SN2010da/NGC 300 ULX-1 was first detected as a supernova impostor in 2010 May and was recently discovered to be a pulsating ultraluminous X-ray source. In this Letter, we present Very Large ...Telescope/X-shooter spectra of this source obtained in 2018 October, covering the wavelength range 350-2300 nm. The J- and H-bands clearly show the presence of a red supergiant (RSG) donor star that is best matched by a MARCS stellar atmosphere with Teff = 3650-3900 K and log(Lbol/L ) = 4.25 0.10, which yields a stellar radius R = 310 70R . To fit the full spectrum, two additional components are required: a blue excess that can be fitted either by a hot blackbody (T 20,000 K) or a power law (spectral index 4) and is likely due to X-ray emission reprocessed in the outer accretion disk or the donor star; and a red excess that is well fitted by a blackbody with a temperature of ∼1100 K, and is likely due to warm dust in the vicinity of SN2010da. The presence of an RSG in this system implies an orbital period of at least 0.8-2.1 yr, assuming Roche-lobe overflow. Given the large donor-to-compact object mass ratio, orbital modulations of the radial velocity of the RSG are likely undetectable. However, the radial velocity amplitude of the neutron star is large enough (up to 40-60 km s−1) to potentially be measured in the future, unless the system is viewed at a very unfavorable inclination.
Swift and NuSTAR observations of GW170817 Evans, P. A.; Cenko, S. B.; Kennea, J. A. ...
Science (American Association for the Advancement of Science),
12/2017, Volume:
358, Issue:
6370
Journal Article
Peer reviewed
Open access
With the first direct detection of merging black holes in 2015, the era of gravitational wave (GW) astrophysics began. A complete picture of compact object mergers, however, requires the detection of ...an electromagnetic (EM) counterpart. We report ultraviolet (UV) and x-ray observations by Swift and the Nuclear Spectroscopic Telescope Array of the EM counter part of the binary neutron star merger GW170817. The bright, rapidly fading UV emission indicates a high mass (≈0.03 solar masses) wind-driven outflow with moderate electron fraction (Yₑ ≈ 0.27). Combined with the x-ray limits, we favor an observer viewing angle of ≈30° away from the orbital rotation axis, which avoids both obscuration fromthe heaviest elements in the orbital plane and a direct view of any ultrarelativistic, highly collimated ejecta (a γ-ray burst afterglow).
GRB 130925A was an unusual gamma ray burst (GRB), consisting of three distinct episodes of high-energy emission spanning ∼20 ks, making it a member of the proposed category of ‘ultralong’ bursts. It ...was also unusual in that its late-time X-ray emission observed by Swift was very soft, and showed a strong hard-to-soft spectral evolution with time. This evolution, rarely seen in GRB afterglows, can be well modelled as the dust-scattered echo of the prompt emission, with stringent limits on the contribution from the normal afterglow (i.e. external shock) emission. We consider and reject the possibility that GRB 130925A was some form of tidal disruption event, and instead show that if the circumburst density around GRB 130925A is low, the long duration of the burst and faint external shock emission are naturally explained. Indeed, we suggest that the ultralong GRBs as a class can be explained as those with low circumburst densities, such that the deceleration time (at which point the material ejected from the nascent black hole is decelerated by the circumburst medium) is ∼20 ks, as opposed to a few hundred seconds for the normal long GRBs. The increased deceleration radius means that more of the ejected shells can interact before reaching the external shock, naturally explaining both the increased duration of GRB 130925A, the duration of its prompt pulses, and the fainter-than-normal afterglow.
