Gamma-ray Burst 110915B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN Circular #12341
E. Del Monte, I. Donnarumma, Y. Evangelista, M. Feroci, F. Lazzarotto, L. Pacciani, P. Soffitta, E. Costa, I. Lapshov, M. Rapisarda (INAF/IASF Rome), G. Barbiellini, F. Longo, E. Moretti (INFN Trieste), A. Bulgarelli, F. Gianotti, M. Trifoglio, G. Di Cocco, C. Labanti, F. Fuschino, M. Marisaldi, M. Galli (INAF/IASF Bologna), A. Giuliani, A. Chen, S. Mereghetti, F. Perotti, P. Caraveo (INAF/IASF Milan), M. Tavani, M. Cardillo, G. Pucella, V. Vittorini, A. Argan, A. Trois, G. Piano, S. Sabatini (INAF/IASF Rome), A. Pellizzoni, M. Pilia (INAF/OA Cagliari), S. Vercellone, F. D'Ammando (INAF/IASF Palermo), P. W. Cattaneo, A. Rappoldi (INFN Pavia), P. Picozza, A. Morselli, E. Striani, (INFN Roma-2), M. Prest, E. Vallazza (Universita` dell'Insubria), P. Lipari, D. Zanello (INFN Roma-1), P. Giommi, C. Pittori, F. Lucarelli, P. Santolamazza, F. Verrecchia (ASDC) and L. Salotti (ASI), on behalf of the AGILE Team, report:
"SuperAGILE detected a gamma ray burst on 15 September 2011, at 18:24:19 UT. The event had a duration of about 18 s in the 20-60 keV energy range, with a single peak structure. Assuming a crab-like energy spectrum, the peak flux on 1-s timescale was 7.73E-08 erg/cm2/s. The burst position was reconstructed as (RA, Dec) (77.548, 1.925) deg, which is:
```
RA(J2000)  = 05h 10m 11.57s
Dec(J2000) = 1d 55' 30.98"
```
with an uncertainty of 4' radius. The given uncertainty accounts for both the statistical and systematic errors.
An analysis of the AGILE Gamma Ray Imager (GRID) data is in progress."
This message may be cited.
GCN Circular #12348
P. D'Avanzo (INAF-OAB), J. K. Cannizzo (NASA/UMBC), P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team:
At 04:36:53 UT, September 16, 2011, Swift began a Target of Opportunity observation of the AGILE discovered burst GRB 110915B (Del Monte et al. et al. GCN Circ. 12341).
We have analysed 2.1 ks of XRT data, from 36.8 ks to 43.2 ks after the AGILE trigger. The data are entirely in Photon Counting (PC) mode. An uncatalogued X-ray source is detected within the AGILE error circle. Using 2132 s of PC mode data and 3 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 77.55470, +1.93280 which is equivalent to:
```
RA (J2000): 05h 10m 13.13s
Dec(J2000): +01d 55' 57.9"
```
with an uncertainty of 1.8 arcsec (radius, 90% confidence). This position is 37 arcsec from the AGILE position. The light curve is consistent with a constant source of mean count rate 7.1e-02 ct/sec. A power-law fit gives an index of -0.3 (+2.3, -1.1).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.85 (+0.36, -0.27). The best-fitting absorption column is 9 (+10, -1) x 10^20 cm^-2, consistent with the Galactic value of 8.5 x 10^20 cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.9 x 10^-11 (4.8 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:             9 (+10, -1) x 10^20 cm^-2
Galactic foreground: 8.5 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:             1.85 (+0.36, -0.27)
```
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00020185.
This circular is an official product of the Swift-XRT team.
GCN Circular #12350
A. de Ugarte Postigo (DARK/NBI), J. C. Tello, V. Casanova, A. J. Castro-Tirado, R. Sanchez-Ramirez, J. Gorosabel, S. Guziy (IAA-CSIC) D. Malesani (DARK/NBI) report on behalf of a larger collaboration:
We have observed the field of the AGILE GRB 110915B (Del Monte et al. GCNC 12341) using the 1.5m OSN telescope at Sierra Nevada Observatory (Granada, Spain). The observation consisted of 46 x 120s exposures in R-band. In the combined exposure we detect an uncatalogued source inside the error box of the XRT afterglow candidate (D'Avanzo et al. GCNC 12348) at the following coordinates (J2000, +/- 0.5"):
```
R.A.: 05:10:13.14
Dec.: +01:55:59.1
```
The preliminary magnitude of the object at an average epoch of Sep. 16.166 UT (9.59 hr after the burst onset) is R = 22.8+/-0.30, as compared to the USNO-B1.0 star at coordinates 05:10:09.720, +01:56:40.12, for which we assume R = 17.61.
Further analysis is ongoing.
