1. arXiv:1512.00778v1 Reporter: Wang Chen
WATCHDOG: A COMPREHENSIVE ALL-SKY DATABASE OF GALACTIC BLACK HOLE X-RAY BINARIES
arXiv: v1
Reporter: Wang Chen

2. Comprehensive black-Hole
WATCHDOG
the Whole-sky Alberta
Time-resolved
Comprehensive black-Hole
Database Of the Galaxy

3. outline Introduction Sample selection Data selection and analysis
Results
Discussion

4. Introduction-database
INTEGRAL, MAXI, RXTE, Swift
132 transient outbursts, 47 transient, 10 persistent accreting BHs.

5. Introduction-BHXB
Transient sources: LMXBs (M2 < 1M⊙ & A type or later )
HXMBs (SAX J )
quiescence: long and faint (∼ ergs-1)
outburst: thermal and viscous instability
Persistent sources: HMXBs (massive companion, type O or B), stellar wind
LMXBs (maintain bright outbursts for decades
GRS )

6. Introduction-outburst mechanism
The disk-instability model:
Quiescence (the accretion disk is in a cool, neutral state)
steady MT
T begins to rise
ionization of hydrogen (the magnetic field is locked into the disk, the disk rotates differentially)
magnetic field lines stretched
effective viscosity (magneto-rotational instability)
the material fall inwards faster (increase mass accretion rate)
Outburst
T decrease, hydrogen recombine

7. Introduction-evidence
systems that have high enough mass transfer rates to keep disks fully ionized tend to be persistent and systems that have mass transfer rates below this threshold tend to be transient (see Coriat et al and this work).
The positive correlation found between peak outburst luminosity and orbital period in transient XRBs.
observed outburst durations match relatively well with the viscous timescales of accretion disks in many BH systems

8. Introduction-arguments
systems have been observed to undergo rapid flux variability on timescales of hours, too quickly to be described by the global disk instability and too strong to be the result of “normal” variability seen in XRBs (e.g., XTE J ;Hjellming et al. 2000; Orosz et al. 2001).
Quiescent ultraviolet and optical flux are variable, presumably the result of variable mass transfer onto the accretion disk impact spot (e.g., 1A ; Cantrell et al. 2010; Froning et al. 2011).

9. Introduction-properties
Light curve:
the most prominently observed type is the fast rise exponential decay (FRED) outburst, numerous other features including linear decays, plateaus, multiple peaks, and complex variability have been observed (Chen et al. 1997).
Spectral:
the thermal disk black body spectral model, typically observed at low energies is attributed to direct soft photons from a geometrically thin, optically thick disk
the hard Comptonized spectral model, typically observed at higher energies, is thought to come from a hot, geometrically thick, optically thin inner coronal flow existing above and around the inner disk.

10. Introduction-the behavior pattern (HID)
Hard (Comptonized) State (HCS)
power-law component, index
high energy cutoff at ~ 100 kev
associated with radio jet
Soft (Disc-Dominated) State (SDS)
disk component peaking at ~1 kev
a weak power-law with
extends past ~ 500 kev
associated with higher luminosities
no radio emission, but have disk wind

11. Introduction-the behavior pattern (HID)
The intermediate State (IMS)
disk & steep power-law, with
an increase in X-ray luminosity
associated with high mass accretion rate
short time scales (hours to days)
Steep power-law state (SPL)
rapid variations in luminosity
softening and/or hardening of the source
‘dragon horn’ like feature
(can be seen in brightest phase of
many BHXBs)

12. Introduction-state transition
not all BHXB systems follow the basic “turtlehead” pattern during outburst. A number of transient systems have been observed to undergo outbursts that do not involve any complete state transitions (i.e., “hard-only” outbursts).
we still do not have a theoretical framework to explain all the observational behavior exhibited by BHXBs. Moreover, the physical parameter(s) that drives the critical instability that precipitates state transitions in BHXBs also remain largely unknown.

13. Introduction-observational techniques
Distance
Trigonometric parallax (3 sources)
Comparing the absolute magnitude to the apparent magnitude of the counterpart star
Using the observed proper motions of jet ejections
The interstellar absorption properties
Mass

14. Introduction-Black-hole determination
Ultra-soft + power law
Low-frequency quasi-periodic oscillations (LFQPOs)
A strong correlation between X-ray and radio emission in the hard spectral state.
The absence of observed type I X-ray bursts.
State transition?

15. Sample selection
Compiled a sample of 77 XRB and BHCs in the Milky Way and Magellanic Clouds.
66 are classified as transient, 8 are persistent, 3 are observed to be transient on long timescales (treated as persistent).
21 dynamically confirmed BH sources, 18 LMXBs, 3 HMXBs.
56 BHCs, 37 LMXBs, 6 HMXBs, 14 undetermined systems
Class A: 21 dynamically confirmed BHs
Class B: BHC sources with BH-like spectra and QPO properties of BHs
Class C: most likely Galactic XRBs with only weak evidence for a BH primary

16. A census of galactic BHs and BHCs--a summary of primary source information
a brief summary of the X-ray discovery;
an outline of optical/IR, radio, and X-ray detections;
an overview of the outburst history/long-term behavior;
a summary of spectral and timing characteristics exhibited during outburst;
a discussion of the past estimates and currently accepted orbital parameters found through dynamical studies of the system;
a justification of BH or BHC status;
an indication of our assigned BH certainty class, within parentheses in the subsection headers.

