and a spin-down luminosity Lsd ∼1.7 × 1034 erg s−1. The source spectrum is well modelled by a blackbody with temperature of about 500 eV plus a power-law component with photon index of about 2. The source showed a moderate long-term variability, with a flux decay of about 25 per cent during the first four months since its discovery, and a re-brightening of the same amount during the second four months. The X-ray data were also used to study the source environment. In particular, we discovered a diffuse emission extending on spatial scales from about 1 arcsec up to at least 1 arcmin around SGR J1935+2154 both in Chandra and XMM–Newton data. This component is constant in flux (at least within uncertainties) and its spectrum is well modelled by a power-law spectrum steeper than that of the pulsar. Though a scattering halo origin seems to be more probable we cannot exclude that part, or all, of the diffuse emission is due to a pulsar wind nebula.
Mining the Aql X-1 long-term X-ray light curve Campana, S; Coti Zelati, F; D'Avanzo, P
Monthly notices of the Royal Astronomical Society,
06/2013, Letnik:
432, Številka:
2
Journal Article
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Aql X-1 is the prototypical low-mass X-ray binary transient. The Rossi X-ray Timing Explorer All-Sky Monitor provided ∼16 yr coverage, revealing 20 outbursts. This is by far the most extensive legacy ...of outbursts from the same source. We investigated the outburst characteristics in terms of energetics, peak luminosities, durations, decays and recurrence times. We found that bright outbursts (peak luminosity 1037 erg s−1) equal dimmer outbursts ( 1036.6 erg s−1) in number. The peak luminosity does not correlate with outburst energetics, durations or quiescent times. We analysed the latest stages of the outbursts, searching for exponential and/or linear decays. Light-curve modelling led to constraints on the outer disc radius and enabled us to estimate the viscosity and the irradiation parameters. The former is larger than has been obtained for other, shorter orbital period transients, while the latter is somewhat smaller. This might be related to the longer orbital period of Aql X-1 with respect to other transient X-ray binaries.
We report on the identification of the new Galactic Centre (GC) transient Swift J174540.7−290015 as a likely low-mass X-ray binary located at only 16 arcsec from Sgr A⋆. This transient was detected ...on 2016 February 6, during the Swift GC monitoring, and it showed long-term spectral variations compatible with a hard- to soft-state transition. We observed the field with XMM–Newton on February 26 for 35 ks, detecting the source in the soft state, characterized by a low level of variability and a soft X-ray thermal spectrum with a high energy tail (detected by INTEGRAL up to ∼50 keV), typical of either accreting neutron stars or black holes. We observed: (i) a high column density of neutral absorbing material, suggesting that Swift J174540.7−290015 is located near or beyond the GC and; (ii) a sub-Solar iron abundance, therefore we argue that iron is depleted into dust grains. The lack of detection of Fe K absorption lines, eclipses or dipping suggests that the accretion disc is observed at a low inclination angle. Radio (Very Large Array) observations did not detect any radio counterpart to Swift J174540.7−290015. No evidence for X-ray or radio periodicity is found. The location of the transient was observed also in the near-infrared (near-IR) with gamma-ray burst optical near-IR detector at MPG/European Southern Observatory La Silla 2.2 m telescope and VLT/NaCo pre- and post-outburst. Within the Chandra error region, we find multiple objects that display no significant variations.
Abstract
A few years after its discovery as a magnetar, SGR J1935+2154 started a new burst-active phase on 2020 April 27, accompanied by a large enhancement of its X-ray persistent emission. Radio ...single bursts were detected during this activation, strengthening the connection between magnetars and fast radio bursts. We report on the X-ray monitoring of SGR J1935+2154 from ∼3 days prior to ∼3 weeks after its reactivation, using Swift, the Nuclear Spectroscopic Telescope Array (NuSTAR), and the Neutron Star Interior Composition Explorer (NICER). We detected X-ray pulsations in the NICER and NuSTAR observations, and constrained the spin period derivative to
s s
−1
(3
σ
c.l.). The pulse profile showed a variable shape switching between single and double-peaked as a function of time and energy. The pulsed fraction decreased from ∼34% to ∼11% (5–10 keV) over ∼10 days. The X-ray spectrum was well fit by an absorbed blackbody model with temperature decreasing from
kT
BB
∼ 1.6 to 0.45–0.6 keV, plus a nonthermal power-law component (Γ ∼ 1.2) observed up to ∼25 keV with NuSTAR. The 0.3–10 keV X-ray luminosity increased in less than 4 days from
erg s
−1
to about
erg s
−1
and then decreased again to
erg s
−1
over the following 3 weeks of the outburst, where
d
6.6
is the source distance in units of 6.6 kpc. We also detected several X-ray bursts, with properties typical of short magnetar bursts.
