Yi-Ping Qin

THE FULL CURVATURE EFFECT EXPECTED IN EARLY X-RAY AFTERGLOW EMISSION FROM GAMMA-RAY BURSTS

We explore the influence of the full curvature effect on the flux of the early X-ray afterglows of gamma-ray bursts (GRBs) in cases where the spectrum of the intrinsic emission is a power law. We find that the well-known t−(2+β) curve appears only when the intrinsic emission is extremely brief or the emission arises from exponential cooling. The timescale of this curve is independent of the Lorentz factor. The resulting light curve exhibits two phases if the intrinsic emission has a power-law spectrum and a temporal power-law profile of infinite duration. The first phase is a rapid decay in which the light curve is well described by the t−(2+β) curve. The second phase is a shallow decay in which the power-law index of the light curve is obviously smaller than in the first phase. The start of the shallow phase is strictly constrained by, and can in turn set a lower limit on, the radius of the fireball. In the case of power-law emission that lasts for only a limited time, there will be a third phase after the t−(2+β) curve and the shallow decay phase, which is much steeper than the shallow phase. As a sample application, we fit the Swift XRT data for GRB 050219A with our model and show that the curvature effect alone can roughly account for this burst. Although the fit parameters cannot be uniquely determined, because of the various choices in the fitting, a lower limit on the fireball radius of this burst can be estimated, which is ~1014 cm.

THE SOFTENING PHENOMENON DUE TO THE CURVATURE EFFECT: IN THE CASE OF AN EXTREMELY SHORT INTRINSIC EMISSION

Both the light curve and spectral evolution of the radiation from a relativistic fireball with extremely short duration are studied in order to examine the curvature effect for different forms of the radiation spectrum. Assuming a δ function emission we get formulae that get rid of the impacts from the intrinsic emission duration, applicable to any forms of the spectrum. It shows that the same form of the spectrum could be observed at different times, with the peak energy of the spectrum shifting from higher energy bands to lower bands following E peak ∝ t –1. When the emission is early enough, the t 2 f ν(t) form as a function of time will possess exactly the same form that the intrinsic spectrum as a function of frequency has. Assuming f ν ∝ ν–β t –α one finds α = 2 + β, which holds for any intrinsic spectral forms. This relation will be broken down and α>2 + β or α 2 + β will hold at much later time when the angle between the moving direction of the emission area and the line of sight is large. An intrinsic spectrum in the form of the Band function is employed to display the light curve and spectral evolution. Caused by the shifting of the Band function spectrum, a temporal steep decay phase and a spectral softening appear simultaneously. The softening phenomenon will appear at different frequencies. It occurs earlier for higher frequencies and later for lower frequencies. The terminating softening time t s,max depends on the observation frequency, following t s,max ∝ ν–1. This model predicts that the softening duration would be linearly correlated with t s,max; the observed βmin and βmax are determined by the low and high-energy indices of the Band function; both βmin and βmax are independent of the observation frequency.

Brightness temperature for 166 radio sources

Using the database of the University of Michigan Radio Astronomy Observatory (UMRAO) at three radio frequencies (4.8, 8 and 14.5 GHz), we determined the short-term variability timescales for 166 radio sources. The timescales are 0.15 d (2007+777) to 176.17 d (0528–250) with an average timescale of Δ t obs = 17 . 1  16 . 5 d for the whole sample. The timescales are used to calculate the brightness temperatures, T B . The value of log T B is in the range of log T B = 10.47 to 19.06 K. In addition, we also estimated the boosting factor for the sources. The correlation between the polarization and the Doppler factor is also discussed.

The Disappearance of a Narrow Mg II Absorption system in Quasar SDSS J165501.31+260517.4

In this paper, we present for the first time the discovery of the disappearance of a narrow Mg II lambda lambda 2796, 2803 absorption system from the spectra of the quasar SDSS J165501.31+260517.4 (z(e) = 1.8671). This absorber is located at z(abs) = 1.7877 and has a velocity offset of 8423 km s(-1) with respect to the quasar. According to the velocity offset and the line variability, this narrow Mg II lambda lambda 2796, 2803 absorption system is likely intrinsic to the quasar. Since the corresponding UV continuum emission and the absorption lines of another narrow Mg II lambda lambda 2796, 2803 absorption system at z(abs) = 1.8656 are very stable, we believe that the disappearance of the absorption system is unlikely to be caused by the change in ionization of absorption gas. Instead, it likely arises from the motion of the absorption gas across the line of sight.

