Emrah Kalemci

X-Ray States and Radio Emission in the Black Hole Candidate XTE J1550–564

We report on radio and X-ray observations of the black hole candidate (BHC) XTE J1550-564 performed during its 2000 X-ray outburst. Observations were conducted with the Australia Telescope Compact Array and allowed us to sample the radio behavior of XTE J1550-564 in the X-ray low hard and intermediate/very high states. We observed optically thin radio emission from XTE J1550-564 5 days after a transition to an intermediate/very high state, but we observed no radio emission 6 days later, while XTE J1550-564 was still in the intermediate/very high state. In the low hard state, XTE J1550-564 is detected with an inverted radio spectrum. The radio emission in the low hard state most likely originates from a compact jet; optical observations suggest that the synchrotron emission from this jet may extend up to the optical range. The total power of the compact jet might therefore be a significant fraction of the total luminosity of the system. We suggest that the optically thin radio emission detected 5 days after the transition to the intermediate/very high state is due to a discrete ejection of relativistic plasma during the state transition. Subsequent to the decay of the optically thin radio emission associated with the state transition, it seems that in the intermediate/very high state the radio emission is quenched by a factor greater than 50, implying a suppression of the outflow. We discuss the properties of radio emission in the X-ray states of BHCs.

Multiwavelength observations of the Galactic black hole transient 4U 1543-47 during outburst decay: state transitions and jet contribution

Multiwavelength observations of Galactic black hole (GBH) transients during state transitions and in the low/hard state may provide detailed information on the accretion structure of these systems. The object 4U 1543-47 is a GBH transient that was covered exceptionally well in X-rays and the infrared (daily observations) and reasonably well in the optical and radio during its outburst decay in 2002. When all the available information is gathered from the intermediate and the low/hard states, 4U 1543-47 makes an important contribution to our understanding of state transitions and the role of outflows in the high-energy emission properties of black hole binaries. The evolution of the X-ray spectral and temporal properties and the infrared light curve place strong constraints on different models to explain the overall emission from accreting black holes. The overall spectral energy distribution is consistent with a synchrotron origin for the optical and infrared emission; however, the X-ray flux is above the power-law continuation of the optical and infrared flux. The infrared light curve, the HEXTE light curve, and the evolution of the X-ray photon index indicate that the major source of hard X-rays cannot be direct synchrotron radiation from an acceleration region in a jet for most of the outburst decay.

The Inclination Angle and Mass of the Black Hole in XTE J1118+480

We have obtained optical and infrared photometry of the quiescent soft X-ray transient XTE J1118+480. In addition to optical and J-band variations, we present the first observed H- and Ks-band ellipsoidal variations for this system. We model the variations in all bands simultaneously with the WD98 light curve modeling code. The infrared colors of the secondary star in this system are consistent with a spectral type of K7 V, while there is evidence for light from the accretion disk in the optical. Combining the models with the observed spectral energy distribution of the system, the most likely value for the orbital inclination angle is 68° ± 2°. This inclination angle corresponds to a primary black hole mass of 8.53 ± 0.60 M☉. Based on the derived physical parameters and infrared colors of the system, we determine a distance of 1.72 ± 0.10 kpc to XTE J1118+480.

The infrared/X-ray correlation of GX 339-4: Probing hard X-ray emission in accreting black holes.

GX 339-4 has been one of the key sources for unravelling the accretion ejection coupling in accreting stellar mass black holes. After a long period of quiescence between 1999 and 2002, GX 339-4 underwent a series of four outbursts that have been intensively observed by many ground-based observatories [radio/infrared (IR)/optical] and satellites (X-rays). Here, we present results of these broad-band observational campaigns, focusing on the optical-IR (OIR)/X-ray flux correlations over the four outbursts. We found tight OIR/X-ray correlations over four decades with the presence of a break in the IR/X-ray correlation in the hard state. This correlation is the same for all four outbursts. This can be interpreted in a consistent way by considering a synchrotron self-Compton origin of the X-rays in which the break frequency varies between the optically thick and thin regime of the jet spectrum. We also highlight the similarities and differences between optical/X-ray and IR/X-ray correlations which suggest a jet origin of the near-IR emission in the hard state while the optical is more likely dominated by the blackbody emission of the accretion disc in both hard and soft state. However, we find a non-negligible contribution of 40 per cent of the jet emission in the V band during the hard state. We finally concentrate on a soft-to-hard state transition during the decay of the 2004 outburst by comparing the radio, IR, optical and hard X-rays light curves. It appears that unusual delays between the peak of emission in the different energy domains may provide some important constraints on jet formation scenario.

