1,985 research outputs found
A search for near infrared counterparts of 3 pulsar wind nebulae
While pulsar wind nebulae (PWNe) and their associated isolated pulsars are
commonly detected at X-ray energies, they are much rarer at near infrared (nIR)
and optical wavelengths. Here we examine three PWN systems in the Galactic
plane - IGR J14003-6326, HESS J1632-478 and IGR J18490-0000 - in a bid to
identify optical/nIR emission associated with either the extended PWNe or their
previously detected X-ray point sources. We obtain optical/nIR images of the
three fields with the ESO - New Technology Telescope and apply standard
photometric and astrometric calibrations. We find no evidence of any extended
emission associated with the PWNe in any of the fields; neither do we find any
new counterparts to the X-ray point sources, except to confirm the magnitude of
the previously identified counterpart candidate of IGR J18490-0000. Further
observations are required to confirm the association of the nIR source to IGR
J18490-0000 and to detect counterparts to IGR J14003-6326 and HESS J1632-478,
while a more accurate X-ray position is required to reduce the probability of a
chance superposition in the field of the latter.Comment: Accepted to A&A (4 pages, 1 figure
The nature of the X-ray binary IGR J19294+1816 from INTEGRAL, RXTE, and Swift observations
We report the results of a high-energy multi-instrumental campaign with
INTEGRAL, RXTE, and Swift of the recently discovered INTEGRAL source IGR
J19294+1816. The Swift/XRT data allow us to refine the position of the source
to RA= 19h 29m 55.9s Dec=+18deg 18' 38.4" (+- 3.5"), which in turn permits us
to identify a candidate infrared counterpart. The Swift and RXTE spectra are
well fitted with absorbed power laws with hard (Gamma ~ 1) photon indices.
During the longest Swift observation, we obtained evidence of absorption in
true excess to the Galactic value, which may indicate some intrinsic absorption
in this source. We detected a strong (P=40%) pulsation at 12.43781 (+-0.00003)
s that we interpret as the spin period of a pulsar. All these results, coupled
with the possible 117 day orbital period, point to IGR J19294+1816 being an
HMXB with a Be companion star. However, while the long-term INTEGRAL/IBIS/ISGRI
18--40 keV light curve shows that the source spends most of its time in an
undetectable state, we detect occurrences of short (~2000-3000 s) and intense
flares that are more typical of supergiant fast X-ray transients. We therefore
cannot make firm conclusions on the type of system, and we discuss the possible
implications of IGR J19294+1816 being an SFXT.Comment: 7 pages, 6 figures, accepted for publication in A&
Digital Quantum Rabi and Dicke Models in Superconducting Circuits
We propose the analog-digital quantum simulation of the quantum Rabi and
Dicke models using circuit quantum electrodynamics (QED). We find that all
physical regimes, in particular those which are impossible to realize in
typical cavity QED setups, can be simulated via unitary decomposition into
digital steps. Furthermore, we show the emergence of the Dirac equation
dynamics from the quantum Rabi model when the mode frequency vanishes. Finally,
we analyze the feasibility of this proposal under realistic superconducting
circuit scenarios.Comment: 5 pages, 3 figures. Published in Scientific Report
Can Maxwell's equations be obtained from the continuity equation?
We formulate an existence theorem that states that given localized scalar and
vector time-dependent sources satisfying the continuity equation, there exist
two retarded fields that satisfy a set of four field equations. If the theorem
is applied to the usual electromagnetic charge and current densities, the
retarded fields are identified with the electric and magnetic fields and the
associated field equations with Maxwell's equations. This application of the
theorem suggests that charge conservation can be considered to be the
fundamental assumption underlying Maxwell's equations.Comment: 14 pages. See the comment: "O. D. Jefimenko, Causal equations for
electric and magnetic fields and Maxwell's equations: comment on a paper by
Heras [Am. J. Phys. 76, 101 (2008)].
INTEGRAL, XMM-Newton and ESO/NTT identification of AX J1749.1-2733: an obscured and probably distant Be/X-ray binary
AX J1749.1-2733 is an unclassified transient X-ray source discovered during
surveys by ASCA in 1993-1999. A multi-wavelength study in NIR, optical, X-rays
and hard X-rays is undertaken in order to determine its nature. AX J1749.1-2733
is a new high-mass X-ray binary pulsar with an orbital period of 185.5+/-1.1 d
(or 185.5/f with f=2,3 or 4) and a spin period of ~66 s, parameters typical of
a Be/X-ray binary. The outbursts last ~12 d. A spin-down of 0.08+/-0.02 s/yr is
also observed, very likely due to the propeller effect. The most accurate X-ray
position is R.A. (2000) =17h49m06.8s and Dec. = -27deg32'32".5 (unc. 2"). The
high-energy broad-band spectrum is well-fitted with an absorbed powerlaw and a
high-energy cutoff with values NH=(20+/-1)e22 cm-2, Gamma=1.0+/-0.1, and
Ecut=21+/-3 keV. The only optical/NIR candidate counterpart within the X-ray
error circle has magnitudes of R=21.9+/-0.1, I=20.92+/-0.09, J=17.42+/-0.03,
H=16.71+/-0.02, and Ks=15.75+/-0.07, which points towards a Be star located far
away (> 8.5 kpc) and highly absorbed (NH~1.7e22 cm-2). The average 22-50 keV
luminosity is (0.4-0.9)e36 erg/s during the long outbursts and 3e36 erg/s
during the bright flare that occurred on MJD 52891 for an assumed distance of
8.5 kpc.Comment: accepted A&A, 11 pages, 9 figure
The Spitzer Atlas of Stellar Spectra
We present the Spitzer Atlas of Stellar Spectra (SASS), which includes 159
stellar spectra (5 to 32 mic; R~100) taken with the Infrared Spectrograph on
the Spitzer Space Telescope. This Atlas gathers representative spectra of a
broad section of the Hertzsprung-Russell diagram, intended to serve as a
general stellar spectral reference in the mid-infrared. It includes stars from
all luminosity classes, as well as Wolf-Rayet (WR) objects. Furthermore, it
includes some objects of intrinsic interest, like blue stragglers and certain
pulsating variables. All the spectra have been uniformly reduced, and all are
available online. For dwarfs and giants, the spectra of early-type objects are
relatively featureless, dominated by Hydrogen lines around A spectral types.
Besides these, the most noticeable photospheric features correspond to water
vapor and silicon monoxide in late-type objects and methane and ammonia
features at the latest spectral types. Most supergiant spectra in the Atlas
present evidence of circumstellar gas. The sample includes five M supergiant
spectra, which show strong dust excesses and in some cases PAH features.
Sequences of WR stars present the well-known pattern of lines of HeI and HeII,
as well as forbidden lines of ionized metals. The characteristic flat-top shape
of the [Ne III] line is evident even at these low spectral resolutions. Several
Luminous Blue Variables and other transition stars are present in the Atlas and
show very diverse spectra, dominated by circumstellar gas and dust features. We
show that the [8]-[24] Spitzer colors (IRAC and MIPS) are poor predictors of
spectral type for most luminosity classes.Comment: Accepted by ApJS; Atlas contents available from:
http://web.ipac.caltech.edu/staff/ardila/Atlas/index.html;
http://irsa.ipac.caltech.edu/data/SPITZER/SASS/; 70 PDF pages, including
figure
- …