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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
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To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

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subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

20382 results found.

  1. EP-WXT trigger 01709201209: Liverpool Telescope upper limits
  2. EP250903a: refined analysis of the EP-WXT and EP-FXT observations
  3. LIGO/Virgo/KAGRA S250904br: Identification of a GW compact binary merger candidate
  4. GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
  5. LIGO/Virgo/KAGRA S250904ae: Identification of a GW compact binary merger candidate
  6. GRB 250903A: LCO optical observation
  7. GRB 250903A: LCO optical afterglow detection
  8. GRB 250903A: SVOM/VT optical confirmation with VHF data
  9. EP250901a: Mondy, Assy and SAO RAS optical limits
  10. GRB 250903A: TRT optical counterpart detection
  11. GRB 250903A: SVOM detection of a burst
  12. EP250903a: TRT optical observations
  13. EP250903a: Einstein Probe detection of an X-ray transient
  14. EP 250827B: Detection of supernova counterpart by LCO.
  15. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  16. GRB 250902B: SVOM/GRM observation
  17. EP250827b: SVOM/VT observation of AT 2025wkm
  18. LIGO/VIRGO/KAGRA S250818k: No evidence for radio variability of AT2025ulz in MeerKAT 3 GHz data
  19. GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
  20. Fermi-LAT Gamma-ray Observations of IceCube-250831A
  21. GRB 250901A: Swift/UVOT Upper Limit
  22. IceCube-250831A: Upper limits from a search for additional neutrino events in IceCube
  23. GRB 250830B: Swift-XRT afterglow detection
  24. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  25. GRB 250902A: SVOM/GRM observation
  26. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  27. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  28. IceCube-Cascade 250828A: Upper limits from a search for additional neutrino events in IceCube
  29. GRB 250901A: SVOM/VT optical afterglow with VHF data
  30. GRB 250901A: Swift-XRT afterglow detection
  31. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  32. GRB 250901A: LCO optical upper limit
  33. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  34. EP250831a: NOT optical observations and tentative afterglow candidate
  35. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  36. GRB 250901A: SVOM detection of a burst
  37. EP250901a: Mephisto optical upper limits
  38. GRB 250830C: AstroSat CZTI detection of a long burst
  39. EP250901a: Einstein Probe detection of an X-ray transient
  40. EP250831a: EP-WXT detection of a fast X-ray transient
  41. GRB 250831A: Swift-XRT counterpart detection
  42. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  43. GRB 250831A: SVOM/VT upper limit with VHF data
  44. GRB 250831A: SVOM detection of a soft burst
  45. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  46. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  47. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  48. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  49. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  50. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  51. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  52. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  53. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  54. GRB 250808B: SVOM detection of a burst through offline search
  55. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  56. EP250828a: Optical counterpart detection with Kinder observations
  57. EP250828a: Liverpool Telescope upper limits
  58. EP-WXT trigger 01709200800 : KAIT optical observations
  59. EP250828a: KAIT optical upper limit
  60. EP250827a: Swift/UVOT Detection
  61. EP250828a: NOT optical counterpart confirmation
  62. EP250828a: SVOM/VT optical candidate
  63. EP250828a: Seimei/TriCCS optical counterpart detection
  64. EP250828a: Optical upper limit with Kinder observations
  65. EP250828a: Einstein Probe detection of an X-ray transient
  66. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  67. GRID detection of GRB 250824A
  68. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  69. EP250827a: confirmation of optical rebrightening with LCO
  70. GRB 250826A: SVOM/GRM observation
  71. EP250827A: An optical rebrightening was detected by LCO.
  72. EP250827a: TRT optical observations
  73. EP250827a: Einstein Probe detection of an X-ray transient
  74. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  75. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  76. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  77. Fermi GRB 250824B: Global MASTER-Net observations report
  78. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  79. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  80. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  81. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  82. EP250821a: MeerKAT radio counterpart
  83. GRB 250823A: COLIBRÍ optical observations
  84. GRB 250823A: SVOM/VT optical observation
  85. GRB 250823A: Swift/UVOT Detection
  86. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  87. GRB 250823A: Enhanced Swift-XRT position
  88. GRB 250823A: LCOGT Optical Detection
  89. GRB 250823A: Swift detection of a burst
  90. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  91. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  92. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  93. GRB 250806A: Gemini observations of host galaxy candidate
  94. GRB 250821A: Kilonova-Catcher optical upper limits
  95. GRB 250812A: SVOM/ECLAIRs refined analysis
  96. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  97. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  98. GRB 250821A: VLT/FORS2 Optical Observation
  99. GRB 250821B: SVOM/GRM observation
  100. EP250821a: SVOM/VT optical observation

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