Truncation of the Inner Accretion Disk around a Black Hole at Low Luminosity

Most black hole binaries show large changes in X-ray luminosity caused primarily by variations in mass accretion rate. An important question for understanding black hole accretion and jet production is whether the inner edge of the accretion disk recedes at low accretion rate. Measurements of the location of the inner edge (Rin) can be made using iron emission lines that arise due to fluorescence of iron in the disk, and these indicate that Rin is very close to the black hole at high and moderate luminosities ( > 2% of the Eddington luminosity, LEdd). Here, we report on X-ray observations of the black hole GX 339‐4 in the hard state by Suzaku and the Rossi X-ray Timing Explorer (RXTE) that extend iron line studies to 0.24% LEdd and show that Rin increases by a factor of >27 over the value found when GX 339‐4 was bright. The exact value of Rin depends on the inclination of the inner disk (i), and we derive 90% confidence limits of Rin > 35Rg at i =0 and Rin > 175Rg at i =3 0 . This provides direct evidence that the inner portion of the disk is not present at low luminosity, allowing for the possibility that the inner disk is replaced by advection- or magnetically-dominated accretion flows.

Tracing the Jet Contribution to the Mid-IR over the 2005 Outburst of GRO J1655-40 via Broadband Spectral Modeling

We present new results from a multiwavelength (radio/infrared/optical/X-ray) study of the black hole X-ray binary GRO J1655-40 during its 2005 outburst. We detected, for the first time, mid-infrared emission at 24 μm from the compact jet of a black hole X-ray binary during its hard state, when the source shows emission from a radio compact jet, as well as a strong nonthermal hard X-ray component. These detections strongly constrain the optically thick part of the synchrotron spectrum of the compact jet, which is consistent with it being flat over 4 orders of magnitude in frequency. Moreover, using this unprecedented coverage, and especially thanks to the new Spitzer observations, we can test broadband disk and jet models during the hard state. Two of the hard-state broadband spectra are reasonably well fitted using a jet model with parameters that overall are similar to those previously found for Cyg X-1 and GX 339-4. Differences are also present; most notably, the jet power in GRO J1655-40 appears to be a factor of at least ~3-5 higher (depending on the distance) than those of Cyg X-1 and GX 339-4 at comparable disk luminosities. Furthermore, a few discrepancies between the model and the data, previously not found for the other two black hole systems for which there was no mid-IR/IR and optical coverage, are evident, and will help to constrain and refine theoretical models.

Search for Polarization from the Prompt Gamma-Ray Emission of GRB 041219a with SPI on INTEGRAL

Measuringthepolarizationof theprompt � -rayemissionfromgamma-raybursts(GRBs)cansignificantlyimprove our understanding of both the GRB emission mechanisms as well as the underlying engine driving the explosion. We searched for polarization in the prompt � -ray emission of GRB 041219a with the SPI instrument on INTEGRAL. Using multiple-detector coincidence events in the 100‐350 keVenergy band, our analysis yields a polarization fractionfromthisGRBof 98% � 33%.Statistically,wecannotclaimapolarizationdetectionfromthissource.Moreover, different event selection criteria lead to even less significant polarization fractions, e.g., lower polarization fractions are obtained when higher energies are included in the analysis. We cannot strongly rule out the possibility that the measuredmodulationisdominatedbyinstrumentalsystematics.Therefore,SPIobservationsof GRB041219adonot significantly constrain GRB models. However, this measurement demonstrates the capability of SPI to measure polarization, as well as the techniques developed for this analysis. Subject headings: gamma rays: bursts — gamma rays: observations — instrumentation: polarimeters — methods: data analysis — polarization — techniques: polarimetric

The Galactic Black Hole Transient H1743-322 During Outburst Decay Connections Between Timing Noise, State Transitions, And Radio Emission

