MAXI GSC observations of a spectral state transition in the black hole candidate XTE J1752-223

We present the first results on the black hole candidate XTE J1752-223 from the Gas Slit Camera (GSC) on-board the Monitor of All-sky X-ray Image (MAXI) on the International Space Station. Including the onset of the outburst reported by the Proportional Counter Array on-board the Rossi X-ray Timing Explorer on 2009 October 23, the MAXI/GSC has been monitoring this source approximately 10 times per day with a high sensitivity in the 2-20 keV band. XTE J1752-223 was initially in the low/hard state during the first 3 months. An anti-correlated behavior between the 2-4 keV and 4-20 keV bands were observed around January 20, 2010, indicating that the source exhibited the spectral transition to the high/soft state. A transient radio jet may have been ejected when the source was in the intermediate state where the spectrum was roughly explained by a power-law with a photon index of 2.5-3.0. The unusually long period in the initial low/hard state implies a slow variation in the mass accretion rate, and the dramatic soft X-ray increase may be explained by a sudden appearance of the accretion disk component with a relatively low innermost temperature (0.4-0.7 keV). Such a low temperature might suggest that the maximum accretion rate was just above the critical gas evaporation rate required for the state transition.Comment: Publication of Astronomical Society of Japan Vol.62, No.5 (2010) [in print

Bright X-ray flares from the BL Lac object Mrk 421, detected with MAXI in 2010 January and February

Strong X-ray flares from the blazar Mrk 421 were detected in 2010 January and February through the 7 month monitoring with the MAXI GSC. The maximum 2 -- 10 keV flux in the January and February flares was measured as 120 +- 10 mCrab and 164 +- 17 mCrab respectively; the latter is the highest among those reported from the object. A comparison of the MAXI and Swift BAT data suggests a convex X-ray spectrum with an approximated photon index of about 2. This spectrum is consistent with a picture that MAXI is observing near the synchrotron peak frequency. The source exhibited a spectral variation during these flares, slightly different from those in the previous observations, in which the positive correlation between the flux and hardness was widely reported. By equating the halving decay timescale in the January flare, $t_{\rm d} \sim 2.5 \times 10^{4}$ s, to the synchrotron cooling time, the magnetic field was evaluated as B = 0.045 G $(\delta/10)^{-1/3}$, where $\delta$ is the jet beaming factor. Assuming that the light crossing time of the emission region is shorter than the doubling rise time, $t_{\rm r} \lesssim 2 \times 10^{4}$ s, the region size was roughly estimated as $R < 6 \times 10^{15}$ cm $(\delta/10)$. These are consistent with the values previously reported. For the February flare, the rise time, $t_{\rm r} < 1.3 \times 10^{5}$ s, gives a loose upper limit on the size as $R < 4 \times 10^{16}$ cm $(\delta/10)$, although the longer decay time $t_{\rm d} \sim 1.4 \times 10^{5}$ s, indicates B = 0.015 G $(\delta/10)^{-1/3}$, which is weaker than the previous results. This could be reconciled by invoking a scenario that this flare is a superposition of unresolved events with a shorter timescale.Comment: 14 pages, 4 figures, accepted for PASJ (Vol. 62 No. 6

A Large X-ray Flare from a Single Weak-lined T Tauri Star TWA-7 Detected with MAXI GSC

We present a large X-ray flare from a nearby weak-lined T Tauri star TWA-7 detected with the Gas Slit Camera (GSC) on the Monitor of All-sky X-ray Image (MAXI). The GSC captured X-ray flaring from TWA-7 with a flux of $3\times10^{-9}$ ergs cm$^{-2}$ s$^{-1}$ in 2--20 keV band during the scan transit starting at UT 2010-09-07 18:24:30.The estimated X-ray luminosity at the scan in the energy band is 3$\times10^{32}$ ergs s$^{-1}$,indicating that the event is among the largest X-ray flares fromT Tauri stars.Since MAXI GSC monitors a target only during a scan transit of about a minute per 92 min orbital cycle, the luminosity at the flare peak might have been higher than that detected. At the scan transit, we observed a high X-ray-to-bolometric luminosity ratio, log $L_{\rm X}/L_{\rm bol}$ = $-0.1^{+0.2}_{-0.3}$; i.e., the X-ray luminosity is comparable to the bolometric luminosity. Since TWA-7 has neither an accreting disk nor a binary companion, the observed event implies that none of those are essential to generate such big flares in T Tauri stars.Comment: 4 pages, 2 figures, 1 table accepted for publication in PAS

The return trip is felt shorter only postdictively: A psychophysiological study of the return trip effect

The return trip often seems shorter than the outward trip even when the distance and actual time are identical. To date, studies on the return trip effect have failed to confirm its existence in a situation that is ecologically valid in terms of environment and duration. In addition, physiological influences as part of fundamental timing mechanisms in daily activities have not been investigated in the time perception literature. The present study compared round-trip and non-round-trip conditions in an ecological situation. Time estimation in real time and postdictive estimation were used to clarify the situations where the return trip effect occurs. Autonomic nervous system activity was evaluated from the electrocardiogram using the Lorenz plot to demonstrate the relationship between time perception and physiological indices. The results suggest that the return trip effect is caused only postdictively. Electrocardiographic analysis revealed that the two experimental conditions induced different responses in the autonomic nervous system, particularly in sympathetic nervous function, and that parasympathetic function correlated with postdictive timing. To account for the main findings, the discrepancy between the two time estimates is discussed in the light of timing strategies, i.e., prospective and retrospective timing, which reflect different emphasis on attention and memory processes. Also each timing method, i.e., the verbal estimation, production or comparative judgment, has different characteristics such as the quantification of duration in time units or knowledge of the target duration, which may be responsible for the discrepancy. The relationship between postdictive time estimation and the parasympathetic nervous system is also discussed

Correction: The Return Trip Is Felt Shorter Only Postdictively: A Psychophysiological Study of the Return Trip Effect

<p>Correction: The Return Trip Is Felt Shorter Only Postdictively: A Psychophysiological Study of the Return Trip Effect</p

Correlation coefficients between ANS and time perception for the round-trip group and the control group.

<p>Correlation coefficients between ANS and time perception for the round-trip group and the control group.</p

Relations between ANS and postdictive time perception.

<p>(A) Correlation of the change of CVI with 11-point scale for the control group, and (B) correlation of the change of SD-HR with 11-point scale for the control group. The change was defined as subtracting the value in the second trip session from that in the first trip session. ANS, autonomic nervous system; CVI, cardiac vagal index; SD-HR, standard deviation of heart rate.</p