Abstract
On 2016 July 30 (MJD 57599), observations of the Small Magellanic Cloud by Swift/XRT found an increase in X-ray counts coming from a position consistent with the Be/X-ray binary pulsar SMC ...X-3. Follow-up observations on 2016 August 3 (MJD 57603) and 2016 August 10 (MJD 57610) revealed a rapidly increasing count rate and confirmed the onset of a new X-ray outburst from the system. Further monitoring by Swift began to uncover the enormity of the outburst, which peaked at 1.2 × 1039 erg s−1 on 2016 August 25 (MJD 57625). The system then began a gradual decline in flux that was still continuing over 5 months after the initial detection. We explore the X-ray and optical behaviour of SMC X-3 between 2016 July 30 and 2016 December 18 during this super-Eddington outburst. We apply a binary model to the spin-period evolution that takes into account the complex accretion changes over the outburst, to solve for the orbital parameters. Our results show SMC X-3 to be a system with a moderately low eccentricity amongst the Be/X-ray binary systems and to have a dynamically determined orbital period statistically consistent with the prominent period measured in the OGLE optical light curve. Our optical and X-ray derived ephemerides show that the peak in optical flux occurs roughly 6 d after periastron. The measured increase in I-band flux from the counterpart during the outburst is reflected in the measured equivalent width of the Hα line emission, though the Hα emission itself seems variable on sub-day time-scales, possibly due to the NS interacting with an inhomogeneous disc.
Two short (< 2 s) γ-ray bursts (GRBs) have recently been localized and fading afterglow counterparts detected. The combination of these two results left unclear the nature of the host galaxies of the ...bursts, because one was a star-forming dwarf, while the other was probably an elliptical galaxy. Here we report the X-ray localization of a short burst (GRB 050724) with unusual γ-ray and X-ray properties. The X-ray afterglow lies off the centre of an elliptical galaxy at a redshift of z = 0.258 (ref. 5), coincident with the position determined by ground-based optical and radio observations. The low level of star formation typical for elliptical galaxies makes it unlikely that the burst originated in a supernova explosion. A supernova origin was also ruled out for GRB 050709 (refs 3, 31), even though that burst took place in a galaxy with current star formation. The isotropic energy for the short bursts is 2-3 orders of magnitude lower than that for the long bursts. Our results therefore suggest that an alternative source of bursts-the coalescence of binary systems of neutron stars or a neutron star-black hole pair-are the progenitors of short bursts.
The Swift-BAT Hard X-Ray Transient Monitor Krimm, H. A.; Holland, S. T.; Corbet, R. H. D. ...
The Astrophysical journal. Supplement series,
11/2013, Volume:
209, Issue:
1
Journal Article
Peer reviewed
Open access
The Swift/Burst Alert Telescope (BAT) hard X-ray transient monitor provides near real-time coverage of the X-ray sky in the energy range 15-50 keV. The BAT observes 88% of the sky each day with a ...detection sensitivity of 5.3 mCrab for a full-day observation and a time resolution as fine as 64 s. The three main purposes of the monitor are (1) the discovery of new transient X-ray sources, (2) the detection of outbursts or other changes in the flux of known X-ray sources, and (3) the generation of light curves of more than 900 sources spanning over eight years. The primary interface for the BAT transient monitor is a public Web site. Between 2005 February 12 and 2013 April 30, 245 sources have been detected in the monitor, 146 of them persistent and 99 detected only in outburst. Among these sources, 17 were previously unknown and were discovered in the transient monitor. In this paper, we discuss the methodology and the data processing and filtering for the BAT transient monitor and review its sensitivity and exposure.We provide a summary of the source detections and classify them according to the variability of their light curves. Finally, we review all new BAT monitor discoveries. For the new sources that are previously unpublished, we present basic data analysis and interpretations.
Until recently, X-ray flares during the afterglow of gamma-ray bursts (GRBs) were a rarely detected phenomenon; thus, their nature is unclear. During the afterglow of GRB 050502B, the largest X-ray ...flare ever recorded rose rapidly above the afterglow light curve detected by the Swift X-Ray Telescope. The peak flux of the flare was >500 times that of the underlying afterglow, and it occurred >12 minutes after the nominal prompt burst emission. The fluence of this X-ray flare, (1.0 c 0.05) x 10 super(-6) ergs cm super(-2) in the 0.2-10.0 keV energy band, exceeded the fluence of the nominal prompt burst. The spectra during the flare were significantly harder than those measured before and after the flare. Later in time, there were additional flux increases detected above the underlying afterglow, as well as a break in the afterglow light curve. All evidence presented below, including spectral and, particularly, timing information during and around the giant flare, suggests that this giant flare was the result of internal dissipation of energy due to late central engine activity, rather than an afterglow-related effect. We also find that the data are consistent with a second central engine activity episode, in which the ejecta is moving slower than that of the initial episode, causing the giant flare and then proceeding to overtake and refresh the afterglow shock, thus causing additional activity at even later times in the light curve.