Multiwavelength observations of Galactic black hole transients during outburst decay are instrumental for our understanding of the accretion geometry and the formation of outflows around black hole systems. H1743-322, a black hole transient observed intensely in X-rays and also covered in the radio band during its 2003 decay, provides clues about the changes in accretion geometry during state transitions and also the general properties of X-ray emission during the intermediate and low-hard states. In this work, we report on the evolution of spectral and temporal properties in X-rays and the flux in the radio band, with the goal of understanding the nature of state transitions observed in this source. We concentrate on the transition from the thermal dominant state to the intermediate state that occurs on a timescale of 1 day. We show that the state transition is associated with a sudden increase in power-law flux. We determine that the ratio of the power-law flux to the overall flux in the 3-25 keV band must exceed 0.6 for us to observe strong timing noise. Even after the state transition, once this ratio was below 0.6, the system transited back to the thermal dominant state for 1 day. We show that the emission from the compact radio core does not turn on during the transition from the thermal dominant state to the intermediate state but does turn on when the source reaches the low-hard state, as seen in 4U 1543-47 and GX 339-4. We find that the photon index correlates strongly with the QPO frequency and anticorrelates with the rms amplitude of variability. We also show that the variability is more likely to be associated with the power-law emission than the disk emission.

A CLOSE LOOK AT THE STATE TRANSITIONS OF GALACTIC BLACK HOLE TRANSIENTS DURING OUTBURST DECAY

We characterize the evolution of spectral and temporal properties of several Galactic black hole transients during outburst decay using the data from well-sampled Rossi X-Ray Timing Explorer Proportional Counter Array observations close to the transition to the low/hard state. We find several global patterns of evolution for spectral and temporal parameters before, during, and after the transition. We show that the changes in temporal properties (sudden increase or decrease in the rms amplitude of variability) are much sharper than the changes in the spectral properties, and it is much easier to identify a state transition with the temporal properties. The spectral index shows a drop 3-5 days before the transition for some of our sources. The ratio of the power-law flux to the total flux in the 3-25 keV band increases close to the transition, which may mean that the system must be dominated by the coronal emission for the transition to occur. We also show that the power-law flux shows a sharp change along with the temporal properties during the transitions, which may indicate a threshold transition volume for the corona. The evolution of the spectral and temporal properties after the transition is consistent with the idea that the inner accretion disk moves away from the black hole. Based on the evolution of spectral and temporal parameters and changes during the transitions, we discuss possible scenarios of how the transition is happening.

Detection of Low-Hard State Spectral and Timing Signatures from the Black Hole X-Ray Transient XTE J1650–500 at Low X-Ray Luminosities

Using the Chandra X-Ray Observatory and the Rossi X-Ray Timing Explorer, we have studied the black hole candidate (BHC) X-ray transient XTE J1650-500 near the end of its 2001-2002 outburst after its transition to the low-hard state at X-ray luminosities down to L = 1.5 × 1034 ergs s-1 (1-9 keV, assuming a source distance of 4 kpc). Our results include a characterization of the spectral and timing properties. At the lowest sampled luminosity, we used an 18 ks Chandra observation to measure the power spectrum at low frequencies. For the three epochs at which we obtained Chandra/RXTE observations, the 0.5-20 keV energy spectrum is consistent with a spectral model consisting of a power law with interstellar absorption. We detect evolution in the power-law photon index from Γ = 1.66 ± 0.05 to 1.93 ± 0.13 (90% confidence errors), indicating that the source softens at low luminosities. The power spectra are characterized by strong (20%-35% fractional rms) band-limited noise, which we model as a zero-centered Lorentzian. Including results from an RXTE study of XTE J1650-500 near the transition to the low-hard state by Kalemci and coworkers, the half-width of the zero-centered Lorentzian (roughly where the band-limited noise cuts off) drops from 4 Hz at L = 7 × 1036 ergs s-1 (1-9 keV, absorbed) to 0.067 ± 0.007 Hz at L = 9 × 1034 ergs s-1 to 0.0035 ± 0.0010 Hz at the lowest luminosity. While the spectral and timing parameters evolve with luminosity, it is notable that the general shapes of the energy and power spectra remain the same, indicating that the source stays in the low-hard state. This implies that the X-ray-emitting region of the system likely keeps the same overall structure, while the luminosity changes by a factor of 470. We discuss how these results may constrain theoretical black hole accretion models.