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GCN Circulars

GCN Circulars are rapid bulletins submitted by and distributed to the community. 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').
Advanced Search

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"

21089 results found.

  1. NuSTAR 261020, a 830s hard X-ray transient
  2. EP261015a: GSP multiband optical follow-up observations
  3. EP261015a: Further optical observations with the 1.3m DFOT
  4. Fermi-LAT Gamma-ray Observations of IceCube-261020A
  5. EP261015a: AZT-20 Assy-Turgen optical observations
  6. GRB 261017A: SAO RAS optical upper limit
  7. EP261015a: Wendelstein 43 cm optical observations
  8. EP261015a: Follow-up with the 1.3m DFOT
  9. EP261007b: Further EP-FXT follow-up observations
  10. EP261015a: COLIBRÍ optical observations of a rebrightening
  11. GRB 261017A: Possible Swift/UVOT Detection
  12. GRB 261017A: Luminance-band upper limit from a 28cm telescope in Chengde
  13. GRB 261017A: R-band upper limit with the 1.3-m DFOT
  14. EP261015b: NOT Optical Observations
  15. GRB 261017A: J band upper limit by the SYSU 80cm infrared telescope
  16. GRB 261017A: Nanshan/NEXT optical upper limit
  17. EP261015a: Tentative fading of the candidate optical counterpart from the NOT
  18. EP261015b: Refined analysis of EP-FXT observations
  19. EP261015b: J-band upper limit by the SYSU 80cm infrared telescope
  20. EP261015a: refined analysis of EP-FXT observations
  21. EP261015c: J-band upper limit with WINTER
  22. EP261015a: J-band upper limit with WINTER
  23. EP261006a / AT 2026aetp: Optical follow-up with the 1.3-m DFOT
  24. GRB 261011A: 1.3m DFOT optical upper limit
  25. EP241111a and EP250125a: Upper limits from SVOM/GRM Observations
  26. GRB 261010A: VLA radio observations
  27. EP261015a: COLIBRÍ optical observations
  28. EP261015c: Einstein Probe detection of a fast X-ray transient
  29. EP261015b: Einstein Probe detection of an X-ray transient
  30. GRB261010A: Keck/MOSFIRE detection of a near-IR source
  31. EP261015a (WXT 11900947714): Possible optical counterpart from NOT and LCO
  32. GRB 261010A: ASKAP non-detection of a radio afterglow
  33. GRB 261010A: LBT tentative near-infrared detection
  34. GRB 261011A: SAO RAS and AbAO optical observations
  35. EP261006a : MeerKAT radio observations.
  36. GRB 261011A: Later-epoch J-band upper limit from the SYSU 80 cm infrared telescope
  37. Fermi-LAT Gamma-ray Observations of IceCube-261012A
  38. GRB 261010A: J-band upper limit by the SYSU 80cm infrared telescope
  39. IceCube-260919A: No transient candidates from the Zwicky Transient Facility
  40. GRB 261010A: a Type I-L (merger-driven) GRB candidate
  41. GRB 261010A: 10.4m GTC spectroscopy of the galaxy 2" from the afterglow
  42. MAXI GRB261012.23: Global MASTER-Net observations report
  43. GRB 261011A: REM optical/NIR observations
  44. GRB 261011A: SOAR optical afterglow observations at ~17 hours
  45. EP261006a: 10 GHz VLA observations
  46. GRB 261011A: VLT/X-shooter redshift constraints
  47. GRB 261011A : MITSuME Akeno optical afterglow candidate detection
  48. GRB 261011A: Optical followup from Sichuan South Observatory
  49. GRB 261011A: Liverpool Telescope optical observations
  50. GRB 261011A: J-band observations by the SYSU 80cm infrared telescope
  51. GRB 261011A: continued LCO optical observations
  52. EP261007b: Global MASTER-Net observations report
  53. GRB 261011A: GROWTH-India Telescope optical observations
  54. GRB 261011A: Luminance-band upper limit from a 28cm telescope in Chengde
  55. Swift GRB 261011A: Global MASTER-Net observations report
  56. GRB 261011A: Optical follow-up observations with Kinder
  57. GRB 261011A: SVOM/C-GFT optical observations
  58. EP261007b: Second EP-FXT follow-up observation and a possible X-ray counterpart to the optical transient
  59. GRB 261011A: LCO optical observations
  60. GRB 261011A: LCO optical observations
  61. GRB 261011A: TRT optical afterglow detection
  62. GRB 261011A: GOTO optical counterpart detection
  63. EP261010a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  64. EP261006a / AT 2026aetp: Luminance-band optical follow-up with small-aperture telescopes
  65. GRB 261010A: possible optical afterglow detected with the 1.5m OSN
  66. GRB 261010A: NOT possible optical counterpart
  67. EP261006a: Kilonova-Catcher optical follow-up and detection
  68. EP261006a / AT 2026aetp: Multiband optical follow-up with the PKU 60cm Telescope
  69. EP261006a: Liverpool Telescope optical follow-up
  70. EP261010a: NOT optical upper limits
  71. EP261010a: Global MASTER-Net observations report
  72. GRB261007A: Lesedi optical afterglow detection
  73. EP261006a: Xinglong 2.16m/BFOSC optical follow-up observations
  74. EP261006a: Optical follow-up observations with MATCH
  75. EP261007b: J-band upper limit by SYSU 80cm infrared telescope
  76. EP261007b: Refined analysis of the EP-WXT and autonomous EP-FXT observations
  77. GRB 261007A: SVOM/ECLAIRs refined analysis
  78. EP261007b: SVOM/VT optical detection of the NOT transient
  79. GRB 261007A / EP261007a: SVOM/GWAC-F60A/B observations
  80. EP261006a / AT 2026aetp: VLT/X-shooter spectroscopic redshift z = 0.1853
  81. GRB 261007A: NOT optical observations
  82. EP261007b: NOT optical observations, variable source outside the FXT region
  83. EP261007b: SVOM/C-GFT optical upper limits
  84. EP261007b: J-band upper limit with WINTER
  85. The EP-WXT trigger 01709321008/EP261007b：Xinglong optical upper limit
  86. EP261006a: Swift/XRT detection of the fading X-ray counterpart
  87. GRB 261007A/EP261007a: Optical follow-up observations with Kinder
  88. EP261006a: Optical follow-up observations with Kinder
  89. EP261006a: Liverpool Telescope optical observations
  90. EP261006a: Early Optical Observations by WFST
  91. GRB 261007A / EP261007a: SVOM/VT optical observations
  92. GRB 261007A: Swift-XRT afterglow detection
  93. GRB 261007A: SVOM/COLIBRÍ (FM-GFT) optical observations
  94. EP Alert 261007.63: Global MASTER-Net observations report
  95. GRB 261007A / EP261007a: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 40-cm telescope at McDonald Observatory
  96. GRB 261007A: Autonomous identification and follow-up of the counterpart to GRB 261007A by BTSbot with ZTF and P60/SEDM
  97. SVOM GRB261007.27: Global MASTER-Net observations report
  98. GRB 261007A: GROWTH-India Telescope optical observations
  99. GRB 261007A / EP261007a: TRT optical observations
  100. GRB 261007A: Swift ToO observations

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