267 research outputs found
A New Narrow-Line Seyfert 1 galaxy : RXJ1236.9+2656
We report identification of a narrow-line Seyfert 1 galaxy RXJ1236.9+2656.
X-ray emission from the NLS1 galaxy undergoes long-term variability with
0.1--2.0 keV flux changing by a factor of 2 within about 3 yr. The ROSAT PSPC
spectrum of RXJ1236.9+2656 is well represented by a power-law of Gamma = 3.7
absorbed by matter in our own Galaxy (N_H = 1.33X10^20 cm**-2). Intrinsic soft
X-ray luminosity of the NLS1 galaxy is estimated to be 1.5X10^43 erg/s in the
energy band of 0.1-2.0 keV. The optical spectrum of RXJ1236.9+2656 is typical
of NLS1 galaxies and shows narrow Balmer emission lines (1100 km/s < FWHM <
1700 km/s) of Hbeta, Halpha, and forbidden lines of [O III] and [N II]. Fe II
multiplets, usually present in optical spectra of NLS1 galaxies, are also
detected in RXJ1236.9+2656.Comment: 4 pages, A&A style Latex, To apear in A&A as a research not
A 10-day ASCA Observation of the Narrow-line Seyfert~1 galaxy IRAS 13224-3809
(Abridged) We present an analysis of a 10-day continuous ASCA observation of
the narrow-line Seyfert 1 galaxy IRAS 13224-3809. The soft (0.7-1.3 keV) and
hard (1.3-10 keV) X-ray band light curves binned to 5000s reveal trough-to-peak
variations by a factor >25 and 20, respectively. The light curves in the soft
and hard bands are strongly correlated without any significant delay. However,
this correlation is not entirely due to changes in the power-law flux alone but
also due to changes in the soft X-ray hump emission above the power law. The
presence of a soft X-ray hump below 2 keV, previously detected in ROSAT and
ASCA data, is confirmed. Time resolved spectroscopy using daily sampling
reveals changes in the power-law slope, with Gamma in the range 1.74-2.47,
however, day-to-day variations in Gamma are not significant. The Soft hump
emission is found to dominate the observed variability on a timescale of a
week, but on shorter timescales (20000s) the power-law component appears to
dominate the observed variability. Flux resolved spectroscopy reveals that at
high flux levels the power law becomes steeper and the soft hump more
pronounced. The steepening of the photon index with the fluxes in the soft and
hard bands can be understood in the framework of disk/corona models in which
accretion disk is heated by viscous dissipation as well as by reprocessing of
hard X-rays following an X-ray flare resulting from coronal dissipation through
magnetic reconnection events.Comment: 29 pages, 16 figures, To apear in A&
Variations in the Cyclotron Resonant Scattering Features during 2011 outburst of 4U 0115+63
We study the variations in the Cyclotron Resonant Scattering Feature (CRSF)
during 2011 outburst of the high mass X-ray binary 4U 0115+63 using
observations performed with Suzaku, RXTE, Swift and INTEGRAL satellites. The
wide-band spectral data with low energy coverage allowed us to characterize the
broadband continuum and detect the CRSFs. We find that the broadband continuum
is adequately described by a combination of a low temperature (kT ~ 0.8 keV)
blackbody and a power-law with high energy cutoff (Ecut ~ 5.4 keV) without the
need for a broad Gaussian at ~ 10 keV as used in some earlier studies. Though
winds from the companion can affect the emission from the neutron star at low
energies (< 3 keV), the blackbody component shows a significant presence in our
continuum model. We report evidence for the possible presence of two
independent sets of CRSFs with fundamentals at ~ 11 keV and ~ 15 keV. These two
sets of CRSFs could arise from spatially distinct emitting regions. We also
find evidence for variations in the line equivalent widths, with the 11 keV
CRSF weakening and the 15 keV line strengthening with decreasing luminosity.
Finally, we propose that the reason for the earlier observed anti-correlation
of line energy with luminosity could be due to modelling of these two
independent line sets (~ 11 keV and ~ 15 keV) as a single CRSF.Comment: 12 pages, 8 figures (4 in colour), 6 tables. Accepted for publication
in MNRAS. Typos corrected, Figure 8 changed and some changes to draf
Detection of the high energy cut-off from the Seyfert 1.5 galaxy NGC 5273
We perform the NuSTAR and Swift/XRT joint energy spectral fitting of
simultaneous observations from the broad-line Seyfert 1.5 galaxy NGC 5273. When
fitted with the combination of an exponential cut-off power-law and a
reflection model, a high energy cut-off is detected at 143 keV
with 2-sigma significance. Existence of such cut-off is also consistent with
the observed Comptonizing electron temperature when fitted with a
Comptonization model independently. We observe a moderate hard X-ray
variability of the source over the time-scale of ~12 years using INTEGRAL/ISGRI
observations in the energy range of 20-100 keV. When the hard band count rate
(6-20 keV) is plotted against the soft band count rate (3-6 keV), a hard offset
is observed. Our results indicate that the cut-off energy may not correlate
with the coronal X-ray luminosity in a simple manner. Similarities in
parameters that describe coronal properties indicate that the coronal structure
of NGC 5273 may be similar to that of the broad-line radio galaxy 3C 390.3 and
another galaxy MCG-5-23-16 where the coronal plasma is dominated by electrons,
rather than electron-positron pairs. Therefore, the coronal cooling is equally
efficient to the heating mechanism keeping the cut-off energy at low even at
the low accretion rate.Comment: 11 pages, 6 figures, 1 table, accepted for publication in MNRA
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