Abstract
We report on the results of a detailed phase-resolved spectroscopy of archival XMM–Newton observations of X-ray dim isolated neutron stars (XDINSs). Our analysis revealed a narrow and ...phase-variable absorption feature in the X-ray spectrum of RX J1308.6+2127. The feature has an energy of ∼740 eV and an equivalent width of ∼15 eV. It is detected only in ∼1/5 of the phase cycle, and appears to be present for the entire timespan covered by the observations (2001 December to 2007 June). The strong dependence on the pulsar rotation and the narrow width suggest that the feature is likely due to resonant cyclotron absorption/scattering in a confined high-B structure close to the stellar surface. Assuming a proton cyclotron line, the magnetic field strength in the loop is B
loop ∼ 1.7 × 1014 G, about a factor of ∼5 higher than the surface dipolar magnetic field (B
surf ∼ 3.4 × 1013 G). This feature is similar to that recently detected in another XDINS, RX J0720.4-3125, showing (as expected by theoretical simulations) that small-scale magnetic loops close to the surface might be common to many highly magnetic neutron stars (although difficult to detect with current X-ray instruments). Furthermore, we investigated the available XMM–Newton data of all XDINSs in search for similar narrow phase-dependent features, but could derive only upper limits for all the other sources.
The Swift satellite monitored the quiescence of the low-mass X-ray binary transient Aql X-1 on a weekly basis during the 2012 March-November interval. A total of 42 observations were carried out in ...the soft X-ray (0.3-10 keV) band with the X-ray telescope on board Swift. We investigated the X-ray variability properties of Aql X-1 during quiescence by tracking luminosity variations and characterizing them with a detailed spectral analysis. The source is highly variable in this phase and two bright flares were detected, with peak luminosities of ∼4 × 1034 erg s− 1 (0.3-10 keV). Quiescent X-ray spectra require both a soft thermal component below ∼2 keV and a hard component (a power-law tail) above ∼2 keV. Changes in the power-law normalization alone can account for the overall observed variability. Therefore, based on our data set, the quiescent X-ray emission of Aql X-1 is consistent with the cooling of the neutron star core and with mechanisms involving the accretion of matter on to the neutron star surface or magnetosphere.
Recent observations have led to the discovery of numerous optically selected binaries containing an undetected component with mass consistent with a compact object (neutron star (NS) or white dwarf). ...Using the Neil Gehrels Swift Observatory, we carried out X-ray and UV observations of a small sample of these binaries. Four systems are wide (with an orbital period P > 300 d), and were chosen because of their small distance ( d < 250 pc) and because the mass of the collapsed component favors a NS. Two others are compact systems ( P < 0.9 d) that show strong signs of containing a NS. The source 2MASS J15274848+3536572 was detected in the X-ray band with a flux of 5 × 10 −13 erg cm −2 s −1 and a spectrum well fitted by a power law or a thermal plasma emission model. This source also shows a UV (2200 Å) excess, which might indicate the presence of mass accretion. For the other targets, we derived X-ray flux upper limits of the order of 10 −13 erg cm −2 s −1 . These results are consistent with the hypothesis that the collapsed component in these six systems is a NS.
ABSTRACT The 6.67 hr periodicity and the variable X-ray flux of the central compact object (CCO) at the center of the supernova remnant RCW 103, named 1E 161348-5055, have been always difficult to ...interpret within the standard scenarios of an isolated neutron star (NS) or a binary system. On 2016 June 22, the Burst Alert Telescope (BAT) on board 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, Nuclear Spectroscopic Telescope Array, 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 2016 July). 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 NS, 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.
ABSTRACT
After 15 yr, in late 2018, the magnetar XTE J1810−197 underwent a second recorded X-ray outburst event and reactivated as a radio pulsar. We initiated an X-ray monitoring campaign to follow ...the timing and spectral evolution of the magnetar as its flux decays using Swift, XMM–Newton, NuSTAR, and NICER observations. During the year-long campaign, the magnetar reproduced similar behaviour to that found for the first outburst, with a factor of 2 change in its spin-down rate from ∼7.2 × 10−12 to ∼1.5 × 10−11 s s−1 after two months. Unique to this outburst, we confirm the peculiar energy-dependent phase shift of the pulse profile. Following the initial outburst, the spectrum of XTE J1810−197 is well modelled by multiple blackbody components corresponding to a pair of non-concentric, hot thermal caps surrounded by a cooler one, superposed to the colder star surface. We model the energy-dependent pulse profile to constrain the viewing and surface emission geometry and find that the overall geometry of XTE J1810−197 has likely evolved relative to that found for the 2003 event.
Abstract Recently, the Galactic magnetar SGR J1935+2154 has garnered attention due to its emission of an extremely luminous radio burst, reminiscent of fast radio bursts (FRBs). SGR J1935+2154 is one ...of the most active magnetars, displaying flaring events nearly every year, including outbursts as well as short and intermediate bursts. Here, we present our results on the properties of the persistent and bursting X-ray emission from SGR J1935+2154 during the initial weeks following its outburst on 2022 October 10. The source was observed with XMM-Newton and NuSTAR (quasi-)simultaneously during two epochs, separated by ∼5 days. The persistent emission spectrum is well described by an absorbed blackbody plus power-law model up to an energy of ∼25 keV. No significant changes were observed in the blackbody temperature ( kT BB ∼ 0.4 keV) and emitting radius ( R BB ∼ 1.9 km) between the two epochs. However, we observed a slight variation in the power-law parameters. Moreover, we detected X-ray pulsations in all the data sets and derived a spin-period derivative of P ̇ = 5.52 ( 5 ) × 10 − 11 s s −1 . This is 3.8 times larger than the value measured after the first recorded outburst in 2014. Additionally, we performed quasi-simultaneous radio observations using three 25–32 m class radio telescopes for a total of 92.5 hr to search for FRB-like radio bursts and pulsed emission. However, our analysis did not reveal any radio bursts or periodic emission.
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