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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').
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"

26276 results found.

  1. GRB 251126A: OHP/T193 optical observations and tentative spectroscopic redshift
  2. GRB 251126A: further SAO RAS optical observations
  3. GRB 251126A NUTTelA-TAO Early Measurements
  4. LIGO/Virgo/KAGRA S251112cm: GECKO/KMTNet tiling observations and transient candidates
  5. GRB251126A: MAO/AZT-22 optical observations
  6. GRB251126A: Continued optical observation from 1.3m DFOT
  7. GRB 251126A: Swift/UVOT Detection
  8. GRB 251126A: Mondy and SAO RAS optical observations
  9. GRB 251126A: Swift-XRT refined Analysis
  10. GRB 251126A : MITSuME Akeno optical afterglow candidate detection
  11. GRB 251126A: NOT optical observations
  12. GRB 251126A: 1.3m DFOT optical afterglow detection
  13. GRB 251126A: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 1-m telescope at McDonald Observatory
  14. GRB 251126A: COLIBRÍ photometric redshift z = 3.5
  15. Fermi GRB 251127A: Global MASTER-Net observations report
  16. GRB 251126A: Enhanced Swift-XRT position
  17. GRB 251126A: Kilonova-Catcher optical afterglow detection
  18. GRB 251126A: Nanshan/HMT optical afterglow detection
  19. Swift GRB 251126A: Global MASTER-Net observations report
  20. GRB 251121A: Fermi GBM Observation
  21. GRB 251126A: GIT discovery of the likely optical afterglow
  22. GRB 251126A: Swift detection of a burst
  23. GRB 251125B: COLIBRÍ further observations and photometric redshift upper limit of z < 3
  24. GRB 251125B: COLIBRÍ observations of fading of the MASTER OT candidate
  25. EP251124b: NOT r- and z-band optical upper limits
  26. Fermi GRB 251125B : MASTER OT J155558.56+581224.1 optical counterpart discovery
  27. Fermi GRB 251125B: Global MASTER-Net observations report
  28. EP251124b: Global MASTER-Net observations report
  29. EP251124b: EP-WXT detection of a fast X-ray transient
  30. EP251124a: Xinglong GWAC-F60A optical observation
  31. Fermi GRB 251125A: Global MASTER-Net observations report
  32. EP251124a: NOT r- and z-band optical upper limits
  33. EP251124a: Global MASTER-Net observations report
  34. EP251124a: Swift-XRT observations
  35. LIGO/Virgo/KAGRA S251112cm: AT 2025adht Kinder follow-up observations
  36. EP251124a: Optical upper limit with Kinder observations
  37. Fermi GRB 251124a: Global MASTER-Net observations report
  38. LIGO/Virgo/KAGRA S251105aj: SVOM/VT optical observations and preliminary results on SVOM J2320.0-2901
  39. LIGO/Virgo/KAGRA S251105aj: EP-FXT follow-up observations and preliminary results on SVOM J2320.0-2901
  40. EP251124a: GROWTH-India Telescope optical upper limits
  41. EP251124a: Einstein Probe detection of an X-ray transient
  42. GRB 251116C: Swift-XRT confirmation of fading
  43. GRB 251122A/EP251122A: 1.3m DFOT optical detection
  44. GRB 251122A / EP251122a: Xinglong 2.16m optical observation
  45. EP251118A: 3.6m DOT optical afterglow detection
  46. GRB 251122A / EP251122a: EP-FXT counterpart detection
  47. EP251122a: refined analysis of the EP-WXT and EP-FXT observations
  48. GRB 251122A / EP251122a: WFST optical observations
  49. GRB 251122A/EP251122a: SVOM/VT optical observations with VHF data
  50. GRB 251122A/EP251122a: Additional, deeper LCO optical r band upper limit
  51. GRB 251122A / EP251122a: LCO optical upper limits
  52. EP251122a / GRB 251122A: optical counterpart candidate with Kinder observations
  53. EP251122a: Global MASTER-Net observations report
  54. GRB 251122A/EP251122a: SVOM/C-GFT upper limit
  55. GRB 251122A / EP251122a: SVOM detection of a long burst
  56. EP251122a: Einstein Probe detection of an X-ray transient
  57. EP251118a: Continued Optical Detection with Kinder observations
  58. LIGO/Virgo/KAGRA S251105aj: SVOM/ECLAIRs detection of a high-energy transient SVOM J2320.0-2901 through targeted search
  59. GRB 251121A: Swift/BAT-GUANO localization skymap of a short burst
  60. GRB 251121A: Glowbug gamma-ray detection of a likely short burst
  61. EP251118a: Xinglong-2.16m optical observation
  62. GRB 251115A: Fermi GBM Observation
  63. Fermi trigger No 785388351: Global MASTER-Net observations report
  64. EP251118A: 1.3m DFOT optical afterglow detection
  65. GRB 251118A: Swift/UVOT Detection
  66. EP251118a / GRB 251118C: SAO RAS optical observations
  67. GRB 251118A: Glowbug gamma-ray detection
  68. GRB 251118A: Fermi GBM Observation
  69. GRB 251118A: Swift-XRT afterglow detection
  70. GRB 251103A: SVOM/ECLAIRs and SVOM/GRM joint refined analysis
  71. EP251118a: Optical detection with Kinder observations
  72. LIGO/Virgo/KAGRA S251112cm: SVOM/VT optical observations and preliminary results
  73. GRB 251118A: NuSTAR detection of bright prompt emission
  74. EP251118a / GRB 251118C: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 1-m telescope at CTIO
  75. GRB 251116C: NOT optical observations
  76. GRB 251118C: Glowbug gamma-ray detection of the fast X-ray transient EP251118A
  77. GRB 251118C: Swift/BAT rates detection of a burst with a possible association with EP 251118A
  78. GRB 251117A: Swift-XRT observations
  79. EP251118A / GRB 251118C : MASTER optical counterpart observations
  80. GRB 251118C: SVOM/GRM observation of a possible gamma-ray counterpart of EP251118a
  81. GRB 251119A: SVOM trigger sb25111901 is not a GRB
  82. EP251118a: VLT near-infrared observation
  83. GRB 251116D: SVOM/GRM observation of a long GRB
  84. GRB 251119A: SVOM detection of a possible burst
  85. EP251118a: Global MASTER-Net observations report
  86. LAT GRB251118.86: Global MASTER-Net observations report
  87. EP251118a: NOT candidate optical counterpart
  88. EP251118a: Einstein Probe detected of a fast X-ray transient
  89. Fermi GRB 251118B: Global MASTER-Net observations report
  90. LIGO/Virgo/KAGRA S251112cm: Upper limits from Glowbug gamma-ray observations
  91. GRB 251118A: BALROG localization (Fermi Trigger 785190695 / GRB 251118855)
  92. GRB 251117A: AstroSat CZTI detection
  93. GRB 251013C: Koshka, SAO RAS, Mondy, and CrAO optical observations, possible SN detection
  94. LIGO/Virgo/KAGRA S251117dq: Updated Sky localization
  95. GRB 251115A: Swift-XRT observations
  96. GRB 251117A: Swift/BAT-GUANO localization skymap of a short burst
  97. GRB 251117A: SVOM/GRM observation of a short burst
  98. LAT GRB251117.51: Global MASTER-Net observations report
  99. LIGO/Virgo/KAGRA S251117dq: Identification of a GW compact binary merger candidate
  100. LIGO/Virgo/KAGRA S251112cm: J-GEM follow-up observations

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