[vsnet-alert 12208] MAXI J1659-152

[Taichi Kato]

   Two selected ATEL articles on the new BH X-ray transient.  The object
may be too absorbed for optical wavelengths, but it would be observable
in the infrared.

===

ATEL #2877                                                           ATEL #2877

Title:          MAXI J1659-152: Swift localization and monitoring 
Author: J. A. Kennea (PSU), H. Krimm (CRESST/GSFC/USRA), V. Mangano
                (INAF-IASFPA), P. Curran (CEA-Saclay),  P. Romano (INAF-IASFPA) and
                P. Evans (U. Leicester), D. N. Burrows (PSU) 
Queries:        kennea at astro.psu.edu
Posted: 28 Sep 2010;  13:04  UT
Subjects:       X-ray, Transients



We report on Swift monitoring of the newly discovered Galactic Transient
source MAXI J1659-152 (Negoro et al, 2010, ATEL #2873; Mangano et al.,
2010, GCN #11296). MAXI J1659-152 was first detected in the Swift/BAT hard
X-ray transient monitor on September 24th, 2010 at a low significance.
The 15-50 keV flux then rose sharply to 0.033 +/- 0.012 ct/s/cm^2 (150
mCrab) on September 25th, 2010. The count rate continues to rise, although
more slowly, and is now 0.046 +/- 0.003 ct/s/cm^2 (~200 mCrab).       

Swift XRT has performed monitoring observations in WT (timing) mode of
this transient since it triggered the Swift/BAT at 08:05UT on September
25th, 2010. The XRT light-curve of MAXI J1659-152 shows a steady rise since
this time, rising from approximately 30 XRT counts/s at the time of the
BAT detection, to ~200 XRT counts/s during on September 27th, 2010. The
XRT light-curve can be roughly modeled as a constant+power-law, with the
best fit value of the rising power law slope being 0.805+/-0.002.     

The light-curve also shows frequent dips, which may be an indication of
eclipses. At this time it is not possible to determine any periodicity
from the XRT data, as it appears that if periodicity exists, it is close
to being a multiple of the Swift orbit timescale, making measurement difficult.
Further Swift observations may allow an eclipse period to be pinned down
if present.      

The spectrum of MAXI J1659-152 is well fit by an absorbed power-law model,
with N_H = 2 x 10^21 cm^-2, and a photon index of ~1.7. However plotting
the hardness ratio as a function of time shows that the source shows some
evidence for softening as the source gets brighter.      

In order to obtain an accurate localization of the transient, we uploaded
an ~1ks imaging observation starting at 14:57UT on September 27th, 2010.
Using 975 s of XRT Photon Counting mode data and 2 UVOT images, we find
an astrometrically corrected X-ray position (using the XRT-UVOT alignment
and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 254.75650,
-15.25848 which is equivalent to:   

RA (J2000): 16 59 1.56   
Dec (J2000): -15 15 30.5   

with an uncertainty of 1.7 arcsec (radius, 90% confidence). This position
lies 2.8 arcseconds from the proposed UVOT counterpart (Marshal 2010, GCN
#11298), given the errors on the XRT and UVOT positions, this equates to
a 2.6 sigma difference,  we therefore suggest that the XRT position is
consistent with the UVOT counterpart to MAXI J1659-152.       

Swift monitoring observations of this source are on-going. Multi-wavelength
observations of this source are encouraged in order to determine the nature
of MAXI J1659-152.       

This work made use of data supplied by the UK Swift Science Data Centre
at the University of Leicester (Evans et al. 2009, MNRAS, 397, 1177). 

===

ATEL #2881                                                           ATEL #2881

Title:          MAXI J1659-152 is a BH candidate
Author: M. Kalamkar (Amsterdam), Y. Yang (Amsterdam), D. Altamirano
                (Amsterdam), P. Casella (Southampton),  M. Linares (MIT), A. Patruno
                (Amsterdam),  M. Armas-Padilla (Amsterdam), Y. Cavecchi (Amsterdam),
                N. Degenaar (Amsterdam), D. Russell (Amsterdam), R. Kaur (Amsterdam),
                M. van der Klis (Amsterdam), A. Watts (Amsterdam), R. Wijnands (Amsterdam),
                N. Rea (CSIC-IEEC)
Queries:        m.n.kalamkar at uva.nl
Posted: 28 Sep 2010;  17:38  UT
Subjects:       X-ray, Binaries, Black Holes, Transients

                (Amsterdam),  M. Armas-Padilla (Amsterdam), Y. Cavecchi (Amsterdam),
                N. Degenaar (Amsterdam), D. Russell (Amsterdam), R. Kaur (Amsterdam),
                M. van der Klis (Amsterdam), A. Watts (Amsterdam), R. Wijnands (Amsterdam),
                N. Rea (CSIC-IEEC)
Queries:        m.n.kalamkar at uva.nl
Posted: 28 Sep 2010;  17:38  UT
Subjects:       X-ray, Binaries, Black Holes, Transients

We report on a pointed RXTE/PCA observation of the transient source MAXI
J1659-152 (Atel #2873,#2874,#2875,#2877,#2880 GCN #11296,#11299,   #11307
        - initially referred to as GRB 100925A). The observation   started on
28th September 2010 at 00:51:10 UT, for a total integration   time of ~
16 ks. We find strong variability in the X-ray light curve (average of
~520 cnts/sec/PCU in the 2-60 keV range). The fractional rms amplitude
in the 0.01-100 Hz frequency range is   23.7(6)%.            We find a
strong QPO with a centroid frequency of 1.646(3) Hz (12.6(1)%   fractional
rms), as well as its second harmonic (peak frequency =   3.34(2) Hz, fractional
rms = 5.4(3)%). The characteristics of the power   spectrum suggest that
it is a type-C QPO, strongly indicating that   MAXI J1659-152 is a stellar-mass
black-hole transient. By analogy with   many other BH candidates (Belloni
et. al. 2010,The Jet Paradigm, Lecture Notes in Physics, Volume 794), we
infer that the source might have started its transition   from the hard
state to the soft state, currently being in its   hard-intermediate state.
An increase in QPO frequency and a decrease in   overall amplitude is expected
in the next few days, leading to a   spectral transition into the soft-intermediate
state and eventually to   the soft state.         We would like to thank
the RXTE Team for promptly scheduling the   observations.