The estimations of four basic parameters for gamma-ray loud blazars

The method used in our previous papers is adopted to estimate four basic parameters (the central black hole mass ( M ), the boosting factor (or Doppler factor) ( δ ), the propagation angle ( Φ ) and the distance along the axis to the site of the γ -ray production ( d )) for 59 γ -ray loud blazars (20 BL Lacertae objects and 39 fl at spectrum radio quasars). The central black hole masses estimated for this sample are in a range of from 10 7 M ⊙ to 10 9 M ⊙ In the case of black hole mass, there is no clear difference between BL Lacertae objects and fl at spectrum radio quasars, which is consistent with the previous results suggesting that the central black hole masses do not play an important role in the evolutionary sequence of blazars

A Subset of Quasars Identified by Large Values of Their Doppler Redshift

We have calculated the Doppler redshifts for a sample of quasars from their observed emission and absorption redshifts. We selected only those absorption redshifts that are larger than the corresponding emission redshifts (i.e., z(abs) > z(em)). The sample was extracted from a quasar catalog that contains spectra of 784 quasars, for which 11,298 absorption systems and 20,837 absorption lines were detected. We obtained 256 absorption systems with z(abs) > z(em) from 123 quasars. We find that there is a bimodal structure in the distribution of the Doppler redshifts, with one peak being located at z(Dopp) similar or equal to 0.00 and the other at zDopp similar or equal to 0.01. Around the second peak, zDopp similar or equal to 0.01, we identify a subset of quasars with Doppler redshifts greater than 0.0088. Our analysis shows that quasars in this subset are generally brighter than those with Doppler redshifts less than 0.0088. The Doppler velocities of the absorbers of these quasars are concentrated around -3000 km s(-1). This velocity likely arises from material falling toward the central region of the quasars that originates beyond the torus.

Hardness ratio evolutionary curves of gamma-ray bursts expected by the curvature effect

We have investigated the gamma-ray bursts (GRBs) pulses with a fast rise and an exponential decay phase, assumed to arise from relativistically expending fireballs, and found that the curvature effect influences the evolutionary curve of the corresponding hardness ratio (hereafter HRC). We find, due to the curvature effect, the evolutionary curve of the pure hardness ratio (when the background count is not included) would peak at the very beginning of the curve, and then would undergo a drop-to-rise-to-decay phase. In the case of the raw hardness ratio (when the background count is included), the curvature effect would give rise to several types of evolutionary curve, depending on the hardness of a burst. For a soft burst, an upside down pulse of its raw HRC would be observed; for a hard burst, its raw HRC shows a pulselike profile with a sinkage in its decaying phase; for a very hard burst, the raw HRC possesses a pulselike profile without a sinkage in its decaying phase. For a pulselike raw HRC as shown in the case of the hard and very hard bursts, its peak would appear in advance of that of the corresponding light curve, which was observed previously in some GRBs. For illustration, we have studied here the HRC of GRB 920216, GRB 920830, and GRB 990816 in detail. The features of the raw HRC expected in the hard burst are observed in these bursts. A fit to the three bursts shows that the curvature effect alone could indeed account for the predicted characteristics of HRCs. In addition, we find that the observed hardness ratio tends to be harder at the beginning of the pulses than what the curvature effect could predict and be softer at the late time of the pulses. We believe this is an evidence showing the existence of intrinsic hard-to-soft radiation which might be due to the acceleration-to-deceleration mode of shocks.

VARIATIONS OF ABSORPTION TROUGHS IN THE QUASAR SDSS J125216.58+052737.7

In this work, we analyze the spectra of quasar J125216.58+052737.7 (z em = 1.9035) which was observed by SDSS-I/II on 2003 January 30 and by BOSS on 2011 April 2. Both the continuum and the absorption spectra of this quasar show obvious variations between the two epochs. In the SDSS-I/II spectrum, we detect 8 absorption systems, which are detected at z abs = 1.9098, 1.8948, 1.8841, 1.8770, 1.8732, 1.8635, 1.8154, and 1.7359, respectively, and one absorption system at z abs = 0.9912. Among these absorption systems, two absorption systems at z abs = 1.9098 and 1.7359 and the absorption system are imprinted on the BOSS spectrum as well, and have similar absorption strengths when compared to those measured from the SDSS-I/II spectrum. Three absorption systems at z abs = 1.8948, 1.8841, and 1.8770 are also detected in the BOSS spectrum, while their absorption strengths are much weaker than those measured from the SDSS-I/II spectrum; three systems at z abs = 1.8732, 1.8635, and 1.8154 disappeared from the BOSS spectrum. Based on the variability analysis, the absorption systems that disappeared and weakened are likely to be intrinsic to the quasar. If these intrinsic absorption gases are blown away from the central region of the quasar, with respect to the quasar system, the absorption systems that disappeared would have separation velocities of 3147 kms–1, 4161 km s–1, and 9241 km s–1, while the absorption systems that weakened would have separation velocities of 900 km s–1, 2011 km s–1, and 2751 km s–1. Well-coordinated variations of the six absorption systems that disappeared and weakened, occurring on a timescale of 1026.7 days at the quasar rest frame, can be interpreted as a result of global changes in the ionization state of the absorbing gas.

Relations between integrated and monochromatic luminosities of flat-spectrum radio quasars

We employ a sample of 362 flat-spectrum radio quasars (FSRQs) to calculate their integrated luminosities by integrating the spectral energy distribution (SED) constructed with multi-band (radio, IR, optical, UV and X-ray) data. We compare these luminosities with those estimated from monochromatic luminosities by multiplying them by the conventional bolometric correction factors. Our analysis shows that the integrated luminosities calculated from the SED are much larger than the bolometric luminosities estimated from monochromatic luminosities. Their departing behavior tightly correlates with radio luminosities. The relations between integrated and monochromatic luminosities are explored, which are regarded as empirical relations that might be more suitable to be applied to estimate integrated luminosities of FSRQs from their monochromatic luminosities.