Abstract
The Swift Deep Galactic Plane Survey (DGPS) is a Swift Key Project consisting of 380 tiled pointings covering ∼40 deg
2
of the Galactic plane between longitude 10 < ∣
l
∣ < 30 deg and ...latitude ∣
b
∣ < 0.5 deg. Each pointing has a 5 ks exposure, yielding a total of 1.9 Ms spread across the entire survey footprint. Phase I observations were carried out between 2017 March and 2021 May. The survey is complete to depth
L
X
> 10
34
erg s
−1
to the edge of the Galaxy. The main survey goal is to produce a rich sample of new X-ray sources and transients, while also covering a broad discovery space. Here, we introduce the survey strategy and present a catalog of sources detected during Phase I observations. In total, we identify 928 X-ray sources, of which 348 are unique to our X-ray catalog. We report on the characteristics of sources in our catalog and highlight sources newly classified and published by the DGPS team.
An anti-glitch in a magnetar Archibald, R F; Kaspi, V M; Ng, C-Y ...
Nature (London),
05/2013, Volume:
497, Issue:
7451
Journal Article
Peer reviewed
Open access
Magnetars are neutron stars with X-ray and soft γ-ray outbursts thought to be powered by intense internal magnetic fields. Like conventional neutron stars in the form of radio pulsars, magnetars ...exhibit 'glitches' during which angular momentum is believed to be transferred between the solid outer crust and the superfluid component of the inner crust. The several hundred observed glitches in radio pulsars and magnetars have involved a sudden spin-up (increase in the angular velocity) of the star, presumably because the interior superfluid was rotating faster than the crust. Here we report X-ray timing observations of the magnetar 1E 2259+586 (ref. 8), which exhibited a clear 'anti-glitch'--a sudden spin-down. We show that this event, like some previous magnetar spin-up glitches, was accompanied by multiple X-ray radiative changes and a significant spin-down rate change. Such behaviour is not predicted by models of neutron star spin-down and, if of internal origin, is suggestive of differential rotation in the magnetar, supporting the need for a rethinking of glitch theory for all neutron stars.
MAXI J1659−152 is a bright X-ray transient black-hole candidate binary system discovered in September 2010. We report here on MAXI, RXTE, Swift, and XMM-Newton observations during its 2010/2011 ...outburst. We find that during the first one and a half week of the outburst the X-ray light curves display drops in intensity at regular intervals, which we interpret as absorption dips. About three weeks into the outbursts, again drops in intensity are seen. These dips have, however, a spectral behaviour opposite to that of the absorption dips, and are related to fast spectral state changes (hence referred to as transition dips). The absorption dips recur with a period of 2.414 ± 0.005 h, which we interpret as the orbital period of the system. This implies that MAXI J1659−152 is the shortest period black-hole candidate binary known to date. The inclination of the accretion disk with respect to the line of sight is estimated to be 65–80°. We propose the companion to the black-hole candidate to be close to an M5 dwarf star, with a mass and radius of about 0.15–0.25 M⊙ and 0.2–0.25 R⊙, respectively. We derive that the companion had an initial mass of about 1.5 M⊙, which evolved to its current mass in about 5–6 billion years. The system is rather compact (orbital separation of ≳1.33 R⊙), and is located at a distance of 8.6 ± 3.7 kpc, with a height above the Galactic plane of 2.4 ± 1.0 kpc. The characteristics of short orbital period and high Galactic scale height are shared with two other transient black-hole candidate X-ray binaries, i.e., XTE J1118+480 and Swift J1735.5−0127. We suggest that all three are kicked out of the Galactic plane into the halo, rather than being formed in a globular cluster.
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