A delayed transition to the hard state for 4U 1630-47 at the end of its 2010 outburst

Journal Article · Sun Aug 10 04:00:00 EDT 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/791/1/70· OSTI ID:22365358

Tomsick, John A. ^[1]; Yamaoka, Kazutaka ^[2]; Corbel, Stephane ^[3]; Kalemci, Emrah ^[4]; Migliari, Simone ^[5]; Kaaret, Philip ^[6]

---

1. Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450 (United States)
2. Solar-Terrestrial Environment Laboratory, Department of Particles and Astronomy, Nagoya University, Furocho, Chikusa-ku, Nagoya, Aichi 464-8601 (Japan)
3. AIM - Unité Mixte de Recherche CEA - CNRS - Université Paris VII - UMR 7158, CEA-Saclay, Service d'Astrophysique, F-91191 Gif-sur-Yvette Cedex (France)
4. Sabanci University, Orhanli-Tuzla, Istanbul 34956 (Turkey)
5. Department d'Astronomia i Meteorologia, Universitat de Barcelona, Marti I Franques 1, E-08028 Barcelona (Spain)
6. Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242 (United States)

Here we report on Swift and Suzaku observations near the end of an outburst from the black hole transient 4U 1630-47 and Chandra observations when the source was in quiescence. 4U 1630-47 made a transition from a soft state to the hard state ∼50 days after the main outburst ended. During this unusual delay, the flux continued to drop, and one Swift measurement found the source with a soft spectrum at a 2-10 keV luminosity of L = 1.07 × 10{sup 35} erg s{sup –1} for an estimated distance of 10 kpc. While such transients usually make a transition to the hard state at L/L{sub Edd} = 0.3%-3%, where L{sub Edd} is the Eddington luminosity, the 4U 1630-47 spectrum remained soft at L/L{sub Edd} = 0.008 M{sub 10}{sup −1}% (as measured in the 2-10 keV band), where M{sub 10} is the mass of the black hole in units of 10 M{sub ☉}. An estimate of the luminosity in the broader 0.5-200 keV bandpass gives L/L{sub Edd} = 0.03 M{sub 10}{sup −1}%, which is still an order of magnitude lower than typical. We also measured an exponential decay of the X-ray flux in the hard state with an e-folding time of 3.39 ± 0.06 days, which is much less than previous measurements of 12-15 days during decays by 4U 1630-47 in the soft state. With the ∼100 ks Suzaku observation, we do not see evidence for a reflection component, and the 90% confidence limits on the equivalent width of a narrow iron Kα emission line are <40 eV for a narrow line and <100 eV for a line of any width, which is consistent with a change of geometry (either a truncated accretion disk or a change in the location of the hard X-ray source) in the hard state. Finally, we report a 0.5-8 keV luminosity upper limit of <2 × 10{sup 32} erg s{sup –1} in quiescence, which is the lowest value measured for 4U 1630-47 to date.

• OSTI ID: 22365358
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 791; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
BLACK HOLES
DECAY
EMISSION
EV RANGE
HARD X RADIATION
IRON
KEV RANGE
LUMINOSITY
MASS
REFLECTION
SPECTRA
STARS
TRANSIENTS