GCN Circular #12354
F. E. Marshall (NASA/GSFC) and J. K. Cannizzo (GSFC/UMBC/CRESST) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 110915B 36,747 s after the AGILE trigger (Del Monte et al., GCN Circ. 12341). No optical afterglow consistent with the position of the X-ray (D'Avanzo et al. GCN Circ.12348) or optical (de Ugarte Postigo et al., GCN Circ. 12350) afterglow candidates is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) for the initial exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white            37077        48670         1468         >22.2
v                42882        48935          542         >20.1
u                36747        52898         1869         >22.0
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.07 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #12356
J. Elliott (MPE Garching), D. A. Kann (TLS Tautenburg), and J. Greiner (also MPE Garching) report on behalf of the GROND team:
We observed the field of the AGILE GRB 110915B (E. Del Monte et al., GCN 12341) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP, 120, 405) mounted at the 2.2 m MPI/ESO telescope at La Silla Observatory (Chile).
Observations were taken starting at 06:59 UT on 18 September 2011 (2.5 days after the GRB trigger). They were performed at an average seeing of 1".4 and at an airmass of 2, with the Moon only 22 degrees away.
We detect the afterglow candidate reported by A. de Ugarte Postigo et al. (GCN 12350). Based on an exposure time of 4502 s in the optical, we estimate an r' magnitude (in AB) of:
r' = 23.2 +/- 0.1.
Compared to the magnitudes reported by A. de Ugarte Postigo et al., the candidate shows no decay over the past 2.1 days and so is likely not the GRB afterglow. We find a flux ratio between optical and X-rays of f_x/f_opt = 4500 which indicates an AGN nature if the X-ray emission (P. D'Avanzo et al., GCN 12348) has not faded.
Given magnitudes are calibrated against GROND zeropoints and shifted based on the USNO-B1.0 star used by A de Ugarte Postigo., RA = 05:10:09.720, Dec. = +01:56:40.12, and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E(B-V) = 0.07 in the direction of the burst (Schlegel et al. 1998).
We are indebted to A. de Ugarte Postigo for providing us a finding chart.
GCN Circular #12372
P. D'Avanzo (INAF-OAB), J. K. Cannizzo (NASA/UMBC), P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team:
Swift continued to monitor the field of the AGILE-detected GRB 110915B (Del Monte et al. GCN Circ. 12341). We have analysed 6.1 ks of XRT data, from 36.8 ks to 442.2 ks after the AGILE trigger. The data comprise 148 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode.
The X-ray source reported in D'Avanzo et al. (GCN Circ. 12348) has faded to a level of 5.8e-3 ct/sec. The light curve can be modelled with a power-law decay with a decay index of alpha=1.05 (+0.57, -0.25).
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00020185.
This circular is an official product of the Swift-XRT team.
GCN Circular #12827
V.V.Golovnya (Main Astro Obs, Kyiv) report:
We have undertaken the review of the sky area in vicinity of GRB 110915B (P. D'Avanzo et al. GCN Circ.12348) on astronegatives, collected in Ukrainian NAS Main astronomical observatory plate archive (1976-1996). All the plates with the possible object appearance are digitized using Microtek ScanMaker 9800XL TMA and Epson Expression 10000XL flatbed scanners and have been placed into Golosiiv Plate Archive database DBGPA with open access to them.
The list of plates is given in the table:
```
YYYYMMDD/TimeUT	--Plates--	Exp.	LimMag	Star USNOA2 
19820210/174605	GUA040C000008A	27.0	15.70	0900-01403360
19820210/174605	GUA040D000009	27.0	15.70	0900-01403360
19911011/014851	GUA040C001873	25.1	15.05	0900-01404372
19911012/015416	GUA040C001880A	18.2	15.05	0900-01408313
19920108/200727	GUA040C001916	23.0	16.45	0900-01406794
19920201/181314	GUA040C001929A	23.0	15.05	0900-01408313
Plates: - the plates archive identifier of DWA (D/F=400/2000, 
GUA040C, M=103"/mm) of the Ukrainian NAS Main Astro obs.
GUA040D  (Marsden's number - 83) the plate number [1].
Exp.   - Duration of the maximum exposure (minutes). 
LimMag - Limited V mag, derived in the 17 minutes area around 
       the location given in GCN Circ.12348: 
       RA(J2000) = 05h 10m 13.13s, Dec(J2000) = +01d 55'57.9"
Star USNOA2 - Comparison star.
```
The preview images of 6 areas together with the 17x17 min.of arc area from SkyMap can be found in http://gua.db.ukr-vo.org/img/grb/110915B/index.html The images with full resolution are available via e-mail on demand.
References:
1.L.Pakuliak DATABASE of GOLOSIIV PLATE ARCHIVE (DBGPA V2.0), http://gua.db.ukr-vo.org

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Jochen Greiner, last update: 11-Jan-2012 [Disclaimer]