376,540 research outputs found
Optical Identification of Four Hard X-ray Sources from the Swift All-Sky Survey
We present the results of our optical identifications of four hard X-ray
sources from the Swift all-sky survey. We obtained optical spectra for each of
the program objects with the 6-m BTA telescope (Special Astrophysical
Observatory, Russian Academy of Sciences, Nizhnii Arkhyz), which allowed their
nature to be established. Two sources (SWIFT J2237.2+6324} and SWIFT
J2341.0+7645) are shown to belong to the class of cataclysmic variables
(suspected polars or intermediate polars). The measured emission line width
turns out to be fairly large (FWHM ~ 15-25 A), suggesting the presence of
extended, rapidly rotating (v~400-600 km/s) accretion disks in the systems.
Apart from line broadening, we have detected a change in the positions of the
line centroids for SWIFT J2341.0+7645, which is most likely attributable to the
orbital motion of the white dwarf in the binary system. The other two program
objects (SWIFT J0003.3+2737 and SWIFT J0113.8+2515) are extragalactic in
origin: the first is a Seyfert 2 galaxy and the second is a blazar at redshift
z=1.594. Apart from the optical spectra, we provide the X-ray spectra for all
sources in the 0.6-10 keV energy band obtained from XRT/Swift data.Comment: 9 pages, 6 figures, will be published in Astronomy Letters, 38, No.5,
pp.281-289 (2012
Swift observations of the dwarf nova ASASSN-18fs
The All Sky Automated Survey for SuperNovae (ASAS-SN) reported a possible
Galactic dwarf nova ASASSN-18fs on 2018 March 19 at 13.2 mag in the V
band, with a quiescent magnitude of V17.6. Here we report on the follow-up
photometry using the {\it Neil Gehrels Swift Observatory}.Comment: Published by AAS Research Note
GRB 081203A: Swift UVOT captures the earliest ultraviolet spectrum of a gamma-ray burst
We present the earliest ultraviolet (UV) spectrum of a gamma-ray burst (GRB) as observed with the Swift Ultra-Violet/Optical Telescope (UVOT). The GRB 081203A spectrum was observed for 50 s with the UV-grism starting 251 s after the Swift-Burst-Alert-Telescope (BAT) trigger. During this time, the GRB was ≈13.4 mag (u filter) and was still rising to its peak optical brightness. In the UV-grism spectrum, we find a damped Lyα line, Lyβ and the Lyman continuum break at a redshift z= 2.05 ± 0.01. A model fit to the Lyman absorption implies a gas column density of log NH i= 22.0 ± 0.1 cm−2, which is typical of GRB host galaxies with damped Lyα absorbers. This observation of GRB 081203A demonstrates that for brighter GRBs (v≈ 14 mag) with moderate redshift (0.5 < z < 3.5) the UVOT is able to provide redshifts, and probe for damped Lyα absorbers within 4–6 min from the time of the Swift-BAT trigger
Swift Observations of GRB 050603: An afterglow with a steep late time decay slope
We report the results of Swift observations of the Gamma Ray Burst GRB
050603. With a V magnitude V=18.2 about 10 hours after the burst the optical
afterglow was the brightest so far detected by Swift and one of the brightest
optical afterglows ever seen. The Burst Alert Telescope (BAT) light curves show
three fast-rise-exponential-decay spikes with =12s and a fluence of
7.6 ergs cm in the 15-150 keV band. With an ergs it was also one of the most energetic
bursts of all times. The Swift spacecraft began observing of the afterglow with
the narrow-field instruments about 10 hours after the detection of the burst.
The burst was bright enough to be detected by the Swift UV/Optical telescope
(UVOT) for almost 3 days and by the X-ray Telescope (XRT) for a week after the
burst. The X-ray light curve shows a rapidly fading afterglow with a decay
index =1.76. The X-ray energy spectral index was
=0.71\plm0.10 with the column density in agreement with the
Galactic value. The spectral analysis does not show an obvious change in the
X-ray spectral slope over time. The optical UVOT light curve decays with a
slope of =1.8\plm0.2.
The steepness and the similarity of the optical and X-ray decay rates suggest
that the afterglow was observed after the jet break. We estimate a jet opening
angle of about 1-2Comment: 14 pages, accepted for publication in Ap
The spectroscopic evolution of the symbiotic-like recurrent nova V407 Cygni during its 2010 outburst. I. The shock and its evolution
On 2010 Mar 10, V407 Cyg was discovered in outburst, eventually reaching V< 8
and detected by Fermi. Using medium and high resolution ground-based optical
spectra, visual and Swift UV photometry, and Swift X-ray spectrophotometry, we
describe the behavior of the high-velocity profile evolution for this nova
during its first three months. The peak of the X-ray emission occurred at about
day 40 with a broad maximum and decline after day 50. The main changes in the
optical spectrum began at around that time. The He II 4686A line first appeared
between days 7 and 14 and initially displayed a broad, symmetric profile that
is characteristic of all species before day 60. Low-excitation lines remained
comparatively narrow, with v(rad,max) of order 200-400 km/s. They were
systematically more symmetric than lines such as [Ca V], [Fe VII], [Fe X], and
He II, all of which showed a sequence of profile changes going from symmetric
to a blue wing similar to that of the low ionization species but with a red
wing extended to as high as 600 km/s . The Na I D doublet developed a broad
component with similar velocity width to the other low-ionization species. The
O VI Raman features were not detected. We interpret these variations as
aspherical expansion of the ejecta within the Mira wind. The blue side is from
the shock penetrating into the wind while the red wing is from the low-density
periphery. The maximum radial velocities obey power laws, v(rad,max) t^{-n}
with n ~ 1/3 for red wing and ~0.8 for the blue. (truncated)Comment: Accepted for publication, A&A (submitted: 9 Oct 2010; accepted: 1 Dec
2010) in press; based on data obtained with Swift, Nordic Optical Telescope,
Ondrejov Observatory. Corrected typo, Fermi?LAT detection was at energies
above 100 MeV (with thanks to C. C. Cheung
Optical, near-IR and -ray observations of SN 2015J and its host galaxy
SN 2015J was discovered on April 27th 2015 and is classified as a type IIn
supernova. At first, it appeared to be an orphan SN candidate, i.e. without any
clear identification of its host galaxy. Here, we present the analysis of the
observations carried out {by the VLT 8-m class telescope with the FORS2 camera
in the R band and the Magellan telescope (6.5 m) equipped with the IMACS
Short-Camera (V and I filters) and the FourStar camera (Ks filter)}. We show
that SN 2015J resides in what appears to be a very compact galaxy establishing
a relation between the SN event and its natural host. We also present and
discuss archival and new -ray data centred on SN 2015J. At the time of the
supernova explosion, Swift/XRT observations were made and a weak X-ray source
was detected at the location of SN 2015J. Almost one year later, the same
source was unambiguously identified during serendipitous observations by
Swift/XRT and -Newton, clearly showing an enhancement of the 0.3-10 keV
band flux by a factor with respect to the initial state. Swift/XRT
observations show that the source is still active in the -rays at a level of
counts s. The unabsorbed X-ray luminosity derived from the
{\it XMM}-Newton slew and SWIFT observations, erg
s, places SN 2015J among the brightest young supernovae in X-rays.Comment: The Astrophysical Journal, Volume 850, Number
- …