17. Data selection and analysis

18. Data selection and analysis
Data are run through a custom pipeline composed of a comprehensive algorithm built to discover, track, and quantitatively classify outburst behavior.
This algorithm consists of a seven stage process; data cleaning, detection, sensitivity selection, X-ray hardness computation, spectral fitting, luminosity function and mass-transfer rate estimation, and empirical classification.
The products produced via this algorithm can then be used to analyze the details of outburst behavior, including duty cycles, recurrence times, total energy released during outburst, long-term outburst rates, state transitions, luminosity functions, and mass transfer rates of Galactic BHXB systems.

19. Results
Observations & Algorithm: 50 years of activity, including over 200 outbursts in 66 transient sources and the long-term activity of 11 persistent sources.
Algorithm: 132 outbursts, 47 transient BHXBs, between

20. Results-outburst detection rates
4-12 BHXB transient
events every year.

22. Results-Hard-only outburst behaviour
Be able to classify 92 of 132 total transient outbursts
32 of the outburst undergone by BHXBs that do not complete the “turtlehead” pattern, failing to transition from the HCS to the SDS, the so-called “hard-only “ outbursts, make up ~40% of all outbursts occurring in Galactic transient BHXBs in the past 19 years.

23. Results-Hard-only outburst behaviour
Hard-only behavior is neither a rare nor recent phenomenon.
the mass-transfer rate onto the BH remaining at a low level rather than increasing as the outburst evolves, resulting in no state transition to the softer states occuring.
All of these outbursts have upper limits < 0.11 Ledd (the mean HCS- SDS transition luminosity)
Selection biases: distance, instrument, different sensitivity between soft and hard X-rays.

24. Results-outburst duration and duty cycles
Successful: ~247 days
Hard-only: ~391 days
They do not arise from the same parent distribution

25. Results-state transitions and transition luminosities

26. Results-peak outburst luminosity
A clear demonstration of the under-luminous nature of a ‘hard-only’ outburst
In the standard picture, the peak luminosity is expected in the SDS, however, a fair number of outbursts that display this (“turtlehead”) outburst behavior appear to exhibit a peak in the HCS. (perhaps: the bolometric corrections are poorly known, missing coverage of the soft state peaks due to Sun constraints, SPL state.)

27. Results-peak outburst luminosity

28. Results- X-ray luminosity functions (XLF)

29. Results- X-ray luminosity functions (XLF)
Transient: double-peaked profile (previous study: power-law type)
one soft state contribution peaking at ∼1038ergs-1
two significant hard state contributions, one peaking between ∼ 1035ergs-1 and ∼ 1036ergs-1 and, another that appears to peak only one bin below the maximum of the soft state contribution.
The result of the “turtlehead” behavior

30. Results- X-ray luminosity functions (XLF)
Persistent: bi-modal profile
two segments at two distances?
random clumping of the very small number of persistent sources?
the effect of SS 433?

31. Discussion
The relationship between average mass transfer rate and orbital period

32. Discussion
The exclusively “hard-only “ outburst transient sources appear to have significant lower average accretion rate. (KS test)
Many persistent sources appear to occupy the region reserved for transient sources (i.e. below the critical accretion rate).
(the smaller radius of accretion disk? Putting significant amount of accretion energy into powering an outflow? A large fraction of the energy released from the accreted material goes into the kinetic (and magnetic) energy of the jet rather than being radiated away.)
Outliers that correspond to sources that in the soft state. (disk winds?)

33. Discussion
The positive correlation between peak outburst luminosity and orbital period?

34. Summary
Taking advantage of the current suite of more sensitive satellites, it is possible to established a comprehensive database of BH (and BHC) XRB activity over the last 19 years.
Assembled the database by running data from seven separate instruments through a custom pipeline composed of a comprehensive algorithm built to discover, track, and quantitatively classify outburst behavior.
132 transient outbursts, 47 transient and 10 persistently accreting BHs
Outburst detection rates, duration, duty cycles, peak luminosity and state transitions.

35. Summary
~4-12 transient outbursts per year, more than a factor of three larger than in the pre-RXTE era.
38% of the outbursts do not complete the typical “turtlehead” pattern.
This “hard-only” behavior, paired with low luminosities that are expected the transition from the hard to the soft indicate that the mass-transfer rate remains in a low-level.
The appearance of a bi-modal distribution present in the luminosity function for the entire transient population, presumably indicative of the cyclic “turtlehead” patterns of temporal evolution in BHXBs.
Numerous outliers from the theoretical expected correlation in the
diagram

36. Summary
enumerating the frequency at which outbursts occur, tracking outburst properties across the population and quantitatively classifying the wide range of behavior exhibited during outburst will be critical to furthering our understanding of the physical mechanisms driving mass-transfer in binary BH systems and a key step toward filling in the many gaps in our knowledge of how BHXBs form, accrete and evolve.
Thanks !