4 research outputs found
Studying the variability of fluorescence emission and the presence of clumpy wind in HMXB GX 3012 using XMM-Newton
We present the results from an analysis of data from an \textit{XMM-Newton}
observation of the accreting high mass X-ray binary pulsar GX 3012. Spectral
analysis in the non-flaring segment of the observation revealed that the
equivalent width of the iron fluorescence emission is correlated with the
observed absorption column density and the ratio of the iron K and
K line strength varied with the flux of the source. Coherent pulsations
were detected with the spin period of the pulsar of 687.90.1 s, and a
secondary pulsation was also detected with a period of 671.80.2 s, most
prominent in the energy band of the iron line. At the spin period of the
neutron star, the pulsation of the iron line has a low amplitude and the
profile is different from the continuum. Pulse phase-resolved spectroscopy also
revealed pulsations of the iron emission line during the non-flaring segment of
the light curve. At the secondary period, both the iron line and the continuum
have nearly identical pulse fraction and pulse profile. The additional
periodicity can be attributed to the beat frequency between the spin of the
neutron star and the Keplerian frequency of a stellar wind clump in retrograde
motion around the neutron star. Reprocessed X-ray emissions originating from
the clump can produce the observed secondary pulsations both in the continuum
and the iron fluorescence line. The clump rotating around the neutron star is
estimated to be approximately five lt-s away from the neutron star.Comment: 11 pages, 15 figures, Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
An investigation of the "10 keV feature" in the spectra of Accretion Powered X-ray Pulsars with NuSTAR
Some of the accreting X-ray pulsars are reported to exhibit a peculiar
spectral feature at 10 keV, known as the "10 keV feature". The feature
has been characterized as either an emission line or an absorption line, and
its origin is unknown. It has been found in multiple observations of the same
source by different observatories, but not all the observations of any
particular source consistently showed the presence of it. In this work, we have
carried out a systematic investigation for the presence of the "10 keV feature"
using data from NuSTAR, a low background spectroscopic observatory having
uninterrupted wide band coverage on either side of 10 keV. We performed a
systematic spectral analysis on 58 archival NuSTAR observations of 30 bright
X-ray pulsars. The 379 keV spectral continua of these selected sources were
fitted with a model chosen on the basis of its fitting quality in 315 keV
and model simplicity, and then inspected for the presence of the "10 keV
feature". Our analysis indicates the presence of such a feature in 16 out of 58
the NuSTAR observations of 11 different sources and is fitted with a Gaussian
absorption model centered around 10 keV. Our analysis also suggests that such a
feature could be wrongly detected if flare data is not analyzed separately from
persistent emission.Comment: 28 pages, 32 figures, Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Detection of a cyclotron line in the Be X-ray pulsar IGR J060742205
IGR J0607.4+2205 is a transient Be X-ray binary discovered two decades ago.
IGR J0607.4+2205 underwent an outburst in 2023 during which it was observed
twice with \textit{NuSTAR}. The main goal of this work is to model the
broadband X-ray spectrum of IGR J0607.4+2205 during the outburst and to study
the variations of the spectral and timing features at different intensities. We
extracted the light curve and spectrum of the source from the two
\textit{NuSTAR} observations carried out during the recent outburst in the
energy range of 378 keV. We used the epoch folding technique to find
pulsation from the source and to study the changes in emission characteristics
from the source with energy across an order of magnitude variation in source
luminosity. IGR J0607.4+2205 shows pulsations with a period of 347.6 s
during both the observations, with a pulse fraction of 50\%. The
broadband spectrum of the source was modelled using a power-law continuum with
a high-energy cutoff. During the first observation, a cyclotron absorption line
at 51 keV was also present in the source with an optical depth of
1.3. However, no cyclotron line feature was detected in the second
observation when the source was an order of magnitude fainter. Additionally,
soft excess was detected in the second observation, which was modelled with a
black body component emerging from close to the neutron star (NS). We report
the first ever detection of a cyclotron line in the broadband spectrum of IGR
J0607.4+2205 centred at 511 keV. The magnetic field strength of the NS is
estimated to be 4 G from the centroid energy of the
absorption line. A significant change is observed in the pulse profile with
luminosity during the decay of the outburst, indicating an associated change in
the beaming pattern.Comment: Accepted for publication in Astronomy & Astrophysic
Science with the Daksha High Energy Transients Mission
We present the science case for the proposed Daksha high energy transients
mission. Daksha will comprise of two satellites covering the entire sky from
1~keV to ~MeV. The primary objectives of the mission are to discover and
characterize electromagnetic counterparts to gravitational wave source; and to
study Gamma Ray Bursts (GRBs). Daksha is a versatile all-sky monitor that can
address a wide variety of science cases. With its broadband spectral response,
high sensitivity, and continuous all-sky coverage, it will discover fainter and
rarer sources than any other existing or proposed mission. Daksha can make key
strides in GRB research with polarization studies, prompt soft spectroscopy,
and fine time-resolved spectral studies. Daksha will provide continuous
monitoring of X-ray pulsars. It will detect magnetar outbursts and high energy
counterparts to Fast Radio Bursts. Using Earth occultation to measure source
fluxes, the two satellites together will obtain daily flux measurements of
bright hard X-ray sources including active galactic nuclei, X-ray binaries, and
slow transients like Novae. Correlation studies between the two satellites can
be used to probe primordial black holes through lensing. Daksha will have a set
of detectors continuously pointing towards the Sun, providing excellent hard
X-ray monitoring data. Closer to home, the high sensitivity and time resolution
of Daksha can be leveraged for the characterization of Terrestrial Gamma-ray
Flashes.Comment: 19 pages, 7 figures. Submitted to ApJ. More details about the mission
at https://www.dakshasat.in