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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.

Advanced Search Examples (click to copy):

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

20366 results found.

  1. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  2. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  3. GRB 250814A: Swift/UVOT Upper Limits
  4. GRB 250813B: Swift/UVOT Upper Limit
  5. IPN triangulation of GRB 250816A (short)
  6. IPN triangulation of GRB 250814C (short)
  7. IPN triangulation of GRB 250804B (short)
  8. GRB 250818B: Kilonova-Catcher optical afterglow detection
  9. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  10. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  11. GRB 250818B: Swift/UVOT Detection
  12. GRB 250818B: SAO RAS optical observations
  13. GRB 250818B: KAIT optical observations
  14. GRB 250818A: Swift/UVOT Upper Limits
  15. GRB 250818A: Enhanced Swift-XRT position
  16. GRB 250813B: SVOM/ECLAIRs refined analysis
  17. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  18. GRB 250814A: Further GRAWITA TNG NIR observations
  19. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  20. GRB 250818A: Swift detection of a burst
  21. GRB 250816A: SVOM/GRM observation of a short burst
  22. GRB 250813B: Liverpool Telescope optical upper limits
  23. GRB 250814A: Further COLIBRÍ optical upper limit
  24. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  25. GRB 250814A: GRAWITA TNG NIR observations
  26. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  27. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  28. GRB250814A: TRT optical upper limits
  29. GRB 250814B: SVOM/GRM observation
  30. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  31. GRB 250814A: P200/WIRC observations of the afterglow candidate
  32. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  33. GRB 250814A: KAIT optical upper limit
  34. GRB 250814A: Swift-XRT refined Analysis
  35. GRB 250814A: Possible afterglow candidate from P200/WIRC
  36. GRB 250813B: Fermi GBM Observation
  37. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  38. GRB 250814A: J-band upper limit from WINTER
  39. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  40. GRB 250813B: NOT observations of the optical afterglow
  41. GRB 250814A: COLIBRÍ optical upper limit
  42. GRB 250813A: AstroSat CZTI detection
  43. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  44. GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
  45. GRB 250814A: DDOTI Optical Upper Limit
  46. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  47. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  48. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  49. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  50. GRB 250813B: SVOM detection of a bright long burst
  51. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  52. EP250812a: Nickel optical upper limit
  53. EP250812a: NOT, NTT, and GS observations
  54. GRB 250812A: Swift/UVOT Detection
  55. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  56. EP250812a: Liverpool Telescope upper limits
  57. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  58. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  59. EP 250812a: GOTO optical upper limit
  60. GRB 250812A: Kilonova-Catcher optical afterglow detection
  61. EP250812a: Swift-XRT counterpart detection
  62. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  63. EP250812a: Einstein Probe detection of an X-ray transient
  64. GRB 250812A: Swift-XRT afterglow detection
  65. GRB 250812A: TRT likely optical counterpart detection
  66. IceCube-Cascade 250809A: Upper limits from a search for additional neutrino events in IceCube
  67. Fermi-LAT Gamma-ray Observations of IceCube-250804A
  68. GRB 250809A: Swift/UVOT Detection
  69. GRB 250809A: Swift-XRT refined Analysis
  70. GRB 250809A: LCOGT Optical Upper Limits
  71. GRB 250808A: VLT X-shooter candidate counterpart
  72. GRB 250809A: Swift detection of a gamma ray burst
  73. GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  74. Konus-Wind detection of GRB 250807A
  75. GRB 250807B: Swift/UVOT Detection
  76. GRB 250807B: Kilonova-Catcher optical afterglow detection
  77. IceCube-250804A: Upper limits from a search for additional neutrino events in IceCube
  78. GRB 250807A: Swift/UVOT Detection
  79. GRB 250807B: VLT/X-Shooter spectroscopic redshift z = 1.522
  80. GRB 250806A: SVOM/ECLAIRs refined analysis
  81. EP250807a: NTT z-band optical upper limit
  82. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
  83. GRB 250807A: SVOM/GRM observation
  84. GRB 250807A: AstroSat CZTI detection of bright long burst
  85. EP250807a: EP-WXT detection of a fast X-ray transient
  86. EP 250807.979: GOTO optical upper limit
  87. EP250807a: COLIBRÍ optical upper limit
  88. GRB 250807B: Enhanced Swift-XRT position
  89. GRB 250807A: Enhanced Swift-XRT position
  90. IceCube-Cascade 250804A: Upper limits from a search for additional neutrino events in IceCube
  91. GRB 250807B: Swift detection of a burst with an optical counterpart.
  92. GRB 250805A: Kilonova-Catcher optical upper limits
  93. GRB 250805A: Swift/UVOT Upper Limits
  94. GRB 250806A: Swift/UVOT U-band detection
  95. EP250806a: Liverpool telescope optical upper limit
  96. GRB 250807A: Swift detection of a burst with an optical counterpart
  97. GRB 250806A: EP-FXT observation
  98. EP250806a: refined analysis of the EP-WXT and EP-FXT observations
  99. EP250806a: SVOM /VT optical candidate
  100. GRB 250806A: J-band upper limit from WINTER

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